JPH06104413A - Manufacturing for semiconductor device - Google Patents

Abstract

PURPOSE:To reduce a productive cost and make quality control easy, by using simple formation steps including a step for grinding and lapping a joining layer to form a flat face of an SIO-structured board. CONSTITUTION:A joining layer 4 made of polysilicon is formed on a side of an active layer substrate (A). After the joining layer 4 is put in a ductility-mode grinding step and a specular grinding face 4b is formed, an insulating layer 7 is formed on the grinding face 4b. Then, a base substrate (B) is bonded to the joining face 7a of the insulating layer 7 to form a semiconductor substrate in an SOI structure. The manufacturing step can be simplified without forming a joining layer in a multi-layered structure. The bonding face is made smooth by this insulating layer 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor substrate in which a monocrystalline / polycrystalline or amorphous silicon layer is formed on a semiconductor substrate in a mirror surface state, and more particularly to a thin film SOI structure substrate or a dielectric isolation substrate. The present invention relates to a method for manufacturing a semiconductor substrate, which simplifies the bonding layer forming step and the grinding / polishing step for facilitating the bonding, and can form a mirror-like bonded surface only by mechanical grinding and polishing.

[0002]

2. Description of the Related Art When forming an integrated circuit, various elements (devices) are formed in a thin film semiconductor layer provided on an oxide film insulating layer, as compared with a method of forming this integrated circuit in a bulk semiconductor substrate. The method is superior in element characteristics such as α-ray interference characteristics and operating speed, and is also advantageous in terms of element separation.

This type of semiconductor substrate is called an SOI (silicon on insulator) wafer,
In such an SOI wafer, the thinner the silicon layer forming the device is, the more the parasitic capacitance of the pn junction can be reduced and the operating speed of the device can be increased. Further, it is effective to realize a three-dimensional structure in order to increase the degree of integration, and as one method therefor, an SOI wafer that can form a basic structure in which an oxide film and a semiconductor layer are superposed is drawing attention. .

By the way, a so-called laminating method is known as a method for obtaining an SOI structure substrate. In the conventional bonding method, first, Si is formed on one surface of a silicon substrate 1 (hereinafter, also referred to as active layer substrate 1 or active layer substrate A).
An oxide film 3 made of O ₂ is formed (see FIG. 7A), and a bonding layer 4 made of polysilicon is formed on the oxide film 3 (see FIG. 7B). Next, the surface of the bonding layer 4 is subjected to mechanochemical polishing to be flattened (see FIG. 7C), and then another silicon substrate 5 (hereinafter referred to as a support substrate 5 or a support substrate) is provided on the polishing surface 4a. (Also referred to as B) (see FIG. 9G), and finally, the surface of the active layer substrate 1 is ground and polished until the oxide film 3 is exposed (FIG. 9).
(See (h)).

However, in the method of manufacturing an SOI substrate by such a bonding method, patterning 2 is performed in advance by a photolithography technique or an etching technique.
When the active layer substrate A (see FIG. 7A) is used and the oxide film 3 is formed on the active layer substrate A, the surface of the polysilicon forming the bonding layer 4 is subjected to grinding and polishing due to the grain size. There was a problem that it was not smooth.

That is, according to what the inventors of the present invention have sought, the polysilicon layer forming the bonding layer 4 is generally used to improve the characteristics such as conductivity, impurity diffusion rate, film stability, and oxidation rate. Although grown at a high reaction temperature, the grain size of polysilicon becomes larger as the reaction temperature becomes higher, so that the grain size of the bonding layer 4 obtained becomes relatively large, and the crystal growth occurs in the direction perpendicular to the surface. Therefore, in the uneven portion of the oxide film 3, polysilicon crystals grow in different directions, and an interface with which these collide is formed. In addition to this, when chemical polishing such as mechanochemical polishing is performed, the polishing rate is
Since it is susceptible to the growth direction and the like, mechanochemical polishing of the surface of polysilicon results in a situation in which selective polishing is performed overall. Therefore, there is a problem that the desired flatness cannot be obtained on the bonding surface 4a, and the intended bonding strength cannot be obtained even when the support substrate B is bonded.

