JP7380517B2 - SOI wafer manufacturing method and SOI wafer - Google Patents

Description

The present invention relates to an SOI wafer manufacturing method and an SOI wafer.

One type of wafer for semiconductor devices is an SOI (Silicon On Insulator) wafer in which a silicon layer (hereinafter sometimes referred to as an SOI layer) is formed on a silicon oxide film, which is an insulating film. This SOI wafer has small parasitic capacitance and radiation resistance because the SOI layer on the surface of the substrate, which is the device fabrication area, is electrically isolated from the inside of the substrate by a buried insulating layer (buried oxide film (BOX layer)). It has characteristics such as high Therefore, SOI wafers are expected to achieve high-speed operation with low power consumption and to prevent soft errors, and are considered promising as substrates for high-performance semiconductor devices.

Typical methods for manufacturing this SOI wafer include the wafer bonding method and the SIMOX method. In the wafer bonding method, for example, a thermal oxide film is formed on the surface of at least one of two silicon single crystal wafers, and then the two wafers are brought into close contact via the formed thermal oxide film, and a bonding heat treatment is performed. This is a method of manufacturing an SOI wafer by increasing the bonding strength by applying bonding, and then thinning one wafer (the wafer on which the SOI layer will be formed (hereinafter referred to as a bond wafer)) by mirror polishing or the like. In addition, methods for thinning the film include grinding and polishing the bond wafer to a desired thickness, and forming an ion-implanted layer by implanting at least one type of hydrogen ion or rare gas ion into the bond wafer. There is a method called an ion implantation delamination method, in which the bond wafer is peeled off using the formed ion implantation layer as a peeling surface to obtain a thin SOI layer.

On the other hand, the SIMOX method implants oxygen ions into a single crystal silicon substrate, and then performs high-temperature heat treatment (oxide film formation heat treatment) to cause the implanted oxygen to react with silicon to form a BOX layer. This is a method of manufacturing wafers.

Of the two typical methods mentioned above, the wafer bonding method has the advantage of being able to freely set the thickness of the SOI layer and BOX layer, so it can be applied to a variety of device applications. It is.

Among these, the ion implantation delamination method has been widely used in recent years because it can provide extremely excellent film thickness uniformity of the produced SOI layer.

On the other hand, in order to suppress warpage of SOI wafers and improve gettering ability, SOI wafers are manufactured using base wafers doped with boron at a high concentration, as described in Patent Documents 1 and 2. This is often done.

When applying such a base wafer doped with boron at a high concentration to the ion implantation delamination method, it may be required to have a buried insulating layer as thick as 2 μm or more, for example. In this case, if an attempt is made to form a thick oxide film on the bond wafer and then bond it together, there will be problems such as the need to use extremely high ion implantation energy and the resulting SOI wafer being warped. It is necessary to form a thick oxide film on the wafer side and bond it to the bond wafer.

At that time, the base wafer doped with boron at a high concentration is thermally oxidized to form a thick oxide film, which results in a large amount of boron being contained in the thermal oxide film, resulting in When performing high-temperature heat treatments such as bonding heat treatment, planarization heat treatment, or epitaxial growth on SOI wafers, boron contained in the thermal oxide film on the backside of the SOI wafer diffuses out and contaminates the SOI layer with dopants. There was a problem of storage (so-called autodope). When such autodoping occurs, the conductivity type and resistivity of the SOI layer change.

Similar problems can occur even when other film thinning methods such as grinding and polishing are used, heat treatment that thickens the SOI layer by epitaxial growth on the SOI layer after thinning, and SOI wafers. It was also caused by heat treatment during the device manufacturing process.

In order to solve these problems, the present inventor disclosed in Patent Document 3 that by forming a CVD insulating film on the surface of the base wafer opposite to the bonding surface before the thermal oxidation process of the base wafer, We proposed a method to simultaneously reduce dopant contamination and warpage of SOI layers.

However, it has been found that even if this method is used, dopant contamination of the SOI layer may not be sufficiently suppressed in some cases.

Japanese Patent Application Publication No. 5-226620 Japanese Patent Application Publication No. 8-37286 Japanese Patent Application Publication No. 2008-294045

As a result of the inventor's intensive investigation into the cause of the above-mentioned problem in the method described in Patent Document 3, the main source of dopant contamination in the SOI layer is outward diffusion from the backside oxide film of the base wafer, but CVD It has become clear that the insulating film may not be able to sufficiently suppress dopant contamination of the SOI layer.

The present invention has been made in view of such problems, and provides a method for manufacturing an SOI wafer, which can manufacture an SOI wafer while suppressing contamination of the SOI layer due to the contamination of dopants contained in the base wafer, and a method for manufacturing an SOI wafer. An object of the present invention is to provide an SOI wafer that can suppress contamination of an SOI layer due to contamination of dopants contained in the wafer.

In order to achieve the above object, the present invention provides at least the following:
a base wafer consisting of a silicon single crystal wafer containing a dopant throughout the wafer and having a first main surface and a second main surface opposite to the first main surface; and a dopant at a lower concentration than the dopant concentration of the base wafer. a step of preparing a bond wafer consisting of a silicon single crystal wafer containing;
a thermal oxidation step of forming a silicon oxide film on the entire surface of the base wafer by thermal oxidation;
a bonding step of bonding one main surface of the bond wafer and the first main surface of the base wafer via the silicon oxide film on the base wafer;
a thinning step of thinning the bond wafer to form an SOI layer;
A method for manufacturing an SOI wafer, comprising:
Further comprising the step of forming a backside silicon film containing a dopant at a lower concentration than the dopant concentration of the base wafer on the second main surface of the base wafer before the thermal oxidation step of the base wafer,
The present invention provides a method for manufacturing an SOI wafer, characterized in that in the thermal oxidation step, the backside silicon film is thermally oxidized to obtain a backside silicon thermal oxide film as a part of the silicon oxide film.

In the SOI wafer manufacturing method of the present invention, in the bonding step, backside silicon is deposited on the second main surface of the base wafer, which is the surface opposite to the bonding surface (first main surface) with the bond wafer. A thermal oxide film is formed, and an SOI wafer can be obtained in which the first main surface of the base wafer and one main surface of the bond wafer are bonded together with the silicon oxide film interposed therebetween. The backside silicon thermal oxide film is obtained by thermally oxidizing a backside silicon film containing a dopant at a lower concentration than that of the base wafer. Such a backside silicon thermal oxide film has a more dense structure than, for example, a CVD insulating film, and can reliably prevent dopant diffusion through this thermal oxide film. In such an SOI wafer, autodoping from the second main surface of the base wafer to the bond wafer can be blocked by the backside silicon thermal oxide film. In addition, in the thermal oxidation process of the base wafer, a silicon oxide film is formed on the entire surface of the base wafer by thermal oxidation, so this silicon oxide film causes autodoping by solid phase diffusion from the first main surface of the base wafer to the bond wafer. Furthermore, it is also possible to suppress out-diffusion of dopants from the terrace portion of the base wafer (the portion where the SOI layer is not formed on the outer periphery of the base wafer) and the edge portion.

Therefore, according to the SOI wafer manufacturing method of the present invention, for example, in the bonding process and the process subsequent to this process, the dopant contained in the base wafer is released outward from the second main surface, which is the back surface of the base wafer. To suppress mixing into the bond wafer or SOI layer by diffusion or mixing into the bond wafer or SOI layer by solid phase diffusion through the silicon oxide film between the base wafer and the bond wafer or SOI layer. I can do it. In particular, even in a process involving heat treatment, the above-mentioned mixing of dopants into the SOI layer can be suppressed.

That is, according to the SOI wafer manufacturing method of the present invention, an SOI wafer can be manufactured while suppressing contamination of the SOI layer due to contamination with dopants contained in the base wafer. Since autodoping can be prevented in this way, changes in the conductivity type and resistivity of the SOI layer can be prevented.

Furthermore, when manufacturing a device using an SOI wafer manufactured by the SOI wafer manufacturing method of the present invention, the dopant contained in the base wafer is heated to the back surface of the second main surface, which is the back surface of the base wafer. It is possible to suppress contamination into the SOI layer due to outward diffusion through the oxide film or contamination into the SOI layer due to solid phase diffusion from the silicon oxide film as the buried oxide film of the SOI wafer.

In addition, when manufacturing devices using the SOI wafer manufactured by the SOI wafer manufacturing method of the present invention, outward diffusion of dopants through the second main surface of the base wafer can be suppressed, so that the parts inside the heat treatment furnace can be Dopant contamination to the wafer can also be sufficiently suppressed, and secondary contamination from the parts inside the furnace to the wafer can also be suppressed.

According to the SOI wafer manufacturing method of the present invention, by using a base wafer containing a dopant, it is possible to manufacture an SOI wafer that can suppress warpage and exhibit an excellent gettering effect.

