JP2910001B2 - Semiconductor substrate and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to a method for manufacturing a semiconductor substrate and its, in particular, the dielectric isolation, or an electronic device created in the single crystal semiconductor layer on an insulator, a light transmissive suitable for integrated circuits it is suitably used in the method for manufacturing a semiconductor substrate and its.

[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 SOI technology,. Easy dielectric separation and high integration. Excellent radiation resistance. The stray capacitance is reduced and the speed can be increased. Well steps can be omitted. 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 advantages in device characteristics, researches have been made on a method of forming an SOI structure for several decades. This content is, for example, Special Issue: “Single-
crystal silicon on non-si
ngle-crystal insulators ";
edited by G. W. Cullen, Jour
nal of Crystal Growth, vol.
ume 63, no3, pp 429-590 (198
It is summarized in 3).

Also, SOS (silicon on sapphire), which is formed by heteroepitaxy of Si on a single crystal sapphire substrate by a CVD method (chemical vapor deposition method), has been known, and the most mature SOI technology has been known. However, a large amount of crystal defects due to lattice mismatch between the Si layer and the underlying sapphire substrate, contamination of aluminum from the sapphire substrate into the Si layer, and above all, the high cost and large area of the substrate The delay in commercialization has hindered the spread of its 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. (1) After oxidizing the surface of the Si single crystal substrate, open a window to open the Si
The substrate is partially exposed, and the portion is epitaxially grown in the lateral direction using the seed as a seed to form a Si single crystal layer on SiO ₂ (in this case, a Si layer is deposited on SiO ₂ ). (2) using the Si single crystal substrate itself as an active layer,
SiO ₂ is formed thereunder (this method does not involve the deposition of a Si layer).

[0005]

As means for realizing the above (1), a method of directly growing a single crystal layer Si in a lateral direction by a CVD method, a method of depositing an amorphous Si, and a heat treatment in a solid state by a heat treatment. A method of growing a single crystal layer on SiO ₂ by converging and irradiating an energy beam such as an electron beam or a laser beam to an amorphous or polycrystalline Si layer, and growing a single crystal layer on SiO ₂ by melting and recrystallization; A method of scanning a molten region in a belt shape by a heater (Zone melting recrystall)
is known. Although each of these methods has advantages and disadvantages, it still has significant problems in controllability, productivity, uniformity, and quality, and there is no industrially practical method yet. For example, the CVD method requires sacrificial oxidation to make a thin film flat, and the solid phase growth method has poor crystallinity. Further, the beam annealing method has a problem in controllability such as processing time by convergent beam scanning, beam overlap, focus adjustment, and the like. Of these, Zone
Melting Recrystalzatio
Although the n-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, making it difficult to produce a minority carrier device. .

In the method (2) in which the Si substrate is not used as a seed for epitaxial growth, there are the following three methods. . 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. Is to form a dielectrically separated Si single crystal region surrounded by V-grooves on a thick polycrystalline Si layer. In this method, the crystallinity is good, but the polycrystalline Si
Requires a process of depositing a few hundred microns thick and a process of polishing a single-crystal Si substrate from the back surface to leave only a separated Si active layer, which is problematic in terms of controllability and productivity. . SIMOX: Seperation
by ion implanted oxygen)
This is a method of forming a SiO ₂ layer by ion implantation of oxygen into a Si single crystal substrate, which is currently the most mature method because of its good compatibility with the Si process. However, in order to form a SiO ₂ layer, it is necessary to implant oxygen ions at a dose of 10 ¹⁸ ions / cm ² or more, the implantation time is long, the productivity is not high, and the wafer cost is low. Is expensive. Furthermore, many crystal defects remain, and the quality has not yet reached a level sufficient to manufacture a minority carrier device from an industrial viewpoint. . This is a method of forming an SOI structure by dielectric isolation by oxidation of porous Si. In this method, an N-type Si layer is implanted with proton ions on the surface of a P-type Si single crystal substrate (Imai et al., J. Crystal Growth, vol. 6).
3, 547 (1983)) or an island formed by epitaxial growth and patterning, and anodized in an HF solution so as to surround the Si island from the surface.
After only the porous Si substrate is made porous, N
This is a method of dielectrically separating the Si islands. In this method, the separated Si region is determined before the device process, and there is a problem that the degree of freedom in device design may be limited.