Therefore, the first bonding layer 4 made of polysilicon grown by the high temperature reaction on the oxide film 3 is formed.
Is formed, and the first bonding layer 4 is ground and polished to make the surface smooth to some extent (see FIG. 7C), and then grown on the surface of the first bonding layer 4 by a low temperature reaction. And a polysilicon layer (second bonding layer) 6 is formed (see FIG. 8).
(See (d)), and this is polished to obtain a predetermined smoothness (see FIG. 8E).

According to this method, since the second bonding layer 6 which becomes the bonding surface 6a is formed of polysilicon having a small grain size, even if mechanochemical polishing is performed, selective polishing is relatively performed. (Apparently), and as a result, the bonding strength when the support substrate B is attached is increased, and peeling can be prevented.

A second oxide film 7 made of SiO ₂ is formed on the bonding surface 6a in order to increase the degree of integration (FIG. 8 (f)).
Also, the support substrate 5 is bonded to the oxide film 7.

[0010]

However, in order to improve the smoothness of the surface of the bonding layer, if the bonding layer has a multilayer structure (the first bonding layer 4 and the second bonding layer 6 in the above-mentioned example), The number of manufacturing processes increased, and there were problems in terms of manufacturing cost and quality control.

The present invention has been made in view of the above problems of the prior art, and in flattening the bonding surface of the SOI structure substrate, the bonding layer forming step and the grinding / polishing step are simplified. By doing so, it is intended to reduce manufacturing cost and facilitate quality control.

[0012]

In order to achieve the above object, a method of manufacturing a semiconductor substrate of the present invention comprises forming a bonding layer on at least one surface of one semiconductor substrate and polishing the bonding layer to bond the bonding surface. In the manufacturing method of manufacturing the semiconductor substrate having the SOI structure by bonding the other semiconductor substrate to the bonding surface after the formation of the bonding layer, the bonding layer is ground by ductile mode grinding to form a mirror-finished ground surface. The feature is that an oxide film is formed on the ground surface.

[0013]

When silicon, which is a hard and brittle material, is ground, brittle fracture processing with cracks is generally performed, and the ground surface becomes a crushed surface. However, even with such a hard and brittle material, if the processing unit is limited to a sufficiently small range such as a minute cut on the order of 0.1 μm, it is possible to perform mirror surface grinding in the plastic region instead of brittle fracture.

Grinding of the hard and brittle material in the plastic region is
Especially called ductile mode grinding or plastic flow type grinding,
The most important parameter for realizing this ductile mode grinding is the critical processing unit dc (also referred to as ductile / brittle pressure transition point Pc) that represents the transition point between brittle fracture and plastic deformation fracture.
Is.

This critical processing unit is a value peculiar to the material, and if grinding is performed while controlling the pushing load below the critical processing unit, even if the material is hard and brittle, brittle fracture is likely to occur Will be shown.

Therefore, in the present invention, the bonding layer formed on one of the semiconductor substrates to be ground / polished is subjected to the above-described ductile mode grinding at least in the final step of grinding / polishing, and the resulting ground surface is obtained. Is mirror-finished, an oxide film is further formed on this ground surface, and this surface is used as a bonding surface.

As a result, it is no longer necessary to have a multi-layer structure for the bonding layer which has been conventionally formed for flattening the bonding surface. For example, on one of the semiconductor substrates, polysilicon is grown by a high temperature reaction to form a bonding layer, and if this bonding layer is subjected to ductile mode grinding, it is possible to obtain a mirror-finished ground surface by itself. Further, after forming an oxide film to form a bonding surface, the other semiconductor substrate is bonded and S
A semiconductor substrate having an OI structure can be manufactured.

