JP3342442B2 - Method for manufacturing semiconductor substrate and semiconductor substrate - 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 for manufacturing a semiconductor substrate, and more particularly, to a semiconductor substrate suitable for an electronic device or an integrated circuit formed on a single crystal semiconductor layer on a dielectric isolation or insulator. It relates to a manufacturing method.

[0002]

2. Description of the Related Art The formation of a single-crystal Si semiconductor layer on an insulator is widely known as a silicon-on-insulator (SOI) technique, and has many advantages that cannot be attained by a bulk Si substrate for fabricating a normal Si integrated circuit. Much research has been done because devices using SOI technology have a. That is, by using the SOI technology, 1. Dielectric separation is easy and high integration is possible. 2. Excellent radiation resistance. 3. Higher speed due to reduced stray capacitance. 4. Well step can be omitted; 5. Latch-up can be prevented. Advantages such as the possibility of a fully depleted field-effect transistor by thinning can be obtained.

[0003] In order to realize many of the above-mentioned advantages in device characteristics, researches have been made on a method of forming an SOI structure for several decades. This content
For example, they are summarized in the following documents. Special
Issue: "Single-crystals
ilicon on non-single-crys
tal insulators ”; edited b
yG. W. Cullen, Journal of C
rystal Growth, volume63,
no 3, pp 429-590 (1983).

Also, SOS (silicon on sapphire), which is formed by heteroepitaxy of Si on a single-crystal sapphire substrate by CVD (chemical vapor deposition), has been known for a long time. However, a large amount of crystal defects due to the lattice mismatch between the Si layer and the underlying sapphire substrate, the incorporation of aluminum from the sapphire substrate into the Si layer, and above all, the high cost of the substrate The delay in area increase has hindered the spread of applications. In recent years, attempts have been made to realize an SOI structure without using a sapphire substrate. This attempt is roughly divided into the following two.

[0005] 1. After the surface of the Si single crystal substrate is oxidized, a window is opened to partially expose the Si substrate, and the portion is laterally epitaxially grown as a seed to form a Si single crystal layer on SiO ₂ (in this case, see FIG. 4). Involves the deposition of a Si layer on SiO _2. )

[0006] 2. The Si single crystal substrate itself is used as an active layer, and SiO ₂ is formed below the active layer (this method does not involve deposition of a Si layer).

[0007]

As means for realizing the above item 1, a method of directly growing a single crystal layer Si in a lateral direction by CVD, a method of depositing amorphous Si,
A method in which solid phase lateral epitaxial growth is performed by heat treatment, an electron beam or a laser is applied to an amorphous or polycrystalline Si layer.
A method of converging and irradiating an energy beam such as light to grow a single crystal layer on SiO ₂ by melting and recrystallization, and a method of scanning a melting region in a band shape by a rod-shaped heater (Zone melting). recrystalli
zation) is known. Each of these methods has its advantages and disadvantages, but its controllability, productivity, uniformity,
It leaves a great deal of quality problems, and none has been commercialized yet. For example, the CVD method requires sacrificial oxidation to make a thin film flat, and the solid phase growth method has poor crystallinity. In the beam annealing method, a convergent beam is used.
There is a problem in the processing time by beam scanning, the degree of beam overlap, and the controllability such as focus adjustment. Of these, Zone M
Although the eluting recrystallization method is the most mature, and relatively large-scale integrated circuits have been prototyped, a large number of crystal defects such as sub-grain boundaries still remain. Not.

In the above-mentioned method 2 in which the Si substrate is not used as a seed for epitaxial growth, there are the following three methods.

1. An oxide film is formed on a Si single crystal substrate having a V-shaped groove anisotropically etched on its surface, and a polycrystalline Si layer is deposited on the oxide film as thick as the Si substrate, and then polished from the back surface of the Si substrate. Thereby, a dielectrically separated Si single crystal region surrounded by V grooves is formed on the thick polycrystalline Si layer.
In this method, the crystallinity is good, but the polycrystalline S
There is a problem in terms of controllability and productivity in the process of depositing i several hundred microns thick and the process of polishing a single crystal Si substrate from the back surface to leave only the separated Si active layer.

[0010] 2. Simox (SIMOX: Sepe
ratio by ion implanted o
xygen) is a method of forming a SiO ₂ layer by ion implantation of oxygen into a Si single crystal substrate, and is the most mature method at present because of its good compatibility with the Si process. However, in order to form a SiO ₂ layer,
Oxygen ions must be implanted at 10 ¹⁸ ions / cm ² or more, but the implantation time is long, the productivity is not high, and the wafer cost is high. In addition, many crystal defects remain, and from an industrial point of view, the quality has not been sufficient to produce a minority carrier device.

3. A method of forming an SOI structure by dielectric isolation by oxidation of porous Si. This method uses P-type Si
Proton ion implantation of an N-type Si layer on the surface of the single crystal substrate,
(Imai et al., J. Crystal Growth, v.
ol 63, 547 (1983)) or an island shape by epitaxial growth and patterning.
In this method, only the P-type Si substrate is made porous by anodizing in an HF solution so as to surround the Si island from the surface, and then the N-type Si island is dielectrically separated by accelerated oxidation. This method has a problem that the Si region to be separated is determined before the device process, which may limit the degree of freedom in device design.

