JPH10135500A - Manufacture of thin film semiconductor, solar cell and light emission element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform easy and sure lead-out of a terminal with low resistance by adopting a process of growing a semiconductor film on the surface of a porous layer and a process or peeling a semiconductor film from a substrate through a porous layer. SOLUTION: After forming a porous layer 12, firstly a heat-treatment, that is anneal treatment of a semiconductor 11 is performed inside a normal atmosphere Si epitaxial growth device in an H2 atmosphere at 1100 deg.C. Thereby, the surface of the porous layer 12 is smoothed thus more weakening a strength near the interface between a middle porous layer and a high porous layer 12H inside the porous layer 12. Then, on the surface of the porous layer 12, an epitaxial semiconductor film 13 with a thickness of about 5μm due to a single crystal Si is formed. In this condition, the epitaxial semiconductor film 13 is peeled from the semiconductor substrate 11. Because of thus peeling, an adhesive material 14 is applied respectively to the surface of the epitaxial semiconductor film 13 and to the back of the semiconductor substrate 11 so as to paste a flexible supporting substrate 15 of a PEt resin sheet by means of these adhesive material 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a thin film semiconductor, a solar cell, and a light emitting device.

[0002]

2. Description of the Related Art Various materials have been studied as solar cell materials. However, silicon Si is mainly used because of its abundant resources and no fear of pollution, and the global production of solar cells is 90%.
The above is the Si solar cell. By the way, the issues of the solar cell are low cost, high light-to-electricity conversion efficiency, high reliability, and short energy recovery years. Single crystal Si is most suitable for high conversion efficiency and high reliability requirements, but this single crystal Si has a problem in cost reduction. Therefore, at present, solar cells, especially high-area solar cells, use thin polycrystalline Si.
Research and development of solar cells based on thin films and solar cells based on thin film amorphous Si are being actively conducted.

[0003] Thin polycrystalline Si solar cells are made by purifying Si from metal-grade Si using a plasma or the like, and then purifying the Si by casting. An ingot is manufactured by a casting method. Crystalline Si is produced. However, such high-speed slicing techniques as removal of boron and phosphorus from metal-grade Si, production of high-quality crystal ingots by a casting method and enlargement of wafers, and high-speed slicing techniques such as multi-wire require high technology. For this reason, it has not yet been possible to produce sufficiently low-cost and high-quality thin polycrystalline Si. The thickness of the thin polycrystalline Si fabricated in this manner is about 200
It is about μm and does not have flexibility.

On the other hand, since amorphous Si can be formed on a resin substrate surface by a CVD (chemical vapor deposition) method, it can be formed as a flexible thin-film amorphous Si. Although a wide solar cell can be formed, the conversion efficiency is lower than that of polycrystalline Si or single crystal Si, and there is a problem in deterioration of the conversion efficiency during use.

[0005] Single crystal Si can be expected to have high conversion efficiency and high reliability. Thin-film single-crystal Si can be manufactured by SOI (Silicon On Insulator) technology, which is a manufacturing technology for integrated circuits and the like, but has low productivity, considerably high manufacturing costs, and has problems in application to solar cells. . In addition, single crystal S
In the production of i, it is difficult to form it on a plastic substrate or a glass substrate having low heat resistance because the process temperature is relatively high. Since it is difficult to form single-crystal Si on a plastic substrate as described above, it is difficult to produce flexible thin-film single-crystal Si.

However, in the case of a solar cell, such as a windowpane with a solar cell in which the solar cell is disposed on the surface of the windowpane or a solar car in which the solar cell is disposed on a roof or the like, a flexible solar cell is used. This is desirable from the viewpoints of simplification of its manufacture and easy arrangement of a rational arrangement with a large light receiving area. However, there is currently only amorphous Si as semiconductor Si that can constitute such a flexible solar cell.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a thin-film semiconductor for forming various semiconductor devices such as a single semiconductor and an integrated circuit, for example, a thin-film single-crystal Si can be surely mass-produced. A method of manufacturing a thin film semiconductor which can reduce the cost by this, and a solar cell capable of reliably and easily manufacturing a solar cell having high light-to-electric conversion efficiency at a low cost. And, in the case of a light-emitting element, a method for producing a light-emitting element having high luminous efficiency easily and reliably.

Further, the present invention provides a method of manufacturing a solar cell in which a terminal of the solar cell can be easily and reliably led out with low resistance.

[0009]

In a method of manufacturing a thin film semiconductor according to the present invention, a step of forming a porous layer composed of two or more layers having different porosity by changing the surface of a semiconductor substrate; A thin film semiconductor is obtained by a step of growing a semiconductor film on the surface of the porous layer and a step of peeling the semiconductor film from the semiconductor substrate via the porous layer.

In the method for manufacturing a solar cell according to the present invention, a step of changing the surface of the semiconductor substrate to form a porous layer composed of two or more layers having different porosity, A solar cell is manufactured by adopting a step of forming a multilayer semiconductor film constituting a solar cell on the surface and a step of separating the multilayer epitaxial semiconductor film from a semiconductor substrate via a porous layer.

Further, a method for manufacturing a light emitting device according to the present invention includes a porous layer forming a light emitting portion on the substrate surface side by changing the surface of the semiconductor substrate, and a separation layer having a high porosity inside the substrate. A light emitting element is manufactured by adopting a step of forming a porous layer composed of at least two layers and a step of peeling the porous layer constituting the light emitting portion from the semiconductor substrate via the separation layer.

As described above, according to the manufacturing method of the present invention, a porous layer is formed by changing the surface of a semiconductor substrate itself, a semiconductor film is formed thereon, and the semiconductor film is The thin film semiconductor is intended to constitute various semiconductor devices and the like or to constitute a solar cell by being peeled from the semiconductor substrate by breaking at the interface with the porous layer or the thin film semiconductor. The thickness can be arbitrarily small by selecting the thickness of the film. Further, the peeling from the semiconductor substrate can be reliably performed by appropriately selecting the strength of the porous layer by, for example, selecting the porosity. Further, according to the method of the present invention, the semiconductor thin film which forms the thin film semiconductor can be formed by epitaxial growth, and can be obtained with a sufficiently thin and arbitrary thickness with good yield. Therefore, in the manufacture of solar cells,
Since the active portion formed by the semiconductor thin film can be configured to be sufficiently thin and the semiconductor thin film can be configured as a single crystallized thin film of an epitaxially grown semiconductor, a solar cell having sufficiently high light-to-electric conversion efficiency can be configured. Furthermore, since it is possible to have a flexible configuration, application to various usage modes, for example, a window glass with a solar cell, a solar car, and the like becomes easy.

Further, in the light emitting device according to the present invention, a superlattice structure can be formed by forming porous layers having different porosity, and luminous efficiency can be improved.

[0014]

Embodiments of the present invention will be described.
In the present invention, the surface of the semiconductor substrate is changed, for example, by anodization to form a porous layer composed of two or more layers having different porosity (porosity). And
A semiconductor film is formed on the surface of the porous layer as, for example, a single crystal film, a polycrystalline film, or an amorphous film formed by epitaxial growth. After that, this semiconductor film is interposed through a porous layer,
The target thin film semiconductor is manufactured by peeling from the semiconductor substrate.

On the other hand, the remaining semiconductor substrate is repeatedly used in the above-mentioned thin film semiconductor production. Further, the semiconductor substrate thinned by repeated use can itself be used as a thin film semiconductor.

In the step of forming the porous layer, a layer having a low porosity is formed facing the surface, and the interface between the porous layer and the semiconductor substrate (in this specification, the interface between the semiconductor substrate and the A layer having a high porosity is formed on the deepest surface of the semiconductor substrate (that is, the surface of the semiconductor substrate that has not been made porous), that is, on a position inward from the surface.

In the porous layer forming step, for example, a surface layer having a low porosity, an intermediate porosity layer formed between the surface layer and the semiconductor substrate and having a porosity higher than that of the surface layer, A high porosity layer having a higher porosity than the intermediate porosity layer can be formed in the porosity layer or at the lower layer of the intermediate porosity layer, that is, at the interface with the semiconductor substrate.