The formation of a semiconductor element on a light-transmitting substrate is important in forming a contact sensor as a light receiving element and a projection type liquid crystal image display device. And pixels (picture elements) of sensors and display devices
In order to further increase the density, resolution, and definition of, an extremely high-performance driving element is required. As a result, a semiconductor element provided over a light-transmitting substrate is required to be manufactured over a single crystal layer having excellent crystallinity. However, on a light-transmitting substrate represented by glass, in general, an amorphous or good crystal reflecting only the disorder of its crystal structure is formed only in a polycrystalline layer and has many defects. Due to the structure, it has been difficult to produce a drive element having the required or sufficient performance in the future. 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. When a semiconductor element is formed on a light-transmitting substrate, any of the above-described methods using a Si single-crystal substrate is inappropriate for the purpose of obtaining a high-quality single-crystal layer on the light-transmitting substrate. is there.

[0008] The present invention aims to provide a manufacturing method of a semiconductor substrate and its to meet requirements such as problems and above as described above. In addition, the present invention provides a semiconductor substrate having excellent 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. Another object of the invention is to provide a method for manufacturing it.

[0009] Further, the present invention is to realize the advantages of conventional SOI structure, to provide a method for manufacturing applicable semiconductor substrate and its also aims. In addition, the present invention is also applicable to manufacturing a large-scale integrated circuit having an SOI structure, such as an expensive SOS or an SOS.
And to provide an alternative semiconductor substrate and its manufacturing method capable enough of IMOX.

[0010]

The method for manufacturing a semiconductor substrate of the present invention In order to achieve the above object, according a first substrate having a porous monocrystalline silicon layer, in a non-oxidizing atmosphere or in vacuum, the porous monocrystalline sheet
By heat treatment at a temperature below the melting point of silicon layer, on the surface of the porous monocrystalline silicon layer, a non-porous monocrystalline sheet
Forming a silicon layer, and said non-porous first substrate monocrystalline silicon <br/> layer is formed and the light transmissive second substrate, the non-porous monocrystalline silicon layer The method is characterized by comprising a step of bonding so that a multilayer structure located inside is obtained, and a step of removing the porous single-crystal silicon layer from the multilayer structure.

[0011] The semiconductor substrate of the present invention is characterized in that:
Produced by the method for producing a semiconductor substrate of
You.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention, a first substrate having a porous monocrystalline silicon layer, in a non-oxidizing atmosphere or in vacuum, by heat treatment at a temperature lower than the melting point of said porous monocrystalline silicon layer, wherein on the surface of the porous monocrystalline silicon layer, by forming a nonporous monocrystalline silicon layer, a silicon layer
Without using a source gas (such as silane)
The crystallinity good non-porous single-crystal silicon layer is formed on the surface of the porous monocrystalline silicon layer of the substrate, further, the first substrate non-porous single-crystal silicon layer is formed and the light transmissive By bonding the second base material so that a multilayer structure in which the non-porous single-crystal silicon layer is located inside is obtained, and removing the porous single-crystal silicon layer from the multilayer structure. And forming a single crystal silicon layer having a good quality single crystal structure, which is uniform and flat over a large area, and has extremely few defects on a light-transmitting second base material.

[0013]

An embodiment 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 an embodiment of the method for producing a semiconductor substrate according to the present invention.

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

The Si single crystal 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 600 angstroms are formed in the porous Si layer.

[0016] Porous Si is manufactured by Uhlir et al.
It was discovered during the research process of electropolishing of semiconductors in 56 (A. Uhril, 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. Electrochem.So
c. , Vol. 127, p. 476 (1980)).

[0017] 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 where e ⁺ and, e ^- respectively represent a positive hole and an electron. 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 Imai (Nagano, Nakajima, Anno, Onaka, Kajiwara; IEICE Technical Report, vol 79, SSD79-9549 (197)
9), K. Imai; Solid-State Elec
tronics 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. vol.
42, 386 (1983)), and 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. Regardless, single crystallinity is maintained. Further, since the porous layer has a large amount of voids formed therein, the 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 ordinary etching rate of the single crystal layer.

