JPH06104412A - 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 joining face 4a is formed, a base substrate (B) is bonded to the joining face 4a to form a semiconductor substrate in an SOI structure. Consequently, the manufacturing step can be simplified without forming a joining layer in a multi-layered structure.

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 In forming an integrated circuit, a method of forming various elements (devices) on a thin film semiconductor layer provided on an oxide insulating layer is more than a method of forming the integrated circuit on 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).
In the OI structure substrate, the thinner the silicon layer forming the element is, the more the parasitic capacitance of the pn junction can be reduced and the operation speed of the element can be increased.

By the way, a so-called laminating method is known as a method for obtaining a thin film SOI structure substrate.
In the conventional bonding method, first, the silicon substrate 1 (hereinafter,
An oxide film 3 made of SiO ₂ is formed on one surface of the active layer substrate 1 or the active layer substrate A) (see FIG. 5A), and a bonding layer 4 made of polysilicon is formed on the oxide film 3.
Are formed (see FIG. 5B). Next, the surface of the bonding layer 4 is mechanochemically polished to planarize it (see FIG. 5).
(See (c)), another silicon substrate 5 is provided on the polishing surface 4a.
(Hereinafter, also referred to as the support substrate 5 or the support substrate B) is bonded (see FIG. 6F), and finally, the surface of the active layer substrate 1 is ground and polished until the oxide film 3 is exposed ( See FIG. 7 (g).

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.
(FIG. 5A) is used, and when 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 surface of the first bonding layer 4 is ground / polished to make the surface smooth to some extent (see FIG. 5C), and then grown on the surface of the first bonding layer 4 by a low temperature reaction. Forming a polysilicon layer (second bonding layer) 6 (see FIG. 6).
(See (d)), and this is polished to obtain a predetermined smoothness (see FIG. 6E).

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. It should be noted that such a bonding method is widely adopted also when manufacturing a dielectric isolation substrate.

[0009]

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.

[0011]

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 for manufacturing a semiconductor substrate having an SOI structure by bonding the other semiconductor substrate to the bonding surface after forming the bonding surface, the bonding layer is ground by ductile mode grinding to form a bonding surface in a mirror surface state. I am trying.

[0012]

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 when grinding is performed while controlling the indentation load below the critical processing unit, even if the material is hard and brittle, brittle fracture is likely to occur, and plastic behavior Will be shown.

Therefore, according to 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 bonding surface is obtained. Is the mirror-like joint surface.

As a result, it is no longer necessary to form the joining layer having a multi-layer structure, which has been conventionally used to flatten the joining surface. For example, on one of the semiconductor substrates, a bonding layer is formed by growing polysilicon by a high temperature reaction, and if this bonding layer is subjected to ductile mode grinding, a bonding surface in a mirror-like state can be obtained by itself, and this bonding surface A semiconductor substrate having an SOI structure can be manufactured by bonding the other semiconductor substrate. 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.

[0017]

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 2 are sectional views for explaining a method of manufacturing a semiconductor substrate according to an embodiment of the present invention.
1A is an oxide film forming process, FIG. 1B is a bonding layer forming process, FIG. 1C is a grinding process, FIG. 2D is a ductile mode grinding process, and FIG. 2E is a laminating process. 2 (f) is a cross-sectional view for explaining each 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 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. 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, the grinding damage generated by the product mode grinding only needs to be removed, so the grinding amount is several μm.

When polysilicon, which is a hard and brittle material, is ground, it is generally subjected to brittle fracture processing accompanied by cracks, 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 (bonding surface) 4b is only 0.05 μm.
It becomes m-0.2 micrometer (= 500-2000 angstrom). Through the above steps, the active layer substrate A, which is one of the semiconductor substrates forming the SOI structure wafer, is obtained.

When the bonding surface 4b in a mirror state is obtained in the state shown in FIG. 2D, 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 4b. They are brought into close contact with each other and thermally bonded by hydrogen bonding to bond them together (see FIG. 2 (e)). 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 supporting substrate 5 in order to prevent warpage of the SOI wafer due to a difference in thermal expansion.

As shown in FIG. 2 (e), 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. 2F, 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 thin film SOI in a state where the oxide film 3 as shown in FIG. 2F is exposed from the surface of the active layer substrate 1, that is, the active layer 6 is separated by the oxide film 3. A structured wafer can be obtained.

The method for manufacturing a semiconductor substrate of the present invention can be applied not only to the above-described thin film SOI structure but also to, for example, manufacturing a laminated dielectric isolation substrate.

3 to 4 are sectional views illustrating a method of manufacturing a semiconductor substrate according to another embodiment of the present invention.
3A is an oxide film forming process, FIG. 3B is a bonding layer forming process, FIG. 3C is a grinding process, FIG. 4D is a ductile mode grinding process, and FIG. 4E is a laminating process. 4F is a cross-sectional view for explaining each grinding process of the active layer substrate.

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 with 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 made of single crystal silicon (hereinafter, also referred to as active layer substrate A or active layer substrate 1) 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 7 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. 3A). 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 on which the separation groove 7 is formed.

In the structure shown in FIG. 3A, a polysilicon film 4 as a bonding layer is further formed on the surface of the oxide film 3 (see FIG. 3B). 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 7 is completely filled (for example, a thickness of 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. 3C, 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. 3C, when the surface of the polysilicon film 4 is flattened to some extent by 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. 4D, ductile mode grinding (ductile mode grinding, DMG) is applied.

In the main grinding step, the grinding damage generated by the product mode grinding only needs to be removed, so the grinding amount is at least several μm. Through the above steps, one active layer substrate A that constitutes the dielectric separated wafer is obtained. As shown in FIG. 4D, 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 separation wafer, the polysilicon film 4 may be ground until the surface of the oxide film 3 is exposed.

When the bonding surface 4b in a mirror state is obtained in the state shown in FIG. 4D, 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 4b. They are brought into close contact with each other and thermally bonded by hydrogen bonding to bond them together (see FIG. 4 (e)). 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. 4E, 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. 4F, 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. 4F 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 embodiments are specific examples for explaining the present invention, and the manufacturing conditions and other conditions shown in the description do not reduce the technical scope of the present invention. Absent.

[0044]

As described above, according to the present invention, the bonding layer for bonding the active layer substrate and the supporting substrate is polished by ductile mode grinding to form a mirror-bonded surface. Therefore, it is not necessary to form the bonding layer, which has been conventionally formed to flatten the bonding surface, into a multi-layered structure, and thus the bonding layer forming step for bonding and the bonding layer grinding / polishing step can be performed. It is possible to simplify. 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.

3A to 3C are cross-sectional views illustrating a method of manufacturing a semiconductor substrate according to another embodiment of the present invention.

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

5A to 5C are cross-sectional views illustrating a conventional method for manufacturing a semiconductor substrate.

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

FIG. 7G is a sectional view showing a sequel to the manufacturing method shown in FIG. 6;

[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 ... 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.
A method of manufacturing a semiconductor substrate having a structure, wherein the bonding layer is ground by ductile mode grinding to form a bonding surface in a mirror surface state.