JPH04349621A - Manufacture of semiconductor substrate - Google Patents

Abstract

PURPOSE:To provide a manufacturing method of a semiconductor substrate which has a silicon layer having crystallinity as excellent as that of a single crystal wafer on a transparent substrate with excellent productivity, uniformity, controllability and cost performance. CONSTITUTION:A non-porous silicon single crystal layer 12 is formed on a porous silicon substrate 11. The surface of the non-porous silicon single crystal layer 12 is bonded to a light transmitting glass substrate 13 and the porous silicon substrate 11 is dipped into mixed solution of fluoric acid and alcohol. Only the porous silicon substrate 11 is removed by nonelectrolytic chemical wet-etching to obtain a substrate composed of the light transmitting glass substrate 13 and the non-porous silicon single crystal layer 12 formed on it. A reference numeral 14 denotes an etching protective film.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing a semiconductor substrate, and more specifically, a light-transmitting semiconductor fabricated on a dielectric separation or a single crystal semiconductor layer on an insulator and suitable for electronic devices and integrated circuits. The present invention relates to a method for producing a base material.

0002

[Prior Art] The formation of a single-crystal Si semiconductor layer on an insulator is widely known as silicon-on-insulator (SOI) technology, and it has many advantages that cannot be achieved with bulk Si substrates used to fabricate ordinary Si integrated circuits. SO
Much research has been done on the characteristics of devices using I technology. That is, by using SOI technology, 1. Dielectric separation is easy and high integration is possible; 2. 3. Excellent resistance to radiation. 4. Stray capacitance is reduced and high speed is possible. 5. Well process can be omitted. Prevents latch-up 6. Advantages include the ability to create fully depleted field effect transistors by thinning the film.

[0003] In order to realize the many advantages in terms of device characteristics as described above, methods for forming SOI structures have been studied over the past several decades. This content is summarized in the following documents, for example. Special
Issue: ”Single-crystal si
licon onnon-single-crysta
l insulators”; edited by
G. W. Cullen, Journal of Cr.
ystalGrowth, volume 63, n
o 3, pp 429-590 (1983).

[0004] In the past, on a single crystal sapphire substrate,
SOS (silicon on sapphire), which is formed by heteroepitaxing Si using CVD (chemical vapor deposition), is known, and although it has achieved some success as the most mature SOI technology, the Si layer and underlying sapphire The spread of its application has been hindered by a large number of crystal defects due to lattice mismatch at the substrate interface, the mixing of aluminum from the sapphire substrate into the Si layer, and above all, the high cost of the substrate and the delay in increasing the size of the substrate. There is. In relatively recent years, attempts have been made to realize an SOI structure without using a sapphire substrate. This attempt can be broadly divided into two parts:
1. After surface oxidation of the Si single crystal substrate, a window is opened to partially expose the Si substrate, and this portion is used as a seed for epitaxial growth in the lateral direction to form a Si single crystal layer on the SiO2 (in this case, involves the deposition of a Si layer on SiO2); 2. The Si single crystal substrate itself is used as the active layer, and SiO2 is formed underneath it (this method does not involve the deposition of a Si layer).

[0005]

[Problems to be Solved by the Invention] As a means for realizing the above 1, there is a method of directly lateral epitaxial growth of a single crystal layer of Si by CVD, a method of depositing amorphous Si,
A method of solid-phase lateral epitaxial growth by heat treatment, in which an amorphous or polycrystalline Si layer is irradiated with a focused energy beam such as an electron beam or laser light, and a single crystal layer is formed by melting and recrystallization. A method of growing on SiO2, and a method of scanning the molten region in a belt shape with a rod-shaped heater (
Zone melting recrystalliz
ation) is known. Each of these methods has its advantages and disadvantages, but many problems remain in controllability, productivity, uniformity, and quality.
As of yet, nothing has been put into practical use industrially. for example,
The CVD method requires sacrificial oxidation to form a flat and thin film, and the solid phase growth method has poor crystallinity. In addition, the beam annealing method has problems in the processing time due to convergent beam scanning and in the controllability of beam overlapping conditions, focus adjustment, etc. Among these, Zone Melting Recryst
Although the allization 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 it is difficult to create minority carrier devices. Not.

[0006] As the above-mentioned method 2, in which the Si substrate is not used as a seed for epitaxial growth, there are the following methods: 1. An oxide film is formed on a Si single crystal substrate with V-shaped grooves anisotropically etched on the surface, and after depositing a polycrystalline Si layer as thick as the Si substrate on the oxide film, polishing is performed from the back side of the Si substrate. By this method, a dielectrically isolated Si single crystal region surrounded by a V-groove is formed on a thick polycrystalline Si layer. Although this method has good crystallinity, it is difficult to control the process of depositing polycrystalline Si to a thickness of several hundred microns, and the process of polishing the single-crystal Si substrate from the back side to leave only the separated Si active layer. There are problems in terms of performance and productivity; 2. SIMOX: Separation
by ion implanted oxygen)
This is a method of forming an SiO2 layer by implanting oxygen ions into a Si single-crystal substrate, and is currently the most mature method as it has good compatibility with the Si process. However, in order to form the SiO2 layer, it is necessary to implant oxygen ions at a rate of 1018 ions/cm2 or more, but the implantation time is long, productivity is not high, and the wafer cost is low. expensive. Furthermore, many crystal defects remain, and from an industrial point of view, the quality is not high enough for manufacturing minority carrier devices; 3. A method of forming an SOI structure by dielectric separation through oxidation of porous Si. This method involves proton ion implantation (Imai et al., J.Cry) to form an N-type Si layer on the surface of a P-type Si single crystal substrate.
stal Growth, vol 63, 547 (1
983)) or epitaxial growth and patterning
A method in which only the P-type Si substrate is made porous by anodization in an HF solution so as to surround the Si islands from the surface, and then the N-type Si islands are dielectrically separated by accelerated oxidation. It is. In this method, the separated Si
The area is determined before the device process, and there is a problem in that the degree of freedom in device design may be restricted.

