JPH0567598A - Manufacture of semiconductor substrate - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing semiconductor substrate which can further improve flatness of a single semiconductor wafer or uniformity of thickness of a semiconductor layer having the thickness of several mum or thinner joined with a supporting substrate. CONSTITUTION:After a wet oxide film 14 is formed in the thickness of about lmum as a protection film on a grinding surface 12 and a rear surface 13 of a silicon wafer 11 of ununiform thickness having TTV of 2 to 4mum, the polishing surface 12 covered with the wet oxide film 14 is placed through close contactness on the flat surface 16 of a surface table 15 and the rear surface 13 of silicon wafer 11 is ground with a rotatable grind stone 17 to make flat the rear surface 13. Thereafter, the wet oxide film 14 on the grinding surface 12 is removed.

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, and more particularly to a method for manufacturing a semiconductor substrate having a high degree of flatness required for high density semiconductor integrated circuits. Along with the miniaturization of patterns forming a semiconductor integrated circuit, a high-resolution exposure apparatus is required. For this reason, it is unavoidable that the depth of focus of the exposure apparatus becomes shallow, and as a result, the demand for flatness of the semiconductor substrate to be exposed becomes strict.

Further, in order to reduce radiation resistance and parasitic capacitance of a semiconductor device and prevent latch-up of a semiconductor device having a CMOS structure, SOI (Silicon On Insulator)
A structured semiconductor substrate is effective and is expected as a substrate for forming future high-density and high-performance semiconductor devices. At present, an SOI substrate having a structure in which two silicon wafers are bonded together via an insulating layer is being developed as one that is closest to practical use. In the SOI substrate by this bonding technique, it is necessary to uniformly thin one silicon wafer to a thickness of about several microns.

[0003]

2. Description of the Related Art FIG. 9 shows a conventional general manufacturing process of a silicon wafer. That is, a silicon single crystal ingot is grown by a pulling method, the ingot is roughly cut into a suitable length, and then the side surface thereof is ground to form a cylindrical shape. This cylindrical ingot is cut into thin disks (slicing), the periphery of the disks is chamfered (beveling), and then the surfaces of the disks are sequentially lapped and etched. This lapping and etching thins the silicon wafer to near the desired final thickness. Then, the surface of the semiconductor device is polished to give a mirror finish.

The difference between the maximum value and the minimum value of the mirror-finished thickness of a silicon wafer having a diameter of 6 inches by the above conventional process, TTV (Total Thickness Variation)
Is about 2 to 4 μm.

[0005]

The present inventor has proposed a method for improving the flatness by applying surface grinding using a grindstone instead of the lapping and etching in the conventional process shown in FIG. Japanese Patent Application No. 02-129725, application dated May 18, 1990 and Japanese Patent Application No. 02-23775,
Application dated September 7, 1990). By this method, it is possible to improve the TTV of a silicon wafer having a diameter of 6 inches to about 1 μm.

However, it is unavoidable that the flatness is deteriorated by the polishing for the mirror finishing which is performed after the surface grinding. The influence of the deterioration of the flatness is more magnified in the SOI substrate based on the bonding technique. This is because in the SOI wafer, the thickness distribution of the SOI layer (silicon layer on the oxide film) directly affects the device characteristics. That is, in the SOI layer, since the thickness distribution of the wafer on the supporting side of the SOI wafer (the side on which the device is not formed) becomes the thickness distribution of the SOI layer as it is, for example, while the thickness of the SOI layer is about 2 μm, If the TTV of the side wafer is 2 μm, a region with an SOI layer and a region without the SOI layer are formed when the SOI wafer is manufactured.

Therefore, when it is required to obtain an active layer which is uniformly thinned to a desired thickness, it is a problem to obtain a wafer having a smaller TTV. Therefore, the present invention provides a method of manufacturing a semiconductor substrate capable of further improving the flatness of a single semiconductor wafer or the uniformity of the thickness of a semiconductor layer having a thickness of several μm or less bonded to a supporting substrate. The purpose is to do.

