JPH10189405A - Manufacture of direct-bonded silicon substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a direct-bonded silicon substrate in which the silicon layer thickness of a silicon wafer for element formation is made easily thin to be 1μm or lower. SOLUTION: A silicon wafer 11, for element formation, having a resistivity of 0.1 to 1Ωcm is used, and a silicon wafer 21, for a support substrate, in which an oxide film 22 is formed on the surface is used. The wafer 11 is treated at 180 deg.C for several tens of minutes in plasma hydrogen, a hydrogen diffusion region 12 having a thickness of less than 1μm is formed, and the resistivity of the region is made larger than 1kΩcm. A hydrogen diffusion face on the wafer 11 is bonded directly to the oxide film 22 on the wafer 12, and a bonded substrate 31 is obtained. The bonded substrate is made thin by a surface grinding method from the rear side of the wafer 11 until a silicon layer in a thickness of about 5μm is left, and the remaining layer is made further thin by a mixed solution of hydrofluoric acid and nitric acid. An SC cleaning operation is perforemd to a bonded substrate 41 which is made thin, the bonded substrate is heat-treated at 350 deg.C in an N2 gas atmosphere, and a bonded substrate 51 as a target is obtained.

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 directly bonded silicon substrate used when forming a semiconductor device.

[0002]

2. Description of the Related Art "Silicon direct bonding technology" in which silicon wafers are directly bonded to each other without interposing a different material such as an adhesive is used for a substrate for SOI (Silicon On Insulator), a substrate having a deep impurity diffusion, and an epi wafer. Various applications such as alternative substrates are conceivable, and are attracting attention as technologies with high potential [eg, Shinbo, Applied Physics 5
6 , 337 (1987)].

[0003] Of the above, SOI substrates formed by the direct bonding technique are excellent as substrates for high-performance semiconductor devices. In particular, substrates having a silicon layer having a thickness of 1 µm or less are used for high-speed operation devices, low power consumption memory devices, Various applications such as quantum effect devices are expected, and some of them have begun to be put into practical use.

FIGS. 2A to 2C show a conventional example of a method for manufacturing a direct-bonded SOI substrate. In this method, a silicon wafer 101 for element formation, which has been mirror-finished as shown in FIG. 2A, and a silicon wafer 201 for a support substrate, having an oxide film 202 formed on one side by subjecting a mirror-finished surface to thermal oxidation, are prepared. I do. Then, as shown in FIG. 2B, the mirror-finished surface of the wafer 101 and the oxide film 202 of the wafer 201 are directly overlapped, and the superposed wafer is heated to a predetermined temperature to form an adhesive substrate 301. 2 (c) by making one of the wafers 101 thinner.
Is obtained, that is, a direct bonding silicon substrate.

[0005] As a method of thinning, (1) after grinding,
Polishing and (2) selective etching after grinding are known. Hereinafter, these will be described specifically. In the method of thinning (1), the thickness is about 650 μm.
The silicon wafer for element formation is mechanically thinned to 3 to 5 μm by a surface grinding method using fixed diamond abrasive grains on the side opposite to the bonding surface with the silicon wafer for a support substrate. After that, the processing damage and the strain layer (1 to 2 μm) introduced by the grinding are removed and finished by a mechanochemical polishing method using an alkali solution of colloidal silica or the like.

Although this method has no problem in terms of cost, crystal quality of the finished surface, etc., it is directly affected by mechanical accuracy, so that the thickness controllability of the silicon layer is poor. At present, the limit is about 2 ± 1 μm. Which is not suitable for forming a thin film silicon layer of 1 μm or less.

In the thinning method (2), a silicon wafer having a silicon epilayer formed on one side is used as a silicon wafer for element formation. The epi layer usually has a specific resistance of 1 to 10
On the order of Ωcm, the thickness depends on the desired layer thickness of the SOI substrate. In addition, a low-resistance substrate having a specific resistance of about 1/100 or less of that of the epitaxial layer is usually used as the silicon wafer for element formation.

That is, an oxide film is formed by thermally oxidizing an epilayer of a silicon wafer for element formation, and the silicon wafer for element formation and the silicon wafer for a support substrate are directly overlapped with each other via the oxide film. A polymerized wafer is bonded by heating the polymerized wafer to a predetermined temperature in a non-oxidizing atmosphere (for example, a nitrogen gas atmosphere) or an oxidizing atmosphere (for example, air). In this bonded wafer, the surface on the side opposite to the epilayer forming surface of the silicon wafer for element formation is thinned to 3 to 5 μm by grinding. Thereafter, the thickness of the element forming silicon wafer is further reduced by selective etching.

In this case, as the etching solution, a solution in which the etching rate of silicon is greatly affected by the specific resistance (this depends on the free carrier concentration), for example, a mixed solution of hydrofluoric acid and nitric acid is used. That is, since the etching rate of the silicon epi layer is lower than the etching rate of silicon, the etching rate at which silicon has been etched is rapidly reduced at the silicon substrate / epi layer interface. It remains with a uniform thickness.