As the back silicon film, for example, a film containing at least one selected from the group consisting of polysilicon, amorphous silicon, and single crystal silicon can be formed.

In this way, various silicon-containing films can be used as the backside silicon film.

Prior to the thermal oxidation step of the base wafer, the method further includes forming a barrier silicon layer containing a dopant at a lower concentration than the dopant concentration of the base wafer on the first main surface of the base wafer,
In the thermal oxidation step, thermally oxidize the barrier silicon layer to obtain a barrier silicon oxide film as a part of the silicon oxide film,
In the bonding step, it is preferable that the one main surface of the bond wafer and the first main surface of the base wafer be bonded via the barrier silicon oxide film that is a part of the silicon oxide film. .

In the SOI wafer obtained by this manufacturing method, the barrier silicon oxide film can act as an additional dopant diffusion prevention layer, so autodoping by solid phase diffusion from the first main surface of the base wafer to the bond wafer is prevented. This can be suppressed more reliably.

The method may further include a step of forming a silicon oxide film on the entire surface of the bond wafer before the bonding step.

By forming a silicon oxide film on the entire surface of the bond wafer in this way, in the bonding process, the base wafer and the bond wafer can be bonded to the silicon oxide film placed on the first main surface of the base wafer and the bond wafer. They can be bonded together via a silicon oxide film. By performing the bonding step in this manner, it is possible to more reliably suppress the dopant from entering the bond wafer or the SOI layer from the first main surface of the base wafer.

Alternatively, when forming the barrier silicon layer, the silicon single crystal surface of the one main surface of the bond wafer and the surface of the barrier silicon oxide film of the base wafer may be directly bonded in the bonding step. good.

Even when a silicon oxide film is not formed on a bond wafer, the incorporation of dopants into an SOI layer by solid phase diffusion from a base wafer through a silicon oxide film disposed on a first principal surface is sufficiently suppressed. I can do it. This aspect is particularly effective when bonding oxide films cannot be applied (for example, when heat treatment at a high temperature (for example, 1150° C. or higher) cannot be performed in the bonding process).

It is preferable to form the barrier silicon layer with a dopant concentration of 1×10 ¹⁶ atoms/cm ³ or less.

By forming such a barrier silicon layer, it is possible to more reliably suppress the incorporation of dopant into the SOI layer due to solid phase diffusion from the base wafer through the silicon oxide film disposed on the first main surface. .

In the thermal oxidation step, thermal oxidation is performed so that a part of the barrier silicon layer remains in an unoxidized state,
Thereafter, annealing may be performed to diffuse the dopant in the base wafer into the unoxidized portion of the barrier silicon layer.

In this way, in the thermal oxidation process, thermal oxidation can be performed such that only a part of the barrier silicon layer, not all of it, is made into a barrier silicon oxide film, and a part of the barrier silicon layer remains in an unoxidized state. In this case, annealing may be performed to diffuse the dopant into a portion of the barrier silicon layer that is not oxidized.

Prior to the bonding step, the method further includes an ion implantation step of implanting at least one type selected from the group consisting of hydrogen ions and rare gas ions into the bond wafer to form an ion implantation layer,
In the thinning step, the bond wafer may be peeled off using the ion implantation layer as a peeling surface, thereby thinning the bond wafer and obtaining the SOI layer.

By performing an ion implantation step to form such an ion implantation layer and utilizing this ion implantation layer in a thinning step, a thinned SOI layer having excellent film thickness uniformity can be obtained.

The base wafer may have a dopant concentration of 1×10 ¹⁷ atoms/cm ³ or more.

According to the SOI wafer manufacturing method of the invention, even if a base wafer with a dopant concentration of 1×10 ¹⁷ atoms/cm ³ or more is used, contamination of the SOI layer due to the contamination of the dopant contained in the base wafer is suppressed, while SOI wafers can be manufactured.

Further, the present invention provides an SOI wafer including a base wafer, a buried oxide film, and an SOI layer bonded to the base wafer via the buried oxide film,
The base wafer is made of a silicon single crystal wafer containing a dopant throughout the wafer and having a first main surface that is a bonding surface with the SOI layer and a second main surface opposite to the first main surface. Become,
A backside silicon thermal oxide film containing a dopant at a lower concentration than the dopant concentration of the base wafer is disposed on the second main surface of the base wafer,
The SOI wafer is characterized in that the SOI layer is made of silicon single crystal containing a dopant at a concentration lower than that of the base wafer.

In the SOI wafer of the present invention, the backside silicon thermal oxide film containing a dopant at a lower concentration than that of the base wafer has a more dense structure than, for example, a CVD insulating film, and the diffusion of the dopant through this thermal oxide film is prevented. It can definitely be prevented. Therefore, in the SOI wafer of the present invention, due to such a backside silicon thermal oxide film, the dopant is released outwardly through the second main surface opposite to the first main surface (bonding surface with the SOI layer) of the base wafer. Can prevent spread. Further, the buried oxide film included in the SOI wafer of the present invention can suppress solid phase diffusion of dopants through the buried oxide film. Therefore, in the SOI wafer of the present invention, dopant can also be prevented from diffusing from the first main surface of the base wafer to the SOI wafer through the buried oxide film. As a result, the SOI wafer of the present invention can suppress contamination of the SOI layer due to mixing of dopants contained in the base wafer.

Furthermore, when manufacturing devices using the SOI wafer of the present invention, dopants contained in the base wafer may be mixed into the SOI layer by out-diffusion through the second main surface, or may be mixed into the SOI layer in the buried oxide film. It is possible to suppress mixing into the SOI layer due to solid phase diffusion.

In addition, when manufacturing devices using the SOI wafer of the present invention, outward diffusion of dopants through the second main surface of the base wafer can be suppressed, so dopant contamination of the internal parts of the heat treatment furnace can also be sufficiently suppressed. This also provides the effect of suppressing secondary contamination from furnace parts to wafers.

Further, since the SOI wafer of the present invention includes a base wafer containing a dopant, warping can be suppressed and an excellent gettering effect can be exhibited.

Preferably, a barrier silicon oxide film as at least a part of the buried oxide film is disposed on the first main surface of the base wafer.

An SOI wafer including such a barrier silicon oxide film can more reliably prevent dopant from entering the SOI layer from the base wafer due to solid phase diffusion through the buried oxide film.

A barrier silicon layer is disposed between the base wafer and the barrier silicon oxide film,
A dopant of the same type as a dopant contained in the base wafer may be diffused into the barrier silicon layer.

In this way, the SOI wafer of the present invention can further include a barrier silicon layer between the base wafer and the barrier silicon oxide film.

As described above, with the method for manufacturing an SOI wafer of the present invention, an SOI wafer can be manufactured while suppressing contamination of the SOI layer due to contamination with dopants contained in the base wafer. Since autodoping can be prevented in this way, changes in the conductivity type and resistivity of the SOI layer can be prevented.

Furthermore, by manufacturing a device using an SOI wafer manufactured by the SOI wafer manufacturing method of the present invention, it is possible to suppress dopants contained in the base wafer from being mixed into the SOI layer.

The SOI wafer manufactured by the SOI wafer manufacturing method of the present invention can suppress warpage and exhibit an excellent gettering effect.

Further, with the SOI wafer of the present invention, contamination of the SOI layer due to the mixing of dopants contained in the base wafer can be suppressed.

Furthermore, during the manufacturing process of devices using the SOI wafer of the present invention, it is possible to suppress contamination of the SOI layer due to mixing of dopants contained in the base wafer.

The SOI wafer of the present invention can suppress warpage and exhibit excellent gettering effects.

1 is a schematic cross-sectional view showing a first example of an SOI wafer of the present invention. FIG. 3 is a schematic cross-sectional view showing a second example of the SOI wafer of the present invention. FIG. 3 is a schematic cross-sectional view showing a third example of the SOI wafer of the present invention. It is a schematic sectional view showing the fourth example of the SOI wafer of the present invention. 1 is a schematic flow diagram showing a first example of a method for manufacturing an SOI wafer of the present invention. FIG. 2 is a schematic flow diagram showing a second example of the SOI wafer manufacturing method of the present invention. FIG. 3 is a schematic flow diagram showing a third example of the method for manufacturing an SOI wafer of the present invention. 7 is a graph showing simulation results in Example 6. 7 is a graph showing simulation results in Example 7.

As described above, there is provided a method for manufacturing an SOI wafer that can manufacture an SOI wafer while suppressing contamination of the SOI layer due to the contamination of the SOI layer due to the contamination of the SOI layer due to the contamination of the dopant contained in the base wafer. There has been a need for the development of SOI wafers that can suppress contamination.