On the other hand, a light-transmitting substrate represented by glass generally has a good amorphous property and a polycrystalline layer, reflecting the disorder of its crystal structure. Can not. This is due to the fact that the crystal structure of the substrate is amorphous, and even if a Si layer is simply deposited, a high-quality single crystal layer cannot be obtained. The light transmissive substrate is important in forming a contact sensor as a light receiving element and a projection type liquid crystal image display device. And the sensor
In order to further increase the density, resolution, and definition of pixels (picture elements) of display devices and display devices, extremely high performance driving elements are required. As a result, it is necessary that the element provided on the light-transmitting substrate be formed using a single crystal layer having excellent crystallinity.

[0013] Therefore, it is difficult to produce a driving element having the required or sufficient performance in amorphous Si or polycrystalline Si due to its crystal structure having many defects.

However, any of the above methods using a Si single crystal substrate is not suitable for the purpose of obtaining a good quality single crystal layer on a light transmitting substrate.

An object of the present invention is to propose a method of manufacturing a semiconductor substrate for manufacturing a semiconductor substrate which meets the above-mentioned problems and the above-mentioned requirements.

Another object of the present invention is to provide a method of manufacturing a semiconductor substrate which can realize the advantages of the conventional SOI structure and can be applied.

Another object of the present invention is to propose a method of manufacturing a semiconductor substrate that can be used as a substitute for expensive SOS or SIMOX even when manufacturing a large-scale integrated circuit having an SOI structure.

Further, the present invention provides a method of manufacturing a semiconductor substrate which is excellent in productivity, uniformity, controllability and cost in obtaining Si having excellent crystallinity on an insulating layer as much as a single crystal wafer. The purpose is to propose.

Further, the present invention is excellent in productivity, uniformity, controllability, and cost in obtaining Si having excellent crystallinity on a transparent substrate (light transmitting substrate) as excellent as a single crystal wafer. It is an object to propose a method for manufacturing a semiconductor substrate.

[0020]

According to a method of manufacturing a semiconductor substrate of the present invention, a step of preparing a first substrate having a porous silicon layer and a step of subjecting the first substrate to a first heat treatment in an oxygen atmosphere are provided. Forming a non-porous single-crystal semiconductor layer on the porous silicon layer, placing the first substrate and the second substrate through an insulating layer, and the non-porous single-crystal semiconductor layer Laminating so as to obtain a multilayer structure positioned thereon, removing the porous silicon layer from the multilayer structure, and removing the porous silicon layer, and forming the insulating layer on the second substrate. Performing a second heat treatment at a temperature lower than the melting point of the non-porous single-crystal semiconductor layer in a reducing atmosphere containing hydrogen and at a temperature lower than the melting point of the non-porous single-crystal semiconductor layer. Features.

According to the method of manufacturing a semiconductor substrate of the present invention, a step of preparing a first substrate having a porous silicon layer is provided.
Performing a first heat treatment on the substrate in an oxygen atmosphere, forming a non-porous single-crystal semiconductor layer on the porous silicon layer, and combining the first substrate and the light-transmitting second substrate with each other. A step of attaching a non-porous single-crystal semiconductor layer to obtain a multilayer structure positioned inside, a step of removing the porous silicon layer from the multilayer structure, and the porous silicon layer being removed, Performing a second heat treatment on the non-porous single-crystal semiconductor layer transferred on the second substrate in a reducing atmosphere containing hydrogen and at a temperature equal to or lower than the melting point of the non-porous single-crystal semiconductor layer; And characterized in that:

According to the present invention, an Si single crystal substrate which is excellent in economical efficiency and is uniform and flat over a large area and has extremely excellent crystallinity is used. By removing the layers and performing a heat treatment in a reducing atmosphere, a Si single crystal having a surface with an insulating layer or a light-transmissive substrate with very few defects and a flat surface similar to a wafer is obtained. Is to get the layers.

In particular, in the present invention, by performing a heat treatment in a reducing atmosphere, the surface properties after removing the porous silicon layer by etching can be made as flat as the wafer.

Further, the present invention provides a method for forming a porous silicon layer
Prior to forming the non-porous silicon layer, the porous silicon layer is heat-treated in an oxygen atmosphere, whereby the porous silicon layer can be efficiently and selectively etched in a later step.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 A method for epitaxially growing a single crystal layer after making a Si substrate porous will be described.

As shown in FIG. 1A, first, a Si single crystal substrate 11 is prepared, and all or a single crystal substrate 11 shown in FIG.
A part is made porous as shown in FIG.

The Si substrate is made porous by an anodizing method using an HF solution. The porous Si layer, the monocrystalline Si as compared with the density of 2.33 g / cm ^3, the density of 1.1~0.6g / cm ³ by changing the density of HF solution concentration to 50 to 20% Range. This porous layer is easily formed on a P-type Si substrate for the following reasons. According to observation with a transmission electron microscope, pores having an average diameter of about 50 to 600 angstroms are formed in the porous Si layer.

The porous Si was prepared by Uhril et al.
It was discovered during the research process of electropolishing semiconductors in 56 (A. Uhlir, Bell Syst. Tech.
J. , Vol 35, p. 333 (1956)). In addition, Unagami et al. Studied the dissolution reaction of Si in anodization and reported that the anodic reaction of Si in an HF solution requires holes, and the reaction is as follows (T Unagi: J. Electroc-hem.S
oc. , Vol. 127, p. 476 (198
0)).

Si + 2HF + (2-n) e + → SiF ₂ + 2H +++ ne−SiF ₂ + 2HF → SiF ₄ + H ₂ SiF ₄ + 2HF → H ₂ SiF ₆ or Si + 4HF + (4-λ) e + → SiF ₄ + 4H ++++ λe-SiF ₄ + 2HF → H ₂ SiF ₆ Here, e + and e− represent a hole and an electron, respectively. Further, n and λ are the number of holes required for dissolving one atom of silicon, respectively, and it is assumed that porous silicon is formed when the condition of n> 2 or λ> 4 is satisfied.