The formation of the porous layer can be carried out by anodization. This anodization is performed in at least two or more steps having different current densities. That is, at least a step of anodizing the surface of the semiconductor substrate with a low current density and a step of subsequently anodizing with a higher current density are employed.

For example, in anodization, a step of anodizing the surface of a semiconductor substrate at a low current density, a step of anodizing at an intermediate low current density slightly higher than the low current density, and a step of further anodizing at a higher current density And a step of chemical formation.

In the anodization, the anodization at a high current density can be performed intermittently at a high current density.

In the anodization at an intermediate low current density in the anodization for forming the porous layer, the current density can be increased gradually or stepwise.

The anodization can be performed in an electrolytic solution containing hydrogen fluoride and ethanol, or in an electrolytic solution containing hydrogen fluoride and methanol.

In the anodization step, when changing the current density, the composition of the electrolytic solution can also be changed.

After the porous layer is formed, it is preferable to heat in a hydrogen gas atmosphere at normal pressure or reduced pressure or in a vacuum, or to heat in a Group 8 element gas such as He, Ne, Ar, or K. . It is preferable that the porous layer is thermally oxidized before the heating step.

The shape of the semiconductor substrate can take various configurations. For example, it can be formed into various shapes such as a wafer shape such as a disk shape, or a cylindrical ingot obtained by pulling a single crystal, and a peripheral surface thereof serving as a substrate surface.

The semiconductor substrate may be a single crystal substrate of silicon Si, a polycrystalline substrate of Si in some cases, or GaAs, G
Although it can be constituted by various semiconductor substrates such as a compound semiconductor substrate such as aP, GaN, and SiGe single crystal,
It is preferable to use a Si single crystal substrate for manufacturing a Si single crystal thin film or a solar cell using the Si single crystal thin film.

Further, the semiconductor substrate can be constituted by a semiconductor substrate doped with n-type or p-type impurities or a semiconductor substrate containing no impurities. However, in the case of performing anodization, it is desirable to use a so-called p ⁺ Si substrate, which is a low-resistivity semiconductor substrate doped with p-type impurities at a high concentration. When ap ⁺ -type Si substrate is used as the semiconductor substrate, a p-type impurity such as boron B
However, it is desirable to use a Si substrate doped at about 10 ¹⁹ atoms / cm ³ and having a resistance of about 0.01 to 0.02 Ωcm. Then, when the p ⁺ -type Si substrate is anodized, fine pores elongated in a direction substantially perpendicular to the surface of the substrate are formed, and the p ⁺ -type Si substrate becomes porous while maintaining the crystallinity. Thus, a desirable porous layer is formed.

A semiconductor film is formed on the porous layer while maintaining the crystallinity. In this case, since the porous layer maintains the crystallinity, the semiconductor film can be epitaxially grown. The semiconductor film is formed by MOCVD (metal organic chemical vapor deposition), CV
D (chemical vapor deposition), MBE (molecular beam epitaxy), sputtering, etc.
It can be formed as a polycrystalline or amorphous film,
Furthermore, for example, after being formed as an amorphous film, it can be polycrystal or single crystal by annealing. In addition, this semiconductor film can be formed of a single-layer semiconductor film, but can be a multilayer semiconductor film of two or more layers in the case of forming a solar cell or the like.

As described above, the semiconductor film epitaxially grown on the semiconductor substrate is separated from the semiconductor substrate. Prior to the separation, a support substrate such as a support substrate flexible resin sheet is bonded to the semiconductor film to form a contact with the support substrate. After the integration with the semiconductor film, the semiconductor film and the supporting substrate can be separated from the semiconductor substrate via the porous layer formed on the semiconductor substrate.

The support substrate is not limited to a flexible sheet, but may be a glass substrate, a resin substrate, or a flexible or rigid, so-called rigid (rigid) transparent printed board on which, for example, required printed wiring is formed. Things.

On the surface of the semiconductor substrate, a porous layer composed of two or more layers having different porosity is formed. The outermost porous layer has a relatively small porosity and a dense porous layer. And a porous layer having a relatively high porosity is formed along the substrate surface inside the surface layer, that is, on the lower layer side, so that the epitaxial semiconductor film can be favorably grown on the porous layer. This reduces the mechanical strength due to its own high porosity, or weakens due to the strain due to the difference in lattice constant between this porous layer and the other layers, and facilitates the separation, ie, separation, of the epitaxial semiconductor film in this layer. Can be done. For example, it is possible to form a porous layer that is weak enough to be separated by application of ultrasonic waves.

In a high porosity layer formed on the inner side of the surface of the porous layer and having a high porosity, the larger the porosity, the easier the above-mentioned peeling becomes. However, if the porosity is too large,
Before the above-described epitaxial semiconductor film peeling treatment, peeling may occur or the porous layer may be damaged. Therefore, the porosity of the high porosity layer is set to 40% or more and 70% or less.

When a high porosity layer is formed on the porous layer, the strain increases as the porosity increases.
When the effect of this strain greatly extends to the surface layer of the porous layer,
There is a possibility that cracks are generated in the surface layer. Also,
In this way, when the influence of strain occurs up to the surface of the porous layer,
Crystal defects are generated in a semiconductor film epitaxially grown thereon. Therefore, the porous layer has a higher porosity than the surface layer and a buffer layer between the high porosity layer and the low porosity surface layer. As a result, an intermediate porosity layer having a low porosity and an intermediate porosity is formed. By doing so, the porosity of the high porosity layer is increased to such an extent that the above-mentioned epitaxial semiconductor film can be reliably separated, and an epitaxial semiconductor film having excellent crystallinity can be formed. .

The anodization for making the surface of the semiconductor substrate porous is performed by a known method, for example, the surface technology Vo by Ito et al.
l. 46, no. 5, pp. 8-13, 1995 [Anodic formation of porous Si]. That is, for example, it can be performed by a double cell method whose schematic configuration diagram is shown in FIG. This method comprises a two-cell electrolytic solution tank 1 having first and second tanks 1A and 1B.
Is used. Then, a semiconductor substrate 11 on which a porous layer is to be formed is arranged between the two tanks 1A and 1B, and a pair of platinum electrodes 3A to which a DC power supply 2 is connected is provided in both tanks 1A and 1B.
And 3B are arranged. First of electrolytic solution tank 1
In the second tanks 1A and 1B, an electrolytic solution 4 containing, for example, hydrogen fluoride HF and ethanol C ₂ H ₅ OH, or hydrogen fluoride HF and methanol CH
An electrolytic solution 4 containing ₃ OH is accommodated, arranged in the first and second tanks 1A and 1B so that both surfaces of the semiconductor substrate 11 are in contact with the electrolytic solution 4 and both electrodes 3
A and 3B are immersed in the electrolytic solution 4. And
A tank 1A on the front side of the semiconductor substrate 11 on which a porous layer is to be formed.
With the electrode 3A side immersed in the electrolytic solution 4 inside as the negative electrode side, the DC power supply 2 is connected and electricity is supplied between the electrodes 3A and 3B. Thus, the semiconductor substrate 11
Power is supplied with the side facing the anode and the electrode 3A facing the cathode, whereby the surface of the semiconductor substrate 11 facing the electrode 3A is eroded and made porous.

According to the two-cell method, it is not necessary to form an ohmic electrode on the semiconductor substrate, and it is possible to prevent impurities from being introduced from the ohmic electrode into the semiconductor substrate.

The anodization is not limited to the above-described two-cell method, but may be, for example, a single-cell method schematically shown in FIG. In this example, a single electrolytic solution tank 1 is provided, and for example, a semiconductor substrate 11 for anodizing is opposed to an opening 1H provided on a bottom surface thereof.
They are arranged in a liquid-tight manner via an O-ring 5. The electrolytic solution 4 is accommodated in the electrolytic solution tank 1 so that the electrolytic solution 4 comes into contact with the surface of the semiconductor substrate 11 disposed at the bottom, on which the anode is formed. One electrode 3A made of, for example, a Pt electrode plate is immersed in the electrolytic solution 4 in the tank 1.
On the back surface of the semiconductor substrate 11, the other electrode 3B made of, for example, a carbon electrode is placed in surface contact so as to face as much as possible over the entire surface on which anodization is performed. Then, the DC power supply 2 is inserted between the electrodes 3A and 3B with the electrode 3A immersed in the electrolytic solution 4 serving as the negative electrode side, and electricity is supplied. Even in this case,
The surface of the semiconductor substrate 11 on the side facing the electrode 3A is anodized.

