JPH05217893A - Manufacture of semiconductor substrate - Google Patents

Abstract

PURPOSE:To produce an Si crystal layer having good crystallinity comparable to that of a single-crystal wafer on an oxide layer in a semiconductor substrate. CONSTITUTION:A manufacturing method for a semiconductor substrate comprises a step for forming a porous silicon substrate, a step for treating the porous silicon substrate 1 at temperatures below the melting point and forming a non-porous monocrystal silicon layer 2 in the surface thereof, a step for bonding the non-porous single-crystal silicon layer 2 with a silicon substrate 3 having an oxidized surface, and a chemical etch step for removing a porous silicon substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a semiconductor substrate, and more particularly to a light transmissive semiconductor substrate suitable for an electronic device or an integrated circuit formed on a dielectric isolation or a single crystal semiconductor layer on an insulator. It is preferably used for the method of manufacturing a material.

[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 reached by a bulk Si substrate for producing a normal Si integrated circuit. Much research has been done because the devices using the SOI technology have. That is, by using the SOI technology ,. Dielectric isolation is easy and high integration is possible. Excellent radiation resistance ,. Stray capacitance is reduced and high speed is possible. The well process can be omitted ,. Latch-up can be prevented ,. Advantages such as a fully depleted field effect transistor can be obtained by thinning the film.

In order to realize the many advantages in device characteristics as described above, a method for forming an SOI structure has been researched for several decades. This content is, for example, Special Issue: “Single-
crystal silicon on non-si
single-crystal insulators ”;
edited by G.E. W. Cullen, Jour
nal of Crystal Growth, vol
ume 63, no3, pp 429-590 (198)
It is summarized in 3).

Further, SOS (silicon on sapphire) formed by heteroepitaxially forming Si on a single crystal sapphire substrate by a CVD method (chemical vapor deposition method) has been known for a long time, and is the most mature SOI technology. However, due to the lattice mismatch between the Si layer and the underlying sapphire substrate interface, a large amount of crystal defects, aluminum from the sapphire substrate mixed into the Si layer, and above all, the high cost and large area of the substrate The delay in commercialization has hampered its widespread application. 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. (1) After the surface of the Si single crystal substrate is oxidized, a window is opened to make Si.
The substrate is partially exposed and laterally epitaxially grown using that portion as a seed to form a Si single crystal layer on SiO ₂ (in this case, with the deposition of the Si layer on SiO ₂ ). (2) Using the Si single crystal substrate itself as the active layer,
SiO ₂ is formed thereunder (this method does not involve deposition of a Si layer).

[0005]

As means for realizing the above (1), a method of directly laterally epitaxially growing a single crystal layer Si by a CVD method, a method of depositing amorphous Si, and performing a heat treatment on a solid-phase lateral Directional epitaxial growth, amorphous or polycrystalline Si layer focused by irradiating an energy beam such as electron beam or laser light, and melt recrystallization to grow single crystal layer on SiO ₂ , and rod-shaped A method of scanning the melted region in a band shape by a heater (Zone melting restal)
ization) is known. Each of these methods has merits and demerits, but there are still many problems in controllability, productivity, uniformity, and quality, and none of them has been industrially put into practical use. For example, the CVD method requires sacrificial oxidation to achieve a flat thin film, and the solid phase growth method has poor crystallinity. Further, the beam annealing method has problems in processing time by convergent beam scanning, controllability such as beam overlapping and focus adjustment. Of these, the Zone
Melting Recrystalzatio
Although the n method is the most mature, and relatively large-scale integrated circuits have been prototyped, many crystal defects such as sub-grain boundaries still remain, and minority carrier devices have not been produced yet. ..

In the method (2) above, in which the Si substrate is not used as seeds for epitaxial growth, there are the following three types of methods.

[0007]. An oxide film is formed on a Si single crystal substrate in which V-shaped grooves are anisotropically etched on the surface, 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. Is a method for forming a dielectrically separated Si single crystal region surrounded by a V groove on a thick polycrystalline Si layer. In this method, the crystallinity is good, but a step of depositing polycrystalline Si to a thickness of several hundreds of microns, and
Since a step of polishing the single crystal Si substrate from the back surface and leaving only the separated Si active layer is required, there is a problem in terms of controllability and productivity.

