JP2866263B2 - Semiconductor substrate manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

[0003] The semiconductor substrate of this type, have been referred to as an SOI (silicon-on-insulator) U E Doha,
In such an SOI wafer, the thinner the silicon layer that forms the element, the smaller the parasitic capacitance of the pn junction and the higher the operation speed of the element. Therefore, ultra-thin silicon layers are being studied. In order to increase the degree of integration, it is effective to realize a three-dimensional structure. As one of the techniques, an SOI wafer capable of forming a basic structure in which an oxide film and a semiconductor layer are stacked has been attracting attention. .

Incidentally, a so-called laminating method is known as a technique for obtaining an SOI structure substrate. In a conventional bonding method, first, a silicon substrate 1 (hereinafter, also referred to as an active layer substrate 1 or an active layer substrate A) is
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, after the surface of the bonding layer 4 is planarized by mechanochemical polishing (see FIG. 7C), another silicon substrate 5 (hereinafter referred to as a support substrate 5 or a support substrate) is formed on the polished surface 4a. B) (see FIG. 9 (g)), and finally, the surface of the active layer substrate 1 is ground and polished until the oxide film 3 is exposed (FIG. 9).
(H)).

However, in a method of manufacturing an SOI substrate by such a bonding method, a patterning method is previously performed by a photolithography technique or an etching technique.
When the oxide film 3 is formed on the active layer substrate A on which the active layer substrate A (see FIG. 7A) has been applied, the surface of the polysilicon forming the bonding layer 4 is ground and polished due to the grain size. However, there was a problem that the surface was not smoothed.

That is, according to what the inventor has searched for, the polysilicon layer forming the bonding layer 4 is generally required to improve properties such as conductivity, impurity diffusion speed, film stability, and oxidation speed. Although the crystal is grown at a high reaction temperature, the grain size of polysilicon increases as the reaction temperature increases, so that the grain size of the bonding layer 4 obtained is relatively large, and crystal growth occurs in a direction perpendicular to the surface. Therefore, polysilicon crystals grow in different directions in the uneven portions of the oxide film 3, and an interface where these crystals collide is formed. In addition to this, when chemical polishing such as mechanochemical polishing is performed, the polishing rate is the crystal grain size, plane orientation,
Since the surface of the polysilicon is mechanochemically polished because of the susceptibility to the growth direction and the like, the overall condition is such that selective polishing is performed. For this reason, there is a problem in that the desired flatness cannot be obtained on the bonding surface 4a, and the desired bonding strength cannot be obtained even when the support substrate B is bonded.

Therefore, a first bonding layer 4 made of polysilicon formed by forming a high-temperature reaction on the oxide film 3 is formed.
After the first bonding layer 4 is ground and polished to make the surface thereof somewhat smooth (see FIG. 7C), it is further grown on the surface of the first bonding layer 4 by a low-temperature reaction. Forming a polysilicon layer (second bonding layer) 6 (FIG. 8)
This is polished to obtain a predetermined smoothness (see FIG. 8E).

According to this method, the second bonding layer 6 serving as the bonding surface 6a is formed of polysilicon having a small grain size. Therefore, 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 bonded is increased, and peeling can be prevented.

In order to increase the degree of integration, a second oxide film 7 made of SiO ₂ is formed on the bonding surface 6a (FIG. 8F).
Reference), and the supporting 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 (in the above-described example, the first bonding layer 4 and the second bonding layer 6), 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 such problems of the prior art, and simplifies a bonding layer forming step and a grinding / polishing step in flattening a bonding surface of an SOI structure substrate. By doing so, the object is to reduce the manufacturing cost and to facilitate the quality control.

[0012]

In order to achieve the above object, a method of manufacturing a semiconductor substrate according to the present invention comprises forming a bonding layer on at least one surface of one semiconductor substrate, and bonding the other semiconductor substrate to the bonding layer. bonding a semiconductor substrate manufacturing method for manufacturing a semiconductor substrate of SOI structure, after forming the ground surface of the mirror state on the Symbol bonding layer was ground by ductile mode grinding, to form an oxide film on the ground surface , Is characterized.