As a result of intensive studies on the above-mentioned problem, the present inventors have found that, before the thermal oxidation process of the base wafer, a dopant concentration higher than that of the base wafer is added to the second main surface of the base wafer on the opposite side to the bonding surface. By forming a backside silicon film containing a dopant at a low concentration, then performing a thermal oxidation process on the base wafer, and then bonding the base wafer and bond wafer, SOI due to the contamination of the dopant contained in the base wafer is eliminated. The present invention was completed by discovering that SOI wafers can be manufactured while suppressing layer contamination.

That is, the present invention provides at least
a base wafer consisting of a silicon single crystal wafer containing a dopant throughout the wafer and having a first main surface and a second main surface opposite to the first main surface; and a dopant at a lower concentration than the dopant concentration of the base wafer. a step of preparing a bond wafer consisting of a silicon single crystal wafer containing;
a thermal oxidation step of forming a silicon oxide film on the entire surface of the base wafer by thermal oxidation;
a bonding step of bonding one main surface of the bond wafer and the first main surface of the base wafer via the silicon oxide film on the base wafer;
a thinning step of thinning the bond wafer to form an SOI layer;
A method for manufacturing an SOI wafer, comprising:
Further comprising the step of forming a backside silicon film containing a dopant at a lower concentration than the dopant concentration of the base wafer on the second main surface of the base wafer before the thermal oxidation step of the base wafer,
The method for manufacturing an SOI wafer is characterized in that in the thermal oxidation step, the backside silicon film is thermally oxidized to obtain a backside silicon thermal oxide film as a part of the silicon oxide film.

The present invention also provides an SOI wafer including a base wafer, a buried oxide film, and an SOI layer bonded to the base wafer via the buried oxide film,
The base wafer is made of a silicon single crystal wafer containing a dopant throughout the wafer and having a first main surface that is a bonding surface with the SOI layer and a second main surface opposite to the first main surface. Become,
A backside silicon thermal oxide film containing a dopant at a lower concentration than the dopant concentration of the base wafer is disposed on the second main surface of the base wafer,
The SOI wafer is characterized in that the SOI layer is made of a silicon single crystal containing a dopant at a concentration lower than that of the base wafer.

Hereinafter, the present invention will be explained in detail with reference to the drawings, but the present invention is not limited thereto.

<SOI wafer>
First, the SOI wafer of the present invention will be explained.

The SOI wafer of the present invention has a base wafer and an SOI layer bonded to each other via a buried oxide film, and a second main surface opposite to a first principal surface of the base wafer that is bonded to the SOI layer. A backside silicon thermal oxide film is disposed on the front surface, and the dopant concentration in the backside silicon thermal oxide film is lower than the dopant concentration of the base wafer. The buried oxide film can prevent dopants from entering the SOI layer from the base wafer by solid phase diffusion therethrough. In addition, the backside silicon thermal oxide film has a more dense structure than, for example, a CVD insulating film, and the dopant from the second main surface opposite to the first main surface of the base wafer is removed through this thermal oxide film. This can prevent further spread. As a result, the SOI wafer of the present invention can suppress contamination of the SOI layer due to mixing of dopants contained in the base wafer.

Furthermore, when manufacturing devices using the SOI wafer of the present invention, dopants contained in the base wafer may be mixed into the SOI layer by out-diffusion through the second main surface, or may be mixed into the SOI layer in the buried oxide film. It is possible to suppress mixing into the SOI layer due to solid phase diffusion.

In addition, when manufacturing devices using the SOI wafer of the present invention, outward diffusion of dopants through the second main surface of the base wafer can be suppressed, so dopant contamination of the internal parts of the heat treatment furnace can also be sufficiently suppressed. This also provides the effect of suppressing secondary contamination from furnace parts to wafers.

In the SOI wafer of the present invention, a barrier silicon oxide film as at least a part of the buried oxide film may be disposed on the first main surface of the base wafer.

An SOI wafer including such a barrier silicon oxide film can more reliably prevent dopant from entering the SOI layer from the base wafer due to solid phase diffusion through the buried oxide film.

In the SOI wafer of the present invention, a barrier silicon layer may be disposed between the base wafer and the barrier silicon oxide film. In this case, the same type of dopant as the dopant contained in the base wafer may be diffused into the barrier silicon layer.

In this way, the SOI wafer of the present invention can further include a barrier silicon layer between the base wafer and the barrier silicon oxide film. SOI wafers of the present invention may also include other layers.

The SOI wafer of the present invention can be manufactured, for example, by the SOI wafer manufacturing method of the present invention described later.

Hereinafter, each component of the SOI wafer of the present invention will be explained in more detail.

(Base wafer)
The base wafer consists of a silicon single crystal wafer containing dopants throughout the wafer. Examples of the dopant include B, Ga, P, Sb, and As. Such a silicon single crystal wafer can be obtained, for example, by slicing a silicon single crystal ingot manufactured by the CZ method or the FZ method.

The dopant concentration of the base wafer is not particularly limited as long as it is higher than the dopant concentration of the SOI layer, but it can be, for example, 1×10 ¹⁷ atoms/cm ³ or more. By using a base wafer having a dopant concentration of 1×10 ¹⁷ atoms/cm ³ or more, it is possible to exhibit an excellent gettering effect and further suppress warpage of the SOI wafer. For the reason explained above, in the SOI wafer of the present invention, even if a base wafer having a dopant concentration of 1×10 ¹⁷ atoms/cm ³ or more is used, the dopant contained in the base wafer will not be absorbed into the SOI layer. It is possible to suppress contamination with

In addition, when the dopant of the base wafer is an n-type dopant, the concentration of the dopant incorporated into the silicon oxide film when forming the silicon oxide film on the base wafer by thermal oxidation is lower than that of the p-type dopant, so the above-mentioned Although the problem of dopant contamination of the SOI layer does not occur so conspicuously, even if the SOI layer is n-type, if the base wafer has a high dopant concentration of 1×10 ¹⁷ atoms/cm ³ or more, the SOI The problem of dopant contamination of the layer cannot be ignored. However, as mentioned above, in the SOI wafer of the present invention, even if the base wafer has such a high dopant concentration, it is difficult to prevent the dopant contained in the base wafer from being mixed into the SOI layer. can.

The upper limit of the dopant concentration in the base wafer is not particularly limited, but can be set to be below the solid solubility limit of the dopant in silicon single crystal. The dopant concentration of the base wafer is preferably 1×10 ¹⁷ atoms/cm ³ or more and 1×10 ²⁰ atoms/cm ³ or less.

(Backside silicon thermal oxide film)
A backside silicon thermal oxide film is disposed on the second main surface opposite to the first main surface, which is the bonding surface with the SOI layer of the base wafer. The backside silicon thermal oxide film contains dopants at a lower concentration than the dopant concentration of the base wafer.

The dopant concentration in the backside silicon thermal oxide film is not particularly limited as long as it is below the dopant concentration of the base wafer, but may be, for example, 1×10 ¹³ atoms/cm ³ or more and 1×10 ¹⁶ atoms/cm ^{3 or} less.

Examples of the dopant include B, Ga, P, Sb, and As. The backside silicon thermal oxide film may contain the same type of dopant as the dopant contained in the base wafer, or may contain a different type of dopant.

The backside silicon thermal oxide film is obtained by subjecting a silicon film containing at least one selected from the group consisting of polysilicon, amorphous silicon, and single crystal silicon and the above dopant to thermal oxidation, for example. obtain. Among these, polysilicon is preferred in view of the gettering effect during heat treatment such as formation of a thermal oxide film on the base wafer. The back silicon thermal oxide film containing polysilicon can also be called a poly back seal oxide film.

Between the backside silicon thermal oxide film and the second main surface of the base wafer, a backside silicon film ( In other words, a silicon film (which has not undergone thermal oxidation) may be disposed.

(Surface silicon oxide film)
Furthermore, a surface silicon oxide film may optionally be disposed on the first main surface of the base wafer, which is the bonding surface with the SOI layer.

The surface silicon oxide film may include a barrier silicon oxide film containing a dopant at a lower concentration than the dopant concentration of the base wafer, or may consist of this barrier silicon oxide film, or may include a barrier silicon oxide film containing a dopant at a lower concentration than that of the base wafer. It doesn't have to be included.

When the surface silicon oxide film does not include a barrier silicon oxide film, the surface silicon oxide film is formed by thermal oxidation of the main surface (first main surface) of the base wafer that is bonded to the SOI layer. It can be a silicon thermal oxide film.

The base wafer can include a portion where the SOI layer is not formed, that is, a terrace portion, on the first main surface. The surface silicon oxide film can also be placed on the terrace portion of the first main surface of the base wafer. In this case, the surface silicon oxide film can block out-diffusion of dopants through the terrace portion of the first main surface of the base wafer.