The selection of the conditions for the anodization changes the structure of the porous layer to be formed, thereby changing the crystallinity and removability of the semiconductor film formed thereon.

In the method of the present invention, as described above,
A porous layer composed of two or more layers having different porosity is formed. In this case, in the anodizing treatment, a multi-step anodizing method of two or more steps having different current densities is employed. Specifically, first anodization is performed at a low current density in order to produce a relatively dense porous layer having a low porosity on the surface, that is, a fine pore having small pores.
Since the thickness of the porous layer is proportional to the time, the anodization is performed for such a time that the desired thickness is obtained. Thereafter, if the second anodization is performed at a considerably high current density, at least the surface layer is formed by the low-porosity porous layer formed first,
On the lower side (inside), a porous layer having a high porosity and a high porosity is formed. That is, a porous layer having at least a low porosity layer having a low porosity and a high porosity layer having a high porosity is formed.

In this case, near the interface between the porous layer having a low porosity and the porous layer having a high porosity, a large strain is generated due to a difference in lattice constant between the two. When this distortion exceeds a certain value, the porous layer separates into two. Therefore, if a porous layer is formed under anodizing conditions near the boundary condition of whether separation due to this strain or separation due to reduction in mechanical strength due to porosity occurs or not, epitaxial growth will occur on this porous layer. Semiconductor film
Separation can be easily performed through this porous layer.

In this case, the first anodization at a low current density uses, for example, a p-type silicon single crystal substrate of 0.01 to 0.02 Ωcm, and uses, for example, hydrofluoric acid (HF) as an electrolytic solution.
And a mixture of ethanol (C ₂ H ₅ OH) and HF
(47-50% solution): C ₂ H ₅ OH (industrial ethanol (approximately 95% solution)) = 1: When 1 (volume ratio),
This is performed at a low current density of about 0.5 to 10 mA / cm ² for several minutes to several tens minutes. The second anodization with a high current density is performed at a current density of, for example, about 40 to 300 mA / cm ^{2 for} 1 to 10 seconds, preferably about 3 seconds.

In the case where the porous layer is formed by the first and second two-stage anodization, if the surface of the porous layer is reduced in porosity in order to form a good semiconductor film thereon, Since the strain occurring between the porous layer and the highly porous layer inside the porous layer becomes considerably large, the influence of the strain extends to the surface of the porous layer, and in this case, as described above, cracks are generated and There is a possibility that crystal defects may occur in the epitaxial semiconductor film formed thereon. Therefore, in the porous layer, between the low porosity surface layer and the high porosity layer, as a buffer layer for relaxing the strain generated by these, the porosity is higher than the surface layer, and the high porosity layer An intermediate porosity layer having a relatively low porosity is formed. Specifically, a first anodization at a low current density is first performed, a second anodization at a current density slightly higher than the first anodization is performed, and then the third anode is formed at a much higher current density than those. Perform chemical conversion. The conditions for the first anodization are not particularly limited. For example, a p-type silicon single crystal substrate of 0.01 to 0.02 Ωcm is used, and the above-mentioned HF: C ₂ H is used as an electrolytic solution.
When using ₅ OH = 1: 1, 0.5 to ³ mA / cm ²
, The current density of the second anodization is, for example, 3 to 20 m
A / cm ² , and the current density of the third anodization is, for example, 4
It is preferable to perform the process at about 0 to 300 mA / cm ² . For example, when anodizing is performed at a current density of 1 mA / cm ² , the porosity is about 16%. When anodizing is performed at a current density of 7 mA / cm ² , the porosity is about 26% and 200 mA / cm ^2.
When anodizing is carried out at a current density of about 40 to 70 porosity,
%. When epitaxial growth is performed on such an anodized porous layer, an epitaxial semiconductor film having good crystallinity can be formed.

When the anodization is performed at three current densities as described above, the low porosity surface layer formed by the first anodization maintains the low porosity as it is, and the second anodization forms the porous layer. An intermediate porosity layer having a slightly higher rate, ie, a buffer layer, is formed below (inside) the surface layer, that is, on the side closer to the interface with the semiconductor substrate from the surface of the porous layer,
The porous layer has a two-layer structure of a surface layer and an intermediate porosity layer.
When the current density of the high porosity layer formed by the third anodization is about 90 mA / cm ² or more, the high porosity layer formed by the third anodization has an intermediate porosity in the intermediate porosity layer formed by the second anodization. It is formed at an intermediate portion in the thickness direction of the porous layer.

In the formation of the intermediate porosity layer, the low porosity surface layer and the high porosity can be obtained by performing the anodic oxidation for forming the intermediate porosity layer in multiple stages or gradually, for example, under conditions in which the current density is changed. An intermediate porosity layer whose porosity is increased stepwise or inclined from the surface layer toward the high porosity layer side is formed between the porosity layer and the porosity layer. By doing so, the strain between the surface layer and the high porosity layer is further alleviated, and an epitaxial semiconductor film having good crystallinity can be more reliably epitaxially grown.

The separation surface is formed by a large strain caused by a difference in lattice constant at the interface between the release layer (separation layer) of the high porosity layer and the buffer layer having a small porosity immediately before the separation layer. If a device is devised when performing the anodization for forming the separation layer, the separation surface is more easily separated. It is a high current density anodization for forming a porosity separation layer. For example, instead of applying a constant current for 3 seconds,
Anodization is stopped after 1 second of energization, and after the required time has elapsed,
For example, after standing for about 1 minute, energizing again at the same or different high current density for another minute, then stopping anodization, and after elapse of a required time, for example, leaving for about 1 minute, again at the same or different high current density This is an intermittent energization method in which anodization is stopped by energizing for one second. When an appropriate anodizing condition is selected by using this method, a release layer of the porous layer is formed at the interface with the semiconductor substrate, that is, on the lowermost surface of the porous layer. That is, in this case, the separation surface is not at the inside of the intermediate porous layer, that is, the buffer layer as described above, but at the interface side of the porous layer with the semiconductor substrate.

As described above, when the buffer layer, ie, the intermediate porosity layer is formed only on the surface layer side of the high porosity layer, the high porosity layer and the surface where distortion occurs in the porous layer are formed. Are maximized, the buffer effect of the intermediate porosity layer is maximized, and a semiconductor film having good crystallinity can be formed. Further, when the intermediate porous layer is formed only on the surface side as described above, the overall thickness of the porous layer can be reduced, and the thickness of the semiconductor substrate consumed for forming the porous layer can be reduced. Can be reduced, and the number of repeated use of the semiconductor substrate can be increased.

Thus, by selecting the anodizing conditions,
On the separation surface, a large strain can be applied, and the influence of the strain can be prevented from being exerted on the epitaxial growth surface of the semiconductor film.

In order to epitaxially grow a semiconductor with good crystallinity on the porous layer, it is desired to reduce the size of micropores which are seeds for crystal growth on the surface layer of the porous layer.
As one of means for reducing the fine pores in the surface layer, there is a method of increasing the HF concentration in the electrolytic solution during anodization. That is, in this case, in the low current anodization for forming the surface layer, an electrolytic solution having a high HF concentration is used. Next, an intermediate porosity layer serving as a buffer layer is formed. After that, the HF concentration of the electrolytic solution is reduced, and finally anodization with a high current density is performed. By doing so, the fine pores in the surface layer can be reduced, so that an epitaxial semiconductor film with good crystallinity can be formed thereon, and in the high porosity layer, Since the porosity can be made sufficiently high, the epitaxial semiconductor film can be satisfactorily peeled off.

The change of the electrolytic solution in the anodization of the porous layer may be performed, for example, in the formation of the surface layer by anodization using an electrolytic solution of HF: C ₂ H ₅ OH = 2: 1 as the electrolytic solution. In the formation of the intermediate porosity layer as the buffer layer, anodization using an electrolytic solution having a slightly lower HF concentration, for example, an electrolytic solution with HF: C ₂ H ₅ OH = 1: 1 is performed to further increase the porosity. In forming the layer, the electrolytic solution further reduces the HF concentration,
For example, high current density anodization is performed using an electrolytic solution of HF: C ₂ H ₅ OH = 1: 1 to 1: 2.