[0008]

The above-mentioned object is to perform a step of mirror-polishing a first surface of a flat plate made of a semiconductor, and a step of forming a protective film for covering the first surface of the flat plate that has been mirror-polished. A step of grinding the second surface of the flat plate in a state where the first surface of the flat plate covered with the protective film is in close contact with a flat surface; and removing the protective film from the first surface of the flat plate And a step of manufacturing the semiconductor substrate.

In the method of manufacturing a semiconductor substrate, the flat plate is made of silicon, and the step of forming the protective film includes dry-oxidizing a first surface of the flat plate to form a first surface on the first surface of the flat plate. And a dry oxide film is formed on the dry oxide film, and then a vapor growth oxide film is formed on the dry oxide film by vapor phase growth.

In the method of manufacturing a semiconductor substrate, the flat plate is made of silicon, and the step of forming the protective film includes wet-oxidizing a first surface of the flat plate to form a first surface on the first surface of the flat plate. A wet oxide film is formed on the substrate, and then dry oxidation is performed to form a dry oxide film between the first surface of the flat plate and the wet oxide film. To be done.

In the method for manufacturing a semiconductor substrate, the temperature for dry-oxidizing the first surface of the flat plate is 10
It is achieved by a method for manufacturing a semiconductor substrate, which is characterized in that the temperature is 00 ° C. or higher. Further, in the above-described method for manufacturing a semiconductor substrate, the dry oxide film formed on the first surface of the flat plate has a film thickness of 50 nm or more. ..

In the method for manufacturing a semiconductor substrate, the flat plate is made of silicon, and at least the second surface of the flat plate is thermally oxidized to form a thermal oxide film subsequent to the step of removing the protective film. And a step of removing the thermal oxide film by etching, which is accomplished by a method for manufacturing a semiconductor substrate. Further, the above-mentioned problems include a step of mirror-polishing the first surface of the supporting substrate,
A step of surface-grinding the second surface of the support substrate in a state where the first surface of the support substrate that has been mirror-polished is in close contact with a flat surface, and a step of mirror-polishing the first surface of a flat plate made of a semiconductor. And a step of joining the flat plate and the support substrate in a state where the first surface of the flat plate and the first surface of the support substrate, which have been mirror-polished, are in close contact, and the support substrate joined to the flat plate And a step of thinning the flat plate by subjecting the second surface of the flat plate to surface grinding while the second surface of the flat plate is in close contact with the flat surface. To be done.

In the method of manufacturing a semiconductor substrate, the step of joining the flat plate and the supporting substrate forms an insulating film on the first surface of the supporting substrate or on the first surface of the flat plate. After that, it is achieved by a method of manufacturing a semiconductor substrate, which is a step of joining the flat plate and the supporting substrate through the insulating film. Further, the above method for manufacturing a semiconductor substrate includes a step of polishing or etching the second surface of the supporting substrate joined to the flat plate, which is achieved by the method for manufacturing a semiconductor substrate. ..

[0014]

The first surface of the flat plate made of a semiconductor, which is mirror-polished, is covered with a protective film, and the second surface of the flat plate is flattened with the first surface being in close contact with a flat surface such as a surface plate. By grinding, the non-flatness caused by polishing can be eliminated, and high uniformity can be obtained in the distance between the polished surface and the surface-ground surface, that is, the thickness of the flat plate. Then, when the protective film is removed, a polished surface on which a semiconductor element can be formed is exposed.

In the case where the flat plate is made of silicon, a dry oxide film is formed on the first surface side of the flat plate, and the dry oxide film is combined with a vapor growth oxide film or a wet oxide film to form a protective film. By doing so, the irregularities on the surface of the polishing surface that are exposed by removing this protective film can be reduced, and therefore the characteristics of the semiconductor element formed on this polishing surface can be improved.

Further, after thermally oxidizing the second surface of the flat plate, the oxide film is removed by etching to remove crystal defects and contaminants generated on the second surface of the flat plate by surface grinding. .. Furthermore, after the polishing surface of the support substrate having a uniform thickness as described above and the first surface of the flat plate that has been mirror-polished are bonded via an insulating layer, the second surface of the flat plate is ground. By making the layer thin, it is possible to obtain high uniformity in the thickness of the layered flat plate required in the bonded SOI substrate.