(Silicon oxide film formed on the entire surface of the base wafer)
Furthermore, a side silicon oxide film may be disposed on the side surface of the base wafer. When a side silicon oxide film is disposed, the front silicon oxide film, the back silicon thermal oxide film, and the side silicon oxide film can constitute a silicon thermal oxide film formed on the entire surface of the base wafer.

(SOI layer)
The SOI layer consists of a silicon single crystal containing dopants at a lower concentration than that of the base wafer.

Examples of the dopant include B, Ga, P, Sb, and As. The SOI layer may contain the same type of dopant as the dopant contained in the base wafer, or may contain a different type of dopant.

The dopant concentration of the SOI layer is not particularly limited as long as it is lower than the dopant concentration of the base wafer, and can be changed as appropriate depending on the conductivity type and resistivity required of the SOI layer. The dopant concentration of the SOI layer can be, for example, 1×10 ¹³ atoms/cm ³ or more and 1×10 ¹⁶ atoms/cm ^{3 or} less.

The SOI layer can also include portions that do not contain dopants.

A silicon oxide film (hereinafter also referred to as SOI-side silicon oxide film) may be disposed on one main surface of the SOI layer, which is the bonding surface with the base wafer.

(buried oxide film)
A buried oxide layer is disposed between the base wafer and the SOI layer.

The buried oxide film may include, at least in part, the surface silicon oxide film described above. The buried oxide film may be made of a surface silicon oxide film.

The buried oxide film may be made of a barrier silicon oxide film. In this case, in the SOI wafer, the silicon single crystal surface of the SOI layer and the surface of the barrier silicon oxide film of the base wafer may be directly bonded.

Alternatively, the buried oxide film may include a surface silicon oxide film or a barrier silicon oxide film, and another oxide film. For example, when an SOI-side silicon oxide film is arranged on one main surface of the SOI layer that is the bonding surface with the base wafer, this SOI-side silicon oxide film may be part of the buried oxide film. . In this case, in the SOI wafer, the surface silicon oxide film or the barrier silicon oxide film and the SOI side silicon oxide film may be directly bonded.

Alternatively, the buried oxide film may not include the barrier silicon oxide film. In this case, for example, the buried oxide film can include the above-described surface silicon oxide film formed by oxidizing one main surface of the base wafer by thermal oxidation.

Next, some specific examples of the SOI wafer of the present invention will be described with reference to FIGS. 1 to 4. However, the SOI wafer of the present invention is not limited to the examples described below. In addition, only the arrangement of each component will be described below. Please refer to the above for details of each component.

[First example]
FIG. 1 is a schematic cross-sectional view showing a first example of an SOI wafer of the present invention.

The SOI wafer 100 of the first example shown in FIG. 1 includes a base wafer 10, a buried oxide film 20, and an SOI layer 30 bonded to the base wafer 10 via the buried oxide film 20.

The base wafer 10 has a first main surface 11 that is a bonding surface with the SOI layer 30, and a second main surface 12 opposite to the first main surface 11.

A surface silicon oxide film 21 is disposed on the first main surface 11 of the base wafer 10 . The surface silicon oxide film 21 may include the barrier silicon oxide film described above, or may not include the barrier silicon oxide film. In the SOI wafer 100 of the first example shown in FIG. 1, the buried oxide film 20 consists of a surface silicon oxide film 21. Note that in the SOI wafer 100 of the first example shown in FIG. It is formed. On the other hand, a back silicon thermal oxide film 51 is disposed on the second main surface 12 of the base wafer 10 . Furthermore, a side silicon oxide film 52 is disposed on the side surface (edge portion) 13 of the base wafer 10 .

That is, in the SOI wafer 100 of the first example shown in FIG. There is.

In the SOI wafer 100 of the first example shown in FIG. 1, one main surface 32 of the SOI layer 30 is directly bonded to the surface silicon oxide film 21, that is, the surface of the buried oxide film 20.

[Second example]
FIG. 2 is a schematic cross-sectional view showing a second example of the SOI wafer of the present invention.

The SOI wafer 100 of the second example shown in FIG. 2 has the following features except that the backside silicon film 40 described above is disposed between the second main surface 12 of the base wafer 10 and the backside silicon thermal oxide film 51. This is similar to the SOI wafer 100 of the first example.

[Third example]
FIG. 3 is a schematic cross-sectional view showing a third example of the SOI wafer of the present invention.

The SOI wafer 100 of the third example shown in FIG. 3 is the same as the SOI wafer 100 of the first example except that a silicon oxide film (SOI side silicon oxide film) 22 is formed on a part of the surface of the SOI layer 30. It is.

Specifically, as shown in FIG. 3, the SOI side silicon oxide film 22 is disposed on one main surface 32 of the SOI layer 30, which is the surface to be bonded to the base wafer 10.

In addition, in the SOI wafer 100 of the third example shown in FIG. A buried oxide film 20 is formed by bonding the silicon oxide film 21 with the silicon oxide film 21 . In other words, the SOI wafer 100 of the third example includes the surface silicon oxide film 21 as part of the buried oxide film 20 and the SOI side silicon oxide film 22 as another part of the buried oxide film 20. .

[Fourth example]
FIG. 4 is a schematic cross-sectional view showing a fourth example of the SOI wafer of the present invention.

The SOI wafer 100 of the fourth example shown in FIG. Same as 100.

<Manufacturing method of SOI wafer>
Next, a method for manufacturing an SOI wafer according to the present invention will be explained.

The SOI wafer manufacturing method of the present invention includes at least the following steps:
a base wafer consisting of a silicon single crystal wafer containing a dopant throughout the wafer and having a first main surface and a second main surface opposite to the first main surface; and a dopant at a lower concentration than the dopant concentration of the base wafer. a step of preparing a bond wafer consisting of a silicon single crystal wafer containing;
a thermal oxidation step of forming a silicon oxide film on the entire surface of the base wafer by thermal oxidation;
a bonding step of bonding one main surface of the bond wafer and the first main surface of the base wafer via the silicon oxide film on the base wafer;
a thinning step of thinning the bond wafer to form an SOI layer;
A method for manufacturing an SOI wafer, comprising:
Further comprising the step of forming a backside silicon film containing a dopant at a lower concentration than the dopant concentration of the base wafer on the second main surface of the base wafer before the thermal oxidation step of the base wafer,
In the thermal oxidation step, the backside silicon film is thermally oxidized to obtain a backside silicon thermal oxide film as a part of the silicon oxide film.

In the SOI wafer manufacturing method of the present invention, in the bonding step, backside silicon is deposited on the second main surface of the base wafer, which is the surface opposite to the bonding surface (first main surface) with the bond wafer. A thermal oxide film is formed, and an SOI wafer can be obtained in which the first main surface of the base wafer and one main surface of the bond wafer are bonded together with the silicon oxide film interposed therebetween. The backside silicon thermal oxide film is obtained by thermally oxidizing a backside silicon film containing a dopant at a lower concentration than that of the base wafer. Such a backside silicon thermal oxide film has a more dense structure than, for example, a CVD insulating film, and can reliably prevent dopant diffusion through this thermal oxide film. In such an SOI wafer, autodoping from the second main surface of the base wafer to the bond wafer can be blocked by the backside silicon thermal oxide film. In addition, in the thermal oxidation process of the base wafer, a silicon oxide film is formed on the entire surface of the base wafer by thermal oxidation, so this silicon oxide film causes autodoping by solid phase diffusion from the first main surface of the base wafer to the bond wafer. Furthermore, it is also possible to suppress out-diffusion of dopants from the terrace and edge portions of the base wafer.

Therefore, according to the SOI wafer manufacturing method of the present invention, for example, in the bonding process and the process subsequent to this process, the dopant contained in the base wafer is released outward from the second main surface, which is the back surface of the base wafer. To suppress mixing into the bond wafer or SOI layer by diffusion or mixing into the bond wafer or SOI layer by solid phase diffusion through the silicon oxide film between the base wafer and the bond wafer or SOI layer. Can be done. In particular, even in a process involving heat treatment, the above-mentioned mixing of dopants into the SOI layer can be suppressed.

That is, according to the SOI wafer manufacturing method of the present invention, an SOI wafer can be manufactured while suppressing contamination of the SOI layer due to contamination with dopants contained in the base wafer. Since autodoping can be prevented in this way, changes in the conductivity type and resistivity of the SOI layer can be prevented.

Furthermore, when manufacturing a device using an SOI wafer manufactured by the SOI wafer manufacturing method of the present invention, the dopant contained in the base wafer is heated to the back surface of the second main surface, which is the back surface of the base wafer. It is possible to suppress contamination into the SOI layer due to outward diffusion through the oxide film or contamination into the SOI layer due to solid phase diffusion from the silicon oxide film as the buried oxide film of the SOI wafer.