In the obtained joint surface, the ground surface of the joint layer constituting the lower layer is an extremely smooth surface, and in addition to this, an oxide film is further formed on this smooth surface, so that it occurs on the ground surface. Grinding damage can be mitigated with an oxide film,
This further promotes the smoothness of the joint surface. Therefore, it becomes possible to simplify the step of forming the bonding layer for bonding and the step of grinding / polishing, and it is possible to reduce the manufacturing cost and facilitate the quality control.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a semiconductor substrate according to the present invention will be specifically described with reference to the accompanying drawings with reference to a preferred embodiment. However, the examples described below are described for facilitating the understanding of the present invention, and not for limiting the present invention. Therefore, each element disclosed in the following embodiments is intended to include all design changes and equivalents within the technical scope of the present invention.

1 to 3 are sectional views for explaining a method of manufacturing a semiconductor substrate according to an embodiment of the present invention.
1 (a) is an oxide film forming step, FIG. 1 (b) is a bonding layer forming step, FIG. 1 (c) is a grinding step, FIG. 2 (d) is a ductile mode grinding step, and FIG. 2 (e) is a second oxidation step. Membrane forming process, FIG.
FIG. 3F is a cross-sectional view illustrating the laminating step, and FIG. 3G is a cross-sectional view illustrating the grinding step of the active layer substrate.

First, as shown in FIG. 1A, a photolithography technique or an etching technique is applied to one surface of a semiconductor substrate 1 (hereinafter also referred to as an active layer substrate A or an active layer substrate 1) made of single crystal silicon. By using, for example, the grooves 2 having a depth of 0.1 μm are formed at intervals of 10 μm. This surface is thermally oxidized to form a SiO ₂ film having a thickness of 0.01 [mu] m, further, the SiO ₂ film by the thermal oxidation, CVD
A SiO ₂ film having a thickness of 0.9 μm is formed by the method. These 1.0 μm SiO ₂ films are used for the surface layer 3 of the active layer substrate.
The oxide film 3 (hereinafter also referred to as the oxide film 3) is formed as a film having irregularities as shown in the drawing according to the surface shape of the patterned active layer substrate A.

In the structure shown in FIG. 1A, a polysilicon film 4 as a bonding layer is further formed on the surface of the oxide film 3 (see FIG. 1B). The polysilicon film 4 has a reaction temperature of 800 ° C. to 1200 ° C., for example, by a CVD method.
As a result, a thickness of 5 μm is grown. The reason why the polysilicon film 4 is formed by reacting at a high temperature is to enhance the properties of the polysilicon film such as conductivity, impurity diffusion rate, film stability, and oxidation rate. Also,
Like the oxide film 3, the oxide film 3 is formed as a film having a slight unevenness according to the uneven shape of the oxide film 3.

Next, as shown in FIG. 1C, the surface of the polysilicon film 4 is ground to remove irregularities on the surface.
This polishing is the so-called product mode grinding (PM
G), for example, with an unsaturated polyester cloth,
Mechanochemical polishing is performed by dropping an alkaline solution in which fine particles of high-purity silica are dispersed and pressing a polysilicon film, which is a grinding surface, onto this cloth.

As shown in FIG. 1C, when the surface of the polysilicon film 4 is subjected to product mode grinding to be flattened to some extent, grinding damage of several μm occurs. In order to remove this grinding damage and to make the surface 4a of the polysilicon film 4 which constitutes the bonded joint surface into a mirror surface state, as shown in FIG. 2D, ductile mode grinding (ductile mode grinding, DMG) is applied.

In the main grinding step, since the grinding damage generated by the product mode grinding only needs to be removed, the grinding amount is several μm.

When polysilicon, which is a hard and brittle material, is ground, brittle fracture processing with cracks is generally performed, and the ground surface becomes a crushed surface, and a mirror-like bonded surface cannot be obtained. However, even with such a hard and brittle material, if the processing unit (specifically, due to the processing pressure) is limited to a sufficiently small range such as a micro-cut in the order of 0.1 μm, it is not a brittle fracture but a plastic region. It enables mirror surface grinding.