Further, the second surface of the supporting substrate bonded to the flat plate is polished or etched to remove crystal defects and contaminants generated on the second surface of the supporting substrate by surface grinding. You can

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on illustrated embodiments. 1A to 1D are process drawings for explaining a method of manufacturing a semiconductor substrate according to a first embodiment of the present invention.
FIG. 1A shows a silicon wafer 11 having a diameter of 6 inches produced by the conventional process shown in FIG. This silicon wafer 11 has a polished surface 12 and a back surface 13 that are mirror-polished, and its average thickness is about 3 times the normal thickness.
It is about 655 μm, which is larger by 0 μm, and has the thickness nonuniformity as shown in the drawing. However, since the back surface 13 with respect to the polishing surface 12 is schematically drawn to be flat, the nonuniformity of the thickness is concentrated on the polishing surface 12. The TTV of the polishing surface 12 at this time is 2 to 4 μm as described above.
m.

A protective film is formed on at least the polishing surface 12 of the silicon wafer 11. This protective film is formed at a temperature of 11 in an atmosphere containing water vapor, for example.
A known method of heat-treating the silicon wafer 11 at 00 ° C. for 4 hours and forming a thermal oxide film on the surface thereof may be used. In this case, as shown in FIG. 1B, the entire surface of the silicon wafer 11 including the polishing surface 12 and the back surface 13 is
A wet oxide film 14 having a thickness of about 1 μm is formed. Instead of using the thermal oxidation method, a well-known CVD (chemical vapor deposition) method may be used to grow a CVD oxide film on the polishing surface 12 to form the protective film.

Next, as shown in FIG. 1C, the polishing surface 12 of the silicon wafer 11 covered with the wet oxide film 14 is brought into close contact with the flat surface 16 of the surface plate 15. This close contact may be performed by a known method of vacuum suction through a through hole (not shown) provided on the surface plate 15.
As a result, the polishing surface 12 becomes flat and the back surface 13 becomes non-flat. Since the polished surface 12 is covered with the wet oxide film 14, generation of defects due to contact with the surface plate 15 is prevented.

Next, the back surface 13 of the silicon wafer 11
Is surface-ground with a rotary grindstone 17. This surface grinding is, for example, about 25 μm with a rotary whetstone with a grain size of 500.
After grinding, about 5μ with a rotary grindstone with a grain size of 2000
It is efficient to grind. In this way, FIG.
As shown in (d), the back surface 13 of the silicon wafer 11 is
Is flattened, and the flattened ground surface 13a is exposed.

Then, the silicon wafer 11 is immersed in a mixed aqueous solution of NH ₄ OH (ammonium hydroxide) and H ₂ O ₂ (hydrogen peroxide) for about 10 minutes for cleaning, and then the silicon wafer 11 is washed with 10 The wet oxide film 14 is removed by immersing in a HF (hydrofluoric acid) aqueous solution. As a result, as shown in FIG.
The polishing surface 12 of is exposed.

Next, a method of manufacturing a semiconductor substrate according to the second embodiment of the present invention will be described with reference to the process chart shown in FIG. The same components as those of the semiconductor substrate shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. FIG. 2A shows the silicon wafer 11 in the state of FIG. 1E produced by the first embodiment. This silicon wafer 1
1 at a temperature of 1 in an atmosphere containing water vapor, for example.
When heat-treated at 100 ° C. for 4 hours, the thermal oxidation oxidizes the polished surface 12 and the ground surface 13a of the silicon wafer 11 to a depth of about 0.44 μm, resulting in a thickness of about 1 μm, as shown in FIG. Wet oxide film 18 is formed.

Then, the silicon wafer 11 is heated to 10% H
The wet oxide film 18 is removed by immersing in the F aqueous solution, as shown in FIG. As a result, the crystal defects and contaminants generated on the ground surface 13a of the silicon wafer 11 by the surface grinding can be removed. The depth at which such defects and contaminants occur depends on the grain size of the grindstone used for surface grinding and other grinding conditions, but in most cases is 1 μm or less, and the contaminants are present in a shallower layer. Therefore, by generating and removing the wet oxide film 18 by thermal oxidation of the back surface 13 of the silicon wafer 11,
The pollutants are almost completely removed. Since the defect functions as a gettering center, it is not always necessary to remove all the defects.