The method of etching each porous Si includes the following. Etch porous Si with aqueous NaOH solution (G. Bonchil, R. Herino, K. Barr)
la, and j. C. Pfister, J .; Elec
trochem. Soc. , Vol. 130, no.
7, 1611 (1983)). . Etch porous Si with an etchant capable of etching single crystal Si. It has been known.

In the above method, an etching solution of hydrofluoric-nitric acid is usually used. At this time, the etching process of Si is performed as shown in the order of Si + 2O → SiO ₂ SiO ₂ + 4HF → SiF ₄ + H ₂ O. There is oxidized with nitric acid, then transformed into SiO _2, the etching of Si proceeds by etching the SiO ₂ with hydrofluoric acid.

Similarly, as a method of 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.

Another important method for selectively etching porous Si is to use hydrofluoric acid or buffered hydrofluoric acid which has 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.

FIG. 2 shows the etched porous material when porous Si and non-porous single-crystal Si were infiltrated into a mixed solution of hydrofluoric acid, alcohol and hydrogen peroxide without stirring. 4 shows the etching time dependency of the thickness of Si and single crystal Si. The porosity and etching process will be specifically described.

The porous Si is prepared 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, but may be Si having another crystal structure. 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 subjected to 49 at room temperature.
% Hydrofluoric acid, alcohol and aqueous hydrogen peroxide (10:
6:50) (open circles) infiltrated without stirring.
Thereafter, the decrease in the thickness of the porous Si was measured. Porous Si is rapidly etched to 107μ in about 40 minutes.
m, and even after lapse of 80 minutes, even 244 μm was uniformly etched with a high degree of surface properties. The etching rate depends on the solution concentration and the temperature.

As described above, in particular, by adding an alcohol, bubbles of a reaction gas produced by etching can be instantaneously removed from the etched surface without stirring, and the porous material can be uniformly and efficiently removed. Si can be etched. In particular, by adding hydrogen peroxide solution, the oxidation of Si can be accelerated, and the reaction rate can be increased as compared with the case of no addition, and by further changing the ratio of the hydrogen peroxide solution, The reaction rate can be controlled.

Further, non-porous Si having a thickness of 500 μm was infiltrated at room temperature into a mixed solution (10: 6: 50) of 49% hydrofluoric acid, alcohol and hydrogen peroxide (black circle) without stirring. . Thereafter, the decrease in the thickness of the non-porous Si was measured. The non-porous Si remains at 10 after 120 minutes.
Only less than 0 Å was etched.

The porous Si and the non-porous Si after the etching with the etching solution described above were washed with water, and the surface thereof was trace-analyzed with secondary ions. As a result, no impurities were detected. As the alcohol used in the present invention, besides ethyl alcohol, an alcohol such as isopropyl alcohol which can be practically used in the production process and the like, and which can exhibit the above-mentioned alcohol addition effect can be used.

The inventor of the present invention has observed the change in the structure of the porous layer due to the heat treatment using a high-resolution scanning electron microscope or the like in detail by changing the atmosphere or the like. Although the number of pores on the porous surface due to the heat treatment varies depending on the conditions, for example, FIG.
As shown in the figure, the amount decreased with time and eventually disappeared, and as a result, it was found that a single-crystal thin layer having a smooth surface was formed. This is the surface of the porous Si substrate formed by the anodizing treatment, and
As a result of the heat treatment in the vicinity thereof, pores disappear in order to reduce the surface energy, and a non-porous single crystal thin layer is formed in order to smooth the surface.