From the above, P-type silicon having holes is easily made porous. In making this porous,
Selectivity has been demonstrated by Nagano et al. And by Imai (Nagano, Nakajima, Anno, Onaka, Kajiwara; IEICE Technical Report, vol 79, SSD 79-9549 (1
979); Imai; Solid-State El
electronics vol 24, 159 (198
1)). P-type silicon having holes as described above is easily made porous, and P-type silicon can be selectively made porous.

On the other hand, it has been reported that high-concentration N-type silicon also becomes porous (RP Holmstorm, IJ.
Y. Chi Appl. Phys. Lett. Vo
l. 42, 386 (1983)), and it is important to select a substrate that can realize porosity regardless of P and N.

Subsequently, epitaxial growth is performed on the porous substrate surface by various growth methods to form the thin film single crystal layer 12.

According to observation by a transmission electron microscope, pores having an average diameter of about 600 angstroms are formed in the porous Si layer, and the density thereof is less than half that of single crystal Si. Nevertheless, single crystallinity is maintained, and it is also possible to epitaxially grow a single crystal Si layer on top of the porous layer. However, 1000 ° C
In the above epitaxial growth, rearrangement of internal holes occurs, and the characteristics of the accelerated etching are impaired. For this reason,
For the epitaxial growth of the Si layer, low-temperature growth such as molecular beam epitaxial growth, plasma CVD, thermal CVD, optical CVD, bias sputtering, and liquid phase growth is preferable.

Further, in the above-described epitaxial growth on porous Si, the porous Si has a structural property, so that it is possible to alleviate the strain generated during heteroepitaxial growth and suppress the generation of defects. .

Further, the density of the porous layer is reduced to less than half since a large amount of voids are formed therein. As a result, the surface area is dramatically increased as compared with the volume, so that the chemical etching rate is significantly increased as compared with the ordinary etching rate of the single crystal layer.

The method for etching porous Si is as follows. Etch porous Si with aqueous NaOH solution (G. Bonchil, R. Herino, K. Barr)
la, and j. C. Pfister, J.M. Ele
trochem. Soc. , Vol. 130, n
o. 7, 1611 (1983)).

2. Etch porous Si with an etchant capable of etching single crystal Si. It has been known.

In the above method 2, an etching solution of a hydrofluoric / nitric acid system is usually used, and the etching process of Si at this time is as follows: Si + 2O → SiO ₂ (10) SiO ₂ + 4HF → SiF ₄ + H ₂ O (11) as shown in, Si is oxidized by nitric acid, and transformed into SiO _2, the etching of Si proceeds by etching the SiO ₂ with hydrofluoric acid.

Similarly, as a method for etching crystalline Si, there are an ethylenediamine-based KOH-based hydrazine-based method and the like in addition to the above-mentioned hydrofluoric-nitric acid-based etchant.

An important method for selectively etching porous Si, which is particularly effective in the present invention, is to use hydrofluoric acid or buffered hydrofluoric acid having no etching effect on crystalline Si. In this etching, hydrogen peroxide acting as an oxidizing agent may be further added. Hydrogen peroxide acts as an oxidizing agent, and the reaction rate can be controlled by changing the ratio of hydrogen peroxide. Further, an alcohol acting as a surfactant may be added. Alcohol acts as a surface active agent, instantaneously removes bubbles of a reaction product gas from the etching surface, and enables uniform and efficient selective etching of porous Si.

As shown in FIGS. 1 (b) and 4 (b),
As a substrate, for example, a substrate in which an insulating layer is disposed on the surface of a base material such as a silicon substrate, or a light-transmitting insulator substrate 13 represented by glass is prepared, and the surface of a single-crystal Si layer on a porous Si substrate is prepared. Is adhered to the substrate surface to form a multilayer structure.

Prior to the bonding, an interface between the single crystal silicon layer and the insulating layer may be formed in advance by forming an oxide layer on the surface of the single crystal Si layer on the porous Si. The oxide layer plays an important role in making a device. That is, the interface level generated by the underlying interface of the Si active layer can be lower at the underlying interface formed by oxidizing the single crystal silicon layer than at the bonding interface, especially at the glass interface. By separating from the active layer, a level that may be generated at the bonding interface can be kept away, so that the characteristics of the electronic device are significantly improved. Further, an oxide layer may be formed on the surface of the single crystal Si layer on the porous Si, and may be bonded to an arbitrary substrate such as a Si substrate or a metal substrate.

Thereafter, the entire porous Si substrate 15 is removed by chemical etching, and as shown in FIG.
The thin single-crystal silicon layer is formed on a substrate having an insulating layer on its surface or on a light-transmitting substrate while remaining.
Prior to the etching, an etching prevention film is formed as necessary. For example, a Si ₃ N ₄ layer is deposited, the whole of the two bonded substrates is covered, and the Si ₃ N ₄ layer on the surface of the porous silicon substrate is removed. Apiezon wax may be used instead of the Si ₃ N ₄ layer as another etching prevention film.