Next, the flatness and crystal quality of the silicon wafer 11 obtained in the first and second embodiments were examined. The crystal quality evaluation items are OSF (oxidation-induced stacking fault) density, breakdown voltage defect density generated when a voltage is applied to the oxide film formed on the polished surface 12, and impurity concentration. The OSF density gives detailed defect information on the surface. The breakdown voltage defect density represents a breakdown voltage breakdown caused by non-uniformity of the surface shape due to defects and contamination, and provides a kind of defect information. A defect having a withstand voltage limit of 8 MV / cm or less was determined as a defect.

A vapor phase decomposition method is used for measuring the impurity concentration.
Atomic absorption spectroscopy was applied. The outline of this method is as follows
Is. HNO₃For (nitric acid) and HF (hydrogen fluoride) vapor
Expose the silicon wafer. HNO liquefied on the surface₃And H
The wafer F is thinly etched by F. In this liquid
The contained impurities are quantified by atomic absorption spectrometry. HNO ₃
And HF are vaporized to improve the purity and
Silicon wafer is etched by a certain amount of liquid
In addition, the detection sensitivity is high.

Impurity elements of interest are Fe (iron) and Ca.
(Calcium). Fe is a main impurity that deteriorates the characteristics of the semiconductor device. In addition, Ca is added to the grindstone used for the surface grinding by C (carbon C), O (oxygen), H (hydrogen).
Since it is the second most abundant component, it was considered suitable as a marker for contaminants by surface grinding. The results of the above investigation are shown in Table 1 in comparison with those of the conventional silicon wafer manufactured in the process of FIG.

[0028]

[Table 1]

Here, * indicates that measurement is impossible because the mirror surface is not polished. As is clear from Table 1, the flatness is best in the first embodiment, and is slightly deteriorated in the second embodiment in which oxidation and etching for removing defects and impurities are performed. However, TT of 1 μm or less
It has a V value and is significantly improved compared to conventional products.

Further, the OSF density and the withstand voltage defect density are higher than those of the conventional products in both the first and second embodiments, but they are values which pose no practical problem. Further, the impurity concentration in the case of the first embodiment is higher than that of the conventional product. However, as shown in the case of the second embodiment, it can be seen that the defects are removed at the same time.

Next, a method of manufacturing a semiconductor substrate according to the third embodiment of the present invention will be described with reference to the process chart shown in FIG. The same components as those of the semiconductor substrate shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. FIG. 3 (a) shows the same mirror-polished polishing surface 12 as that shown in FIG. 1 (a).
3 shows a silicon wafer 11 having an average thickness of about 655 μm and a back surface 13. This silicon wafer 11 is heated in a dry O ₂ (oxygen) atmosphere at a temperature of 1100 ° C. for 15
Heat treatment is performed for a minute to thermally oxidize the surface of the silicon wafer 11. By this dry oxidation, a dry oxide film 19 having a thickness of 50 nm is formed on the entire surface of the silicon wafer 11 including the polished surface 12 and the back surface 13.

Then, using the CVD method, the flow rate of each gas is SiH ₄ (silane) = 2.0 l / min, O ₂ = 1.2.
l / min, N ₂ (nitrogen) = 13.8 l / min, wafer temperature of 400 ° C., and deposition time of 27 minutes. The CVD oxide film 20 is grown. As a result, as shown in FIG. 3B, a protective film composed of the dry oxide film 19 and the CVD oxide film 20 is formed on the polished surface 12 of the silicon wafer 11.

Then, similarly to the steps shown in FIGS. 1C to 1D, the dry oxide film 19 and the CVD oxide film 2 are formed.
Polished surface 12 of silicon wafer 11 covered by 0
The silicon wafer 11 to the flat surface of the surface plate.
The back surface 13 is ground by, for example, a rotating grindstone having a grain size of 800 to about 10 μm, and further ground by a rotating grindstone having a grain size of about 5 μm. By this surface grinding, FIG.
As shown in (c), the back surface 13 of the silicon wafer 11
Is flattened to expose the ground surface 13a.

Then, the silicon wafer 11 is washed with a mixed aqueous solution of NH ₄ OH and H ₂ O _2, and then 1
The CVD oxide film 20 and the dry oxide film 19 are removed with a 0% HF aqueous solution. Thus, as shown in FIG. 3D, it is possible to obtain a silicon wafer 11 having a uniform thickness in which the distance between the mirror-polished polishing surface 12 and the surface-ground grinding surface 13a is constant.