The non-porous single crystal layer having a smooth surface is a single crystal layer that inherits the orientation of the substrate.
And electron beam channeling patterns. This phenomenon is accelerated as the temperature increases and the pressure decreases. The non-oxidizing atmosphere referred to herein refers to an atmosphere in which an oxide layer is not formed on the surface of the porous layer during heat treatment, and more preferably a reducing atmosphere, for example, an atmosphere containing hydrogen,
Alternatively, a hydrogen atmosphere may be used. The heat treatment temperature is
Although it depends on the composition and pressure of the atmosphere, the temperature is generally 300 ° C. or higher, more preferably 500 ° C. or higher, and the melting point or lower. As for the pressure, the smoothing is promoted even at a higher pressure as the reducing property is higher, but the pressure is generally equal to or lower than the atmospheric pressure,
Below Torr, there is no particular lower limit. Also, an ultra-high vacuum is not particularly required. In the present invention, the term “in vacuum” refers to 1 × 10 ⁻³ without introducing an atmospheric gas in a state where there is no leak in the reaction tank.
The pressure is maintained at a pressure of Torr or less, more preferably 1 × 10 ⁻⁵ Torr or less.

This phenomenon starts when heat treatment is performed with the porous surface in a clean state. When a natural oxide film is formed on the surface of the porous Si substrate, the heat treatment is started. Prior to this, by removing this with dilute hydrofluoric acid, the smoothing of the surface is further promoted.

As shown in FIG. 1B, a light transmissive glass substrate 3 is prepared and attached to the surface of a single crystal Si layer 2 on a porous Si substrate 1. In this sticking 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. Oxide layer 6 is formed to reduce the interface state of single crystal silicon layer 2 which is the final active layer.

As shown in FIG. 1C, if necessary,
As an etching prevention film, a Si ₃ N ₄ layer 5 is deposited,
The entirety of the two bonded substrates is 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. Thereafter, the entirety of the porous Si substrate 1 is etched to form a thin film of the single crystal silicon layer 2 on the light transmitting glass 3.

Prior to the etching, the porous Si substrate 1 may be thinned in advance from the back side by machining such as grinding or polishing. In particular, in the case where the entire Si substrate is not made porous, it is preferable that the thickness be reduced by machining until the porous layer is exposed.

FIG. 1C 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, the single crystal Si layer 2 having a crystallinity equivalent to that of a silicon wafer is flattened on the light transmitting glass substrate 3. In addition, it is formed into a large area over the entire area of the light transmissive glass substrate by being uniformly and thinly formed. Thereafter, if necessary, the thickness of the single-crystal thin layer may be increased by epitaxial growth from the single-crystal Si layer. This growth method may be any method such as a CVD method, a sputtering method, a liquid phase growth method, and a solid phase growth method.

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

[0038]

The present invention will be described below with reference to specific examples. (Example 1) P-type (100) single crystal S having a thickness of 200 microns
The i-substrate was anodized in a 50% HF solution. The current density at this time was 5 mA / cm ² . At this time, the rate of making porous is 0.9 μm / min. And 2
The entire P-type (100) Si substrate having a thickness of 00 microns was made 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 This smooth layer on the surface was subjected to high resolution scanning electron microscopy, RH
Observation by EED revealed that the thickness was 20 in the same direction as the substrate.
A single-crystal thin layer having a thickness of nm was formed.

Next, an optically polished fused silica glass substrate is superimposed on the surface of the single crystal thin layer, and heated at 800 ° C. for 0.5 hour in an oxygen atmosphere, so that both substrates are firmly bonded. Joined. Si ₃ N by low pressure CVD
₄ is deposited to a thickness of 0.1 μm to cover the two bonded substrates, and only the nitride film on the porous substrate is removed by reactive ion etching.

After that, the bonded substrate is mixed with a mixture of 49% hydrofluoric acid, alcohol and aqueous hydrogen peroxide (10: 6: 5).
In step 0), selective etching is performed without stirring. After 65 minutes, only the single crystal Si layer remains without being etched,
Using single crystal Si as an etch stop material, porous S
The i-substrate was selectively etched and completely removed. Si
After removal of the ₃ N ₄ layer is a thin film monocrystalline Si layer was formed on a quartz glass substrate. As a result of a cross-sectional observation with a transmission electron microscope, no new crystal defects were introduced into the Si layer, and it was confirmed that good crystallinity was maintained. (Example 2) P-type (100) single crystal S having a thickness of 200 microns
The i-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) Si with a thickness of 200 microns
The entire substrate was made 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: 50 Torr Time: 45 minutes The smooth layer on this surface was subjected to high-resolution scanning electron microscopy, RH
Observation by EED showed that the thickness was 50 in the same direction as the substrate.
nm, a non-porous single-crystal thin layer was formed.