In addition, when manufacturing devices using the SOI wafer manufactured by the SOI wafer manufacturing method of the present invention, outward diffusion of dopants through the second main surface of the base wafer can be suppressed, so that the parts inside the heat treatment furnace can be Dopant contamination to the wafer can also be sufficiently suppressed, and secondary contamination from the parts inside the furnace to the wafer can also be suppressed.

According to the SOI wafer manufacturing method of the present invention, by using a base wafer containing a dopant, it is possible to manufacture an SOI wafer that can suppress warpage and exhibit an excellent gettering effect.

Hereinafter, the SOI wafer manufacturing method of the present invention will be explained in more detail.

The SOI wafer manufacturing method of the present invention includes at least a step of preparing a base wafer and a bond wafer, a step of thermally oxidizing the base wafer, a step of bonding, and a step of thinning the base wafer. The method further includes a step of forming a backside silicon film.

The SOI wafer manufacturing method of the present invention includes a step of forming a barrier silicon layer containing a dopant at a lower concentration than the dopant concentration of the base wafer on the first main surface of the base wafer before the thermal oxidation step. It is preferable to further include. In this case, in the thermal oxidation process, the barrier silicon layer is thermally oxidized to obtain a barrier silicon oxide film as part of the silicon oxide film formed on the entire surface of the base wafer, and in the bonding process, one side of the bond wafer is It is preferable that the main surface and the first main surface of the base wafer are bonded together via a barrier silicon oxide film that is part of the silicon oxide film.

The SOI wafer manufacturing method of the present invention may further include a step of forming a silicon oxide film on the entire surface of the bond wafer before the bonding step.

The method for manufacturing an SOI wafer of the present invention includes ion implantation in which at least one type selected from the group consisting of hydrogen ions and rare gas ions is implanted into the inside of the bond wafer to form an ion implantation layer before the bonding process. The method may further include a step. In this case, in the thinning process, the bond wafer may be thinned by peeling off the bond wafer using the ion implantation layer as a peeling surface to obtain the SOI layer.

The SOI wafer manufacturing method of the present invention may further include other steps.

Next, each step of the SOI wafer manufacturing method of the present invention will be explained in more detail.

(Process of preparing base wafer and bond wafer)
In this process, a base wafer consisting of a silicon single crystal wafer containing a dopant throughout the wafer and having a first main surface and a second main surface opposite to the first main surface, and a base wafer having a dopant concentration lower than that of the base wafer are used. A bond wafer consisting of a silicon single crystal wafer containing a dopant is prepared.

Examples of the base wafer to be prepared include the base wafers mentioned in the description of the SOI wafer of the present invention. In particular, by using a base wafer having a dopant concentration of 1×10 ¹⁷ atoms/cm ³ or more, it is possible to exhibit an excellent gettering effect and further suppress warpage of the manufactured SOI wafer. For the reasons explained above, in the SOI wafer manufacturing method of the present invention, even if a base wafer with a dopant concentration of 1×10 ¹⁷ atoms/cm ³ or more is used, no dopant is contained in the base wafer. This can prevent dopants from entering the bond wafer or SOI layer.

The bond wafer becomes an SOI layer in a thinning process explained later. Therefore, it is preferable to prepare a bond wafer having the conductivity type and resistivity required for the SOI layer of the SOI wafer to be manufactured. Specifically, as the bond wafer to be prepared, the bond wafer made of silicon single crystal of the SOI layer mentioned in the description of the SOI wafer of the present invention can be mentioned.

(Process of forming a silicon oxide film on the entire surface of the bond wafer)
In this optional step, a silicon oxide film is formed on the entire surface of the prepared bond wafer before the bonding step described later.

The means for forming the silicon oxide film is not particularly limited, but for example, the silicon oxide film can be formed by thermally oxidizing the surface of a bond wafer.

(Ion implantation process)
In this optional step, at least one type selected from the group consisting of hydrogen ions and rare gas ions is implanted into the bond wafer to form an ion implantation layer.

The specific means for implanting ions is not particularly limited, and any known method can be used.

(Step of forming backside silicon film)
In this step, a back silicon film is formed on the second main surface of the base wafer (the back surface with respect to the bonding surface (first main surface) of the bond wafer).

As the backside silicon film, for example, a film containing at least one selected from the group consisting of polysilicon, amorphous silicon, and single crystal silicon can be formed. As mentioned above, among these, polysilicon is preferable in consideration of the gettering effect during heat treatment such as thermal oxide film formation on the base wafer. The back silicon film containing polysilicon can also be called a poly back seal.

The backside silicon film contains a dopant. The dopant in the backside silicon film may be the same type of dopant as the dopant contained in the base wafer, or may be different from the dopant contained in the base wafer. The dopant concentration in the backside silicon film is not particularly limited as long as it is lower than the dopant concentration in the base wafer, but can be set to, for example, 1×10 ¹³ atoms/cm ³ or more and 1×10 ¹⁶ atoms/cm ³ or less.

The backside silicon film is formed by, for example, placing the base wafer on a susceptor in a CVD furnace with its first main surface facing down, and then depositing a dopant-containing polyester on the second main surface, which is the opposite surface. It can be formed by depositing a silicon or amorphous silicon film by CVD (Chemical Vapor Deposition). Furthermore, a single crystal silicon film containing a dopant can also be formed as a backside silicon film by an epitaxial method.

(Step of forming barrier silicon layer)
This optional step forms a barrier silicon layer containing a dopant at a lower concentration than the dopant concentration of the base wafer on the first major surface of the base wafer.

The barrier silicon layer formed in this arbitrary step can be made into a barrier silicon oxide film as part of the silicon oxide film to be formed over the entire surface of the base wafer in a later thermal oxidation step. Since such a barrier silicon oxide film can act as an additional dopant diffusion prevention layer, autodoping due to solid phase diffusion from the first main surface of the base wafer to the bond wafer can be suppressed more reliably.

The barrier silicon layer can be formed on the first main surface of the base wafer by, for example, epitaxial growth.

It is preferable to form the barrier silicon layer with a dopant concentration of 1×10 ¹⁶ atoms/cm ³ or less.

By forming such a barrier silicon layer, it is possible to more reliably suppress the incorporation of dopant into the SOI layer due to solid phase diffusion from the base wafer through the silicon oxide film disposed on the first main surface. .

The dopant concentration of the barrier silicon layer can be so-called non-doped, and can be set to a level that is unavoidably mixed. The dopant contained in the barrier silicon layer may be the same type as the dopant in the base wafer, or may be different from the dopant in the base wafer.

The thickness of the barrier silicon layer is not particularly limited, but is, for example, half the total thickness of the silicon oxide film (buried oxide film) between the SOI layer and the base wafer of the SOI wafer obtained by the SOI wafer manufacturing method of the present invention. It can be more than that. By forming a barrier silicon layer having such a thickness and using it as a barrier silicon oxide film through a thermal oxidation process described later, the bond wafer or bond wafer can be thinned from the first main surface of the base wafer. Incorporation of dopant into the resulting SOI layer by solid phase diffusion can be more fully suppressed. The thickness of the barrier silicon oxide film is preferably 400 nm or more, more preferably 500 nm or more, and even more preferably 600 nm or more. The thickness of the barrier silicon oxide film can be, for example, 1000 nm or less.

Note that increasing the thickness of the barrier silicon layer makes it easier to suppress dopant diffusion from the base wafer, but a layer with a low dopant concentration compared to the thickness of the buried oxide film (BOX layer) of the SOI wafer If it is too thick, a layer with low dopant concentration will be formed directly under the BOX layer. If it is not desirable to manufacture such an SOI wafer, one way to prevent this is to reduce the thickness of the barrier silicon layer, for example, by reducing the thickness of the buried oxide film of the SOI wafer to be manufactured. It is desirable that the thickness be about half of the thickness of . Here, the oxidation ratio of Si/SiO ₂ =0.45 (the ratio of the film thicknesses of the Si layer and the SiO ₂ layer when the entire Si layer is changed to the SiO ₂ layer by thermal oxidation) was set to about half.

According to the SOI wafer manufacturing method of the present invention, it is possible to manufacture an SOI wafer in which the first main surface of the base wafer includes a portion that does not support an SOI layer, that is, a terrace portion. In this case, in any step of forming the barrier silicon layer, the barrier silicon layer may also be formed on the portion of the first main surface of the base wafer that will become the terrace portion. By converting the barrier silicon layer into a barrier silicon oxide film through a thermal oxidation process to be described later, the portion of the barrier silicon layer formed on the terrace portion also becomes part of the barrier silicon oxide film. This portion of the barrier silicon oxide film can further suppress out-diffusion of dopants from the terraces of the SOI wafer.

Therefore, in this case, even if there is a portion on the outer periphery of the base wafer where the SOI layer is not formed, that is, a terrace portion, the barrier silicon oxide film further prevents dopants from entering the SOI layer through this terrace portion. Can be done.