In this embodiment, as the protective film, the dry oxide film 19 is formed on the polishing surface 12 of the silicon wafer 11 by dry oxidation, because the unevenness of the Si / SiO ₂ interface formed by dry oxidation does not become large. This is because it is known that the unevenness is reduced particularly by dry oxidation at a temperature of 900 ° C. or higher. Therefore, the unevenness on the surface of the polishing surface 12 of the silicon wafer 11 after removing the dry oxide film 19 becomes small. Even if the state of the interface between the dry oxide film 19 and the CVD oxide film 20 formed on the dry oxide film 19 is not good, both the CVD oxide film 20 and the dry oxide film 19 are finally removed, which causes a problem. Absent.

The reason for forming the protective film by combining the dry oxide film 19 having a thickness of 50 nm with the CVD oxide film 20 having a thickness of about 1 μm is as follows. In order to prevent the occurrence of defects when the polished surface 12 of the silicon wafer 11 is brought into close contact with the flat surface 16 of the surface plate 15, the entire protective film needs to have a thickness of about 1 μm. However, a graph showing the oxidation rates of the wet oxidation and the dry oxidation shown in FIG.
utF. Wolf, International Series of Monographs on Se
As is clear from "Miconductors", Pergamion Press, p.549), the oxide film formation rate of dry oxidation is extremely small, and it takes 1000 minutes to oxidize at a temperature of 1200 ° C to obtain a thickness of 1 µm. For this reason, it is not appropriate in terms of cost to form the entire protective film by dry oxidation, and therefore, by combining this dry oxide film 19 with the CVD oxide film 20 having a high growth rate, the thickness required for the protective film is increased. It was decided to secure the quality.

Next, a method of manufacturing a semiconductor substrate according to the fourth embodiment of the present invention will be described with reference to the process chart shown in FIG. It should be noted that the same components as those of the semiconductor substrate shown in FIG. FIG. 5A shows the same mirror-polished polishing surface 12 as that shown in FIG.
3 shows a silicon wafer 11 having an average thickness of about 655 μm and a back surface 13. When this silicon wafer 11 is heat-treated at a temperature of 1100 ° C. for 250 minutes in an atmosphere containing water vapor, for example, the polishing surface 12 and the back surface 13 of the silicon wafer 11 are wet-oxidized to have a thickness of about 1 μm.
Wet oxide film 21 is formed. As is clear from the graph showing the oxidation rates of the wet oxidation and the dry oxidation in FIG. 4, the oxidation rate at this time is 5% as compared with the dry oxidation.
Since it is 10 times faster, a desired film thickness can be obtained in a relatively short time.

Subsequently, the silicon wafer 11 having the wet oxide film 21 formed thereon is heat-treated at a temperature of 1000 ° C. for 25 minutes in a dry O ₂ atmosphere. By this dry oxidation, the silicon wafer 11 and the wet oxide film 2
A dry oxide film 22 having a thickness of 40 nm is formed on the interface with 1. As a result, as shown in FIG. 5B, a protective film composed of the dry oxide film 22 and the wet oxide film 21 is formed on the polished surface 12 of the silicon wafer 11.

Then, after the polishing surface 12 of the silicon wafer 11 covered with the dry oxide film 22 and the wet oxide film 21 is brought into close contact with the flat surface of the surface plate, the back surface 13 of the silicon wafer 11 is subjected to surface grinding. Figure 5
As shown in (c), the back surface 13 of the silicon wafer 11
Is flattened to expose the ground surface 13a. Then NH
After cleaning the silicon wafer 11 with a mixed aqueous solution of ₄ OH and H ₂ O ₂ , the wet oxide film 21 and the dry oxide film 22 are removed with a 10% HF aqueous solution. Thus, as shown in FIG. 5D, it is possible to obtain the silicon wafer 11 having a uniform thickness in which the distance between the mirror-polished polishing surface 12 and the surface-ground rear surface 13 is constant.