The method (2) is not affected by the mechanical accuracy of the apparatus, and the epitaxial layer plays a role as a stopper against etching. Therefore, the silicon wafer of the element forming silicon wafer after the thinning is completed. Layer thickness controllability is ± 0.1
μm, which is good. However, it is expensive because an epi layer is formed in advance, and an epi layer having a thickness of 1 μm or less has a problem in terms of crystallinity.

[0011]

SUMMARY OF THE INVENTION In view of the above background, an object of the present invention is to make it possible to easily reduce the thickness of a silicon layer of a silicon wafer for element formation to 1 μm or less.
In addition, it is an object of the present invention to provide a method for manufacturing a direct bonding silicon substrate for manufacturing an SOI substrate or the like, which can form a high-quality silicon layer at a low cost with high uniformity of the layer thickness.

[0012]

SUMMARY OF THE INVENTION According to the present invention, a silicon wafer for element formation and a silicon wafer for a support substrate are brought into direct contact with their mirror-finished surfaces to obtain an adhesive wafer. In a method of manufacturing a bonded silicon substrate by thinning a silicon wafer for formation, a silicon wafer for element formation is previously formed on a surface to be bonded to a silicon wafer for a support substrate while maintaining the temperature at 200 ° C. or lower. After performing plasma hydrogen treatment,
In the thinning process, at least wet etching is performed on the silicon wafer for element formation, and in the wet etching, a chemical solution is used as an etchant, the etching rate of the silicon wafer being slower as the specific resistance is higher. This is a method for producing a direct bonding silicon substrate characterized by the following.

When plasma hydrogen treatment is performed while maintaining the silicon crystal at a temperature of 200 ° C. or lower, activated hydrogen ions diffuse from the silicon crystal surface into the inside (formation of a hydrogen diffusion region) and combine with the dopant. Since the dopant is inactivated, the carrier concentration in this region decreases and the resistance value increases. Therefore, plasma hydrogen is diffused in advance at a desired depth of the silicon wafer for element formation (this is set in consideration of a desired thickness of the final silicon layer) at a temperature of 200 ° C. or less to lower the carrier concentration in the region. (High resistance)
The wafer is bonded to the supporting substrate silicon wafer via the diffusion surface, and then the silicon wafer for element formation is thinned from the back surface (the surface opposite to the diffusion surface side).

At the time of thinning, first, a surface grinding method is used to form a thin film.
After thinning to 5 μm, 1 μm
m or less evenly. Although the element formation region of the element formation silicon wafer has a low carrier concentration due to hydrogen diffusion, the bond between the hydrogen and the dopant is broken by a high temperature treatment of 200 ° C. or more, and the original carrier concentration (resistivity) is reduced. Since it returns, there is no hindrance to the subsequent element forming process. The high-temperature treatment may be performed in a non-oxidizing atmosphere or an oxidizing atmosphere.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to FIGS.
This will be described with reference to FIG. Example 6 inch φ, CZ,
(100), B-doped (specific resistance: 0.1 to 1 Ωcm) was used. As shown in FIG. 1A, the silicon wafer 11 for element formation is subjected to a treatment at 180 ° C. for several tens of minutes in plasma hydrogen to diffuse hydrogen to a desired depth (less than 1 μm). , A hydrogen diffusion region 12 was formed.
The specific resistance of the hydrogen diffusion region 12 became larger than 1 kΩcm. As the silicon wafer 21 for the support substrate, an oxide film 22 (having a thickness of about 1 μm) is previously formed on the surface by CVD.
m) was used.

As shown in FIGS. 1B and 1C, the hydrogen diffusion surface of the element forming silicon wafer 11 and the oxide film 22 of the supporting substrate silicon wafer 21 are brought into direct contact with each other. Bonding was performed by the method to obtain an adhesive substrate (adhesive wafer) 31 shown in FIG. About 5 μm in thickness of the adhesive substrate 31 from the back surface side (the side opposite to the hydrogen diffusion surface) of the element forming silicon wafer 11 by a plane grinding method.
Until the silicon layer remained. Next, hydrofluoric acid
The remaining layer was further thinned with a nitric acid mixture. The cross-sectional structure of the adhesive substrate 41 after thinning is as shown in FIG.

Since the etching rate of the mixed solution is high in a region with a high carrier concentration and slow in a region with a low carrier concentration, the etching speed is reduced at the interface between the silicon layer and the hydrogen diffusion region 12 on the substrate 11. At a desired depth and uniformly over the entire surface of the interface. In this embodiment, 6 inches φ
Using the wafer, the silicon layer thickness of the element formation silicon wafer could be controlled to 0.8 ± 0.15 μm. From the start of the bonding step to the end of the thinning of the silicon element forming layer, the bonding substrate is
The temperature was controlled so as not to be heated to a temperature of not less than ° C.