The most important parameter for realizing this ductile mode grinding is the critical processing unit dc (ductile / brittle pressure transition point P which represents the transition point between brittle fracture and plastic deformation fracture).
Also referred to as c), and the critical processing unit is a value peculiar to the material. Therefore, first, the critical processing unit of the polysilicon film 4 to be subjected to the ductile mode grinding is obtained, and grinding is performed while controlling the grinding device with a pushing load equal to or less than this critical processing unit. As a result, even polysilicon that is prone to brittle fracture exhibits plastic behavior.

When such ductile mode grinding is performed, the grinding damage on the grinding surface 4b is only 0.05 μm to 0.2 μm.
μm (= 500 to 2000 angstrom).

In the present invention, the second oxide film 7 is formed on the ground surface 4b as shown in FIG. 2 (e) in order to increase the degree of integration and further alleviate the grinding damage generated on the ground surface. Is formed. This oxide film 7 is, for example, C
The SOI insulating layer is formed by the VD method or the thermal oxidation method, or the sacrificial oxide film is formed by etching off the oxide film after oxidizing the crushed layer by thermal oxidation. Through the above steps, S
An active layer substrate A, which is one of the substrates forming the OI structure wafer, is obtained. At this time, the bonding surface 7 forming the SOI structure
Since a has a structure in which the oxide film 7 is formed on the ground surface 4b in a mirror surface state, the surface a is more smooth than the mirror surface state.

When the bonding surface 7a in a mirror state is obtained in the state shown in FIG. 2 (e), another semiconductor substrate 5 (hereinafter also referred to as the supporting substrate 5) to be the supporting substrate B is next formed on the bonding surface 7a. They are brought into close contact with each other and thermally bonded by hydrogen bonding to bond them together (see FIG. 2 (f)). The bonding strength is, for example, 20
0 kg / cm ² or more, the bonding temperature is 1100 ° C., and it is preferable to use the same silicon substrate as the active layer substrate 1 as the support substrate 5 in order to prevent warping of the SOI wafer due to the difference in thermal expansion.

As shown in FIG. 2 (f), after laminating the active layer substrate A and the supporting substrate B, chamfering of the side peripheral portion is performed and the thickness of the active layer substrate 1 becomes about 2 μm. Grind in advance.

Finally, as shown in FIG. 3G, the active layer substrate 1 is selectively ground. In this selective grinding, for example, a high-purity aluminum oxide surface plate having a surface roughness of 0.01 μm is rotated, and 5.0 wt% of fine particles of high-purity silica having a particle size of 0.02 μm are dispersed on the surface of the surface plate. This is performed by dropping the alkaline solution (polishing solution) having a pH of 10.5 and pressingly rubbing the active layer substrate 1 on the surface plate surface at a pressure of 100 g / cm ² .

When the selective grinding is performed, the active layer substrate 1 is gradually ground, but when the surface plate reaches the oxide film 3 made of SiO ₂ , the oxide film 3 is more mechanochemical than the active layer substrate 1. Since it is difficult to be polished, the grinding speed decreases rapidly. By detecting this grinding speed, the oxide film 3 as shown in FIG. 3 (g) is exposed from the surface of the active layer substrate 1, that is, the active layer 6 is separated by the oxide film 3 and its lower layer. SO with the second oxide film 7 laminated on the
An I structure wafer can be obtained.

The semiconductor substrate manufacturing method of the present invention can be applied to, for example, manufacturing of a laminated dielectric isolation substrate, in addition to the above-described thin film SOI structure.

4 to 6 are sectional views for explaining a method of manufacturing a semiconductor substrate according to another embodiment of the present invention.
4A is an oxide film forming step, FIG. 4B is a bonding layer forming step, FIG. 4C is a grinding step, FIG. 5D is a ductile mode grinding step, and FIG. 5E is a second oxidation step. Membrane forming process, FIG.
FIG. 5F is a cross-sectional view illustrating a laminating step, and FIG. 5G is a cross-sectional view illustrating an active layer substrate grinding step.