[0008] SIMOX: Sepe
relation by ion implemented o
Xygen) is a method of forming a SiO ₂ layer by ion implantation of oxygen in a Si single crystal substrate, and is the most mature method at present because it has good compatibility with the Si process. However, in order to form the SiO ₂ layer,
Oxygen ions need to be implanted at 10 ¹⁸ ions / cm ² or more, the implantation time is long, the productivity cannot be said to be high, and the wafer cost is high. Furthermore, many crystal defects remain, and the quality is industrially insufficient to produce a minority carrier device.

[0009]. This is a method of forming an SOI structure by dielectric isolation by oxidation of porous Si. This method is
Ion implantation of an N-type Si layer on the surface of a Si-type single crystal substrate, (Imai et al., J. Crystal Growth,
vol 63, 547 (1983)), or
It is formed into an island shape by epitaxial growth and patterning, and only the P-type Si substrate is made porous by the anodization method in the HF solution so as to surround the Si island from the surface, and then the N-type Si island is separated by the dielectric by accelerated oxidation. Is the way to do it. This method has a problem that the separated Si region is determined before the device process, which may limit the degree of freedom in device design.

It is an object of the present invention to provide a method for manufacturing a semiconductor substrate that meets the above problems and the above requirements.

Further, the present invention provides a semiconductor substrate excellent in productivity, uniformity, controllability and cost in obtaining Si having crystallinity as excellent as that of a single crystal wafer on an insulating layer (oxide layer). It is an object to provide a method for manufacturing a material.

A further object of the present invention is to provide a method for manufacturing a semiconductor substrate which realizes the advantages of the conventional SOI structure and is applicable.

It is another object of the present invention to provide a method of manufacturing a semiconductor base material which can replace expensive SOS and SIMOX even when manufacturing a large scale integrated circuit having an SOI structure.

[0014]

A method of manufacturing a semiconductor substrate according to the present invention comprises a step of making a silicon substrate porous and a step of heat-treating the porous silicon substrate at a temperature equal to or lower than a melting point. The step of forming the surface layer of the formed silicon substrate into a non-porous silicon single crystal layer, the step of attaching the non-porous silicon single crystal layer to the other surface-oxidized silicon substrate, and the step of forming the porous silicon substrate portion. And a step of removing by chemical etching.

In the present application, the semiconductor base material means a substrate in which a silicon single crystal layer is formed on an oxide layer of a silicon substrate.

[0016]

According to the present invention, after the silicon substrate is made porous, it is heat-treated at a temperature below the melting point to make the surface layer of the porous silicon substrate a non-porous silicon single crystal layer, so that silane etc. Without using the source gas, the silicon single crystal layer with good crystallinity is formed on the surface of the porous silicon substrate, and the formed silicon single crystal layer is attached to the other surface-oxidized silicon substrate. In addition, by chemically etching and removing the porous silicon substrate portion whose etching rate has been significantly increased by making it porous, it has a good single crystal structure on the oxide layer (SiO ₂ ) It is intended to form a uniform and flat single crystal silicon layer with extremely few defects.

In the present invention, one surface side is N
The other side of the molded silicon substrate may be made porous.

[0018]

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view for explaining the steps of one embodiment of the method for producing a semiconductor substrate of the present invention.

As shown in FIG. 1A, first, a Si single crystal substrate is prepared and made porous. The porosification may be performed entirely, only on the front surface side, or on both the front surface and the back surface. Subsequently, heat treatment in a non-oxidizing atmosphere or in a vacuum is performed at a temperature equal to or lower than the melting point to make the porous S
The surface layer of the i single crystal substrate 1 is a thin film non-porous single crystal layer 2.