When the porous Si is formed only on a part of the substrate as in the steps shown in FIGS. 4A and 4B, grinding, which is usually used in the Si wafer manufacturing step, is performed until the porous layer is exposed. After removing the non-porous Si on the back surface side of the substrate on which the porous layer has been formed by polishing or etching with a mixed solution of hydrofluoric acid, nitric acid, and acetic acid, the porous silicon is removed by the chemical etching described above. And FIG. 4 (c)
As shown in (1), a thin single-crystal silicon layer is formed on a substrate having an insulating layer on its surface or on a light-transmitting substrate.

Thereafter, a substrate having a non-porous single-crystal silicon layer on the insulating layer obtained by removing the porous silicon is heat-treated in a reducing atmosphere to obtain a substrate shown in FIG.
As shown in FIG. 4D, a single crystal silicon layer having a flat surface is formed on a substrate having an insulating layer on the surface or a light-transmitting substrate.

The present inventors have studied a method using heat treatment for removing minute roughness on the surface of the non-porous silicon single crystal that has appeared after etching. As a result, the heat treatment in a reducing atmosphere is the same as that of the device process. It has been found that roughening of the surface of the non-porous silicon single crystal can be removed by a heat treatment at a temperature lower than the level. Here, the reducing atmosphere is
For example, an atmosphere containing hydrogen or a hydrogen atmosphere can be given. However, it is not limited to this. When the change in surface roughness due to heat treatment was observed in detail using a high-resolution scanning electron microscope or atomic force microscope while changing the atmosphere, as shown in FIG.
It has been found that a single-crystal thin layer having a flat surface is reduced by a heat treatment in a reducing atmosphere and is obtained.
Moreover, when the surface roughness is removed by polishing or the like, the thickness of the single crystal layer may be distributed in the plane,
In the case of the heat treatment in a reducing atmosphere according to the present invention, only the fine irregularities are removed, and the film thickness distribution does not change.

When the fine structure of the surface of the non-porous silicon single crystal layer obtained by etching is observed, irregularities having a height of several nm to several tens nm and a period of several nm to several hundred nm are observed. (FIG. 5 (a)), but by performing a heat treatment in a reducing atmosphere, at least the height difference is several nm.
Hereinafter, if the conditions are adjusted, a flat surface of 2 nm or less (FIG. 5)
(B)) is obtained. This phenomenon is believed to be a surface reconstruction rather than etching. That is,
Rough surfaces have numerous ridges with high surface energy, and many higher-order planes are exposed on the surface compared to the plane orientation of the crystal layer. Is higher than the surface energy in the plane orientation of the surface of the first substrate. In a heat treatment in a reducing atmosphere, for example, a natural oxide film on the surface is removed by a heat treatment in a hydrogen atmosphere due to a reducing action of hydrogen, and is constantly removed during the heat treatment and does not adhere again. It is considered that Si atoms excited by thermal energy move to form a flat surface with low surface energy.

As a result, in a nitrogen atmosphere or a rare gas atmosphere, the surface is sufficiently flattened even at a temperature of 1200 ° C. or less so that the surface is not flattened. The flattening temperature according to the present invention depends on the gas composition, pressure, etc., but it is effective at about 300 ° C. or higher but not higher than the melting point, more preferably at 500 ° C. or higher, especially 1200 ° C. or lower. The flattening is promoted even at a higher pressure as the pressure is higher as the reducing property is higher.

This phenomenon starts when heat treatment is performed with the surface being clean. When a natural oxide film is thickly formed on the surface, this phenomenon occurs before the heat treatment. Is removed by etching with dilute hydrofluoric acid or the like, so that the flattening of the surface starts earlier.

FIGS. 1C and 4C show a semiconductor substrate obtained by the present invention. That is, a substrate having an insulating layer on the surface, or a single-crystal Si layer 12 having a crystallinity equivalent to that of a silicon wafer is flat on a light-transmitting substrate 13,
Moreover, the layer is uniformly thinned and formed over a large area over the entire wafer.

The semiconductor substrate thus obtained can be suitably used from the viewpoint of producing an insulated and separated electronic device.

Embodiment 2 Hereinafter, a method for manufacturing a semiconductor substrate according to the present invention will be described in detail with reference to the drawings.

FIGS. 3A to 3C are process diagrams for explaining a method of manufacturing a semiconductor substrate according to the present invention, and are shown as schematic cross-sectional views in each process.

First, as shown in FIG. 3A, a low impurity concentration layer 32 is formed by epitaxial growth using various thin film growth methods. Alternatively, protons are ion-implanted into the surface of the P-type Si single-crystal substrate 31 to form the N-type single-crystal layer 32.

Next, as shown in FIG.
The single crystal substrate 31 is transformed from the rear surface into porous Si33 by an anodizing method using an HF solution. This porous S
The i-layer is changed in density from 1.1 to 0.6 g / cm ³ by changing the density of the HF solution to 50 to 20% compared to the density of single crystal Si of 2.33 g / cm ^3. Can be done. This porous layer, as described above,
It is formed on a P-type substrate.

As shown in FIG. 3C, a substrate 34 having an insulating layer on the surface is prepared, and the surface of the single-crystal Si layer on the porous Si substrate or the surface of the single-crystal Si layer oxidized is prepared. It is attached to the second substrate 34. In addition, porous Si
An oxide layer may be formed on the surface of the upper single crystal Si layer, and may be bonded to an arbitrary substrate such as a Si substrate.

As shown in FIG. 3C, the porous S
The entire porosity of the i-substrate 33 is removed by etching, and a thin single-crystal silicon layer is formed and left on a substrate having an insulating layer on the surface.