Incidentally, a light-transmitting substrate is important in constructing a contact sensor, which is a light-receiving element, and a projection type liquid crystal image display device. In order to further increase the density, resolution, and definition of pixels (picture elements) of sensors and display devices, extremely high-performance driving elements are required. As a result, an element provided on a light-transmitting substrate also needs to be created using a single crystal layer having excellent crystallinity.

However, reflecting the disordered crystal structure of a light-transmitting substrate typified by glass, simply depositing a Si layer will result in an amorphous or, at best, polycrystalline Si layer. Only layers can be formed, and high-performance devices cannot be created. This is because the crystal structure of the substrate is amorphous, and simply depositing a Si layer does not yield a high-quality single crystal layer. Due to the defect-rich crystal structure of amorphous Si and polycrystalline Si, it is difficult to create a driving element with performance sufficient to meet the required or future requirements.

Furthermore, any of the above methods using a Si single crystal substrate is unsuitable for the purpose of obtaining a high quality single crystal layer on a light transmitting substrate.

An object of the present invention is to provide a method for producing a semiconductor base material (the base material also includes a substrate) that meets the above-mentioned problems and demands. do.

[0011] The present invention also provides a single crystal wafer with crystallinity on a transparent substrate (a light-transmitting substrate; the substrate also includes a substrate).
It is an object of the present invention to provide a method for producing a semiconductor substrate that is excellent in terms of productivity, uniformity, controllability, and cost while obtaining excellent Si.

A further object of the present invention is to provide a method for fabricating a semiconductor substrate that realizes the advantages of conventional SOI structures and is applicable.

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

[0014]

[Means and effects for solving the problems] The method for manufacturing a semiconductor substrate of the present invention includes a step of making a silicon substrate porous, and forming a non-porous silicon single crystal layer on the porous silicon substrate. a step of bonding the surface of the non-porous silicon single crystal layer to a light-transmitting glass substrate; and a step of immersing the porous silicon substrate in a mixed solution of hydrofluoric acid and alcohol to remove only the porous silicon. A selective etching process for removing porous silicon by electroless wet chemical etching.

[0015] Furthermore, the method for manufacturing a semiconductor substrate of the present invention includes:
a step of making the other side of a silicon single crystal substrate with one side N-type porous; a step of bonding the one side of the silicon single crystal substrate to a light-transmitting glass substrate;
A selective etching step for porous silicon in which only the porous silicon is removed by electroless wet chemical etching by immersing the porous silicon single crystal substrate in a mixed solution of hydrofluoric acid and alcohol. .

[0016] In the present invention, the light-transmissive glass substrate includes those provided with a metal layer such as Al or ITO on the surface.

[0017] The present invention uses a Si single crystal substrate which is economical, uniform and flat over a large area, and has extremely excellent crystallinity. It is possible to obtain a Si single crystal layer with extremely few defects on a light-transmitting glass substrate by removing up to the layers.

To facilitate understanding of the present invention, a general technical explanation regarding porous silicon and its removal by chemical etching will now be provided.

Porous Si has been described by Uhlir et al.
It was discovered in 1956 during the research process of electrolytic polishing of semiconductors (A. Uhlir, Bell Syst. Tech.
．． J. , vol 35, p. 333 (1956))
. In addition, Unagami et al. studied the dissolution reaction of Si in anodic formation and reported that holes are required for the anodic reaction of Si in HF solution, and the reaction is as follows (T .Unagami: J. Electrochem.S
oc. , vol. 127, p. 476 (1980
) ): Si + 2HF + (2-n)e+ → SiF
2 +2H+ + ne-SiF2 + 2HF →
SiF4 + H2SiF4 + 2HF →
H2SiF6 or Si + 4HF + (4-λ)e+ → SiF
4+ 4H++ λe-SiF4 + 2HF →
H2SiF6 where e+ and e- are respectively
Represents holes and electrons. In addition, n and λ are the number of holes required for dissolving one silicon atom, respectively, and n>
It is said that porous silicon is formed when the condition 2 or λ>4 is satisfied.

From the above, P-type silicon in which holes exist is made porous, but N-type silicon is not made porous. The selectivity in this porosity formation has been demonstrated by Nagano et al.
(Nagano, Nakajima, Yasuno, Onaka, Kajiwara; Institute of Electronics and Communication Engineers Technical Research Report, vol. 79)
, SSD 79-9549 (1979), and K. Not good;Solid-State Electronic
s vol 24, 159 (1981)). In this way, P-type silicon in which holes exist is easily made porous, and P-type silicon can be selectively made porous.