The Si single crystal substrate is made porous by an anodization method using an HF solution. This porous Si layer has a density of 1.1 to 0.6 g / cm ³ by changing the density of the single crystal Si from 2.33 g / cm ³ to an HF solution concentration of 50 to 20%. It can be changed into a range. This porous layer is easily formed on the P-type Si substrate for the following reason. According to observation with a transmission electron microscope, pores having an average diameter of about 600 angstroms are formed in this porous Si layer.

Porous Si has been described by Uhril et al.
It was discovered in the process of research on electropolishing of semiconductors in 1957 (A. Uhril, Bell System. Tech.
J. , Vol 35, p. 333 (1956)). Also, Unami 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 Unagami: J. Electrochem. So
c. , Vol. 127, p. 476 (1980)).

Si + 2HF + (2-n) e ⁺ → Si
F 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 ⁻ respectively represent a hole and an electron. Further, n and λ are the numbers of holes required for dissolving one silicon atom, respectively, and porous silicon is formed when the condition of n> 2 or λ> 4 is satisfied.

From the above, P-type silicon having holes is likely to be made porous. In this porosity,
The selectivity has been demonstrated by Nagano et al. And Imai (Nagano, Nakajima, Anno, Onaka, Kajiwara; IEICE Technical Report, vol 79, SSD 79-9549 (197).
9), K. Imai; Solid-State Elec
tronics vol 24, 159 (198
1)). As described above, the P-type silicon in which holes are present is easily made porous, and the P-type silicon can be selectively made porous.

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

According to observation with 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.

Further, since the porous layer has a large amount of voids formed therein, its density is reduced to less than half. 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 etching rate of a normal single crystal layer.

The method of etching each porous Si is as follows. Etching porous Si with aqueous NaOH solution (G. Bonchill, R. Herino, K. Bar)
la, and J. C. Pfister, J .; Elec
trochem. Soc. , Vol. 130, no.
7, 1611 (1983)).

.. Porous Si is etched with an etchant capable of etching single crystal Si. It has been known.

In the above method, a hydrofluoric nitric acid-based etching solution is usually used. The etching process of Si at this time is as follows: Si + 2O → SiO ₂ SiO ₂ + 4HF → SiF ₄ + H ₂ O Is oxidized by nitric acid to be transformed into SiO ₂ , and the SiO ₂ is etched with hydrofluoric acid, whereby Si etching proceeds.

Similarly, as a method of etching crystalline Si, there are ethylenediamine-based, KOH-based, hydrazine-based, and the like in addition to the hydrofluoric / nitric acid-based etching solution.

Another important selective etching method for porous Si is to use hydrofluoric acid or buffered hydrofluoric acid which has no etching action on crystalline Si. In this etching, hydrogen peroxide which acts as an oxidizing agent may be added. Hydrogen peroxide acts as an oxidizing agent, and it is possible to control the reaction rate by changing the ratio of hydrogen peroxide. Moreover, you may add alcohol which acts as a surface-active agent. Alcohol acts as a surface-active agent, and instantaneously removes bubbles of a reaction product gas due to etching from the etching surface, and enables selective etching of porous Si uniformly and efficiently.

In FIG. 2, etching was performed when porous Si and non-porous single crystal Si were infiltrated into a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution without stirring. The etching time dependence of the thickness of porous Si and single crystal Si is shown.

The porosification and etching process will be specifically described.

Porous Si is produced by anodizing single crystal Si and the conditions are as follows. The starting material of porous Si formed by anodization is not limited to single crystal Si, and Si having another crystal structure is also possible.

Applied voltage: 2.6 (V) Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1:
1: 1 time: 2.4 (hour) Thickness of porous Si: 300 (μm) Porosity: 56 (%) The porous Si prepared under the above conditions was buffered hydrofluoric acid (4.5% HF + 36% NH 3) at room temperature. ₄ F + H ₂
O), alcohol and a mixture of 30% hydrogen peroxide (1)
(0: 6: 50) (white circles) were infiltrated without stirring. After that, the decrease in the thickness of the porous Si was measured. Porous Si is rapidly etched, and 83μ in 40 minutes.
m, and even after 120 minutes, 140 μm had a high degree of surface property and was uniformly etched. The etching rate depends on the solution concentration and the temperature.