In the formation of the porous layer described above,
When changing the current density from the formation of the surface layer to the formation of the intermediate porosity layer, it is possible to temporarily stop the anodization and then start the energization for the next anodization, or to perform the anodization once. The current density can be continuously changed without stopping, that is, without stopping energization.

When the anodization is performed in a dark place where light is blocked, the irregularities on the surface of the porous layer are reduced.
The crystallinity of a semiconductor film epitaxially grown thereon can be improved.

The porous layer of anodized silicon can be used as a visible light emitting device. In this case, it is preferable to perform anodization while irradiating light, thereby increasing luminous efficiency. Further, when oxidized, a blue shift occurs in the wavelength. The semiconductor substrate may be p-type or n-type, but is preferably a high-resistance semiconductor with no impurity introduced.

Through the above steps, a semiconductor substrate having a porous layer formed on its surface (one or both surfaces) can be obtained. The thickness of the entire porous layer is not particularly limited, but is 1 to 50 μm, preferably 3 to 15 μm, and usually 8 μm.
It can be about as thick. It is preferable that the thickness of the entire porous layer be as small as possible so that the semiconductor substrate can be used as repeatedly as possible.

In addition, prior to epitaxially growing a semiconductor on the porous layer, for example, when annealing is performed in a hydrogen gas atmosphere, the natural oxide film formed on the surface of the porous layer is completely removed, and Oxygen atoms in the porous layer can be removed as much as possible, the surface of the porous layer becomes smooth, and an epitaxial semiconductor film having good crystallinity, for example, can be formed. In addition, the above-described pretreatment by annealing in hydrogen can further reduce the strength of the interface between the high porosity layer and the intermediate porosity layer, thereby making it easier to separate the epitaxial semiconductor film from the substrate. be able to. In this case, the hydrogen annealing is performed in a temperature range of, for example, about 950 ° C. to 1150 ° C.

If the porous layer is oxidized at a low temperature before hydrogen annealing, the inside of the porous layer is oxidized. Therefore, even if thermal annealing is performed in a hydrogen gas atmosphere, the porous layer has a large structure. No change occurs. That is, distortion from the peeling layer to the surface of the porous layer is not easily transmitted, and a high-quality crystalline epitaxial semiconductor film can be formed. In this case, the low-temperature oxidation is performed, for example, in a dry oxidation atmosphere at 40.degree.
It can be performed at 0 ° C. for about 1 hour.

Then, as described above, the semiconductor is epitaxially grown on the surface of the porous layer. In the epitaxial growth of this semiconductor, since the porous layer formed on the surface of the single crystal semiconductor substrate maintains the crystallinity while being porous, the epitaxial growth on the porous layer is possible. The epitaxial growth on the surface of the porous layer can be performed by, for example, a CVD method at a temperature of, for example, 700 ° C. to 1200 ° C.

In any of the above-described annealing and the formation of the semiconductor film, the semiconductor substrate may be heated to a predetermined substrate temperature by a so-called susceptor heating method, or may be directly applied to the semiconductor substrate itself. It is possible to adopt an electric heating method or the like in which an electric current is applied to heat.

The semiconductor film epitaxially grown on the porous layer may be a single-layer semiconductor film or a multi-layer semiconductor film formed by laminating a plurality of semiconductor layers. The semiconductor film may be the same material as the semiconductor substrate, or may be a different material. For example, a single crystal Si semiconductor substrate is used, and a porous semiconductor layer formed on the surface thereof is made of Si or a compound semiconductor such as GaAs, or a Si compound such as Si _1-y G
Toka an e _y is epitaxially grown, they equal to appropriately combined lamination, can make various epitaxial growth.

On the other hand, when a thin film semiconductor made of a compound semiconductor is formed, a compound semiconductor substrate can be used as a semiconductor substrate. In this case, if anodization is performed on the substrate, a porous layer is similarly formed on the surface. A semiconductor substrate can be configured. When a compound semiconductor is epitaxially grown on the porous layer, a lattice mismatch can be reduced as compared with, for example, the case where the compound semiconductor is epitaxially grown on a Si semiconductor substrate. Therefore, a thin film compound semiconductor having good crystallinity can be obtained. Can be formed.

The semiconductor film formed on the porous layer includes:
An n-type or p-type impurity can be introduced during the film formation, for example, during epitaxial growth. Or,
After the formation of the semiconductor film, the introduction of impurities can be performed entirely or selectively by ion implantation, diffusion, or the like. In this case, the conductivity type, impurity concentration, and type are selected according to the purpose of use.

The thickness of the semiconductor film can also be appropriately selected according to the use of the thin film semiconductor. For example, when a semiconductor integrated circuit is formed on a thin film semiconductor, the operating layer of the semiconductor element has a thickness of about several μm, and thus can be formed to a thickness of about 5 μm, for example.

When a thin film semiconductor is formed by forming a semiconductor film of single crystal silicon by epitaxial growth or the like to form a solar cell, the semiconductor film is, for example, a p-type semiconductor film in order from the porous layer side. A multi-layer semiconductor film can be formed by epitaxially growing a p ⁺ semiconductor layer having a high impurity concentration, a p ⁻ semiconductor layer having a low p-type impurity concentration, and an n ⁺ semiconductor layer having an n-type high impurity concentration. Although the impurity concentration and the film thickness of these layers are not particularly limited, for example, the p ⁺ type semiconductor layer has a film thickness in the range of 0 to 1 μm, typically about 0.5 μm, and a boron B concentration of 10 μm.
^{18 ~10 20} atoms / cm ³ range, typically about 10 ¹⁹ the atom
s / cm ³ , the p-type semiconductor layer has a thickness of 1 to 30 μm, typically about 5 μm, and a boron concentration of 10 ¹⁴ to 10
^The thickness of the n ⁺ type semiconductor layer is in the range of 0.1 to 1 μm, in the range of ¹⁷ atoms / cm ³ , typically about 10 ¹⁶ atoms / cm ³ ,
Typically, the concentration of phosphorus P or arsenic As is in the range of 10 ¹⁸ to 10 ²⁰ atoms / cm ³ , typically about 1 μm.
It is preferable to be about 0 ¹⁹ atoms / cm ³ .

Further, the semiconductor film is formed by forming a p ⁺ -type Si layer, a p-type Si _1-x Ge _x graded layer, an undoped Si _1-y Ge _y layer, and an n-type Si _1-x Ge _x from the porous layer side. A semiconductor film is formed by epitaxially growing a graded layer and an n ⁺ -type silicon layer in this order, whereby a double heterostructure solar cell can be manufactured. A typical example of each layer constituting the double hetero structure is p ⁺
The type Si layer, about impurity concentration 10 ¹⁹ atoms / cm ^3, thickness of 0.5μm or so, as the p-type Si _1-x Ge _x graded layers, the impurity concentration is 10 ¹⁶ atoms / cm ³ or so, The thickness of the undoped Si _1-y Ge _y layer is about 0.7 μm, the thickness is about 1 μm, and the thickness of the n-type Si
_1-x Ge as the _x graded layer, an impurity concentration of 1
0 ¹⁶ atoms / cm ³ or so, the thickness is 1μm or so, as the and n ⁺ -type Si layer, an impurity concentration of ¹⁰ 10 cm ^-3 or so, it is preferable that the film thickness is set to about 0.5 [mu] m. In addition, p-type,
The composition ratio x of Ge in the n-type Si _1-x Ge _x graded layer may be gradually increased from x = 0 of each of the layers present on both sides to _{y of} undoped Si _1-y Ge _y. preferable. Thereby, since lattice constants are matched at each interface, good crystallinity can be obtained.

In such a solar cell having a double hetero structure, carriers and light can be effectively confined in the undoped Si _1-y Ge _y layer at the center thereof, so that high conversion efficiency can be obtained.

The above-described semiconductor film can be peeled off from the semiconductor substrate and used as it is as a thin-film semiconductor.