In this embodiment, the reason why the dry oxide film 22 and the wet oxide film 21 are combined to form the protective film is as follows. After the wet oxide film 21 is formed by wet oxidation of the silicon wafer 11, the dry oxidation is subsequently performed, so that the silicon oxide film 21 shown in FIGS.
As shown in the schematic view showing the change of the Si / SiO ₂ interface, but irregularities in the Si / SiO ₂ interface between the silicon wafer 11 and a wet oxide film 21 formed by the first wet oxidation is formed, followed by By the dry oxidation performed, a dry oxide film 22 is formed between the silicon wafer 11 and the wet oxide film 21.
Since the Si / SiO ₂ interface between the 1 and the dry oxide film 22 is formed, the Si / SiO ₂ interface of the irregularities is reduced.

Si / SiO produced by wet oxidation
Experiments have shown that the amplitude of the irregularities at the _two interfaces is about 5 nm. Therefore, it is considered that when a dry oxide film having a thickness of about 10 times this amplitude is formed, the unevenness caused by wet oxidation is significantly reduced. Therefore, in this embodiment, the dry oxide film 22 having a thickness of 40 nm is formed.

It is also known that when the oxidation temperature of dry oxidation is raised, the unevenness of the Si / SiO ₂ interface is further reduced. Therefore, the oxidation temperature of dry oxidation should be 1000
By increasing the temperature from ℃ to even higher, S
An i / SiO ₂ interface can be obtained. Thus, also in this embodiment, as in the third embodiment, the unevenness on the surface of the polishing surface 12 of the silicon wafer 11 after removing the wet oxide film 21 and the dry oxide film 22 can be similarly reduced. ..

Next, the polished surface 12 of the silicon wafer 11
The effect of the irregularities in Example 1 on the characteristics of the semiconductor device formed on the polished surface 12 was examined. Specifically, the first and fourth
An oxide film having a predetermined thickness was formed on the polished surface 12 of the silicon wafer 11 obtained in Example 1, and the oxide film breakdown voltage was measured to compare the two. The result is shown in FIG. 7.

As is clear from the graph of FIG. 7, in the case of the first embodiment in which the wet oxide film 14 is used as the protective film for covering the polishing surface 12 of the silicon wafer 11, the breakdown voltage breakdown of B mode occurs. On the other hand, the wet oxidation is followed by the dry oxidation, and the silicon wafer 1
In the case of the second embodiment in which the dry oxide film 22 and the wet oxide film 21 are combined on the polished surface 12 of No. 1 to form the protective film, the density of the B mode withstand voltage strength is remarkably reduced, and the high electric field is high. Concentrate on intrinsic destruction at strength. The improvement of the oxide film withstand voltage characteristic in the case of the second embodiment is due to the reduction of the irregularities on the surface of the polishing surface 12 of the silicon wafer 11.

Next, a method of manufacturing a semiconductor substrate according to a fifth embodiment of the present invention will be described with reference to the process chart shown in FIG. The same components as those of the semiconductor substrate shown in FIG. 1 or 2 are designated by the same reference numerals and the description thereof will be omitted. Figure 8
As shown in (a), the silicon wafer 11 produced by the first or second embodiment is prepared as a supporting substrate, and the silicon wafer 31 produced by the conventional process shown in FIG. 9 is prepared. Silicon wafer 11
Has a uniform thickness in which the distance between the mirror-polished polishing surface 12 and the surface-ground grinding surface 13a is constant, while the silicon wafer 31 has a mirror-polished polishing surface 32 and a back surface 33. It has a non-uniform thickness.

Then, as shown in FIG. 8B, the polishing surface 12 of the mirror-polished silicon wafer 11 and the polishing surface 32 of the same mirror-polished silicon wafer 31 are superposed so as to face each other. At this time, an insulating film is formed in advance on either or both of the polishing surface 12 of the silicon wafer 11 and the polishing surface 32 of the silicon wafer 31.

FIG. 8A shows a case where a wet oxide film 34 having a thickness of about 1 μm is formed on the entire surface of the silicon wafer 31 as the insulating film. The wet oxide film 34 is formed, for example, by heat-treating the silicon wafer 31 at a temperature of 1100 ° C. for 4 hours in an atmosphere containing water vapor to thermally oxidize its surface.
Therefore, in this case, the polishing surface 3 of the silicon wafer 31
2 and the wet oxide film 34 is formed on the entire surface including the back surface 33. Note that instead of using the thermal oxidation method, the well-known CVD
The insulating film may be formed by growing a CVD oxide film on the polished surface 12 of the silicon wafer 11 or the polished surface 32 of the silicon wafer 31 by using the method.