As described above, in particular, by adding alcohol, the bubbles of the reaction product gas due to etching can be instantly removed from the etching surface without stirring, and the porous material can be uniformly and efficiently porous. Si can be etched. Further, in particular, by adding hydrogen peroxide water, it becomes possible to accelerate the oxidation of Si and increase the reaction rate as compared with no addition, and by further changing the ratio of hydrogen peroxide water, The reaction rate can be controlled.

Further, 500 μm thick non-porous Si was buffered with hydrofluoric acid (4.5% HF + 36% NH 3) at room temperature.
₄ F + H ₂ O), alcohol and a 30% hydrogen peroxide solution (10: 6: 50) (black circles) were infiltrated without stirring. Afterwards, the reduction in the thickness of the non-porous Si was measured. Non-porous Si remains 1 even after 120 minutes.
Only less than 00 Å was etched.

When porous Si and non-porous Si after etching with the above-described etching solution were washed with water and the surface thereof was microanalyzed by secondary ions, no impurities were detected.

As the alcohol used in the present invention, in addition to ethyl alcohol, isopropyl alcohol or the like which can be practically used in the manufacturing process and which is desired to have the above-mentioned alcohol addition effect can be used.

The inventor of the present invention observed the change in the structure of the porous layer due to the heat treatment in detail by changing the atmosphere and the like by using a high resolution scanning electron microscope and the like, and found that it was in a non-oxidizing atmosphere or in a vacuum. Although the number of pores on the porous surface due to the heat treatment varies depending on the conditions, for example, as shown in FIG.
It has been found that, as shown in Fig. 3, the single crystal thin layer having a smooth surface is formed as a result of the decrease over time and the disappearance. This is the surface of a porous Si substrate formed by anodization, and
As a result of the heat treatment of the portion in the vicinity thereof, a non-porous single crystal thin layer is formed in order to reduce the surface energy thereof, vanish pores, and smooth the surface.

The non-porous single crystal layer having a smooth surface is a single crystal layer which inherits the orientation of the substrate.
And electron beam channeling pattern.

This phenomenon is accelerated as the temperature rises and the pressure drops. The non-oxidizing atmosphere here means an atmosphere in which an oxide layer is not formed on the surface of the porous layer during the heat treatment, more preferably a reducing atmosphere, for example, an atmosphere containing hydrogen, or a hydrogen atmosphere. Can be mentioned. The temperature of the heat treatment varies depending on the composition of the atmosphere and the pressure, but is generally 300 ° C. or higher, more preferably 500 ° C. or higher and the melting point or lower. In addition, the pressure is such that the stronger the reducing property is, the higher the pressure is, so that smoothing is promoted.
More preferably, it is 200 Torr or less, and there is no particular lower limit. Ultra high vacuum is not particularly required. In the present invention, the term “in vacuum” means that the atmosphere gas is not introduced into the reaction tank without leakage and the pressure is maintained at 1 × 10 ⁻³ Torr or less, more preferably 1 × 10 ⁻⁵ Torr or less. I mean something.

Further, this phenomenon starts to progress by heat treatment in a state where the porous surface is clean. If a natural oxide film is formed on the surface of the porous Si substrate, heat treatment is performed. Prior to this, by removing this by etching with hydrofluoric acid or the like, smoothing of the surface is further promoted.

As shown in FIG. 1B, another Si
After the substrate 3 is prepared and the oxide layer 4 is formed on the surface, the Si substrate 3 having the oxide layer 4 on the surface is attached to the surface of the single crystal Si layer 2 on the porous Si substrate 1. In this attaching step, the cleaned surfaces are brought into close contact with each other and then heated in an oxygen atmosphere or a nitrogen atmosphere.

Prior to the bonding step, the oxide layer 6 may be formed on the surface of the non-porous single crystal silicon layer 2 and bonded to the Si substrate. The oxide layer 6 is formed to reduce the interface state of the single crystal silicon layer 2 which is the final active layer. In this case, an oxide layer may or may not be formed on the surface of the other Si substrate.