Thereafter, a substrate having a non-porous single-crystal silicon layer on an insulating layer obtained by removing porous silicon is heat-treated in a reducing atmosphere in the same manner as in the first embodiment. Thus, a semiconductor substrate obtained by improving the surface roughness and obtained by the present invention as shown in FIG. 3E is shown. That is, a single-crystal Si layer 32 having a crystallinity equivalent to that of a silicon wafer is flattened and uniformly thinned on a substrate having an insulating layer on the surface or on a light-transmitting substrate 34, and a large area is formed over the entire wafer. Formed.

The semiconductor substrate thus obtained can be suitably used from the viewpoint of producing an insulated electronic device.

The above is a method in which the N-type layer is formed before the formation of the porous body, and thereafter only the P-type substrate is selectively made porous by anodizing.

[0061]

The present invention will be described below with reference to specific examples.

Example 1 A P-type (100) single crystal Si substrate having a thickness of 600 microns was anodized in a 50% HF solution for 20 minutes. The current density at this time was 5 mA / cm ² . At this time, the rate of making porous is 1 μm / min. And a P-type (100) Si substrate having a thickness of 600 microns was made porous by about 20 μm.

CV is applied on the P-type (100) porous Si substrate.
A 2 nm Si epitaxial layer was grown by the D method. The deposition conditions are as follows.

Temperature: 950 ° C. Pressure: 80 Torr Gas: SiH ₂ Cl ₂ / H ₂ ; 0.5 / 180 (l / min) Growth rate: 0.33 nm / sec

Next, the surface of this epitaxial layer was
nm. A single crystal silicon substrate was superposed on the thermal oxide film, and heated at 1000 ° C. for 2 hours in a nitrogen atmosphere, whereby both substrates were firmly joined.

Thereafter, the porous substrate side was ground from the back surface to remove the nonporous silicon substrate region, exposing the porous layer.

Thereafter, the bonded substrates are selectively etched without stirring with a mixed solution (10: 6: 50) of hydrofluoric acid, alcohol and hydrogen peroxide solution. After 20 minutes, only the single crystal Si layer remained without being etched, and the porous Si substrate was selectively etched using the single crystal Si as a material for the etch stop, and completely removed.

The etching rate of the non-porous Si single crystal with respect to the etching solution is extremely low, and is 40
The selectivity with the etching rate of the porous layer reaches about 10 times or more, and the etching amount (several tens of angstroms) in the non-porous layer is a practically negligible decrease in film thickness. That is, the porous Si substrate having a thickness of 200 microns is removed,
After removing the Si ₃ N ₄ layer, a single-crystal Si layer having a thickness of 0.5 μm was formed on the silicon substrate having the silicon oxide layer on the surface.

Thereafter, in a hydrogen atmosphere at 950 ° C. and 80 T
Heat treatment was performed at orr. The flatness of the surface of this sample was evaluated using an atomic microscope or the like. As a result, the surface roughness was as good as 1.5 nm with a roughness of 20 nm before hydrogen treatment.

As a result of observation of a cross section by a transmission electron microscope, no new crystal defects were introduced into the Si layer.
It was confirmed that good crystallinity was maintained.

Example 2 A P-type (100) single-crystal Si substrate having a thickness of 200 μm was anodized in a 50% HF solution. The current density at this time is 10
It was 0 mA / cm ² . The porosity rate at this time is
8.4 μm / min. The entire P-type (100) Si substrate having a thickness of 200 microns was made porous in 24 minutes.

The porous substrate is placed in an oxygen atmosphere at 3
Heat treatment was performed at 00 ° C. for 1 hour.

The MB was placed on the P-type (100) porous Si substrate.
E (Molecular Beam Epitaxy: Molecular Beam)
An Si epitaxial layer was grown at a low temperature of 0.5 μm by the mEpelxy) method. The deposition conditions are as follows.

Temperature: 700 ° C. Pressure: 1 × 10 ⁻⁹ Torr Growth rate: 0.1 nm / sec

Next, the surface of this epitaxial layer was
0 nm was thermally oxidized. A single crystal silicon substrate is superposed on the thermal oxide film by a thermal oxidation method,
By heating at 2 ° C. for 2 hours, both substrates were firmly joined.

[0086] Si ₃ N ₄ is reduced to 0.
1 μm is deposited, and the two bonded substrates are covered,
Only the nitride film on the porous substrate is removed by reactive ion etching.

After that, the bonded substrates were mixed with a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution (10:
6:50), selective etching is performed without stirring.
After 204 minutes, only the single crystal Si layer remains without being etched, and the single crystal Si is used as an etch stop material.
The porous Si substrate was selectively etched and completely removed.

The etching rate of the non-porous Si single crystal with respect to the etching solution is extremely low, and the etching rate is 4 even after 204 minutes.
The selectivity with respect to the etching rate of the porous layer reaches about 10 times or more, and the etching amount (several tens of angstroms) in the non-porous layer is a film thickness reduction that can be ignored in practical use. That is, the porous Si substrate having a thickness of 200 microns is removed, and after the Si ₃ N ₄ layer is removed, the silicon substrate having a silicon oxide layer on the surface has a thickness of 0.5 μm. A single-crystal Si layer was formed.

Then, at 950 ° C. and 80 T in a hydrogen atmosphere.
Heat treatment was performed at orr. When the flatness of the surface of this sample was evaluated using an atomic force microscope or the like, the roughness of the surface was improved to 1.5 nm from a roughness of 20 nm before hydrogen treatment.

As a result of observation of a cross section by a transmission electron microscope, no new crystal defects were introduced into the Si layer.
It was confirmed that good crystallinity was maintained.