On the other hand, it has been reported that highly concentrated N-type silicon also becomes porous (RP Holmstorm, I.J.
Y. Chi Appl. Phys. Lett. Vol.
．． 42, 386 (1983)), and it is important to select a substrate that can be made porous, regardless of P or N.

Furthermore, since a large number of voids are formed inside the porous layer, the density is reduced to less than half that of the original silicon. As a result, the surface area increases dramatically compared to the volume, so the chemical etching rate is significantly increased compared to the etching rate of a normal single crystal layer.

Next, removal of the porous layer Si by chemical etching will be discussed. Generally, P=(2.33-A)/2. 33
(1) is called Porosity, and this value can be changed during anodization, and can be expressed as follows: P = (m1 - m2) / (m1 - m3)
(2) Or, P=(m1 - m2)/ρAt
(3) Here, m1: Total weight before anodization m2: Total weight after anodization m3: Total weight after porous Si is removed ρ: Density of single crystal Si A: Porous area t: Thickness of porous Si There are many cases where it is not possible to accurately calculate the area of the region to be made porous. In this case, equation (2) is valid, but m3
In order to measure , porous Si must be etched.

[0024] Furthermore, in the epitaxial growth on porous Si described above, due to its structural properties, porous Si can alleviate the strain that occurs during heteroepitaxial growth and suppress the generation of defects. . However, even in this case, it is clear that the porosity of porous Si is a very important parameter. Therefore, the measurement of Porosity described above is essential in this case as well.

Conventional methods for etching porous Si include 1. Method of etching porous Si with NaOH aqueous solution (G. Bonchil, R. Herino, K.B.
arla, and J. C. Pfister, J. E
electrochem. Soc. , vol. 130,
no. 7, 1611 (1983)), and 2. A method of etching porous Si using an etching solution capable of etching single crystal Si is known.

[0026] In method 2 above, a fluoro-nitric acid-based etching solution is usually used, and the Si etching process at this time is as follows: Si +2O → SiO2 SiO2 +4HF → Si F4 +H2
As shown in O, Si is oxidized with nitric acid to form SiO2
By etching the SiO2 with hydrofluoric acid, etching of Si progresses.

However, in the case of etching as in method 2 above, although porous Si can be etched, crystalline Si is also etched.

Similarly, as an etching solution for etching crystalline Si, in addition to the above-mentioned fluoronitric acid-based etching solution, there are ethylenediamine-based, KOH-based, hydrazine-based etching solutions, and the like.

For these reasons, in order to perform selective etching of porous Si, it is necessary to select an etching solution capable of etching porous Si other than the above-mentioned Si etching solution.

The selective etching of porous Si that has been conventionally performed is only the etching described in 1 above using an aqueous NaOH solution as an etching solution.

However, the conventional NaOH
In the selective etching method of porous Si using an aqueous solution,
It is inevitable that Na ions will be adsorbed on the etched surface. These Na ions are the main cause of impurity contamination, and only have negative effects such as forming interface states.
This is a substance that must not be introduced in semiconductor processes.

Therefore, in the present invention, the selective etching method for porous Si uses a mixed solution of hydrofluoric acid and alcohol, which does not have an etching effect on crystalline Si, as the selective etching solution. Features. The present invention selectively chemically etches non-porous crystalline Si and porous Si coexisting in the same substrate using a solution used in normal semiconductor processes.

The alcohol in the selective wet chemical etching solution for porous Si of the present invention acts as a surface active agent, and instantly removes the gas bubbles produced by the reaction from the etching surface without stirring, thereby uniformly and efficiently. Selective etching of porous Si becomes possible.

According to observation using a transmission electron microscope, pores with 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℃
Above this, rearrangement of the internal pores occurs, and the characteristics of accelerated etching are impaired. For this reason, epitaxial growth of the Si layer requires molecular beam epitaxial growth, plasma carbon
CVD methods such as VD, low pressure CVD, and optical CVD, bias
Low-temperature growth methods such as sputtering and liquid phase growth are preferred.

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

[0036]

Embodiment Example 1 A method of epitaxially growing a single crystal layer after making the entire substrate porous will be described. FIGS. 1(a) to 1(c) are process diagrams for explaining the method for manufacturing a semiconductor substrate according to the present invention, and each is shown as a schematic cross-sectional view in each step.

As shown in FIG. 1(a), first, a Si single crystal substrate 11 is prepared and made entirely porous, and then epitaxial growth is performed on the surface of the porous substrate by various growth methods. Then, a thin single crystal Si layer 12 is formed. The Si substrate is formed by anodization using an HF solution.
Make it porous. This porous Si layer has a density of 1.1 to 0.0 by changing the HF solution concentration from 50 to 20%, compared to the density of single crystal Si of 2.33 g/cm3.
It can be varied within a range of 6 g/cm3.