As shown in FIG. 1 (c), if necessary,
A Si ₃ N ₄ layer 5 is deposited as an etching prevention film,
The entire two bonded silicon wafers are covered to remove the Si ₃ N ₄ layer on the porous surface of the porous silicon substrate. Apiezon wax may be used instead of the Si ₃ N ₄ layer as another etching prevention film. After this,
The porous Si substrate 1 is wholly etched to form a thinned single crystal silicon layer 2 on SiO ₂ .

Prior to the etching, the porous Si substrate 1 may be thinned in advance from the back surface side by mechanical processing such as grinding or polishing. Particularly, when the Si substrate is not entirely made porous, it is preferable that the Si substrate is thinned by machining until the porous layer is exposed.

FIG. 1 (c) shows a semiconductor substrate obtained by the present invention. That is, by removing the Si ₃ N ₄ layer 5 as an etching prevention film in FIG. 1B, a single crystal Si layer having a crystallinity similar to that of a silicon wafer is formed on the insulator substrate 3 via SiO _2. 2 is evenly and uniformly thinned and formed in a large area over the entire wafer. Thereafter, if necessary, the single crystal Si layer may be epitaxially grown to reduce the thickness of the single crystal thin layer. This growth method may be any of a CVD method, a sputtering method, a liquid phase growth method, a solid phase growth method and the like.

The semiconductor substrate thus obtained can be preferably used from the viewpoint of producing an electronic element which is insulated and separated.

[0051]

EXAMPLES The present invention will be described below with reference to specific examples. (Example 1) A P-type (10
0) The single crystal Si substrate was anodized in a 50% HF solution. The current density at this time was 5 mA / cm ² . The porosification rate at this time is 0.9 μm / mi
n. And a P-type (10
0) The entire Si substrate became porous in 223 minutes.

The porous Si substrate was heat-treated in a hydrogen atmosphere to obtain a smooth layer on the surface. The heat treatment conditions were as follows.

Temperature: 950 ° C. Pressure: 80 Torr Time: 25 minutes A smooth layer on this surface was taken by a high resolution scanning electron microscope, RH.
When observed by EED, the thickness is 20 in the same direction as the substrate.
A single crystal thin layer of nm was formed.

Next, on the surface of this single crystal thin layer, 5
The other Si substrate on which an oxide layer having a thickness of 000 angstroms has been formed is laid on top of one another, and the temperature is set to 800 ° C. in an oxygen atmosphere at 0.
By heating for 5 hours, both Si substrates were firmly bonded.

Si ₃ N ₄ was added to 0.1 by the low pressure CVD method.
The two Si substrates that have been deposited by μm and bonded to each other are covered, and only the nitride film on the porous substrate is removed by reactive ion etching.

Then, the bonded substrates are mixed with a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution (10:
At 6:50), selective etching is performed without stirring.
After 205 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. After removing the Si ₃ N ₄ layer, a thin film single crystal Si layer could be formed on the SiO ₂ . As a result of cross-sectional observation with a transmission electron microscope, it was confirmed that new crystal defects were not introduced into the Si layer and good crystallinity was maintained. (Example 2) A P-type (10
0) The single crystal Si substrate was anodized in a 50% HF solution. The current density at this time is 100 mA / cm
^{Was 2} . The porosity rate at this time was 8.4 μm / m.
in. And a P-type (10
0) The entire Si substrate became porous in 24 minutes. The porous Si substrate was heat-treated in a hydrogen atmosphere to obtain a layer having a smooth surface. The heat treatment conditions were as follows.

Temperature: 950 ° C. Pressure: 50 Torr Time: 45 minutes A smooth layer on this surface was taken by a high resolution scanning electron microscope, RH.
When observed by EED, the thickness is 50 in the same direction as the substrate.
A thin non-porous single crystal layer of nm was formed.

Next, another Si substrate having a 5000 angstrom oxide layer formed on the surface was superposed on the surface of this epitaxial layer oxidized by 10 nm, and heated in an oxygen atmosphere at 900 ° C. for 0.5 hour. The Si substrates of both were firmly bonded.