Alternatively, while the semiconductor film is weakly fixed to the semiconductor substrate via the porous layer, the semiconductor film is subjected to necessary processing, for example, as a solar cell, and then the supporting substrate is bonded to the semiconductor film. Then, after the support substrate and the semiconductor film are integrated, the semiconductor film is separated from the semiconductor substrate together with the support substrate.

The support substrate in the solar cell can be constituted by various substrates such as a glass plate such as a window glass, a metal substrate, a ceramic substrate, or a flexible substrate made of a transparent resin film or sheet (hereinafter simply referred to as a sheet). .

Next, steps for constructing a solar cell will be described. This step can be performed after the semiconductor film is separated from the semiconductor substrate described above, or can be performed while being integrated with the semiconductor substrate.

As described above, a multilayer silicon semiconductor film is formed on the semiconductor substrate having the above-described porous layer formed on the surface, for example, by epitaxial growth. afterwards,
For example, a thermal oxidation process is performed to form an oxide film having a thickness of about 10 to 200 nm on the surface. Then, if necessary, an oxide film on the surface of the semiconductor film is formed in a pattern of a wiring layer using a photolithography technique. Alternatively, an opening may be formed only at a place where connection with the semiconductor film is necessary. afterwards,
For example, a conductive layer constituting an electrode and a wiring layer, for example, a single-layer metal layer such as Al or a multilayer metal layer formed by laminating a plurality of metal layers is entirely formed by vapor deposition or the like, and this is formed by photolithography. It is patterned into required electrodes and wiring patterns by etching. Also, the formation of this electrode and wiring patterning
For example, a printing method can be used.

Further, for example, a so-called printed board on which required electrodes and wiring patterns, so-called printed wiring are formed, is prepared in advance on a transparent resin sheet, and this printed board and the porous layer on the surface of the semiconductor substrate described above are prepared. Corresponding portions are electrically bonded and bonded to the semiconductor film formed thereon. At this time, the electrodes are connected to each other by, for example, soldering. Further, portions other than the electrodes can be bonded using a transparent adhesive such as an epoxy resin.

As described above, it has been conventionally impossible to bond a printed circuit board and a thin film single crystal silicon (Si), but in the present invention, it can be performed very easily. The invention is not limited to a printed circuit board, and a transparent resin sheet may be attached. After bonding a supporting substrate such as a printed circuit board or a transparent resin sheet, a tensile stress is applied between the substrate and the semiconductor substrate to form a porous layer having a high porosity or a high porosity layer and an intermediate porous layer. interface,
Alternatively, destruction occurs at the interface between the high porosity layer and the semiconductor substrate or the like, and the epitaxial semiconductor film can be easily peeled off from the semiconductor substrate in a state where the epitaxial semiconductor film is bonded to a supporting substrate such as a printed circuit board. In this manner, for example, a flexible solar cell in which a thin-film semiconductor solar cell is formed on the surface of a supporting substrate such as a printed circuit board can be obtained.

In this case, a porous layer may remain on the back surface of the semiconductor film opposite to the side where the printed circuit board is bonded, for example, due to peeling from the semiconductor substrate. In this case, the porous layer can be removed by, for example, etching, but in a state where the porous layer is left, a metal film such as a silver paste is formed on the porous layer, and the other ohmic electrode of the solar cell is formed. In other words, by increasing the light utilization rate as the light reflecting surface, it is possible to effectively improve the photoelectric conversion efficiency. Furthermore, a protective layer can be formed by laminating a metal plate or forming a resin layer on this surface.

On the other hand, the surface of the semiconductor substrate from which the semiconductor film has been peeled is polished and the same operation is repeated again to form a solar cell or the like. The thickness of the semiconductor substrate can be, for example, about 200 to 300 μm,
On the other hand, for example, the thickness of the semiconductor substrate consumed for one solar cell fabrication is about 3 to 20 μm, and therefore, the thickness consumed even for ten repeated uses is about 30 to 200 μm.
m, the semiconductor substrate can be used sufficiently repeatedly. Therefore, according to the method of the present invention, an expensive single crystal semiconductor substrate can be repeatedly used, so that the cost can be reduced and the solar cell can be manufactured with low energy. Further, the semiconductor substrate whose thickness has been sufficiently reduced by this repetitive operation can constitute a solar cell by itself.

Next, an embodiment of the present invention will be described.
However, the invention is not limited to this embodiment. First, an embodiment of a method for manufacturing a thin film semiconductor according to the present invention will be described. In each example, the HF constituting the electrolytic solution was a 49% solution, and the C ₂ H ₅ OH was industrial ethanol.

The temperature in each embodiment was measured using a picometer.

[Embodiment 1] FIGS. 2 and 3 show a manufacturing process of this embodiment 1. FIG. First, a wafer-shaped semiconductor substrate 11 made of single crystal Si doped with boron B at a high concentration and having a specific resistance of, for example, 0.01 to 0.02 Ωcm was prepared (FIG. 2A).

Then, the surface of the semiconductor substrate 11 was anodized in a dark place to form a porous layer on the surface of the semiconductor substrate 11. In this example, anodization was performed using the anodizing apparatus having the two-tank structure described with reference to FIG. That is, the single crystal S is placed between the first and second tanks 1A and 1B.
i, a semiconductor substrate 11 is arranged, and both tanks 1A and 1B
In each case, an electrolytic solution of HF: C ₂ H ₅ OH = 1: 1 was injected. Then, a current was supplied by the DC power supply 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solutions of the electrolytic solution tanks 1A and 1B.

First, a current was applied for 13 minutes at a low current of 7 mA / cm ² . As a result, a surface layer 12S having a porosity of about 26% and a thickness of about 10 μm was formed (FIG. 2B).

After the energization is stopped once, the current is reduced to 200 mA / cm ²
At a high current density for 3 seconds. As a result, the high porosity layer 12H having a high porosity of about 60% and having a higher porosity than the surface layer 12S is sandwiched between the surface layer 12S, that is, the surface layer 12S. (FIG. 2C). Thus, the porous layer 12 was formed by superimposing the surface layer 12S and the high porosity layer 12H.

The porous layer 12 thus formed has a large difference in porosity between the surface layer 12S and the high porosity layer 12H. Distortion is applied, and the strength near this becomes extremely weak.

Thus, after the formation of the porous layer 12,
First, the semiconductor substrate 11 was subjected to a heat treatment, that is, an annealing treatment at 1100 ° C. in an H ₂ atmosphere in a normal pressure Si epitaxial growth apparatus. This heating step is performed from room temperature to 110
The heating time to 0 ° C. was about 20 minutes, and then this 1
The test was carried out by maintaining the temperature at 100 ° C. for about 30 minutes. By the annealing in H ₂ , the surface of the porous layer 12 becomes smooth, and the intermediate porosity layer 12M inside the porous layer 12 and the high porosity layer 12
The strength near the interface with H was further weakened.

Thereafter, the temperature was lowered from an annealing temperature of 1100 ° C. in an H ₂ atmosphere to 1030 ° C., and epitaxial growth of Si was performed for 17 minutes using SiH ₄ gas as a source gas. Thus, the epitaxial semiconductor film 1 of single crystal Si having a thickness of about 5 μm is formed on the surface of the porous layer 12.
3 was formed (FIG. 3A).

In this state, the epitaxial semiconductor film 13
Is peeled off from the semiconductor substrate 11. This peeling is performed by applying an adhesive 14 to each of the front surface of the epitaxial semiconductor film 13 and the back surface of the semiconductor substrate 11, and attaching a flexible support substrate 15 made of a PET (polyethylene terephthalate) resin sheet with the adhesive 14 (FIG. 3).
B). The adhesive strength of the support substrate 15 by the adhesive 14 was selected to be stronger than the separation strength of the porous layer 12.

An external force for separating the two substrates 15 from each other is applied. In this way, in the fragile porous layer 12,
Peeling occurs at or near the high porosity layer 12H or the interface with the high porosity layer 12H, and the epitaxial semiconductor film 13 is separated from the semiconductor substrate 11 (FIG. 3C).

Thus, a thin film semiconductor 23 is constituted by the separated epitaxial semiconductor film 13 (FIG. 3D). In this example, the porous layer attached to the thin film semiconductor 23 was removed by etching.