Example 3 A P-type (100) single crystal Si substrate having a thickness of 200 μm was anodized in a 50% HF solution. The current density at this time is 10
It was 0 mA / cm ² . The porosity rate at this time is
8.4 μm / min. The entire P-type (100) Si substrate having a thickness of 200 microns was made porous in 24 minutes.

An Si epitaxial layer was grown at a low temperature of 5 μm on the P-type (100) porous Si substrate by a plasma CVD method. The deposition conditions are as follows.

Gas: SiH ₄ High frequency power: 100 W Temperature: 800 ° C. Pressure: 1 × 10 ⁻¹ Torr Growth rate: 2.5 nm / sec

Next, the surface of this epitaxial layer was
nm. An optically polished fused silica substrate is superimposed on the thermal oxide film,
By heating at 400 ° C. for 20 hours in an oxygen atmosphere, both substrates were firmly joined.

Thereafter, the bonded substrates are selectively etched while being stirred with a mixed solution (1: 5) of hydrofluoric acid and hydrogen peroxide solution. After 62 minutes, only the single-crystal Si layer remained without being etched, and the porous Si substrate was selectively etched using the single-crystal Si as a material for the etch stop and completely removed.

The etching rate of the non-porous Si single crystal with respect to the etching solution is extremely low, even after 62 minutes.
The selectivity with the etching rate of the porous layer reaches about 10 times or more, and the etching amount (several tens of angstroms) in the non-porous layer is a practically negligible decrease in film thickness. That is, the porous Si substrate having a thickness of 200 microns is removed,
A single-crystal Si layer having a thickness of 5 μm was formed on the fused quartz substrate.

Thereafter, in a hydrogen atmosphere, at 1000 ° C. and 76 ° C.
Heat treatment was performed at 0 Torr. When the flatness of the surface of this sample was evaluated using an atomic force microscope or the like, the roughness of the surface became good, with a roughness of 20 nm before hydrogen treatment being 1.6 nm.

As a result of observation of a cross section with a transmission electron microscope, no new crystal defects were introduced into the Si layer.
It was confirmed that good crystallinity was maintained.

Example 4 A P-type (100) single-crystal Si substrate having a thickness of 200 μm was anodized in a 50% HF solution. The current density at this time is 10
It was 0 mA / cm ² . The porosity rate at this time is
8.4 μm / min. The entire P-type (100) Si substrate having a thickness of 200 microns was made porous in 24 minutes.

The CV was placed on the P-type (100) porous Si substrate.
By the method D, a Si epitaxial layer was grown at a low temperature of 1 micron. The deposition conditions are as follows.

Gas: SiH ₄ (0.6 l / min), H ₂ (100 l / min) Temperature: 850 ° C. Pressure: 40 Torr Growth rate: 0.3 μm / min

Next, the surface of this epitaxial layer was
nm. Optical polishing was performed on the thermal oxide film.
By laminating a glass substrate having a softening point near 0 ° C. and heating at 450 ° C. for 0.5 hour in an oxygen atmosphere,
Both substrates were firmly joined.

Then, the bonded substrates were mixed with a mixed solution of buffered hydrofluoric acid, alcohol and aqueous hydrogen peroxide (10:
6:50), selective etching is performed without stirring.
After 204 minutes, only the single crystal Si layer remains without being etched, and the single crystal Si is used as an etch stop material.
The porous Si substrate was selectively etched and completely removed.

The etching rate of the non-porous Si single crystal with respect to the etching solution was extremely low even after 204 minutes.
The selectivity with respect to the etching rate of the porous layer reaches about 10 times or more, and the etching amount (several tens of angstroms) in the non-porous layer is a film thickness reduction that can be ignored in practical use. That is, the porous Si substrate having a thickness of 200 microns is removed,
1μm thick single crystal Si on low softening point glass substrate
A layer could be formed.

Then, in a hydrogen atmosphere, 900 deg.
Heat treatment was performed at 10 Torr. When the flatness of the surface of this sample was evaluated using an atomic force microscope or the like, the roughness of the surface was as good as 1.7 nm with a roughness of 20 nm before hydrogen treatment.

As a result of observation of a cross section by a transmission electron microscope, no new crystal defects were introduced into the Si layer.
It was confirmed that good crystallinity was maintained.

Example 5 A P-type (100) single-crystal Si substrate having a thickness of 525 μm was anodized in a 50% HF solution. The current density at this time is 5 m
A / cm ² . At this time, the rate of making porous is 1 μm
/ Min. The surface of a P-type (100) Si substrate having a thickness of 525 μm was made 20 μm porous.

The porous substrate was placed in an oxygen atmosphere at 3
Heat treatment was performed at 00 ° C. for 1 hour.

An Si epitaxial layer was grown at a low temperature of 1.0 μm on the P-type (100) porous Si substrate by a bias sputtering method. The growth conditions are as follows.

RF frequency: 100 MHz High frequency power: 600 W Temperature: 300 ° C. Ar gas pressure: 8 × 10 ⁻³ Torr Growth time: 120 minutes Target DC bias: −200 V Substrate DC bias: +5 V

Next, a 500 nm silicon oxide layer was formed on the surface of the epitaxial layer by a thermal oxidation method. An Si substrate is superimposed on the thermal oxide film, and is placed in a nitrogen atmosphere for 1 hour.
By heating at 000 ° C. for 2 hours, both substrates are
Strongly joined.

Thereafter, the nonporous silicon substrate region is removed by grinding the porous substrate side from the back surface, exposing the porous layer.