Si ₃ N ₄ was added to 0.1 by the low pressure CVD method.
The two Si substrates that have been deposited by μm and bonded to each other are covered, and only the nitride film on the porous substrate is removed by reactive ion etching.

As described above, ordinary Si single crystal KOH
The etching rate for the 6M solution is about 1 micron per minute, but the etching rate for the porous layer is increased by a factor of 100. That is, the porous, Si substrate with a thickness of 200 microns was removed in 2 minutes. S
After removing the i ₃ N ₄ layer, a single crystal Si layer having good crystallinity could be formed on SiO ₂ . (Example 3) A P-type (10
0) The single crystal Si substrate was anodized in a 50% HF solution. The current density at this time is 100 mA / cm
^{Was 2} .

The porosification rate at this time was 8.4 μm / m.
in. And a P-type (10
0) The entire Si substrate became porous in 24 minutes.

The porous Si substrate was washed with 1.5% diluted hydrofluoric acid and then immediately heat-treated in an argon atmosphere to obtain a smooth layer on the surface. The heat treatment conditions were as follows.

Temperature: 950 ° C. Pressure: 1 Torr Time: 60 minutes The smooth layer on this surface was analyzed by a high resolution scanning electron microscope, RH.
When observed by EED, the thickness is 20 in the same direction as the substrate.
A single crystal thin layer of nm was formed.

On the surface of the single crystal thin layer, another Si substrate having an oxide layer of 5000 angstrom formed on the surface was superposed and heated in an oxygen atmosphere at 800 ° C. for 0.5 hour to obtain both Si substrates. Was tightly bonded.

Si ₃ N ₄ was added to 0.1 by the low pressure CVD method.
The two Si substrates that have been deposited by μm and bonded to each other are covered, and only the nitride film on the porous substrate is removed by reactive ion etching.

As described above, the etching rate of a normal Si single crystal with respect to the hydrofluoric acid / nitric acid solution is about 1 micron per minute (fluorine / nitric acid / acetic acid solution 1: 3: 8). Is accelerated by a hundred times. That is, the porous Si substrate having a thickness of 200 μm was removed in 2 minutes. After removing the Si ₃ N ₄ layer, a single crystal Si layer could be formed on SiO ₂ .

Further, the same effect was obtained when Apiezon wax was coated instead of the Si ₃ N ₄ layer, and only the porous Si substrate could be completely removed. (Example 4) A P-type (10
0) The single crystal Si substrate was anodized in a 50% HF solution. The current density at this time was 5 mA / cm ² . The porosification rate at this time is 0.9 μm / mi
n. And a P-type (10
0) The surface of the Si substrate was made 30 μm porous.

The porous Si substrate was heat-treated in a hydrogen atmosphere to obtain a layer having a smooth surface. The heat treatment conditions were as follows.

Temperature: 950 ° C. Pressure: 60 Torr Time: 25 minutes A smooth layer on this surface was taken by a high resolution scanning electron microscope, RH.
When observed by EED, the thickness 30 in the same direction as the substrate
A single crystal thin layer of nm was formed. This thin single crystal layer was oxidized to 100 angstroms, and the surface was oxidized 500 times.
The other Si with a 0 Å oxide layer formed
By closely contacting the substrates and heating at 700 ° C. for 0.5 hours, the Si substrates of both were firmly bonded.

This porous substrate was ground from the back surface by a normal wafer lapping process to 275 μm to expose the porous silicon.

Si ₃ N ₄ was added to 0.1 by the low pressure CVD method.
The two Si substrates that have been deposited by μm and bonded to each other are covered, and only the nitride film on the porous substrate is removed by reactive ion etching.

Then, the bonded substrates are mixed with a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution (10:
At 6:50), selective etching is performed without stirring.
After 30 minutes, only the single crystal Si layer remained without being etched, and the porous Si was selectively etched and completely removed using the single crystal Si as a material for the etching stop. S
After removing the i ₃ N ₄ layer, a single crystal Si is formed on the SiO _2.
A layer could be formed.