[Embodiment 2] FIGS. 4 and 5 show a manufacturing process of this embodiment 2. FIG. First, similarly to the first embodiment, boron B is doped at a high concentration and the specific resistance is, for example, 0.01.
A wafer-like semiconductor substrate 11 made of single-crystal Si having a thickness of about 0.02 Ωcm was prepared (FIG. 4A).

Then, the surface of the semiconductor substrate 11 was anodized in a dark place to form a porous layer on the surface of the semiconductor substrate 11. In the second embodiment, as in the first embodiment, the anodizing apparatus having the two-tank structure described with reference to FIG. 1 is used, and the first and second tanks 1A and 1B are both HF: C ₂ H ₅ OH.
= 1: 1 electrolyte solution was injected. Then, a current was supplied by the DC power supply 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solutions of the electrolytic solution tanks 1A and 1B.

In Example 2, first, a current was supplied for 8 minutes at a low current density of 1 mA / cm ² . In this case, compared to the surface layer 12S in the first embodiment, the fine porosity is smaller, the dense porosity is about 16%, and the thickness is 1.7.
A μm surface layer 12S is formed (FIG. 4B). After the current was once stopped, current was applied at a current density of 7 mA / cm ² for 8 minutes. In this way, the intermediate porosity layer 12M having a porosity of about 26%, which has a larger diameter than the micropores of the surface layer 12S, and a thickness of 6.3 μm is formed below the surface layer 12S, that is, the surface layer 12S.
It was formed along the surface of the surface layer 12S inside S (FIG. 4C). Further, after the current is once stopped, the current is reduced to 200 mA / cm.
A current was passed for 3 seconds at a high current density of ² . By doing so, the intermediate porosity layer 12M, that is, the intermediate porosity layer 1
The porosity of the intermediate porosity layer is higher than that of the intermediate porosity layer 12M at the position sandwiched by the 2M, that is, the high porosity layer 12H having a porosity of about 60% and a thickness of 0.05 μm is a surface of the intermediate layer 12M. It was formed along the direction (FIG. 4D). In this way, the surface layer 12S, the intermediate porosity layer 12M,
The porous layer 12 was formed by overlapping with the high porosity layer 12H.

In the porous layer 12 thus formed, the porosity of the intermediate porosity layer 12M and that of the high porosity layer 12H are significantly different. A large strain is applied in the vicinity of the interface, and the strength in the vicinity becomes extremely weak.

After the formation of the porous layer 12 in this manner, annealing is performed in the same manner as in Example 1, epitaxial growth of Si is performed, and peeling treatment is performed.

That is, first, the semiconductor substrate 11 was annealed in a normal pressure Si epitaxial growth apparatus in an H ₂ atmosphere. This annealing or heating step is performed from room temperature to 11
The heating and heating time to 00 ° C. was set to about 20 minutes, and then the temperature was kept at 1100 ° C. for about 30 minutes. Since the H ₂ annealing becomes smoother when the micropores in the porous layer are small, the surface layer 12S in which the micropores in the porous layer 12 are small becomes smoother by the annealing in H _2. 12, an intermediate porosity layer 12M and a high porosity layer 12
The strength near the interface with H was further weakened.

Thereafter, the temperature was lowered from an annealing temperature of 1100 ° C. in H ₂ to 1030 ° C., and epitaxial growth of Si was performed for 17 minutes using SiH ₄ gas as a source gas. In this way, an epitaxial semiconductor film 13 of single-crystal Si having a thickness of about 5 μm was formed on the surface layer 12S of the porous layer 12 (FIG. 5A).

In this state, an adhesive 14 is applied to the front surface of the semiconductor film 13 and the back surface of the semiconductor substrate 11, respectively, and a PET sheet (not shown) is bonded by the adhesive 14 to a strength higher than the separation strength of the porous layer 12. Adhesion is applied with high strength, and an external force for pulling apart each other is applied in the same manner as in Example 1. By doing so, the highly porous layer 12
H or the interface between the intermediate porosity layer 12M and the high porosity layer 12H or in the vicinity thereof, separation occurs, and the epitaxial semiconductor film 13 is separated from the semiconductor substrate 11 (FIG. 5).
B).

The thin film semiconductor 23 is constituted by the epitaxial semiconductor film 13 thus separated. In this example, the porous layer attached to the thin film semiconductor 23 was removed by etching.

In Example 2, the surface layer 12S having a small porosity, that is, a denser surface layer 12S was formed. Since the surface layer 12S became smoother by the above-described annealing in H ₂ , The semiconductor film 13 epitaxially grown thereon, that is, the thin film semiconductor 23 formed by this, is formed as a semiconductor having more excellent crystallinity.

Further, despite the formation of the surface layer 12S having a small porosity, an intermediate porosity layer 12M having an intermediate porosity is provided between the high porosity layer 12H and the surface layer 12S. With this arrangement, since this acts as a buffer layer for the strain applied to the surface layer, the effect of the presence of the high porosity layer 12 on the surface on which the porous layer 12 is epitaxially grown is effectively reduced. Can be done.

[Embodiment 3] FIGS. 6 and 7 show a manufacturing process of this embodiment 3. FIG. First, similarly to Examples 1 and 2, a wafer-like semiconductor substrate 11 made of single crystal Si doped with boron B at a high concentration and having a specific resistance of, for example, 0.01 to 0.02 Ωcm was prepared (FIG. 6A). ).

Then, the surface of the semiconductor substrate 11 is anodized in a dark place to form a porous layer on the surface of the semiconductor substrate 11. In Example 3, as in Examples 1 and 2, the anodizing apparatus having the two-tank structure described in FIG.
The first and second tanks 1A and 1B are both HF: C ₂
H ₅ OH = 1: electrolytic solution was injected by 1. Then, a current was supplied by the DC power supply 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solutions of the electrolytic solution tanks 1A and 1B.

[0098] Also in Example 3, first, current was supplied for 8 minutes at a low current of 1 mA / cm ² . In this manner, a dense surface layer 12S having a small diameter of the fine holes is formed as in the second embodiment (FIG. 6B).

After the current was once stopped, in Example 3, the current was supplied at a current density of 4 mA / cm ² for 3 minutes. In this way, the surface layer having a large diameter porosity 22% compared to the micropores of the 12S, the first intermediate porosity layer 12M ₁ thick 1.8μm is lower in the surface layer 12S or surface layer 12
It was formed along the surface of the surface layer 12S inside S (FIG. 6C).

After the current supply was once stopped, the current was further supplied at a current density of 10 mA / cm ² for 6 minutes. In this way, further porosity of about 30% inward from the lower or first intermediate porosity layer 12M ₁ first intermediate porosity layer 12M _1,
The thickness second intermediate porosity layer 12M _second 6.6μm is formed along the first surface of the intermediate layer 12M ₁ (Figure 6D).

Further, after the current was once stopped, the current was reduced to 200 mA /
A current was passed for 3 seconds at a high current density of cm ² . In this way, the second intermediate porosity layer 12M _2, i.e. the second
The high porosity layer 12H having a porosity of about 60% and a thickness of about 0.5 μm having a higher porosity than the intermediate porosity layer 12M ₂ is provided at a position sandwiched by the middle porosity layer 12M _2.
Was formed along the surface of each layer (FIG. 6E). In this way, the surface layer 12S, the first and second intermediate porosity layer 12M ₁ and 12M _2, the porous layer 12 is formed by superposition of the high porosity layer 12H.

[0102] Also in the thus formed porous layer 12, since the intermediate porosity layer 12M ₂ and the high porosity layer 12H is porosity greatly differs, these intermediate porosity layer 12M ₁
A large strain is applied at the interface between and the high porosity layer 12H and the vicinity of the interface, and the strength near this interface is extremely weakened.

After forming the porous layer 12 in this manner, annealing is performed in the same manner as in Examples 1 and 2,
An epitaxial semiconductor film 13 is formed by epitaxial growth of (FIG. 7A), and a PET sheet as a support substrate is joined (not shown), and the epitaxial semiconductor film 13 and the semiconductor substrate 11 are connected to each other by a high porosity 12 of the porous layer 12.
A peeling process is performed by destruction of H or its vicinity (FIG. 7B).

Thus, the thin film semiconductor 23 is formed by the epitaxial semiconductor film 13.