As shown in FIG. 1(b), a light transmitting substrate 13 typified by glass is prepared, and the light transmitting substrate 13 is attached to the surface of the single crystal Si layer 12 on the porous Si substrate. Put on. As shown in FIG. 1(b), a Si3N4 layer 14 is deposited as an etching prevention film to cover the entire two bonded substrates, and the Si3N4 layer on the surface of the porous silicon substrate 11 is removed. . As another etching prevention film, Apiezone wax or the like may be used instead of the Si3N4 layer. After this, the porous Si substrate 11 is immersed in a mixed solution of hydrofluoric acid and alcohol.
A light-transmissive substrate 1 is formed by electroless wet chemical etching only on i.
A thin non-porous single-crystal silicon layer 12 is formed to remain on top of the silicon layer 12.

FIG. 1(c) shows a semiconductor substrate obtained by the present invention. That is, by removing the Si3N4 layer 14, which is an etching prevention film in FIG. The layer is thinned and formed over a large area, ie, the entire wafer.

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

A selective etching method in which only porous Si is subjected to electroless wet chemical etching using a mixed solution of hydrofluoric acid and alcohol will be described below.

FIG. 2 shows porous Si and non-porous single crystal Si.
Etched porous Si and single crystal Si when infiltrated into a mixture of hydrofluoric acid and alcohol without stirring
The dependence of the thickness on etching time is shown. Porous Si is produced by anodizing non-porous single crystal Si, and the conditions are shown below. Porous Si formed by anodization
The starting material is not limited to single crystal Si,
It is also possible to use Si with other crystal structures: Applied voltage: 2.6 (V)
Current density: 30 (m
A・cm−2) Anodizing solution:
HF:H2O:C2H5OH=1:1:1 hour
: 2. 4 (hours)
Thickness of porous Si: 300 (μm) Por
Osity: 56 (%).

[0043] The porous Si prepared under the above conditions was treated with a mixed solution of 49% hydrofluoric acid and alcohol (10:1) at room temperature.
) without stirring. Later, the porous Si
The decrease in thickness was measured (white circles in Figure 2). Porous Si is rapidly etched to 85 μm in about 40 minutes.
Further, after 80 minutes, a thickness of 195 μm was uniformly etched with a high degree of surface roughness. Etching rate depends on solution concentration and temperature. The solution concentration and temperature conditions are set within a range that does not cause any practical problems. In this specification, the results for a mixed solution of 49% hydrofluoric acid and ethyl alcohol (10:1) and room temperature are shown as an example.
The present invention is not limited to this condition. In the etching solution, the HF concentration is preferably 1 to 95%, more preferably 5 to 90%, even more preferably 5 to 80%, and the alcohol concentration is preferably 80% or less, more preferably 60% or less, and even more preferably is 40% or less, and is set to a value that provides the effect of adding alcohol. The temperature is preferably 0 to 100°C, more preferably 5 to 80°C, still more preferably 5 to 60°C. As the alcohol in the etching solution, in addition to ethyl alcohol, isopropyl alcohol or the like can be used.

[0044] In addition, 500 μm thick non-porous single crystal Si
A mixture of 49% hydrofluoric acid and alcohol (1
0:1) without stirring. Later, the decrease in the thickness of the single crystal Si was measured (black circle in FIG. 2). Even after 120 minutes, non-porous single crystal Si has 10
Less than 0 angstroms were etched.

After etching, the porous Si and non-porous single crystal Si were washed with water, and their surfaces were subjected to microanalysis using secondary ions, and no impurities were detected.

[0046]

[Embodiment Example 2] Forming an N-type layer before making it porous,
Thereafter, a method of selectively making only the P-type substrate porous by anodization will be described. FIGS. 3(a) to 3(d) are process diagrams for explaining the method for manufacturing a semiconductor substrate according to the present invention, and each is shown as a schematic cross-sectional view in each step.

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

Next, as shown in FIG. 3(b), P-type Si
The single crystal substrate 31 is transformed into a porous Si substrate 33 from the back side by an anodization method using an HF solution. This porous Si layer has a density of 1.1 to 0.6 g/cm3 by changing the HF solution concentration from 50 to 20%, compared to the density of single crystal Si, which is 2.33 g/cm3. It can be changed. This porous layer is formed in the P-type region, as described above.

As shown in FIG. 3(c), a light-transmitting substrate 34 typified by glass is prepared, and the light-transmitting substrate 34 is attached to the surface of the single-crystal Si layer 32 on the porous Si substrate. Put on. As shown in FIG. 3(c), a Si3N4 layer 35 is deposited as an etching prevention film to cover the entire two bonded substrates, and the Si3N4 layer on the surface of the porous silicon substrate 33 is removed. . As another etching prevention film, Apiezone wax or the like may be used instead of the Si3N4 layer. Thereafter, by immersing the porous Si substrate 33 in a mixed solution of hydrofluoric acid and alcohol without stirring, only the porous Si is subjected to electroless wet chemical etching to form a thin film on the transparent substrate 34. A porous single crystal silicon layer 32 is left and formed.

FIG. 3(d) shows a semiconductor substrate obtained by the present invention. That is, by removing the Si3N4 layer which is the etching prevention film in FIG. 3(c),
A monocrystalline Si layer 32 having crystallinity equivalent to that of a silicon wafer is formed on a light-transmissive substrate 34 in a flat and uniformly thin layer over a large area covering the entire wafer.

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

[0052]

[Examples] The present invention will be explained below with reference to specific examples.