Then, the bonded substrate was mixed with a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution (10:
6:50), selective etching is performed without stirring.
After 20 minutes, only the single crystal Si layer remained without being etched, and the porous Si substrate was selectively etched using the single crystal Si as a material for the etch stop, and completely removed.

The etching rate of the non-porous Si single crystal with respect to the etching solution was extremely low, and the etching rate was 4 minutes even after 204 minutes.
The selectivity with respect to the etching rate of the porous layer reaches about 10 times or more, and the etching amount (several tens of angstroms) in the non-porous layer is a film thickness reduction that can be ignored in practical use. That is, the porous Si substrate having a thickness of 200 microns is removed,
0.75 μm on a Si substrate via a 500 nm oxide layer
A single-crystal Si layer having a thickness of m was formed.

Thereafter, in a hydrogen atmosphere, 900 deg.
Heat treatment was performed at 10 Torr. When the flatness of the surface of this sample was evaluated using an atomic force microscope or the like, the roughness of the surface was as good as 1.7 nm with a roughness of 20 nm before hydrogen treatment.

As a result of observation of a cross section with a transmission electron microscope, no new crystal defects were introduced into the Si layer.
It was confirmed that good crystallinity was maintained.

(Example 6) A P-type (100) single crystal Si substrate having a thickness of 600 microns was anodized in a 50% HF solution. At this time, the current density was 5 mA
/ Cm ² . At this time, the rate of making porous is 1 μm /
min. And a P-type (1
00) The Si substrate was made 20 μm porous.

A 10 μm low-temperature Si epitaxial layer was grown on the P-type (100) porous Si substrate by a liquid phase growth method. The deposition conditions are as follows.

Solvent: Sn Growth temperature: 900 ° C. Growth atmosphere: H ₂ Growth time: 20 minutes

On the surface of the Si epitaxial layer, 1 μm
The single-crystal silicon substrates on which the silicon oxide layers were formed were superposed and heated at 700 ° C. for 5 hours in an oxygen atmosphere, whereby both substrates were firmly joined.

Thereafter, the nonporous silicon substrate region was removed by grinding the porous substrate side from the back surface, exposing the porous layer.

Thereafter, the bonded substrates were mixed with a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution (10:
6:50), selective etching is performed without stirring.
After 20 minutes, only the single crystal Si layer remained without being etched, and the porous Si substrate was selectively etched using the single crystal Si as a material for the etch stop, and completely removed.

The etching rate of the non-porous Si single crystal with respect to the etching solution was extremely low, even after 20 minutes.
The selectivity with the etching rate of the porous layer reaches about 10 times or more, and the etching amount (several tens of angstroms) in the non-porous layer is a practically negligible decrease in film thickness. That is, the porous Si substrate was removed, and a single-crystal Si layer having a thickness of 10 μm was formed on the silicon substrate having an oxide layer on the surface.

Thereafter, in a hydrogen atmosphere, at 950 ° C. and 80 T
Heat treatment was performed at orr. When the flatness of the surface of this sample was evaluated using an atomic force microscope or the like, the roughness of the surface was as good as 1.7 nm with a roughness of 20 nm before hydrogen treatment.

As a result of observation of a cross section by a transmission electron microscope, no new crystal defects were introduced into the Si layer.
It was confirmed that good crystallinity was maintained.

Example 7 A Si epitaxial layer was grown to 0.5 μm on a P-type (100) Si substrate having a thickness of 200 μm by CVD. The deposition conditions are as follows.

Reaction gas flow rate: SiH ₂ Cl ₂ 1000 SCCM: H ₂ 230 / min Temperature: 1080 ° C. Pressure: 80 Torr Time: 1 min

The substrate was anodized in a 50% HF solution. The current density at this time is 100 mA / c
m ² . The porosity rate at this time is 8.4 μm /
min and a P-type (10
0) The entire Si substrate was made porous in 24 minutes. As described above, in this anodization, only the P-type (100) Si substrate was made porous and the Si epitaxial layer did not change.

Next, the surface of this epitaxial layer was
nm. An optically polished solution silica glass (Fused Silicon) substrate was overlaid on the thermal oxide film, and heated at 800 ° C. for 3 hours in an oxygen atmosphere, whereby both substrates were firmly joined.

Then, the bonded substrates were mixed with a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution (10:
6:50), selective etching is performed without stirring.
After 204 minutes, only the single crystal Si layer remains without being etched, and the single crystal Si is used as an etch stop material.
The porous Si substrate was selectively etched and completely removed.

The etching rate of the non-porous Si single crystal with respect to the etching solution is extremely low, and the
The selectivity with respect to the etching rate of the porous layer reaches about 10 times or more, and the etching amount (several tens of angstroms) in the non-porous layer is a film thickness reduction that can be ignored in practical use. That is, the porous Si substrate having a thickness of 200 microns is removed,
After removing the Si ₃ N ₄ layer, a single-crystal Si layer having a thickness of 0.5 μm was formed on the fused silica glass substrate.

Thereafter, in a hydrogen atmosphere, at 950 deg.
Heat treatment was performed at 80 Torr. When the flatness of the surface of this sample was evaluated using an atomic force microscope or the like, the roughness of the surface was as good as 1.7 nm with a roughness of 20 nm before hydrogen treatment.

As a result of cross-sectional observation by a transmission electron microscope,
No new crystal defects were introduced into the Si layer, and it was confirmed that good crystallinity was maintained.