[0013]

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

Grinding of such a hard and brittle material in a plastic region is as follows.
Especially called ductile mode grinding or plastic flow type grinding,
The most important parameter for realizing this ductile mode grinding is a critical working unit dc (also called ductile-brittle pressure transition point Pc) representing a transition point between brittle fracture and plastic deformation fracture.
It is.

The critical working unit is a value inherent to the material. If the grinding is performed while controlling the indentation load to be equal to or less than the critical working 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 semiconductor substrate to be ground and polished is subjected to the above-described ductile mode grinding at least in the final step of grinding and polishing, and the resulting ground surface is obtained. Are mirror-finished, an oxide film is further formed on the ground surface, and this surface is used as a bonding surface.

This eliminates the need for a bonding layer, which has been conventionally formed for flattening the bonding surface, to have a multilayer structure. For example, on one semiconductor substrate, polysilicon is grown by a high-temperature reaction to form a bonding layer, and if this bonding layer is subjected to ductile mode grinding, a mirror-like ground surface can be obtained by itself, and this ground surface 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.

The obtained bonding surface has an extremely smooth ground surface of the bonding layer constituting the lower layer. In addition to this, an oxide film is further formed on this smooth surface. Grinding damage can be mitigated by the oxide film,
This further promotes the smoothness of the joint surface. Therefore, it is possible to simplify the step of forming a bonding layer for bonding and the steps of grinding and polishing, thereby realizing a reduction in manufacturing cost and facilitation of quality control.

[0019]

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

1 to 3 are cross-sectional views illustrating a method for manufacturing a semiconductor substrate according to one embodiment of the present invention.
1A shows an oxide film forming step, FIG. 1B shows a bonding layer forming step, FIG. 1C shows a grinding step, FIG. 2D shows a ductile mode grinding step, and FIG. Film forming process, FIG. 2
(F) is a laminating step, and (g) of FIG.
It is sectional drawing explaining each polishing process.

First, as shown in FIG. 1A, a photolithography technique or an etching technique is applied to one surface of a semiconductor substrate 1 made of single crystal silicon (hereinafter also referred to as an active layer substrate A or an active layer substrate 1). For example, 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
An SiO ₂ film having a thickness of 0.9 μm is formed by the method. These 1.0 μm SiO ₂ films form the surface layer 3 of the active layer substrate.
(Hereinafter, also referred to as an oxide film 3), and 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 patterned.

In the structure shown in FIG. 1A, a polysilicon film 4 as a bonding layer is formed on the surface of the oxide film 3 (see FIG. 1B). The polysilicon film 4 is formed, for example, at a reaction temperature of 800 ° C. to 1200 ° C. by a CVD method.
Is grown by a thickness of 5 μm. The reason why the polysilicon film 4 is formed by reacting at a high temperature is to enhance the conductivity of the polysilicon film, the diffusion speed of impurities, the stability of the film, the oxidation speed, and the like. Also,
Like the oxide film 3, it is formed as a film having slightly irregularities according to the irregularities 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 research work is, so-called product-mode grinding (PM
G) Ru Der.

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 occurs by several μm. In order to remove the grinding damage and bring the surface 4a of the polysilicon film 4 forming the bonding surface of bonding into a mirror state, as shown in FIG. DMG).

In the present grinding step, the grinding amount generated by the product mode grinding only needs to be removed, so that the grinding amount is several μm.

Grinding polysilicon, which is a hard and brittle material, generally results in brittle fracture with cracks, and the ground surface becomes a crushed surface, making it impossible to obtain a mirror-finished joint surface. 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 minute cut on the order of 0.1 μm, it is not a brittle fracture but a plastic region. Mirror grinding is possible.