(Example 1) A P-type (100) single crystal Si substrate having a thickness of 200 microns was anodized in a 50% HF solution. The current density at this time is 1
00 mA/cm2. The porosity formation rate at this time was 8.4 μm/min. The entire P-type (100) Si substrate with a thickness of 200 microns was made porous in 24 minutes.

MB on the P-type (100) porous Si substrate
E (Molecular Bea Epitaxy)
A Si epitaxial layer was grown to a thickness of 0.5 microns at a low temperature by the mEpitaxy method. Deposition conditions are as follows: Temperature: 700°C Pressure: 1 x 10-9 Torr Growth rate:
0.1 nm/sec.

Next, a fused silica glass substrate that has been optically polished is placed on the surface of this epitaxial layer, and the two substrates are firmly bonded by heating at 800° C. for 0.5 hours in an oxygen atmosphere. Ta.

Si3 N4 by plasma CVD method
was deposited to a thickness of 0.1 μm to cover the two bonded substrates, and only the nitride film on the porous substrate was removed by reactive ion etching. After that, the bonded substrates were
Selective etching was performed with a mixed solution of 9% hydrofluoric acid and alcohol (10:1) without stirring. After 82 minutes, only the single crystal Si layer remained unetched, and the porous Si substrate was selectively etched and completely removed using the single crystal Si as an etch stop material.

The etching rate of non-porous Si single crystal with this etching solution is extremely low, reaching 50% even after 82 minutes.
angstrom or less, and the selectivity with respect to the etching rate of the porous layer reaches the fifth power of ten or more, and the amount of etching (several tens of angstroms) in the non-porous layer is a decrease in film thickness that can be ignored in practical terms. That is, the porous Si substrate with a thickness of 200 microns is removed and the S
After removing the i3N4 layer, 0.5
A single crystal Si layer with a thickness of μm was formed.

As a result of cross-sectional observation using a transmission electron microscope, S
It was confirmed that no new crystal defects were introduced into the i-layer, and good crystallinity was maintained.

(Example 2) A P-type (100) single crystal Si substrate having a thickness of 200 microns was anodized in a 50% HF solution. The current density at this time is 1
00 mA/cm2. The porosity formation rate at this time was 8.4 μm/min. The entire P-type (100) Si substrate with a thickness of 200 microns was made porous in 24 minutes. A 5 μm Si epitaxial layer was formed on the P-type (100) porous Si substrate by plasma CVD.
Grown at low temperature. The deposition conditions are as follows: Gas: SiH4 Radio frequency power: 100 W Temperature:
800°C Pressure: 1 x 10-2 Torr Growth rate:
2.5 nm/sec.

Next, a glass substrate with a softening point around 500° C. whose surface has been optically polished is placed on top of the epitaxial layer, and both substrates are heated at 450° C. for 0.5 hours in an oxygen atmosphere. were strongly bonded.

Si3 N4 by plasma CVD method
was deposited to a thickness of 0.1 μm to cover the two bonded substrates, and only the nitride film on the porous substrate was removed by reactive ion etching.

Thereafter, the bonded substrates were selectively etched with a mixed solution of 49% hydrofluoric acid and alcohol (10:1) without stirring. After 82 minutes, only the single crystal Si layer remained unetched, and the porous Si substrate was selectively etched and completely removed using the single crystal Si as an etch stop material.

The etching rate of non-porous Si single crystal with this etching solution is extremely low, reaching 50% even after 82 minutes.
angstrom or less, and the selectivity with respect to the etching rate of the porous layer reaches the fifth power of ten or more, and the amount of etching (several tens of angstroms) in the non-porous layer is a decrease in film thickness that can be ignored in practical terms. That is, the porous Si substrate with a thickness of 200 microns is removed and the S
After removing the i3N4 layer, a single crystal Si layer with a thickness of 5 μm was formed on the low softening point glass substrate.

(Example 3) A P-type (100) single crystal Si substrate having a thickness of 200 microns was anodized in a 50% HF solution. The current density at this time is 1
00 mA/cm2. The porosity formation rate at this time was 8.4 μm/min. The entire P-type (100) Si substrate with a thickness of 200 microns was made porous in 24 minutes. One Si epitaxial layer was deposited on the P-type (100) porous Si substrate by bias sputtering.
．． 0 micron grown at low temperature. The deposition conditions are as follows: RF frequency: 100 MHz radio frequency power:
600 W Temperature: 300°C Ar gas pressure: 8 x 10-3 Torr Growth time: 120 minutes Target DC bias: -200 V Substrate DC bias: +5 V.

Next, a glass substrate with a softening point around 500° C. whose surface has been optically polished is placed on top of the epitaxial layer, and both substrates are heated at 450° C. for 0.5 hours in an oxygen atmosphere. were strongly bonded.

Si3 N4 by plasma CVD method
was deposited to a thickness of 0.1 μm to cover the two bonded substrates, and only the nitride film on the porous substrate was removed by reactive ion etching.

Thereafter, the bonded substrates were selectively etched with a mixed solution of 49% hydrofluoric acid and alcohol (10:1) without stirring. After 82 minutes, only the single crystal Si layer remained unetched, and the porous Si substrate was selectively etched and completely removed using the single crystal Si as an etch stop material.