Next, an optically polished glass substrate having a softening point near 500 ° C. is superposed on the surface of the oxidized epitaxial layer having a thickness of 10 nm.
By heating at a temperature of 0.5 ° C. for 0.5 hour, the two substrates were firmly joined. 0.1% Si ₃ N ₄ by low pressure CVD
The two substrates that have been deposited in μm and bonded together are covered, and only the nitride film on the porous substrate is removed by reactive ion etching.

As described above, ordinary single crystal KOH
The etch rate for a 6M solution is on the order of less than 1 micron per minute, but the etch rate for the porous layer is increased by a factor of 100. That is, the porous Si substrate having 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 the low softening point glass substrate. (Example 3) P-type (100) single crystal S having a thickness of 200 microns
The i-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 / m
in. And a P-type (10
0) The entire Si substrate was made porous in 24 minutes. After the porous Si substrate was washed with 1.5% diluted hydrofluoric acid, it was 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 subjected to high-resolution scanning electron microscopy, RH
Observation by EED revealed that the thickness was 20 in the same direction as the substrate.
A single-crystal thin layer having a thickness of nm was formed.

The surface of the single crystal thin layer was subjected to optical polishing 5
A glass substrate having a softening point near 00 ° C. was overlaid and heated at 450 ° C. for 0.5 hour in an oxygen atmosphere, whereby both substrates were firmly joined. Si ₃ N ₄ is deposited to a thickness of 0.1 μm by a low pressure CVD method, the two bonded substrates are coated, 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 to a fluorinated nitric acid solution is about 1 micron per minute (1: 3: 8 fluorinated nitric acid solution). Is increased by a factor of about 100. That is, the porous Si substrate having a thickness of 200 microns was removed in 2 minutes. After removing the Si ₃ N ₄ layer, a single-crystal Si layer could be formed on the low softening point glass substrate.

The same effect can be obtained when apiesone wax is used instead of the Si ₃ N ₄ layer, and only the porous Si substrate can be completely removed. (Example 4) P-type (100) single crystal S having a thickness of 300 microns
The i-substrate was anodized in a 50% HF solution. The current density at this time was 5 mA / cm ² . At this time, the rate of making porous is 0.9 μm / min. And 3
The surface of a P-type (100) Si substrate having a thickness of 00 microns was made 30 μm porous.

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: 60 Torr Time: 25 minutes This smooth layer on the surface was subjected to high-resolution scanning electron microscopy, RH
Observation by EED revealed that the thickness was 30 in the same direction as the substrate.
A single-crystal thin layer having a thickness of nm was formed. A fused silica glass substrate was brought into close contact with the surface of the single crystal thin layer oxidized by 100 Å and heated at 700 ° C. for 0.5 hour, whereby both substrates were firmly joined.

The porous substrate was scraped from the back surface by a usual wafer lapping process to a thickness of 170 μm to expose the porous silicon. Si ₃ N ₄ is deposited to a thickness of 0.1 μm by a low pressure CVD method, the two bonded substrates are coated, and 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 aqueous hydrogen peroxide (10:
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 using the single-crystal Si as a material for the etch stop and completely removed. S
After removing the i ₃ N ₄ layer, a single-crystal Si layer could be formed on the fused silica glass substrate.

The same effect can be obtained when apiezone wax is used instead of the Si ₃ N ₄ layer, and only the porous Si substrate can be completely removed. (Example 5) P-type (100) single crystal S having a thickness of 200 microns
The i-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) Si with a thickness of 200 microns
The entire substrate was made 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 The smooth layer on this surface was subjected to high-resolution scanning electron microscopy, RH
Observation by EED revealed that the thickness was 20 in the same direction as the substrate.
A single-crystal thin layer having a thickness of nm was formed. An optically polished glass substrate having a softening point near 800 ° C. was brought into close contact with the surface of the single crystal thin layer, and heated at 700 ° C. for 0.5 hour, whereby both substrates were firmly joined.