The most important parameter for realizing this ductile mode grinding is a critical working unit dc (transition point between ductile and brittle pressure P, which represents a transition point between brittle fracture and plastic deformation fracture).
c), and the critical processing unit is a value specific to the material. Therefore, first, a critical processing unit of the polysilicon film 4 to be subjected to ductile mode grinding is determined, and the grinding is performed while controlling the grinding apparatus with an indentation load equal to or less than the critical processing unit. As a result, even if polysilicon is apt to cause brittle fracture, it will exhibit 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 (= 500-2000 angstroms).

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

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

As shown in FIG. 2 (f), after the active layer substrate A and the supporting substrate B are bonded to each other, chamfering of the peripheral portion is performed, and the thickness of the active layer substrate 1 is reduced to about 2 μm. Is ground in advance.

[0032] Finally, as shown in FIG. 3 (g), performing a selection Migaku Ken the active layer substrate 1. The selection Migaku Ken, for example, the surface roughness is to rotate the high-purity oxide aluminum plate of 0.01 [mu] m, was 5.0 wt% dispersing fine particles of high purity silica particle size 0.02μm on the surface of the platen The active layer substrate 1 is pressed and rubbed against the surface of the surface plate at a pressure of 100 g / cm ² while dropping an alkaline solution (polishing liquid) having a pH of 10.5.

[0033] When performing the selection Migaku Ken, although the active layer substrate 1 Yuku is gradually <br/> Migaku Ken, the platen reaches the oxide film 3 made of SiO _2, the oxide film 3 is an active layer substrate since hard to be polished mechanochemical compared to 1, Migaku Ken speed decreases rapidly. By detecting this Migaku Ken rate, state of the oxide film 3 as shown in FIG. 3 (g) is exposed from the surface of the active layer substrate 1, i.e., the active layer 6 is separated by the oxide film 3, moreover, the SO in the state where the second oxide film 7 is laminated on the lower layer
An I-structure wafer can be obtained.

The method of manufacturing a semiconductor substrate according to the present invention can be applied to, for example, manufacturing of a bonded dielectric separation substrate in addition to the above-mentioned thin film SOI structure.

FIGS. 4 to 6 are sectional views for explaining a method of manufacturing a semiconductor substrate according to another embodiment of the present invention.
4 (a) is an oxide film forming step, FIG. 4 (b) is a bonding layer forming step, FIG. 4 (c) is a grinding step, FIG. 5 (d) is a ductile mode grinding step, and FIG. Film forming process, FIG.
(F) is a laminating step, and (g) of FIG.
It is sectional drawing explaining each polishing process.

In an LSI having a high withstand voltage of several tens of volts to several hundreds of volts between elements, it is necessary to completely separate each element by a dielectric film such as an oxide film. So-called dielectric isolation substrates are widely used. This embodiment shows a specific example in which the present invention is applied to the method for manufacturing a dielectric isolation substrate.

Firstly, a semiconductor substrate 1 made of single crystal silicon by oxidizing the one surface (hereinafter, also referred to the active layer substrate A, or an active layer substrate 1), after forming the SiO ₂ film on the entire surface, the SiO ₂ film Is opened, and using an SiO ₂ film as a mask, for example, by anisotropic etching or the like,
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,
Again, the surface of the semiconductor substrate 1 is 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 addition to the structure shown in FIG. 4A, a polysilicon film 4 as a bonding layer is formed on the surface of the oxide film 3 (see FIG. 4B). The polysilicon film 4 is formed, for example, at a reaction temperature of 800 ° C. to 1200 ° C. by a CVD method.
Is grown until at least the separation groove 8 is completely filled (for example, with a thickness of 100 μm). This polysilicon layer 4 is also formed as a film having slightly irregularities according to the irregularities of the oxide film 3, similarly to the oxide film 3.

Next, as shown in FIG. 4C, the surface of the polysilicon film 4 is ground to remove irregularities on the surface.
This research work is, so-called product-mode grinding (PM
G) Ru Der.

As shown in FIG. 4C, when the surface of the polysilicon film 4 is subjected to product mode grinding to be flattened to some extent, grinding damage occurs by several μm. In order to remove the grinding damage and bring the surface 4a of the polysilicon film 4 forming the bonding surface of bonding into a mirror state, as shown in FIG. DMG).