Further, the same effect was obtained when Apiezon wax was coated instead of the Si ₃ N ₄ layer, and only the porous Si substrate could be completely removed. (Example 5) A P-type (10
0) The single crystal Si substrate was anodized in a 50% HF solution. The current density at this time is 100 mA / cm
^{Was 2} . The porosity rate at this time was 8.4 μm / m.
in. And a P-type (10
0) The entire Si substrate became porous in 24 minutes.

The porous Si substrate was heat-treated in a hydrogen atmosphere to obtain a smooth layer on the surface. The heat treatment conditions were as follows.

Temperature: 950 ° C. Pressure: 760 Torr Time: 80 minutes A smooth layer on this surface was taken by a high resolution scanning electron microscope, RH.
When observed by EED, the thickness is 20 in the same direction as the substrate.
A single crystal thin layer of nm was formed. The surface of this single crystal thin layer was brought into close contact with another Si substrate having an oxide layer of 5000 angstrom formed on the surface thereof, and the temperature was maintained at 700 ° C.
By heating for 5 hours, both Si substrates were firmly bonded.

Si ₃ N ₄ was added to 0.1 by the low pressure CVD method.
The two Si substrates that have been deposited by μm and bonded to each other are covered, and only the nitride film on the porous substrate is removed by reactive ion etching.

As described above, the etching rate of a normal Si single crystal with respect to the hydrofluoric nitric acid acetic acid solution is about 1 micron per minute (fluorine nitric acid acetic acid solution 1: 3: 8), but the etching rate of the porous layer is small. Is accelerated by a hundred times. That is, the porous Si substrate having a thickness of 200 μm was removed in 2 minutes. After removing the Si ₃ N ₄ layer, a single crystal Si layer could be formed on SiO ₂ .

Next, the single crystal thin layer was epitaxially grown by the CVD method which is usually used, and the thickness of the single crystal silicon layer was set to 2 μm. The growth conditions were as follows.

Gas: SiH ₂ Cl ₂ / H ₂ ; 1/180 (1 / mi
n. ) Temperature: 1080 ° C. Pressure: 80 Torr As a result, a single crystal Si layer having a thickness of 2 μm could be formed on SiO ₂ . (Example 6) A P-type (10
0) The single crystal Si substrate was anodized in a 50% HF solution. The current density at this time is 100 mA / cm
^{Was 2} .

The rate of porosification at this time was 8.4 μm / m.
in. And a P-type (10
0) The entire Si substrate became porous in 24 minutes.

The porous Si substrate was washed with 1.5% diluted hydrofluoric acid and then immediately heat-treated in a vacuum chamber to obtain a smooth layer on the surface. The heat treatment conditions were as follows.

Temperature: 950 ° C. Pressure: 1 × 10 ⁻⁸ Torr Time: 100 minutes The smooth layer on this surface was analyzed by a high resolution scanning electron microscope, RH.
When observed by EED, the thickness is 15 in the same direction as the substrate.
A single crystal thin layer of nm was formed.

On the surface of the single crystal thin layer, another Si substrate having an oxide layer of 5000 angstrom formed on the surface was superposed and heated in an oxygen atmosphere at 800 ° C. for 0.5 hour to obtain both Si substrates. Was tightly bonded.

Si ₃ N ₄ was added to 0.1 by the low pressure CVD method.
The two Si substrates that have been deposited by μm and bonded to each other are covered, and only the nitride film on the porous substrate is removed by reactive ion etching.

Then, the bonded substrates are mixed with a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution (10:
At 6:50), selective etching is performed without stirring.
After 205 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. After removing the Si ₃ N ₄ layer, a thin film single crystal Si layer could be formed on the SiO ₂ .

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

Further, the same effect can be obtained when Apiezon wax is coated instead of the Si ₃ N ₄ layer, and only the porous Si substrate can be completely removed.

[0088]

As described in detail above, according to the present invention,
Si with excellent crystallinity on an insulator substrate as well as a single crystal wafer
It is possible to provide a method excellent in productivity, uniformity, controllability, and economic efficiency in obtaining a crystal layer.