Note that the order of the step of forming a backside silicon film and the step of forming an arbitrary barrier silicon layer, which is performed before the thermal oxidation step of the base wafer, is not particularly limited. In addition, in order to reduce bonding defects, the surface of the bonding side of the base wafer on which both the backside silicon film and the barrier silicon layer have been formed (i.e., the barrier silicon layer) is repolished before the thermal oxidation process. You can also do that.

(Thermal oxidation process)
In this step, a silicon oxide film is formed on the entire surface of the base wafer by thermal oxidation. Further, in this step, the backside silicon film formed on the second main surface of the base wafer is thermally oxidized to obtain a backside silicon thermal oxide film as a part of the silicon oxide film to be formed on the entire surface of the base wafer.

In this step, thermal oxidation may be performed so that a portion of the backside silicon film remains unoxidized.

In addition, when a barrier silicon layer is not formed on the first main surface of the base wafer, the first main surface of the base wafer (the surface to be bonded to the bond wafer) is also thermally oxidized in this step, and the surface silicon layer described above is It becomes an oxide film. After this step, the surface of the base wafer that is in contact with the surface silicon oxide film becomes a new first main surface.

In addition, when a barrier silicon layer is formed on the first main surface of the base wafer, in this step, at least a portion of the barrier silicon layer is thermally oxidized to form a part of the silicon oxide film formed on the entire surface of the base wafer. A barrier silicon oxide film can be obtained.

In this step, thermal oxidation may be performed so that a portion of the barrier silicon layer remains unoxidized.

In the thermal oxidation process, thermal oxidation is performed so that the barrier silicon layer is not completely oxidized and a residual unoxidized thickness remains to form a silicon oxide film that will become at least a part of the buried oxide film (BOX layer). Directly below the oxide film, a portion of the barrier silicon layer in an unoxidized state with a low dopant concentration is formed. In that case, by adding a dopant diffusion heat treatment (annealing) after the thermal oxidation step, it is possible to compensate for the dopant concentration directly under the silicon oxide film. This diffusion heat treatment can be supplemented with a bonding heat treatment or an extension of the heat treatment time.

Alternatively, the entire barrier silicon layer may be thermally oxidized to form a barrier silicon oxide film, and the portion of the base wafer directly below the barrier silicon layer may be further thermally oxidized.

The degree of thermal oxidation can be adjusted by, for example, the thermal oxidation temperature and time.

Among the silicon oxide films obtained by this thermal oxidation, the barrier silicon oxide film is obtained by thermally oxidizing at least a portion of the barrier silicon layer, and the back silicon thermal oxide film is obtained by thermally oxidizing the back silicon film. be.

In addition, when an SOI wafer including a terrace portion is manufactured using the SOI wafer manufacturing method of the present invention and a device is manufactured using this, the silicon oxide film formed on the entire surface of the base wafer in this thermal oxidation step is It is possible to suppress not only the out-diffusion of the dopant through the second main surface of the SOI wafer, but also the out-diffusion of the dopant through the silicon oxide film on the terrace portion of the SOI wafer. Therefore, according to the SOI wafer manufacturing method of the present invention, it is possible to sufficiently suppress dopant contamination to the internal parts of the heat treatment furnace, and it is also possible to obtain the effect of suppressing secondary contamination from the furnace internal parts to the wafer.

(Lamination process)
In this step, one main surface of the bond wafer and the first main surface of the base wafer are bonded together via the silicon oxide film on the base wafer.

If a silicon oxide film is formed on the entire surface of the bond wafer before this bonding process, in the bonding process, the base wafer and the bond wafer are They can be bonded together via a silicon oxide film placed on the surface. By performing the bonding step in this manner, it is possible to more reliably suppress the dopant from entering the bond wafer or the SOI layer from the first main surface of the base wafer.

Alternatively, in this bonding step, the silicon single crystal surface of one main surface of the bond wafer and the surface of the surface silicon oxide film of the base wafer may be directly bonded.

Even when a silicon oxide film is not formed on a bond wafer, the incorporation of dopants into an SOI layer by solid phase diffusion from a base wafer through a silicon oxide film disposed on a first principal surface is sufficiently suppressed. I can do it. This aspect is particularly effective when bonding oxide films cannot be applied (for example, when high temperature heat treatment cannot be performed in the bonding process).

In particular, when forming a barrier silicon oxide film, in this bonding process, by directly bonding the silicon single crystal surface on one main surface of the bond wafer and the surface of the barrier silicon oxide film on the base wafer, The incorporation of dopant into the SOI layer due to solid phase diffusion through the silicon oxide film disposed on the first main surface of the SOI layer can be sufficiently suppressed.

(Thinning process)
In this step, the bond wafer is thinned to form an SOI layer.

The method for thinning the film is not particularly limited, and may be grinding, polishing, etching, etc., but it is preferable to thin the film by ion implantation and peeling. When performing the ion implantation stripping method, the ion implantation process described above is performed in advance to form an ion implantation layer on the bond wafer. Then, by peeling off the bond wafer using this ion-implanted layer as a peeling surface, the bond wafer can be made into a thin film and an SOI layer can be obtained.

By performing such an ion implantation peeling method, a thin SOI layer having excellent film thickness uniformity can be obtained.

Following the film thinning process, a sacrificial oxidation process, a flattening heat treatment process, a polishing process, a mirror polishing process, a cleaning process, etc. may be performed.

In the SOI wafer manufacturing method of the present invention, an SOI wafer can be obtained through a thinning process or any subsequent process. According to the SOI wafer manufacturing method of the present invention, for example, the SOI wafer of the present invention described above can be manufactured.

Next, some specific examples of the SOI wafer manufacturing method of the present invention will be described with reference to FIGS. 5 to 7. However, the SOI wafer manufacturing method of the present invention is not limited to the example described below.

[First example]
FIG. 5 is a schematic flow diagram showing a first example of the SOI wafer manufacturing method of the present invention. According to the manufacturing method of this example, it is possible to manufacture, for example, the SOI wafer of the first example described with reference to FIG. 1, in which the surface silicon oxide film 21 does not include a barrier silicon oxide film. .

First, in step (a), a base wafer 10 and a bond wafer 31 are prepared. The base wafer 10 has a first main surface 11 facing upward in FIG. 5, a second main surface 12 opposite to the first main surface 11, and a side surface connecting the first main surface 11 and the second main surface 12. (edge portion) 13. The bond wafer 31 has one main surface 32 that will be bonded to the first main surface 11 of the base wafer 10 later. Both the base wafer 10 and the bond wafer 31 contain dopants, but the concentration of dopants is higher in the base wafer 10.

Next, in step (b), a back silicon film 40 is formed on the second main surface 12 of the base wafer 10 prepared in step (a). The backside silicon film 40 contains a dopant at a lower concentration than the dopant concentration of the base wafer 10 .

Next, in step (c), the base wafer 10 is subjected to thermal oxidation to obtain a silicon oxide film 50. In this example, in this thermal oxidation step (c), the entire back silicon film 40 is turned into a back silicon thermal oxide film 51. Furthermore, the portion of the base wafer 10 that included the first main surface 11 also becomes the surface silicon oxide film 21, and a new first main surface 11 is formed in the base wafer 10 in contact with this surface silicon oxide film 21. Then, a side silicon oxide film 52 is formed on the side surface 13 of the base wafer 10. The front silicon oxide film 21, the back silicon thermal oxide film 51, and the side silicon oxide film 52 form a silicon oxide film 50 that covers the entire surface of the base wafer 10.

Next, in step (d), one main surface 32 of the bond wafer 31 prepared in step (a) and the first main surface 11 of the base wafer 10 subjected to thermal oxidation in step (c) are separated. , and are bonded via the silicon oxide film 50, specifically, the surface silicon oxide film 21.

Next, in step (e), the bond wafer 31 is thinned to obtain the SOI layer 30.

Before the bonding step (d), an ion implantation step is performed in which at least one type selected from the group consisting of hydrogen ions and rare gas ions is implanted into the bond wafer 31 to form an ion implantation layer. The converting step (e) can also be performed by an ion implantation stripping method.

By performing the film thinning step (e), the SOI wafer 100 of the first example shown in FIG. 1 can be obtained.

Note that if the degree of thermal oxidation in the thermal oxidation step (c) is weakened, the SOI wafer 100 of the second example shown in FIG. 2 can also be obtained.

[Second example]
FIG. 6 is a schematic flow diagram showing a second example of the SOI wafer manufacturing method of the present invention. According to the manufacturing method of this example, it is possible to manufacture, for example, an SOI wafer of the first example described with reference to FIG. 1, in which the surface silicon oxide film 21 is a barrier silicon oxide film.