Si ₃ N ₄ is reduced to 0.1 by a low pressure CVD method.
The two substrates that have been deposited in μm and bonded together 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 a hydrofluoric-nitric acid-acetic acid solution is about 1 micron per minute or less (hydrofluoric-nitric acid-acetic acid solution 1: 3: 8).
The etching rate of the porous layer is increased by a factor of about 100.
That is, the porous Si substrate having a thickness of 200 microns was removed in 2 minutes. After removing the Si ₃ N ₄ layer, a single-crystal Si layer could be formed on the glass substrate.

Next, the single-crystal thin layer was epitaxially grown from the single-crystal thin layer by using a commonly used CVD method to reduce the thickness of the single-crystal silicon layer 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 was formed on the glass substrate. (Example 6) P-type (100) single crystal S having a thickness of 200 microns
The i-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 / m
in. And a P-type (10
0) The entire Si substrate was made porous in 24 minutes. After the porous Si substrate was washed with 1.5% diluted hydrofluoric acid, it was 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 subjected to high-resolution scanning electron microscopy, RH
Observation by EED showed that the thickness was 15
A single-crystal thin layer having a thickness of nm was formed.

An optically polished fused silica glass substrate is superimposed on the surface of the single crystal thin layer, and is placed in an oxygen atmosphere for 800 hours.
By heating at a temperature of 0.5 ° C. for 0.5 hour, the two substrates were firmly joined. 0.1% Si ₃ N ₄ by low pressure CVD
The two substrates that have been deposited in μm and bonded together are covered, and only the nitride film on the porous substrate is removed by reactive ion etching.

After that, the bonded substrate is mixed with a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution (10:
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 quartz glass substrate.

As a result of observation of a cross section by a transmission electron microscope,
No new crystal defects were introduced into the i-layer, and it was confirmed that good crystallinity was maintained. In addition, Si ₃
The same effect was obtained when apiezone wax was applied instead of the N ₄ layer, and only the porous Si substrate could be completely removed.

[0062]

As described in detail above, according to the present invention,
In order to obtain a single-crystal silicon layer with excellent crystallinity on a light-transmissive substrate represented by glass, comparable to a single-crystal wafer, a method that is outstanding in terms of productivity, uniformity, controllability, and economy Can be provided.

Further, according to the present invention, it is possible to realize the advantages of the conventional SOI device and to provide a method of manufacturing a semiconductor substrate which can be applied. Further, according to the present invention, the SOI
When fabricating large-scale integrated circuits with structures, expensive SOS
Further, it is possible to provide a method for manufacturing a semiconductor substrate which can be substituted for SIMOX.

According to the present invention, an originally high-quality single-crystal silicon
Using a substrate as a starting material, the surface of the porous layer is transformed into a non-porous single-crystal layer by heat treatment in a non-oxidizing atmosphere or in a vacuum after being made porous by anodizing, The porous silicon layer is removed and transferred onto a light-transmitting substrate. A non-porous single-crystal layer can be formed on the porous material without using a source gas such as silane, so that it is economical. . Further, as described in detail in the embodiment, it is possible to perform a large number of processes in a short time, and there is a great improvement in productivity and economy.

Further, according to the present invention, since an extremely thin single crystal layer can be formed on an oxide layer, it is suitable for an SOI circuit using a thin film.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view for explaining steps of a method for manufacturing a semiconductor substrate of the present invention.