Further, according to the present invention, it is possible to realize the advantages of the conventional SOI device and provide an applicable semiconductor substrate manufacturing method.

Further, according to the present invention, even when a large-scale integrated circuit having an SOI structure is manufactured, expensive SOS and SIM are used.
A method for manufacturing a semiconductor substrate which can be a substitute for OX can be provided.

According to the present invention, originally, a good quality single crystal Si substrate is used as a starting material, and after being made porous by anodization,
After the surface of the porous layer is transformed into a non-porous single crystal layer by heat treatment in a non-oxidizing atmosphere or vacuum, the lower Si substrate is chemically removed and transferred onto SiO _2. Therefore, since a non-porous single crystal layer can be formed on a porous layer without using a source gas such as silane,
Excellent economy. In addition, as described in detail in the examples, it is possible to perform a large number of processes in a short time, which is a great improvement in productivity and economic efficiency. Furthermore, according to the present invention, an extremely thin single crystal can be formed on an oxide layer, and therefore, it is suitable for an SOI circuit using a thin film.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining a step of a method for manufacturing a semiconductor base material of the present invention.

FIG. 2 is an etching characteristic diagram when porous Si and non-porous Si are soaked in a mixed solution of buffered hydrofluoric acid, alcohol, and hydrogen peroxide solution.

FIG. 3 is a diagram showing a temporal change in the number density of pores on the surface during heat treatment of porous Si.

[Explanation of symbols]

1 Porous Si Substrate 2 Non-porous Si Single Crystal Layer 3 Si Substrate 4 Surface Oxidation Layer 5 Si ₃ N ₄ Etch Prevention Film 6 Surface Oxidation Layer

Claims (14)

[Claims] 1. A step of making a silicon substrate porous, and subjecting the porous silicon substrate to a heat treatment at a temperature equal to or lower than a melting point to convert a surface layer of the porous silicon substrate into a non-porous silicon single crystal layer. And a step of adhering the non-porous silicon single crystal layer to another surface-oxidized silicon substrate, and a step of removing the porous silicon substrate portion by chemical etching. Method for manufacturing semiconductor substrate. 2. The method for producing a semiconductor substrate according to claim 1, wherein the heat treatment is performed in a non-oxidizing atmosphere or vacuum. 3. The method for producing a semiconductor substrate according to claim 1, wherein after the etching step, a single crystal silicon layer is grown from the non-porous silicon single crystal layer by epitaxial growth. 4. The method for producing a semiconductor substrate according to claim 1, wherein the silicon substrate to be made porous is P-type. 5. After the bonding step and prior to the etching step, portions of the porous silicon substrate other than the porous surface are covered with a material excellent in chemical etching resistance. The method for producing a semiconductor substrate according to claim 1. 6. The method for manufacturing a semiconductor substrate according to claim 1, wherein the bonding step includes a step performed in an atmosphere containing oxygen. 7. The method for manufacturing a semiconductor substrate according to claim 1, wherein the bonding step includes a step performed in an atmosphere containing nitrogen. 8. The method for producing a semiconductor substrate according to claim 1, wherein the step of making the silicon substrate porous is anodization. 9. The method for producing a semiconductor substrate according to claim 1, wherein the porous silicon substrate portion is thinned by mechanical processing prior to the etching step. 10. An oxide layer is formed on the surface of the formed non-porous single crystal layer after the heat treatment in the non-oxidizing atmosphere or in vacuum and prior to the bonding step. 2. The method for producing a semiconductor substrate according to 2. 11. The method for manufacturing a semiconductor substrate according to claim 2, wherein the non-oxidizing atmosphere is a reducing atmosphere. 12. The method for producing a semiconductor substrate according to claim 2, wherein the porous silicon substrate is washed with hydrofluoric acid prior to the heat treatment in the non-oxidizing atmosphere or vacuum. . 13. The method for producing a semiconductor substrate according to claim 8, wherein the anodization is performed in an HF solution. 14. The method for producing a semiconductor substrate according to claim 11, wherein the reducing atmosphere is an atmosphere containing hydrogen.