The etching rate of a non-porous Si single crystal with this etching solution is extremely low, reaching 50% even after 82 minutes.
angstrom or less, and the selectivity with respect to the etching rate of the porous layer reaches the fifth power of ten or more, and the amount of etching (several tens of angstroms) in the non-porous layer is a decrease in film thickness that can be ignored in practical terms. That is, the porous Si substrate with a thickness of 200 microns is removed and the S
After removing the i3N4 layer, a single crystal Si layer with a thickness of 1.0 μm was formed on the low melting point glass substrate.

A similar effect was obtained when Apiezon wax or Electron wax was coated instead of the Si3 N4 layer, and only the porous Si substrate could be completely removed.

(Example 4) An N-type (100) single crystal Si substrate having a thickness of 200 microns was anodized in a 50% HF solution. The current density at this time is 1
00 mA/cm2. The porosity formation rate at this time was 8.4 μm/min. The entire N-type (100) Si substrate with a thickness of 200 microns was made porous in 24 minutes. A Si epitaxial layer of 10 microns was grown at a low temperature on the N-type (100) porous Si substrate by liquid phase growth. The growth conditions are as follows: Solvent: Sn Growth temperature: 900°C Growth atmosphere: H2 Growth time: 20 minutes.

Next, a glass substrate with a softening point around 800° C. whose surface has been optically polished is placed on top of the epitaxial layer, and both substrates are heated at 750° C. for 0.5 hours in an oxygen atmosphere. were strongly bonded.

Si3 N4 by plasma CVD method
was deposited to a thickness of 0.1 μm to cover the two bonded substrates, and only the nitride film on the porous substrate was removed by reactive ion etching.

Thereafter, the bonded substrates were selectively etched with a mixed solution of 49% hydrofluoric acid and alcohol (10:1) without stirring. After 82 minutes, only the single crystal Si layer remained unetched, and the porous Si substrate was selectively etched and completely removed using the single crystal Si as an etch stop material.

The etching rate of non-porous Si single crystal with this etching solution is extremely low, reaching 50% even after 82 minutes.
angstrom or less, and the selectivity with respect to the etching rate of the porous layer reaches the fifth power of ten or more, and the amount of etching (several tens of angstroms) in the non-porous layer is a decrease in film thickness that can be ignored in practical terms. That is, the porous Si substrate with a thickness of 200 microns is removed and the S
After removing the i3N4 layer, a 10μ layer was deposited on the glass substrate.
A single crystal Si layer with a thickness of m was formed.

[0075] A similar effect is also obtained when Apiezon wax is coated instead of the Si3N4 layer.
Only the porous Si substrate could be completely removed.

(Example 5) A P-type (100) single crystal Si substrate having a thickness of 200 microns was anodized in a 50% HF solution. The current density at this time is 1
00 mA/cm2.

[0077] The porosity formation rate at this time was 8.4 μm/m
in. It is P type (1
00) The entire Si substrate was made porous in 24 minutes. The P
Type (100) on a porous Si substrate by low pressure CVD method.
A 1.0 micron Si epitaxial layer was grown at low temperature. The deposition conditions are as follows: Source gas: SiH4 800 SCCM carrier gas: H2 150 liters/mi
n Temperature: 850°C Pressure: 1 x 10-2 Torr Growth rate:
3.3 nm/sec.

Next, an optically polished fused silica glass substrate was placed on the surface of this epitaxial layer, and the two substrates were firmly bonded by heating at 800° C. for 0.5 hours in an oxygen atmosphere. Ta.

Si3 N4 by plasma CVD method
was deposited to a thickness of 0.1 μm to cover the two bonded substrates, and only the nitride film on the porous substrate was removed by reactive ion etching.

Thereafter, the bonded substrates were selectively etched with a mixed solution of 49% hydrofluoric acid and alcohol (10:1) without stirring. After 82 minutes, only the single crystal Si layer remained unetched, and the porous Si substrate was selectively etched and completely removed using the single crystal Si as an etch stop material.

The etching rate of non-porous Si single crystal with this etching solution is extremely low, reaching 50% even after 82 minutes.
angstrom or less, and the selectivity with respect to the etching rate of the porous layer reaches the fifth power of ten or more, and the amount of etching (several tens of angstroms) in the non-porous layer is a decrease in film thickness that can be ignored in practical terms. That is, the porous Si substrate with a thickness of 200 microns is removed and the S
After removing the i3N4 layer, 1
．． A single crystal Si layer with a thickness of 0 μm was formed.

When SiH2Cl2 was used as the source gas, it was necessary to raise the growth temperature by several tens of degrees, but the accelerated etching characteristics characteristic of porous substrates were maintained.

(Example 6) A Si epitaxial layer of 1 micron was grown on a P-type (100) Si substrate with a thickness of 200 micron by CVD. The deposition conditions are
The reaction gas flow rate is as follows: SiH2Cl2 1000
SCCMH2 230 liters/min. Temperature: 1080℃ Pressure: 760 Torr Time:
2 min.

[0084] This substrate was anodized in a 50% HF solution. The current density at this time is 100mA/
It was cm2. Also, the porosity formation rate at this time was 8.4
μm/min. P with a thickness of 200 microns
The entire type (100) Si substrate was made porous in 24 minutes. As mentioned above, in this anodization, P-type (100)S
Only the i-substrate was made porous, and the Si epitaxial layer remained unchanged.