In the third embodiment, the high porosity layer 12
H and the surface layer 12S, the first and second two-layer intermediate porosity layers 12M ₁ and M ₂ whose porosity is increased toward the high porosity layer 12H between the _two. Is provided, which acts as a buffer layer for the strain applied to the surface layer.
Can more effectively reduce the influence of strain on the surface on which the porous layer 12 is epitaxially grown.

[Embodiment 4] In this embodiment, FIG.
Similarly to Example 2 described with reference to FIG. 5, the surface layer 12S, the intermediate porosity layer 12M, and the inside of the intermediate porosity layer 12M are formed by anodizing the surface of the single crystal Si semiconductor substrate 11 in a dark place. The porous layer 12 is formed by the high porosity layer 12H formed on the substrate, and an epitaxial semiconductor film constituting a target thin film semiconductor is epitaxially grown thereon. The layer 12S and the intermediate porosity layer 12M were formed by changing the amount of current by continuous energization.

In this embodiment, the first and second embodiments are also described.
Similarly, the boron B-doped resistivity is 0.01 to
A semiconductor substrate 11 made of single-crystal Si of 0.02 Ωcm is prepared (FIG. 4A).

Then, the first and second tanks 1A and 1A are applied to the semiconductor substrate 11 by using the two-tank anodizing apparatus described with reference to FIG.
B, in both cases, an electrolyte solution of HF: C ₂ H ₅ OH = 1: 1 was injected. A DC power source 2 is connected between the Pt electrodes 3A and 3B immersed in the electrolytic solution of the electrolytic solution tanks 1A and 1B.
Caused the current to flow.

Also in Example 4, first, a current was applied for 8 minutes at a low current density of 1 mA / cm ² . Thus, the surface layer 12S having a porosity of 16% and a thickness of 1.7 μm is formed.
Is formed (FIG. 4B).

In this embodiment, after the formation of the surface layer 12S, the current is not stopped once,
The amount of current is changed from 1 mA / cm ² to 10 mA / cm ^2.
The thickness is about 6.8 μm at which the porosity changes from about 16% to about 30% by gradually changing the porosity in 16 minutes.
m of the intermediate porosity layer 12M was formed (FIG. 4C).

Then, after the power supply is stopped once,
A current was applied at a high current density of A / cm ² for 3 seconds. By doing so, a porosity of about 60, which is higher in porosity than the intermediate porosity layer 12M, is provided in the intermediate porosity layer 12M, that is, at a position sandwiched by the intermediate porosity layer 12M.
%, And a high porosity layer 12H having a thickness of about 0.5 μm was formed (FIG. 4D). Thus, the porous layer 12 was formed by laminating the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H.

In the porous layer 12 thus formed, the porosity of the intermediate porosity layer 12M and that of the high porosity layer 12H are significantly different. A large strain is applied in the vicinity of the interface, and the strength in the vicinity becomes extremely weak.

After the formation of the porous layer 12 in this manner, the same annealing as in Examples 1 and 2 is performed in a normal pressure Si epitaxial growth apparatus in an H ₂ atmosphere to form the surface layer of the porous layer 12. 12S is smoothed and the porous layer 12
The strength is weakened near the interface between the inner middle porosity layer 12M and the high porosity layer 12H.

Thereafter, in a normal-pressure Si epitaxial growth apparatus annealed in the same manner as in Examples 1 and 2, Si was epitaxially grown for 17 minutes to obtain an epitaxial semiconductor film 13 of single-crystal Si having a thickness of about 5 μm.
Was formed (FIG. 5A).

In this state, as in the second embodiment, P
A target thin film semiconductor 23 is obtained by attaching (not shown) a support substrate using an ET sheet, peeling (FIG. 5B), and the like. Also in this case, the peeling is performed by breaking the porous layer, that is, breaking the high porosity layer 12H or its vicinity.

Also in Example 4, the porosity is small, that is, the denser surface layer 12S is formed. Since the surface layer 12S becomes smoother by the above-described annealing in H ₂ , The epitaxial semiconductor film 13 epitaxially grown thereon, that is, the thin film semiconductor 23 formed by the epitaxial semiconductor film 13 is formed as a semiconductor having better crystallinity.

In the fourth embodiment, since the current density is gradually increased in the formation of the intermediate porosity layer 12M from the surface 12S in the formation of the porous layer 12, the high porosity layer 12H is formed. from porosity between the surface layer 12S is relaxed ie buffer by intermediate porosity layer 12M strain occurring between them is effectively made from changing gradually, after an H ₂ atmosphere during annealing, flatter A smooth surface can be formed.
Therefore, the epitaxial semiconductor film formed thereon, that is, the finally obtained thin film semiconductor can be formed as a highly reliable thin film semiconductor having more excellent crystallinity.

[Embodiment 5] FIG. 8 shows a process chart of this embodiment. In this embodiment, in the porous layer 12, the high porosity layer is replaced with the semiconductor substrate of the porous layer 12. 11, that is, on the side of the interface with the nonporous portion of the substrate 11.

Also in this embodiment, the first and second embodiments are described.
Similarly, the boron B-doped resistivity is 0.01 to
A semiconductor substrate 11 made of single-crystal Si of 0.02 Ωcm is prepared (FIG. 8A).

Then, the semiconductor substrate 11 is placed in a dark place in the same manner as in Examples 1 and 2, using the two-tank anodizing apparatus described with reference to FIG.
1B and 1B, an electrolyte solution of HF: C ₂ H ₅ OH = 1: 1 was injected. And each electrolytic solution tank 1A and 1B
An electric current was passed between the Pt electrodes 3A and 3B immersed and arranged in the electrolytic solution by the DC power supply 2.

In the fifth embodiment, as in the second embodiment, first, a current was applied for 8 minutes at a low current of 1 mA / cm ² . By doing so, the porosity is 16% and the thickness is about 1.
A 7 μm surface layer 12S is formed (FIG. 8B). Then, in the same manner as in Example 2, the energization was temporarily stopped, and the energization amount was changed to 7 mA / cm ^{2 for} 8 minutes to form an anodized film.
A 6% -thick 6.3 μm-thick intermediate porosity layer 12M is
S (FIG. 8C).

Thereafter, after the current supply was once stopped, in this embodiment, a high current density of 200 mA / cm ² was intermittently supplied. That is, first, 200 mA / cm ²
Energize for 0.7 seconds, stop energizing again and hold for 1 minute, then apply 200 mA / cm ² for 0.7 seconds, stop energizing again and hold for 1 minute, then 200 m / cm ²
A / cm ² was energized for 0.7 seconds. That is, anodization was performed by supplying power three times at an intermittent high current density.
In this way, a high porosity layer 12H having a higher porosity than the intermediate porosity layer 12M, a porosity of about 60%, and a thickness of about 50 nm was formed below the intermediate porosity layer 12M (FIG. 8).
D). Thus, the porous layer 12 is formed by laminating the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H.

In the porous layer 12 thus formed, the porosity between the high porosity layer 12H and the intermediate porosity layer 12M and between the high porosity layer 12M and the base 11 are greatly different. In addition, a large strain is applied in the vicinity of the interface, and the strength in the vicinity becomes extremely weak.

After the formation of the porous layer 12 in this manner, annealing is performed at normal pressure S, as described in the second embodiment.
This is performed in an H ₂ atmosphere in an i-epitaxial growth apparatus to smooth the surface layer 12S of the porous layer 12 and at the same time to weaken the high porosity layer 12H.

Then, in the same manner as in Example 2, the annealing was performed in the annealed normal-pressure Si epitaxial growth apparatus.
The epitaxial growth of i is performed for about 17 minutes to obtain a thickness of about 5 μm.
The epitaxial semiconductor film 13 of single crystal Si was formed (FIG. 8E).

Then, as in the above-described embodiments, the epitaxial semiconductor film 13 and the semiconductor substrate 11 are separated (FIG. 8F).

As described above, the high porosity layer 12H formed by the intermittent high-current application allows the interface with the semiconductor substrate 11
Alternatively, the porosity can be extremely high, and the porosity of the highly porous layer 12H can be significantly increased by annealing in an H ₂ atmosphere. Therefore, peeling of the epitaxial semiconductor film 12 in the porous layer 12 formed by this method is very easily performed in or near the high porosity layer 12H.