In the present grinding process, it is only necessary to remove the grinding damage caused by the product mode grinding, so that the grinding amount is at least several μm.

In this embodiment, in order to increase the degree of integration and further reduce the grinding damage generated on the 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 crushed layer is oxidized by thermal oxidation, this oxide film is used as a sacrificial oxide film to be etched off. Through the above steps,
An active layer substrate A which is one of the substrates constituting the SOI structure wafer is obtained. At this time, since the bonding surface 7a constituting the SOI structure has a structure in which the oxide film 7 is formed on the mirror-finished ground surface 4b, the bonding surface 7a is a surface having more excellent smoothness than the mirror-finished surface.

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 to be formed, the polysilicon film 4 may be ground until the surface of the oxide film 3 is exposed.

When the mirror-finished 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) serving as the supporting substrate B is formed on the bonding surface 7b. The two are brought into close contact 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, bonding temperature was 1100 ° C., also in order to prevent the warpage of the SOI wafer due to thermal expansion difference, it is preferable to use the same silicon substrate and the active layer substrate 1 as the support substrate 5.

As shown in FIG. 6 (f), after the active layer substrate A and the supporting substrate B are bonded to each other, chamfering of the peripheral portion is performed, and the thickness of the active layer substrate 1 is reduced to about 2 μm. Is ground in advance.

[0046] Finally, as shown in FIG. 6 (g), performing a selection Migaku Ken the active layer substrate 1. The selection Migaku Ken, for example, the surface roughness is to rotate the high-purity oxide aluminum plate of 0.01 [mu] m, was 5.0 wt% dispersing fine particles of high purity silica particle size 0.02μm on the surface of the platen The active layer substrate 1 is pressed and rubbed against the surface of the surface plate at a pressure of 100 g / cm ² while dropping an alkaline solution (polishing liquid) having a pH of 10.5.

[0047] When performing the selection Migaku Ken, although the active layer substrate 1 Yuku is gradually <br/> Migaku Ken, the platen reaches the oxide film 3 made of SiO _2, the oxide film 3 is an active layer substrate since hard to be polished mechanochemical compared to 1, Migaku Ken speed decreases rapidly. By detecting this Migaku Ken rate, state of the oxide film 3 as shown in FIG. 6 (g) is exposed from the surface of the active layer substrate 1, i.e., fully oxide film 3 active layer 1 is a dielectric A separated dielectric isolation wafer can be obtained.

The embodiment described above is one specific example for explaining the present invention, and various conditions such as manufacturing conditions shown in the description may 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. Since the bonding surface of the bonding layer is formed, it is not necessary to form the bonding layer, which has been conventionally formed for flattening the bonding surface, into a multilayer structure. This makes it possible to simplify the grinding and polishing steps 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 the drawings]

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

FIGS. 2D to 2F are cross-sectional views showing a continuation of the manufacturing method shown in FIG.

FIG. 3 (g) is a cross-sectional view showing a continuation of the manufacturing method shown in FIG.

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

5D to 5E are cross-sectional views showing a continuation of the manufacturing method shown in FIG.

6 (f) to 6 (g) are cross-sectional views showing a continuation of the manufacturing method shown in FIG.

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

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

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

[Explanation of symbols]

 A: Active layer substrate B: Support substrate 1: Silicon substrate on active layer substrate side 3: Surface layer (oxide film) 4: Bonding layer 5: Silicon substrate on support substrate side 6: Active layer 7: Second oxide film 7a ... joining surface 8 ... separation groove

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 27/12 H01L 21/304 H01L 21/762

Claims (1)

(57) [Claims] 1. A method of manufacturing a semiconductor substrate , comprising: forming a bonding layer on at least one surface of one semiconductor substrate; and bonding the other semiconductor substrate to the bonding layer to manufacture a semiconductor substrate having an SOI structure. Forming a mirror-finished ground surface by grinding the bonding layer by ductile mode grinding, and then forming an oxide film on the ground surface.