In an LSI having a high withstand voltage of several tens V to several hundreds V between elements, it is necessary to completely separate each element by a dielectric film such as an oxide film. In such a technical field. A so-called dielectric isolation substrate is widely used. In this embodiment, a specific example in which the present invention is applied to the method for manufacturing such a dielectric isolation substrate is shown.

First, one side of a semiconductor substrate 1 (hereinafter also referred to as an active layer substrate A or an active layer substrate 1) made of single crystal silicon is oxidized to form a SiO ₂ film on the entire surface, and then this SiO ₂ film is formed. Is opened at a predetermined location, and the SiO ₂ film is used as a mask, for example, by anisotropic etching,
For example, the separation groove 8 having a depth of about 60 μm is formed. Then, after removing the SiO ₂ film used as a mask,
The surface of the semiconductor substrate 1 is again oxidized to form an insulating oxide film 3 having a thickness of 1.2 μm on the entire surface (see FIG. 4A). The oxide film 3 is formed as a film having irregularities as shown in the figure according to the surface shape of the active layer substrate A in which the separation groove 8 is formed.

In the structure shown in FIG. 4A, a polysilicon film 4 as a bonding layer is further formed on the surface of the oxide film 3 (see FIG. 4B). The polysilicon film 4 has a reaction temperature of 800 ° C. to 1200 ° C., for example, by a CVD method.
As a result, the growth is performed until at least the separation groove 8 is completely filled (for example, the thickness is 100 μm). Similar to the oxide film 3, the polysilicon layer 4 is also formed as a film having slight unevenness according to the uneven shape of the oxide film 3.

Next, as shown in FIG. 4C, the surface of the polysilicon film 4 is ground to remove the irregularities on the surface.
This polishing is the so-called product mode grinding (PM
G), for example, with an unsaturated polyester cloth,
Mechanochemical polishing is performed by dropping an alkaline solution in which fine particles of high-purity silica are dispersed and pressing a polysilicon film, which is a grinding surface, onto this cloth.

As shown in FIG. 4C, when the surface of the polysilicon film 4 is flattened to some extent by performing product mode grinding, grinding damage of several μm occurs. In order to remove this grinding damage and to make the surface 4a of the polysilicon film 4 constituting the bonded joint surface into a mirror surface state, as shown in FIG. 5D, ductile mode grinding (ductile mode grinding, DMG) is applied.

In the main grinding step, since it is only necessary to remove the grinding damage caused by the product mode grinding, the grinding amount is at least several μm.

In this embodiment, in order to increase the degree of integration and to further reduce the grinding damage that occurs on this ground surface, as shown in FIG.
Oxide film 7 is formed. This oxide film 7 is, for example,
An SOI insulating layer formed by CVD or thermal oxidation,
Alternatively, after the fractured layer is oxidized by thermal oxidation, this oxide film is used as a sacrificial oxide film that is etched off. By the above process,
An active layer substrate A, which is one of the substrates forming the SOI structure wafer, is obtained. At this time, since the bonding surface 7a forming the SOI structure has a structure in which the oxide film 7 is formed on the ground surface 4b in a mirror surface state, the bonding surface 7a is more smooth than the mirror surface state.

As shown in FIG. 5D, in this embodiment, the product mode grinding and the ductile mode grinding are performed so that the polysilicon film 4 is slightly left from the surface of the oxide film 3. Depending on the dielectric isolation wafer, the polysilicon film 4 may be ground until the surface of the oxide film 3 is exposed.

When the mirror-bonded bonding surface 7b is obtained in the state shown in FIG. 5 (e), another semiconductor substrate 5 (hereinafter also referred to as the supporting substrate 5) to be the supporting substrate B is next formed on this bonding surface 7b. They are brought into close contact with each other and thermally bonded by hydrogen bonding to bond them together (see FIG. 6 (f)). The bonding strength is, for example, 20
0 kg / cm ² or more, the bonding temperature is 1100 ° C., and it is preferable to use the same silicon substrate as the active layer substrate 1 as the support substrate 5 in order to prevent warping of the SOI wafer due to the difference in thermal expansion.