Example 8 An N-type Si layer was formed to a thickness of 1 μm on the surface of a P-type (100) Si substrate having a thickness of 200 μm by ion implantation of protons. The H + implantation dose was 5 × 10 ¹⁵ (ions / cm ² ). This substrate was anodized in a 50% HF solution. The current density at this time was 100 mA / cm ² . At this time, the rate of making porous is 8.4 μm / min. P-type (100) S with a thickness of 200 microns
The entire i-substrate was made porous in 24 minutes. As described above, in this anodization, only the P-type (100) Si substrate was made porous, and the N-type Si layer did not change.

Next, the surface of this N-type single crystal layer was
Thermally oxidized. A fused silica glass substrate that has been optically polished is superimposed on the thermal oxide film, and is placed at 800 ° C. in an oxygen atmosphere.
By heating for 0.5 hour, both substrates were firmly joined.

0.1 μm of Si ₃ N ₄ is formed by a low pressure CVD method.
Then, the two substrates that have been deposited and adhered are covered, and only the nitride film on the porous substrate is removed by reactive ion etching.

Thereafter, the bonded substrate was mixed with a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution (10:
6:50), selective etching is performed without stirring.
After 204 minutes, only the single crystal Si layer remains without being etched, and the single crystal Si is used as an etch stop material.
The porous Si substrate was selectively etched and completely removed.

The etching rate of the non-porous Si single crystal with respect to the etching solution was extremely low, even after 204 minutes.
The selectivity with respect to the etching rate of the porous layer reaches about 10 times or more, and the etching amount (several tens of angstroms) in the non-porous layer is a film thickness reduction that can be ignored in practical use. That is, the porous Si substrate having a thickness of 200 microns is removed,
After removing the Si ₃ N ₄ layer, a 1.0 μm
A single-crystal Si layer having a thickness of m was formed.

The same effect can also be obtained when apiesone wax or electron wax is applied instead of the Si ₃ N ₄ layer, and only the porous Si substrate can be completely removed.

Thereafter, in a hydrogen atmosphere, at 950 deg.
Heat treatment was performed at 80 Torr. When the flatness of the surface of this sample was evaluated using an atomic force microscope or the like, the roughness of the surface was as good as 1.7 nm with a roughness of 20 nm before hydrogen treatment.

As a result of observation of a cross section by a transmission electron microscope, S
No new crystal defects were introduced into the i-layer, and it was confirmed that good crystallinity was maintained.

[0132]

As described in detail above, according to the present invention,
It is possible to propose a method for manufacturing a semiconductor substrate which can solve the above problems and the above requirements.

According to the present invention, a substrate having an insulating layer on the surface or a light-transmissive insulating substrate represented by glass is formed on a single-crystal wafer having crystallinity and surface flatness.
Productivity, uniformity,
An excellent method in terms of controllability and economy can be provided. Further, according to the present invention, the porous silicon layer can be selectively etched efficiently.

In particular, according to the present invention, the surface of the single-crystal silicon thin layer can be flattened without polishing or etching to remove the single-crystal silicon thin layer. Variations in the thickness of the single crystal silicon thin layer can be reduced.

Further, according to the present invention, an advantage of a conventional SOI device can be realized, and a method of manufacturing a semiconductor substrate which can be applied can be proposed.

According to the present invention, even when a large-scale integrated circuit having an SOI structure is manufactured, an expensive SOS or SIM is required.
It is possible to propose a method for manufacturing a semiconductor substrate which can be substituted for OX.

According to the present invention, a high-quality single-crystal Si substrate is used as a starting material, and a single-crystal layer is left only on the surface, and the lower Si substrate is chemically removed to form on the light-transmitting insulator substrate. As described in detail in the embodiment, it is possible to perform many processes in a short time, and there is a great improvement in productivity and economic efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a process of the present invention.

FIG. 2 is a graph showing etching characteristics of porous and non-porous Si.

FIG. 3 is a schematic diagram for explaining a process of the present invention.

FIG. 4 is a schematic diagram for explaining a process of the present invention.

FIG. 5 is a diagram showing a crystal structure on the surface of a non-porous silicon single crystal.

Claims (3)

(57) [Claims] 1. A step of preparing a first substrate having a porous silicon layer, a step of performing a first heat treatment on the first substrate in an oxygen atmosphere, and a step of forming a non-porous single crystal semiconductor on the porous silicon layer. Forming a layer, bonding the first substrate and the second substrate through an insulating layer, and obtaining a multilayer structure in which the non-porous single-crystal semiconductor layer is located inside; Removing the porous silicon layer from the multilayer structure, and removing the porous silicon layer from the non-porous single-crystal semiconductor layer transferred to the second substrate via the insulating layer. In a reducing atmosphere containing hydrogen,
And performing a second heat treatment at a temperature equal to or lower than the melting point of the non-porous single-crystal semiconductor layer. 2. A step of preparing a first substrate having a porous silicon layer, a step of subjecting the first substrate to a first heat treatment in an oxygen atmosphere, and a step of forming a non-porous single crystal semiconductor on the porous silicon layer. Forming a layer, bonding the first substrate and the light-transmitting second substrate so as to obtain a multilayer structure in which the non-porous single crystal semiconductor layer is located, and the multilayer structure Removing the porous silicon layer from the body, and removing the porous silicon layer, transferring the non-porous single crystal semiconductor layer transferred on the second substrate in a reducing atmosphere containing hydrogen, And performing a second heat treatment at a temperature equal to or lower than the melting point of the non-porous single-crystal semiconductor layer. 3. A semiconductor substrate manufactured by the method for manufacturing a semiconductor substrate according to claim 1.