After the thinning of the silicon layer is completed, FIG.
SC cleaning (SC-1) for the adhesive substrate 41 shown in FIG.
That is, a mixed solution of ammonia, hydrogen peroxide, and water was used), and then heat treatment was performed at 350 ° C. in an N ₂ gas atmosphere. Thereby, the carrier concentration of the element formation layer becomes
The state before the plasma hydrogen treatment could be returned, and finally, an adhesive substrate (directly bonded silicon substrate) 51 shown in FIG. 1E was obtained.

In the case where an oxide film is formed only on a silicon wafer for element formation instead of the above embodiment in which an oxide film is formed on the silicon wafer for a support substrate, plasma hydrogen treatment is performed after the oxide film is formed. If an adhesive substrate is manufactured and the same processing as described above is performed, a result equivalent to that of the embodiment can be obtained. If desired, an oxide film can be formed on both the silicon wafer for the support substrate and the silicon wafer for element formation, and these oxide films can be brought into direct contact with each other to produce an adhesive substrate.

Further, in the above embodiment, a mixed solution of hydrofluoric acid and nitric acid is used as a chemical solution for selective etching. However, any other chemical solution that causes a difference in etching rate due to a difference in carrier concentration may be used. Can also. Further, the type of the substrate (silicon wafer) and the specific resistance are not limited to those in the above-described embodiment, and a P-type or non-doped substrate can be adopted according to a desired final bonded substrate structure. , Plasma hydrogen treatment, selective etching, etc. may be set according to the characteristics of the substrate to be used.

Further, in the above embodiment, the silicon wafer for element formation and the silicon wafer side for the support substrate are bonded via an oxide film (insulating layer) to obtain a bonded wafer effective for an SOI substrate (directly). Manufacturing of SOI substrate by bonding)
However, the present invention is not limited to this, and is also effective when manufacturing a bonded wafer in which an insulating film is not interposed between wafers.

[0022]

As described above, the method for producing a direct bonding silicon substrate according to the present invention provides a method for producing a silicon wafer for element formation on a surface to be bonded to a silicon wafer for a support substrate by using a plasma for increasing the specific resistance. After reducing the wet etching rate of the surface by performing hydrogen treatment, the silicon wafer for element formation and the silicon wafer for the support substrate are bonded to each other. The thickness is reduced by performing wet etching from the opposite side.

According to the present invention, a silicon layer of a silicon wafer for element formation can be easily and inexpensively reduced to a thickness of 1 μm or less at a low cost, and the thickness of the layer is high and the crystal quality is good. A silicon nitride layer can be formed. Therefore, there is an effect that it is possible to provide a low cost direct bonding silicon substrate for manufacturing a high quality SOI substrate.

[Brief description of the drawings]

FIG. 1 is a wafer sectional view showing an embodiment of the present invention in the order of steps.

FIG. 2 is a wafer cross-sectional view showing a conventional example in the order of steps.

[Explanation of symbols]

11: silicon wafer for element formation, 12: hydrogen diffusion region, 21: silicon wafer for support substrate, 22: oxide film, 31: adhesive substrate (unprocessed), 41: adhesive substrate (grinding / selection) After etching), 51 ... adhesive substrate (after high-temperature heat treatment), 101 ... silicon wafer for element formation, 2
01: silicon wafer for supporting substrate, 202: oxide film, 301, 401: adhesive substrate.

Claims (7)

[Claims] 1. A silicon wafer for element formation and a silicon wafer for a support substrate are brought into direct contact with their mirror-finished surfaces to obtain an adhesive wafer, and the silicon wafer for element formation of the adhesive wafer is thinned. In the method for producing a bonded silicon substrate by the above, after the surface of the silicon wafer for element formation, which is to be bonded to the silicon wafer for the support substrate, is subjected to plasma hydrogen treatment while maintaining the temperature at 200 ° C. or lower, In the thinning process, at least wet etching is performed on the silicon wafer for element formation, and in the wet etching, a chemical solution is used as an etchant, the etching rate of the silicon wafer being slower as the specific resistance is higher. A method for producing a direct bonding silicon substrate, characterized by comprising: 2. The method according to claim 1, wherein after performing the wet etching, the bonded wafer is heat-treated at a temperature of 200 ° C. or higher. 3. In the thinning step, after the element forming silicon wafer is thinned by a surface grinding method,
3. The method according to claim 1, wherein the wet etching is performed. 4. The method according to claim 1, wherein a mixed solution of hydrofluoric acid and nitric acid is used as the etching solution. 5. The device according to claim 1, wherein an oxide film is formed on the surface of the silicon wafer for the support substrate, and the silicon wafer for element formation is bonded through the oxide film. A method for manufacturing a directly bonded silicon substrate. 6. An oxide film is formed on the surface of an element-forming silicon wafer, and the oxide film is subjected to the plasma hydrogen treatment. Then, the element-forming silicon wafer and the supporting substrate silicon wafer are interposed via the oxide film. 5. The method for producing a direct bonding silicon substrate according to claim 1, wherein the bonding is performed. 7. The method according to claim 1, wherein the silicon wafer for element formation and the silicon wafer for support substrate are bonded to each other without forming an oxide film.
5. The method for producing a directly bonded silicon substrate according to 2, 3, or 4.