Since the silicon wafer 31 manufactured by the process of FIG. 9 has a non-uniform thickness, the silicon wafer 31 shown in FIG.
As shown in FIG. 3, the silicon wafer 3 in a state of being superposed on the silicon wafer 11 via the wet oxide film 34.
Although the non-flatness appears on the back surface 33 of No. 1, there is no problem because it is ground later. Instead of the silicon wafer 11 as the supporting substrate, a substrate made of an insulating material such as quartz glass may be used by mirror-polishing the surface and surface-polishing the back surface in the same manner as in the first embodiment. In that case, the formation of the insulating film may be omitted.

The silicon wafer 11 and the silicon wafer 31 thus superposed on each other with the wet oxide film 34 interposed therebetween are heated to a temperature of 100 in a nitrogen atmosphere, for example.
A strong bond is obtained by heat treatment at 0 ° C. for 30 minutes. Then, in the same manner as the step shown in FIG. 1C, the back surface 13 of the silicon wafer 11 is fixed to the flat surface of the surface plate by closely adhering it, and then the back surface 33 of the silicon wafer 31 is surface-ground by a rotary grindstone. Thin layer down to about 3 μm.
As a result, the silicon wafer 31 becomes a silicon layer 31a having a thickness of about 3 μm, and the ground surface 33a is exposed. FIG. 8C shows the state immediately after this. For this surface grinding, for example, after grinding about 600 μm with a rotary whetstone with a grain size of 500, about 20 μm with a rotary whetstone with a grain size of 2000
It is efficient to grind.

The silicon layer 3 thus thinned
As shown in FIG. 8 (d), the exposed ground surface 33a of 1a is further mirror-finished by ordinary chemical / opportunity polishing. The final thickness at this time is 2 μm. As a result, the ground surface 33a of the silicon layer 31a becomes the mirror-finished polishing surface 33b. Further, the ground surface 13a of the silicon wafer 11 is polished or etched to remove crystal defects.

Thus, the wet oxide film 34 having a thickness of about 1 μm is formed on the silicon wafer 11 as the supporting substrate.
The silicon layer 31a having a thickness of 2 μm is formed through the S
A semiconductor substrate having an OI structure, that is, an SOI substrate is completed. The TTV of the polished surface of this SOI substrate is 1.0 ± 0.2
μm, TT of SOI substrate with conventional bonding structure
Compared with V being 2.1 ± 1.0 μm, a significantly flat surface, that is, a uniform layer thickness can be obtained.

[0052]

As described above, according to the present invention, the surface of the semiconductor device is mirror-polished and then the back surface is ground, so that the flatness of the flat plate is remarkably improved.
Can be made smaller. The problem that defects may occur on the polishing surface due to contact with a surface plate or the like during surface grinding is prevented by covering the polishing surface with a protective film in advance. In addition, a dry oxide film is formed in contact with the polishing surface, and the dry oxide film is combined with a vapor growth oxide film or a wet oxide film to form a protective film, thereby removing the protective film to expose the surface. The unevenness on the surface can be reduced. Further, crystal defects and contamination generated on the back surface due to surface grinding are removed to a level that does not hinder practical use by thermal oxidation on the back surface and etching of the thermal oxide film.

As a result, there is an effect that it is possible to provide a semiconductor substrate having a single or SOI structure which can be applied to the manufacture of future high density / high performance semiconductor integrated circuits.

[Brief description of drawings]

FIG. 1 is a process chart for explaining a method for manufacturing a semiconductor substrate according to a first embodiment of the present invention.

FIG. 2 is a process drawing for explaining a manufacturing method of a semiconductor substrate according to a second embodiment of the present invention.

FIG. 3 is a process drawing for explaining a manufacturing method of a semiconductor substrate according to a third embodiment of the present invention.

FIG. 4 is a graph showing the oxidation rates of wet oxidation and dry oxidation.