Next, a fused silica glass substrate that has been optically polished is placed on the surface of this epitaxial layer and heated at 800° C. for 0.5 hours in an oxygen atmosphere to firmly bond the two substrates. Ta.

Si3 N4 by plasma CVD method
was deposited to a thickness of 0.1 μm to cover the two bonded substrates, and only the nitride film on the porous substrate was removed by reactive ion etching.

Thereafter, the bonded substrates were selectively etched with a mixed solution of 49% hydrofluoric acid and alcohol (10:1) without stirring. After 82 minutes, only the single crystal Si layer remained unetched, and the porous Si substrate was selectively etched and completely removed using the single crystal Si as an etch stop material.

The etching rate of non-porous Si single crystal with this etching solution is extremely low, reaching 50% even after 82 minutes.
angstrom or less, and the selectivity with respect to the etching rate of the porous layer reaches the fifth power of ten or more, and the amount of etching (several tens of angstroms) in the non-porous layer is a decrease in film thickness that can be ignored in practical terms. That is, the porous Si substrate with a thickness of 200 microns is removed and the S
After removing the i3N4 layer, 1
A single crystal Si layer with a thickness of μm was formed.

As a result of cross-sectional observation using a transmission electron microscope, S
It was confirmed that no new crystal defects were introduced into the i-layer, and good crystallinity was maintained.

(Example 7) A Si epitaxial layer of 0.5 microns was grown on a P-type (100) Si substrate with a thickness of 200 microns by the CVD method. The deposition conditions are as follows: Reaction gas flow rate: SiH2Cl2 1000
SCCMH2 230 liters/min. Temperature: 1080℃ Pressure: 80 Torr Time:
1 min.

[0091] This substrate was anodized in a 50% HF solution. The current density at this time is 100mA/
It was cm2. Also, the porosity formation rate at this time was 8.4
μm/min. P with a thickness of 200 microns
The entire type (100) Si substrate was made porous in 24 minutes. As mentioned above, in this anodization, P-type (100)S
Only the i-substrate was made porous, and the Si epitaxial layer remained unchanged.

Next, a fused silica glass substrate that has been optically polished is placed on the surface of this epitaxial layer, and heated at 800° C. for 0.5 hours in an oxygen atmosphere to firmly bond the two substrates. Ta.

Si3 N4 by plasma CVD method
was deposited to a thickness of 0.1 μm to cover the two bonded substrates, and only the nitride film on the porous substrate was removed by reactive ion etching.

Thereafter, the bonded substrates were selectively etched with a mixed solution of 49% hydrofluoric acid and alcohol (10:1) without stirring. After 82 minutes, only the single crystal Si layer remained unetched, and the porous Si substrate was selectively etched and completely removed using the single crystal Si as an etch stop material.

The etching rate of non-porous Si single crystal with this etching solution is extremely low, reaching 50% even after 82 minutes.
angstrom or less, and the selectivity with respect to the etching rate of the porous layer reaches the fifth power of ten or more, and the etching amount (several tens of angstroms) in the non-porous layer is a decrease in film thickness that can be ignored in practical terms. That is, the porous Si substrate with a thickness of 200 microns is removed and the S
After removing the i3N4 layer, 0
．． A single crystal Si layer with a thickness of 5 μm was formed.

As a result of cross-sectional observation using a transmission electron microscope, S
It was confirmed that no new crystal defects were introduced into the i-layer, and good crystallinity was maintained.

(Example 8) An N-type Si layer of 1 micron was formed on the surface of a P-type (100) Si substrate with a thickness of 200 microns by ion implantation of protons. The H+ injection volume was 5×1015 (ions/cm2).

[0098] This substrate was anodized in a 50% HF solution. The current density at this time is 100mA/
It was cm2. Also, the porosity formation rate at this time was 8.4
μm/min. P with a thickness of 200 microns
The entire type (100) Si substrate was made porous in 24 minutes. As mentioned above, in this anodization, P-type (100)S
Only the i-substrate was made porous, and the N-type Si layer remained unchanged.

Next, a fused silica glass substrate that has been optically polished is placed on the surface of this N-type Si layer, and heated at 800°C for 0.5 hours in an oxygen atmosphere to make both substrates strong. joined.

[0100] Si3 N4 by plasma CVD method
was deposited to a thickness of 0.1 μm to cover the two bonded substrates, and only the nitride film on the porous substrate was removed by reactive ion etching.

Thereafter, the bonded substrates were selectively etched with a mixed solution of 49% hydrofluoric acid and alcohol (10:1) without stirring. After 82 minutes, only the single crystal Si layer remained unetched, and the porous Si substrate was selectively etched and completely removed using the single crystal Si as an etch stop material.

The etching rate of non-porous Si single crystal with this etching solution is extremely low, reaching 50% even after 82 minutes.
angstrom or less, and the selectivity with respect to the etching rate of the porous layer reaches the fifth power of ten or more, and the amount of etching (several tens of angstroms) in the non-porous layer is a decrease in film thickness that can be ignored in practical terms. That is, the porous Si substrate with a thickness of 200 microns is removed and the S
After removing the i3N4 layer, 1
A single crystal Si layer with a thickness of μm was formed.