The manufacturing method of the second example is a step of forming a barrier silicon layer 60 on the first main surface 11 of the base wafer 10 after forming the backside silicon film in step (b) and before the thermal oxidation step (c). This is different from the manufacturing method of the first example in that (f) is performed.

In step (f), a barrier silicon layer 60 having a lower dopant concentration than the base wafer 10 is formed.

In the manufacturing method of this example, a surface silicon oxide film 21 made of a barrier silicon oxide film is formed by the thermal oxidation step (c).

Note that if the degree of thermal oxidation in the thermal oxidation step (c) is weakened, the SOI wafer 100 of the fourth example shown in FIG. 4 can also be obtained.

[Third example]
FIG. 7 is a schematic flow diagram showing a third example of the SOI wafer manufacturing method of the present invention. According to the manufacturing method of this example, for example, the SOI wafer of the third example described with reference to FIG. 3 can be manufactured.

In the manufacturing method of the third example, one main surface 32 of the bond wafer 31 prepared in step (a) on the side to be bonded to the base wafer 10, the main surface (back surface) 36 on the opposite side, and a side surface connecting these. This manufacturing method differs from the first example in that it includes a step (g) of forming a silicon oxide film 34 on the entire surface including the edge portion 33.

The silicon oxide film 34 formed in step (g) includes the SOI side silicon oxide film 22 formed on one main surface 32 of the bond wafer 31, the back silicon oxide film 37 formed on the main surface 36, and the side surface 33. and a side silicon oxide film 35 formed on the surface.

Further, in the manufacturing method of the third example, in the bonding step (d), the base wafer 10 and the bond wafer 31 are bonded via the front silicon oxide film 21 and the SOI side silicon oxide film 22.

In the manufacturing method of the third example, in the thinning step (e), a portion of the bond wafer 31 including the portion where the backside silicon oxide film 37 is formed is peeled off to obtain the SOI layer 30. By performing such a thinning step (e), it is possible to obtain the SOI wafer 100 of the third example shown in FIG. 3.

[Measuring method]
The dopant concentration in the base wafer, bond wafer, back silicon film, back silicon thermal oxide film, barrier silicon layer, barrier silicon oxide film, etc. can be measured using, for example, a secondary ion mass spectrometer (SIMS).

The thickness of each component included in the SOI wafer, as well as the thickness of each wafer prepared in the SOI wafer manufacturing method and the thickness of each layer formed, can be confirmed by, for example, cross-sectional SEM, light reflection method, ellipsometry, etc.

Hereinafter, the present invention will be specifically explained using Examples and Comparative Examples, but the present invention is not limited thereto.

(Example 1)
In Example 1, the SOI wafer 100 was manufactured in a flow similar to the flow schematically shown in FIG.

<Step (a)>
First, as the bond wafer 31, a p-type silicon single crystal wafer (resistivity: 10 Ωcm) having a diameter of 300 mm and doped with boron (dopant concentration 1×10 ¹⁵ atoms/cm ³ ) was prepared. Further, as the base wafer 10, a p-type silicon single crystal wafer (resistivity: 0.1 Ωcm) having a diameter of 300 mm and doped with boron (dopant concentration 1×10 ¹⁷ atoms/cm ³ ) was prepared.

Furthermore, hydrogen ions were implanted into the prepared bond wafer 31 from the one main surface 32 side, which is the bonding surface, under the conditions shown in Table 1 below to form an ion-implanted layer.

<Step (b)>
Next, the base wafer 10 is placed on a susceptor of a CVD furnace with the first main surface 11 facing down, and a boron-doped polysilicon film is formed on the second main surface 12 as the back silicon film 40. was formed by CVD method. The thickness of the formed polysilicon film was 500 nm. The dopant concentration of the formed polysilicon film was 1×10 ¹⁵ atoms/cm ³ .

<Step (f)>
Next, a barrier silicon layer 60 was epitaxially grown on the first main surface 11, which is the bonding surface of the base wafer 10. The barrier silicon layer had a p-type conductivity, a thickness of 400 nm, a resistivity of 10 Ωcm, and a dopant concentration of 1×10 ¹⁵ atoms/cm ³ .

<Step (c)>
Next, the entire surface of the base wafer 10 was thermally oxidized to form a silicon oxide film 50 covering the entire surface of the base wafer 10.

The thermal oxidation was performed so that the thickness of the silicon oxide film 50 was 1000 nm. Therefore, in this thermal oxidation step (c), the entire backside silicon film 40 was oxidized to become a backside silicon thermal oxide film 51. Further, the entire barrier silicon layer 60 was also oxidized to become a barrier silicon oxide film 21.

<Step (d)>
Next, the base wafer 10 subjected to thermal oxidation in step (c) and the bond wafer 31 on which the ion-implanted layer has been formed are placed so that the barrier silicon oxide film 21 and one main surface 32 of the bond wafer 31 are in contact with each other. Pasted together.

<Step (e)>
This bonded wafer is subjected to a peeling heat treatment for 30 minutes in an argon atmosphere at 500°C, and the bond wafer 31 is peeled off using the ion-implanted layer as a peeling surface, thereby thinning the bond wafer 31 and forming the SOI layer 30. Obtained.

Subsequently, in order to remove damage to the SOI layer 30, sacrificial oxidation treatment was performed under the conditions shown in Table 1 below. This sacrificial oxidation treatment also serves as bonding heat treatment to strengthen the bond between the wafers. Then, planarization heat treatment was performed under the conditions shown in Table 1 below, and SOI wafer 100 was manufactured.

(Examples 2 to 5 and Comparative Example 1)
The SOI wafers 100 of each example were manufactured under the same conditions as in Example 1 except that the manufacturing conditions were as shown in Tables 1 to 3 below.

<Evaluation>
The dopant concentration in the SOI layer 30 of the SOI wafer 100 of each example was measured using SIMS. The results are shown in Tables 1 to 3 below.

(Comparative Examples 2 and 3)
In Comparative Examples 2 and 3, SOI wafers 100 of each example were manufactured under the same conditions as Examples 3 and 5, respectively, except that a polysilicon film was not formed on the second main surface 12 of the base wafer 10. . The boron concentration of the SOI layer of the SOI wafer of Comparative Example 2 was 8×10 ¹⁷ atoms/cm ³ . Further, the phosphorus concentration of the SOI layer of the SOI wafer of Comparative Example 3 was 3×10 ¹⁵ atoms/cm ³ .

From the comparison of the results of Example 1 and Comparative Example 1 shown in Table 1, the SOI wafer of Example 1 in which a backside silicon film was formed had a lower temperature than the SOI wafer of Comparative Example 1 in which a backside silicon film was not formed. It can be seen that the increase in the boron concentration in the SOI layer due to the mixing of boron from the base wafer could be significantly suppressed.

Furthermore, from a comparison of the results of Examples 2 and 3 shown in Table 2 and Comparative Example 2 shown above, it was found that the SOI wafers of Examples 2 and 3 in which a back silicon film was formed did not have a back silicon film. It can be seen that the increase in the boron concentration in the SOI layer due to the mixing of boron from the base wafer was able to be significantly suppressed compared to Comparative Example 2 in which no boron was present.

Furthermore, from the comparison of the results of Example 2 and Example 3 shown in Table 2, the SOI wafer of Example 2 in which a barrier silicon layer was further formed was different from the SOI wafer of Example 3 in which a barrier silicon layer was not formed. It can be seen that it was possible to further suppress the increase in boron concentration in the SOI layer due to the mixing of boron from the base wafer.

Furthermore, from a comparison of the results of Examples 4 and 5 shown in Table 3 and Comparative Example 3 shown above, it was found that the SOI wafers of Examples 4 and 5 in which a back silicon film was formed did not have a back silicon film. It can be seen that the increase in the phosphorus concentration in the SOI layer due to the mixing of phosphorus from the base wafer was able to be significantly suppressed compared to Comparative Example 3 where no phosphorus was present.

From the comparison of the results of Example 4 and Example 5 shown in Table 3, the SOI wafer of Example 4 in which a barrier silicon layer was further formed was different from the SOI wafer of Example 5 in which no barrier silicon layer was formed. It can be seen that it was possible to further suppress the increase in the phosphorus concentration in the SOI layer due to the mixing of phosphorus from the base wafer.

(Example 6)
In Example 6, the thickness of the barrier silicon layer (epilayer) and the SOI layer/buried oxidation were measured when an SOI wafer was manufactured under the same conditions as in Example 2 except that the thickness of the barrier silicon layer to be formed was changed. The relationship with the boron concentration in the SOI layer near the film (BOX layer) interface was simulated. The results calculated graphically are shown in FIG. 8.