FIG. 5 is a process drawing for explaining a manufacturing method of a semiconductor substrate according to a fourth embodiment of the present invention.

FIG. 6 is a schematic diagram showing changes in the Si / SiO ₂ interface.

FIG. 7 is a graph showing breakdown voltage characteristics of an oxide film formed on a polished surface of a silicon wafer according to the first and fourth examples of the present invention.

FIG. 8 is a process drawing for explaining a manufacturing method of a semiconductor substrate according to a fifth embodiment of the present invention.

FIG. 9 is a diagram illustrating a process of manufacturing a conventional silicon wafer.

[Explanation of symbols]

 11, 31 ... Silicon wafer 12, 32, 33b ... Polishing surface 13, 33 ... Back surface 13a, 33a ... Grinding surface 14, 18, 21, 34 ... Wet oxide film 15 ... Surface plate 16 ... Flat surface 17 ... Rotating grindstone 19, 22 ... Dry oxide film 20 ... CVD oxide film 31a ... Silicon layer

Front Page Continuation (72) Inventor Yoshihiro Kiyokawa 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (9)

[Claims] 1. A step of mirror-polishing a first surface of a flat plate made of a semiconductor, a step of forming a protective film covering the first surface of the flat plate that has been mirror-polished, and a step of covering the protective film with the protective film. And a step of surface-grinding the second surface of the flat plate in a state where the first surface of the flat plate is in close contact with the flat surface, and a step of removing the protective film from the first surface of the flat plate. And a method for manufacturing a semiconductor substrate. 2. The method of manufacturing a semiconductor substrate according to claim 1, wherein the flat plate is made of silicon, and the step of forming the protective film is performed by dry-oxidizing the first surface of the flat plate to make the first surface of the flat plate. A method of manufacturing a semiconductor substrate, which comprises the step of forming a dry oxide film on the surface of the substrate and then forming a vapor growth oxide film on the dry oxide film by vapor growth. 3. The method of manufacturing a semiconductor substrate according to claim 1, wherein the flat plate is made of silicon, and the step of forming the protective film is performed by wet-oxidizing the first surface of the flat plate to make the first surface of the flat plate. Forming a dry oxide film between the first surface of the flat plate and the wet oxide film by performing a dry oxidation after forming a wet oxide film on the surface of the semiconductor substrate. Method. 4. The method of manufacturing a semiconductor substrate according to claim 2, wherein the temperature at which the first surface of the flat plate is dry-oxidized is 1000.
A method of manufacturing a semiconductor substrate, wherein the temperature is not lower than ° C. 5. The method of manufacturing a semiconductor substrate according to claim 3, wherein the dry oxide film formed on the first surface of the flat plate has a film thickness of 50 nm or more. Production method. 6. The method of manufacturing a semiconductor substrate according to claim 1, wherein the flat plate is made of silicon, and at least the second surface of the flat plate is formed following the step of removing the protective film. A method of manufacturing a semiconductor substrate, comprising: a step of thermally oxidizing to form a thermal oxide film; and a step of removing the thermal oxide film by etching. 7. A step of mirror-polishing a first surface of a supporting substrate, and a step of planarizing a second surface of the supporting substrate with the first surface of the mirror-polished supporting substrate being in close contact with a flat surface. A step of grinding; a step of mirror-polishing a first surface of a flat plate made of a semiconductor; a step of bringing the first surface of the flat plate that has been mirror-polished into close contact with a first surface of the supporting substrate; A step of bonding the support plate and the support substrate, and the second surface of the support plate bonded to the flat plate is brought into close contact with a flat surface, and the second surface of the flat plate is surface-ground to reduce the thickness of the flat plate. And a step of layering the semiconductor substrate. 8. The method of manufacturing a semiconductor substrate according to claim 7, wherein the step of joining the flat plate and the support substrate is performed by forming an insulating film on the first surface of the support substrate or on the first surface of the flat plate. A method of manufacturing a semiconductor substrate, comprising the step of joining the flat plate and the supporting substrate via the insulating film after forming the. 9. The method of manufacturing a semiconductor substrate according to claim 7, further comprising a step of polishing or etching the second surface of the supporting substrate bonded to the flat plate. Substrate manufacturing method.