As shown in FIG. 6 (f), after laminating the active layer substrate A and the supporting substrate B, chamfering of the side peripheral portion is performed and the thickness of the active layer substrate 1 becomes about 2 μm. Grind in advance.

Finally, as shown in FIG. 4G, the active layer substrate 1 is selectively ground. In this selective grinding, for example, a high-purity aluminum oxide surface plate having a surface roughness of 0.01 μm is rotated, and 5.0 wt% of fine particles of high-purity silica having a particle size of 0.02 μm are dispersed on the surface of the surface plate. This is performed by dropping the alkaline solution (polishing solution) having a pH of 10.5 and pressingly rubbing the active layer substrate 1 on the surface plate surface at a pressure of 100 g / cm ² .

When the selective grinding is performed, the active layer substrate 1 is gradually ground. However, when the surface plate reaches the oxide film 3 made of SiO ₂ , the oxide film 3 is more mechanochemical than the active layer substrate 1. Since it is difficult to be polished, the grinding speed decreases rapidly. By detecting this grinding speed, the oxide film 3 as shown in FIG. 4G is exposed from the surface of the active layer substrate 1, that is, the active layer 6 is completely separated by the oxide film 3 which is a dielectric. It is possible to obtain the dielectrically separated wafer in the separated state.

The above-described embodiment is one specific example for explaining the present invention, and various conditions such as manufacturing conditions shown in the description reduce the technical scope of the present invention. is not.

[0049]

As described above, according to the present invention, the bonding layer for bonding the active layer substrate and the supporting substrate is ground by ductile mode grinding, and an oxide film is formed on the ground surface to form a mirror surface state. Since the joint surface is formed as described above, it is not necessary to form the joint layer, which has been conventionally formed to flatten the joint surface, into a multi-layer structure. It is possible to simplify the grinding / polishing process of the bonding layer. As a result, the manufacturing cost of the semiconductor substrate can be reduced, and the quality control is facilitated as the process is simplified.

[Brief description of drawings]

1A to 1C are cross-sectional views illustrating a method of manufacturing a semiconductor substrate according to an embodiment of the present invention.

2 (d) to (f) are sectional views showing the continuation of the manufacturing method shown in FIG.

3G is a sectional view showing a sequel to the manufacturing method shown in FIG. 2; FIG.

4A to 4C are cross-sectional views illustrating a method of manufacturing a semiconductor substrate according to another embodiment of the present invention.

5 (d) to (e) are cross-sectional views showing a continuation of the manufacturing method shown in FIG.

6F to 6G are cross-sectional views showing the continuation of the manufacturing method shown in FIG.

7A to 7C are cross-sectional views illustrating a conventional method for manufacturing a semiconductor substrate.

8D to 8F are cross-sectional views showing the continuation of the manufacturing method shown in FIG.

9 (g) to (h) are sectional views showing the continuation of the manufacturing method shown in FIG.

[Explanation of symbols]

 A ... Active layer substrate B ... Support substrate 1 ... Active layer substrate side silicon substrate 3 ... Surface layer (oxide film) 4 ... Bonding layer 5 ... Support substrate side silicon substrate 6 ... Active layer 7 ... Second oxide film 7a … Joining surface 8… Separation groove

Claims (1)

[Claims] 1. A bonding layer is formed on at least one surface of one semiconductor substrate, the bonding layer is polished to form a bonding surface, and the other semiconductor substrate is bonded to the bonding surface.
In a manufacturing method for manufacturing a semiconductor substrate having a structure, the bonding layer is ground by ductile mode grinding to form a ground surface in a mirror surface state, and then an oxide film is formed on the ground surface. Method.