[0103] As a result of cross-sectional observation using a transmission electron microscope, S
It was confirmed that no new crystal defects were introduced into the i-layer, and good crystallinity was maintained.

[0104]

[Effects of the Invention] As detailed above, according to the present invention,
It is possible to provide a method for manufacturing a semiconductor base material that can meet the problems and demands described above.

[0105] Furthermore, according to the present invention, productivity, uniformity, and control can be achieved in order to obtain a Si crystal layer on a light-transmissive insulating substrate typified by glass, with crystallinity comparable to that of a single-crystal wafer. It is possible to provide an excellent method in terms of efficiency and economy.

Furthermore, according to the present invention, it is possible to realize the advantages of conventional SOI devices and to propose a method for manufacturing an applicable semiconductor substrate.

Furthermore, according to the present invention, even when manufacturing a large-scale integrated circuit with an SOI structure, expensive SOS and SIM
A method for manufacturing a semiconductor substrate that can be used as a substitute for OX can be provided.

According to the present invention, a single crystal Si substrate of high quality is used as a starting material, and the lower Si substrate is chemically removed, leaving the single crystal layer only on the surface, and then transferred onto a light-transmitting substrate. As described in detail in the examples,
It has become possible to perform a large number of processes in a short time, and there have been significant advances in productivity and economy.

[Brief explanation of the drawing]

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

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

FIG. 3 is a schematic cross-sectional view for explaining the steps of the present invention.

[Explanation of symbols]

11 Porous Si substrate 12 Epitaxial Si single crystal layer 13
Glass light transmitting substrate 14 Etching prevention film 31 P type Si single crystal substrate 32 N type Si single crystal layer 33 Porous Si substrate 34 Glass light transmitting substrate 35 Etching prevention film

Claims (20)

[Claims] [Claim 1] A step of making a silicon substrate porous;
forming a non-porous silicon single crystal layer on the porous silicon substrate; bonding the surface of the non-porous silicon single crystal layer to a light-transmitting glass substrate; and the porous silicon substrate. a selective etching step of porous silicon in which the porous silicon is removed by electroless wet chemical etching by immersing the substrate in a mixed solution of hydrofluoric acid and alcohol. 2. The method for manufacturing a semiconductor substrate according to claim 1, wherein the silicon substrate to be made porous is of P type. 3. The method for manufacturing a semiconductor substrate according to claim 1, wherein the silicon substrate to be made porous is of N type. 4. The method of manufacturing a semiconductor substrate according to claim 1, wherein the non-porous silicon single crystal formed on the porous silicon substrate has a thickness of 50 microns or less. 5. The method for manufacturing a semiconductor substrate according to claim 1, wherein the bonding step is performed in an atmosphere containing oxygen. 6. The method for manufacturing a semiconductor substrate according to claim 1, wherein the bonding step is performed in an atmosphere containing nitrogen. 7. The method for manufacturing a semiconductor substrate according to claim 1, wherein the non-porous silicon single crystal layer is formed by epitaxial growth. 8. Forming the non-porous silicon single crystal layer by a method selected from molecular beam epitaxial method, CVD method, liquid phase growth method, and bias sputtering method.
A method for manufacturing a semiconductor substrate according to claim 1. 9. The method for manufacturing a semiconductor substrate according to claim 8, wherein the CVD method is a plasma CVD method, a low pressure CVD method, or a photoCVD method. 10. The method for producing a semiconductor substrate according to claim 1, wherein the step of making it porous is anodization. 11. The anodization is performed in an HF solution.
The method for manufacturing a semiconductor substrate according to claim 10. 12. The method for manufacturing a semiconductor substrate according to claim 1, wherein the non-porous silicon single crystal layer is neutral or N-type. 13. The method for manufacturing a semiconductor substrate according to claim 1, wherein a material having excellent chemical etching resistance is coated after the bonding step and before the selective etching step. 14. A step of making the other side of a silicon single crystal substrate with one side N-type porous, and bonding the one side of the silicon single crystal substrate to a light-transmitting glass substrate. and a porous silicon selective etching step of removing porous silicon by electroless wet chemical etching by immersing the porous silicon single crystal substrate in a mixed solution of hydrofluoric acid and alcohol. A method for manufacturing a semiconductor substrate. 15. The method for manufacturing a semiconductor substrate according to claim 14, wherein the silicon single crystal substrate has one surface made of N type and the other surface of the silicon single crystal substrate made of P type. 16. The method of manufacturing a semiconductor substrate according to claim 14, wherein the thickness of the N-type region of the silicon single crystal substrate with one surface side made N-type is 50 microns or less. 17. The method for producing a semiconductor substrate according to claim 14, wherein the step of making it porous is anodization. 18. The anodization is performed in an HF solution.
The method for manufacturing a semiconductor substrate according to claim 17. 19. Preparation of the semiconductor substrate according to claim 14, wherein the N-type region of the silicon single crystal substrate whose one surface side is N-type is formed by proton irradiation or epitaxial growth. Method. 20. The method for manufacturing a semiconductor substrate according to claim 14, wherein a material having excellent chemical etching resistance is coated after the bonding step and before the selective etching step.