FIG. 2 is an etching characteristic diagram when porous Si and non-porous Si are infiltrated into a mixed solution of 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]

DESCRIPTION OF SYMBOLS 1 Porous Si substrate 2 Non-porous Si single crystal layer 3 Light transmissive glass substrate 5 Si ₃ N ₄ etching prevention film 6 Surface oxide layer

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H01L 21/02 H01L 21/20 H01L 21/762 H01L 27/12

Claims (23)

(57) [Claims] The method according to claim 1 first substrate having a porous monocrystalline silicon layer, in a non-oxidizing atmosphere or in vacuum, by heat treatment at a temperature lower than the melting point of said porous monocrystalline silicon layer, the porous the surface of the single crystal silicon layer, forming a non-porous monocrystalline silicon layer, said non-porous single-crystal sheet
Bonding a first substrate having a recon layer formed thereon and a light-transmissive second substrate such that a multilayer structure in which the non-porous single-crystal silicon layer is located is obtained; and Removing the porous single-crystal silicon layer from the multilayer structure. 2. The method according to claim 1, wherein the heat treatment of the first substrate is performed in a reducing atmosphere. 3. The method according to claim 2, wherein the heat treatment of the first substrate is performed in an atmosphere containing hydrogen or in a hydrogen atmosphere. 4. The method of manufacturing a semiconductor substrate according to claim 1, wherein the heat treatment of the first substrate is performed under a pressure equal to or lower than the atmospheric pressure. 5. The heat treatment of the first base material is performed at 200 To
The method for producing a semiconductor substrate according to claim 4, wherein the method is performed under a pressure of rr or less. 6. The method according to claim 1, wherein the heat treatment of the first substrate is performed under a pressure of 1 × 10 ⁻³ Torr or less without introducing an atmospheric gas. 7. The method according to claim 6, wherein the heat treatment of the first substrate is performed under a pressure of 1 × 10 ⁻⁵ Torr or less without introducing an atmospheric gas. 8. The method of manufacturing a semiconductor substrate according to claim 1, wherein the heat treatment of the first substrate is performed at a temperature of 300 ° C. or higher. 9. The method according to claim 8, wherein the heat treatment of the first substrate is performed at a temperature of 500 ° C. or higher. Wherein said porous monocrystalline silicon layer, a method for manufacturing a semiconductor substrate according to claim 1 comprising a P-type silicon. Wherein said porous monocrystalline silicon layer, according to claim 1-1 where at least a portion of the first substrate made of a non-porous single-crystal silicon formed by porous
0. The method for producing a semiconductor substrate according to any one of the above items. 12. The porous single-crystal silicon layer is formed by partially making the first substrate made of non-porous single-crystal silicon porous, and after the bonding step, the porous single-crystal silicon layer is made of a porous single-crystal silicon. Before removing the crystalline silicon layer, the first
The method for manufacturing a semiconductor substrate according to claim 11 , further comprising a step of removing a region of the substrate that has not been made porous. Wherein said remaining region without being porous of the first substrate, a method for manufacturing a semiconductor substrate according to claim 12 which is removed by polishing or grinding. 14. The method of manufacturing a semiconductor substrate according to claim 11 , wherein said porous material is formed by anodization. 15. Prior to the heat treatment of the first substrate,
The method for manufacturing a semiconductor substrate according to any one of claims 1 to 14 for cleaning the surface of the porous monocrystalline silicon layer by hydrofluoric acid. Of 16. After further removing the porous monocrystalline silicon layer, a semiconductor according to any one of claims 1 to 15, epitaxially growing a single-crystal silicon layer from the non-porous monocrystalline silicon layer of the multilayer structure How to make a substrate. 17. The second substrate, the method for manufacturing a semiconductor substrate according to any one of claims 1 to 16 made of a glass substrate. 18. The method according to claim 17 , wherein the second base is made of a quartz glass substrate. Before 19. The bonding step, the non-porous method for manufacturing a semiconductor substrate according to any one of claims 1 to 18, forming an oxide layer by oxidizing the surface of the single crystal silicon layer . 20. The porous removal of the monocrystalline silicon layer, a method for manufacturing a semiconductor substrate according to any one of claims 1 to 19 made by etching. 21. The method according to claim 20 , wherein an aqueous solution containing hydrofluoric acid is used as the etchant for the etching. 22. of the bonding process, according to claim comprising a process of heating in an oxygen atmosphere or a nitrogen atmosphere 1-21
The method for producing a semiconductor substrate according to any one of the above. 23. A semiconductor substrate manufactured by the method according to any one of claims 1 to 22.