According to FIG. 8 and Table 2, it can be seen that by forming a barrier silicon layer, the increase in the boron concentration of the SOI layer can be further suppressed compared to Example 3 in which no barrier silicon layer was formed. Furthermore, according to FIG. 8, if the barrier silicon layer is formed to a thickness of 400 nm, the increase in the boron concentration in the SOI layer can be suppressed to within twice, and furthermore, the increase in the boron concentration in the SOI layer can be suppressed to within half that of the buried oxide film that will be formed later. It can be seen that if the SOI layer is formed with a thickness of 500 nm, the increase in boron concentration in the SOI layer can be almost suppressed.

(Example 7)
In Example 7, a simulation was performed under the same conditions as Example 6 except that the thickness of the buried oxide film was 2 μm. FIG. 9 shows simulation results for calculating the relationship between the thickness of the barrier silicon layer (epilayer) and the boron concentration in the SOI layer near the SOI layer/buried oxide film interface.

According to FIG. 9 and Table 2, even if the thickness of the buried oxide film is increased to 2 μm, if a barrier silicon layer is formed, boron in the SOI layer is It can be seen that the increase in concentration can be significantly suppressed.

Furthermore, according to FIG. 9, even if the thickness of the buried oxide film is increased to 2 μm, the boron concentration in the SOI layer can be sufficiently increased by forming a barrier silicon layer of about 400 to 500 nm, as in the case of 1 μm. It can be seen that this can be suppressed.

This is because an oxide film containing a high concentration of boron from the base wafer is formed in the latter half of the 2 μm thick buried oxide film (apart from the SOI layer), but the barrier silicon layer is oxidized. This means that boron does not diffuse into the SOI layer and does not affect the boron concentration in the SOI layer because the diffusion rate of boron in the buried oxide film including the barrier silicon oxide film is slow. Therefore, even if the buried oxide film is thicker than 2 μm, it is possible to suppress the increase in dopant concentration in the SOI layer by forming a barrier silicon layer, and the thickness of the barrier silicon layer is 400 to 500 nm. It is suggested that a thickness of about 600 to 1000 nm is sufficient from a safety standpoint.

Note that the present invention is not limited to the above embodiments. The above-mentioned embodiments are illustrative, and any embodiment that has substantially the same configuration as the technical idea stated in the claims of the present invention and has similar effects is the present invention. covered within the technical scope of.

DESCRIPTION OF SYMBOLS 10... Base wafer, 11... First main surface (bonding surface), 12... Second main surface, 13... Side surface (edge part), 14... Terrace part, 20... Buried oxide film, 21... Surface silicon oxide film ( barrier silicon oxide film), 22... SOI side silicon oxide film, 30... SOI layer, 31... bond wafer, 32... one main surface (bonding surface) 33... side surface, 34... silicon oxide film, 35... side silicon oxide Film, 36... Other main surface (back surface), 37... Back silicon oxide film, 40... Back silicon film, 50... Silicon oxide film, 51... Back silicon thermal oxide film, 52... Side silicon oxide film, 60... Barrier silicon Layer, 100...SOI wafer.

Claims (13)

at least,
a base wafer consisting of a silicon single crystal wafer containing a dopant throughout the wafer and having a first main surface and a second main surface opposite to the first main surface; and a dopant at a lower concentration than the dopant concentration of the base wafer. a step of preparing a bond wafer consisting of a silicon single crystal wafer containing;
a thermal oxidation step of forming a silicon oxide film on the entire surface of the base wafer by thermal oxidation;
a bonding step of bonding one main surface of the bond wafer and the first main surface of the base wafer via the silicon oxide film on the base wafer;
a thinning step of thinning the bond wafer to form an SOI layer;
A method for manufacturing an SOI wafer, comprising:
Further comprising the step of forming a backside silicon film containing a dopant at a lower concentration than the dopant concentration of the base wafer on the second main surface of the base wafer before the thermal oxidation step of the base wafer,
In the thermal oxidation step, the backside silicon film is thermally oxidized to obtain a backside silicon thermal oxide film as a part of the silicon oxide film ;
A method for manufacturing an SOI wafer, characterized in that in the thermal oxidation step, all of the backside silicon films are made into the backside silicon thermal oxide film . 2. The method for manufacturing an SOI wafer according to claim 1, wherein a film containing at least one selected from the group consisting of polysilicon, amorphous silicon, and single crystal silicon is formed as the backside silicon film. Prior to the thermal oxidation step of the base wafer, the method further includes forming a barrier silicon layer containing a dopant at a lower concentration than the dopant concentration of the base wafer on the first main surface of the base wafer,
In the thermal oxidation step, thermally oxidize the barrier silicon layer to obtain a barrier silicon oxide film as a part of the silicon oxide film,
In the bonding step, the one main surface of the bond wafer and the first main surface of the base wafer are bonded via the barrier silicon oxide film that is a part of the silicon oxide film. The method for manufacturing an SOI wafer according to claim 1 or claim 2. 4. The method for manufacturing an SOI wafer according to claim 1, further comprising the step of forming a silicon oxide film on the entire surface of the bond wafer before the bonding step. The SOI wafer according to claim 3, wherein in the bonding step, the silicon single crystal surface of the one main surface of the bond wafer and the surface of the barrier silicon oxide film of the base wafer are directly bonded. manufacturing method. 6. The method of manufacturing an SOI wafer according to claim 3, wherein the barrier silicon layer is formed with a dopant concentration of 1×10 ¹⁶ atoms/cm ³ or less. In the thermal oxidation step, thermal oxidation is performed so that a part of the barrier silicon layer remains in an unoxidized state,
7. Annealing is then performed to diffuse the dopant in the base wafer into the unoxidized portion of the barrier silicon layer. A method for manufacturing an SOI wafer. Prior to the bonding step, the method further includes an ion implantation step of implanting at least one type selected from the group consisting of hydrogen ions and rare gas ions into the bond wafer to form an ion implantation layer,
In the thinning step, the bond wafer is peeled using the ion implantation layer as a peeling surface, thereby thinning the bond wafer and obtaining the SOI layer. The method for manufacturing an SOI wafer according to item 1. 9. The method for manufacturing an SOI wafer according to claim 1, wherein the base wafer is prepared having a dopant concentration of 1×10 ¹⁷ atoms/cm ³ or more. An SOI wafer comprising a base wafer, a buried oxide film, and an SOI layer bonded to the base wafer via the buried oxide film,
The base wafer is made of a silicon single crystal wafer containing a dopant throughout the wafer and having a first main surface that is a bonding surface with the SOI layer and a second main surface opposite to the first main surface. Become,
A backside silicon thermal oxide film containing a dopant at a lower concentration than the dopant concentration of the base wafer is disposed on the second main surface of the base wafer in direct contact with the second main surface ,
An SOI wafer, wherein the SOI layer is made of a silicon single crystal containing a dopant at a concentration lower than that of the base wafer. 11. The SOI wafer according to claim 10, wherein a barrier silicon oxide film as at least a part of the buried oxide film is disposed on the first main surface of the base wafer. A barrier silicon layer is disposed between the base wafer and the barrier silicon oxide film,
12. The SOI wafer according to claim 11, wherein a dopant of the same type as a dopant contained in the base wafer is diffused into the barrier silicon layer. at least,
a base wafer consisting of a silicon single crystal wafer containing a dopant throughout the wafer and having a first main surface and a second main surface opposite to the first main surface; and a dopant at a lower concentration than the dopant concentration of the base wafer. a step of preparing a bond wafer consisting of a silicon single crystal wafer containing;
a thermal oxidation step of forming a silicon oxide film on the entire surface of the base wafer by thermal oxidation;
a bonding step of bonding one main surface of the bond wafer and the first main surface of the base wafer via the silicon oxide film on the base wafer;
a thinning step of thinning the bond wafer to form an SOI layer;
A method for manufacturing an SOI wafer, comprising:
Further comprising the step of forming a backside silicon film containing a dopant at a lower concentration than the dopant concentration of the base wafer on the second main surface of the base wafer before the thermal oxidation step of the base wafer,
In the thermal oxidation step, the backside silicon film is thermally oxidized to obtain a backside silicon thermal oxide film as a part of the silicon oxide film;
Prior to the thermal oxidation step of the base wafer, the method further includes forming a barrier silicon layer containing a dopant at a lower concentration than the dopant concentration of the base wafer on the first main surface of the base wafer,
In the thermal oxidation step, thermally oxidize the barrier silicon layer to obtain a barrier silicon oxide film as a part of the silicon oxide film,
In the bonding step, the one main surface of the bond wafer and the first main surface of the base wafer are bonded via the barrier silicon oxide film that is a part of the silicon oxide film,
In the thermal oxidation step, thermal oxidation is performed so that a part of the barrier silicon layer remains in an unoxidized state,
A method for manufacturing an SOI wafer, comprising: thereafter applying annealing to diffuse the dopant in the base wafer into a portion of the unoxidized layer of the barrier silicon layer.

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