FIGS. 23 and 24 show before and after annealing in the above-described H ₂ atmosphere of the cross section of the porous layer in the present embodiment between the intermediate porous layer 12M and the highly porous layer 12H. These are schematic diagrams based on microphotographs of 100,000 times each. As can be clearly understood from these comparisons, annealing in H ₂ causes crystal grains to grow, and particularly in the highly porous layer 12H, the growth of the pores is remarkable. The frost column shape (Fig. 24
In this case, a very rough layer (cross section at a portion where no column exists) is formed, and the brittleness in this portion becomes remarkable.

In the fifth embodiment, the case where the high porosity layer 12H is formed at the interface with the semiconductor substrate 11 by intermittent high-current application is performed. The high porosity layer 12H can be formed at the interface with the semiconductor substrate 11. Embodiments in this case are shown in Embodiments 6, 7 and 8.

[Embodiment 6] In this embodiment as well, FIG.
A description will be given with reference to the process chart of FIG. In this example,
The formation of the surface layer 12S and the intermediate porosity layer of the porous layer 12 was performed in the same manner as described in Example 2.

That is, in this embodiment, similarly to the second embodiment, a wafer-like semiconductor made of single crystal Si doped with boron B at a high concentration and having a specific resistance of, for example, 0.01 to 0.02 Ωcm. A substrate 11 was prepared (FIG. 8A).

Also in this case, both the first and second tanks 1A and 1B are made of HF: C ₂ H ₅ O in the dark place by using the two-tank anodizing apparatus described with reference to FIG.
An electrolyte solution of H = 1: 1 was injected. And the Pt electrode 3 immersed and arranged in the electrolytic solution of each electrolytic solution tank 1A and 1B
A current was passed between A and 3B by DC power supply 2.

First, a current was applied for 8 minutes at a low current density of 1 mA / cm ² . By doing so, the same surface layer 12S as in Example 2 is formed (FIG. 8B). After the current is stopped once, the current is applied at a current density of 7 mA / cm ² for 8 minutes to form an intermediate porosity layer 12M similar to that in Example 2 below the surface layer 12S, that is, inside the surface layer 12S (FIG. 8C). ). Further, after the current is once stopped, in this embodiment, the current is lower than the large current passed in the second embodiment, and is lower than the current passed when the surface layer 12S and the intermediate porosity layer 12M are formed. Is high, so-called medium current of 60m
A / cm ² was supplied with electricity for 1.9 seconds. This way,
As in Example 5, a high porosity layer 12H having a porosity of about 60% and a thickness of about 50 nm is formed at the interface with the surface of the semiconductor substrate 11 under the intermediate porosity layer 12M (FIG. 8).
D). Thus, the porous layer 1 in which the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H are laminated
2 are formed.

Also in the porous layer 12 thus formed, the porosity between the high porosity layer 12H and the intermediate porosity layer 12M and the substrate 11 is greatly different, so that the porosity is large at these interfaces and near the interfaces. Distortion is applied, and the strength near this becomes extremely weak.

After the formation of the porous layer 12 in this manner, the annealing is performed at normal pressure S, as described in the second embodiment.
This is performed in an H ₂ atmosphere in an i-epitaxial growth apparatus to smooth the surface layer 12S of the porous layer 12, and at the same time, the intermediate porosity layer 12M inside the porous layer 12 and the high porosity layer 12H
The weakness of the strength near the interface with the steel is measured.

Thereafter, in the same manner as in Example 2, the annealing was performed in the annealed normal-pressure Si epitaxial growth apparatus.
The epitaxial growth of i is performed for about 17 minutes to obtain a thickness of about 5 μm.
The epitaxial semiconductor film 13 of single crystal Si was formed (FIG. 8E).

Then, the epitaxial semiconductor film 13 is peeled off from the semiconductor substrate 11 in the same manner as in the above-described embodiments to obtain the desired thin film semiconductor 23 (FIG. 8).
F).

[Embodiment 7] In this embodiment as well, FIG.
A description will be given with reference to the process chart of FIG. Also in this example,
As in Example 2, a wafer-shaped semiconductor substrate 11 made of single crystal Si doped with boron B at a high concentration and having a specific resistance of, for example, 0.01 to 0.02 Ωcm was prepared (FIG. 8A).

Also in this case, in the dark place, the anodizing apparatus having the two-tank structure described with reference to FIG. 1 was used, and the first and second tanks 1A and 1B were both HF: C ₂ H ₅ OH = 1: 1. 1
Was injected. Then, Pt electrodes 3A and 3 immersed and arranged in the electrolytic solution of each electrolytic solution tank 1A and 1B
A current was passed between B by the DC power supply 2.

First, in this example, a current was supplied at a low current of 1 mA / cm ² for 6 minutes. In this way, a surface layer 12S having a porosity of 16% and a thickness of 1.7 μm was formed (FIG. 8B). After turning off the power once,
Energization was performed at a current density of 4 mA / cm ² for 10 minutes. In this way, the lower layer of the surface layer 12S, that is, the surface layer 12S
An intermediate porosity layer 12M having a porosity of 22% and a thickness of about 5.8 μm is formed inside S (FIG. 8C). Further, once the energization is stopped, in this embodiment, the medium current of 60 m
A / cm ² was applied for 2 seconds. In this manner, a high porosity layer 12H having a porosity of about 60% and a thickness of about 50 nm is formed at the interface with the semiconductor substrate 11 below the intermediate porosity layer 12M (FIG. 8D). Thus, the porous layer 12 is formed by laminating the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H.

Also in the porous layer 12 thus formed, the porosity between the high porosity layer 12H and the intermediate porosity layer 12M and the substrate 11 is greatly different. Distortion is applied, and the strength near this becomes extremely weak.

After the formation of the porous layer 12 in this manner, annealing is performed at normal pressure Si as described in the second embodiment.
This is performed in an H ₂ atmosphere in an epitaxial growth apparatus to smooth the surface layer 12S of the porous layer 12,
The strength is weakened near the interface between the intermediate porosity layer 12M and the high porosity layer 12H inside 2.

Thereafter, in the normal pressure Si epitaxial growth apparatus where annealing was performed in the same manner as in Example 2, Si
Is epitaxially grown for 17 minutes to form an epitaxial semiconductor film 13 of single crystal Si having a thickness of about 5 μm (FIG. 8E), and the epitaxial semiconductor film 13 is separated from the semiconductor substrate 11 to obtain a thin film semiconductor 23 (FIG. 8).
F).

[Embodiment 8] In this embodiment as well, FIG.
A description will be given with reference to the process chart of FIG. Also in this example,
As in Example 2, a wafer-shaped semiconductor substrate 11 made of single crystal Si doped with boron B at a high concentration and having a specific resistance of, for example, 0.01 to 0.02 Ωcm was prepared (FIG. 8A).

Also in this case, anodization is performed in a dark place using the anodizing apparatus having the two-tank structure described with reference to FIG. 1, but in this embodiment, the first tank 1A is used. the _{HF: C 2 H 5 OH =} 1.2: 1 in the electrolyte solution was injected, HF in a second tank _{1B: C 2 H 5 OH =} 1: injected with 1 of the electrolytic solution. And each electrolytic solution tank 1A and 1
Pt electrodes 3A and 3B immersed in the electrolytic solution of B
During this time, a current was supplied by the DC power supply 2.

First, a current was supplied for 5 minutes at a low current of a current density of 1 mA / cm ² . By doing so, the porosity is 13%,
A surface layer 12S having a thickness of 1.5 μm was formed.
B). After the current supply was once stopped, current was supplied at a current density of 5 mA / cm ² for 5 minutes. By doing so, the intermediate porosity layer 12M having a porosity of 18% and a thickness of 5 μm is provided below the surface layer 12S.
Was formed (FIG. 8C). Furthermore, once the power supply is stopped,
A middle current of 80 mA / cm ² was applied for 3 seconds. By doing so, the interface with the surface of the semiconductor substrate 11 that has not been made porous under the intermediate porosity layer 12M has a porosity of about 60%.
%, A high porosity layer 12H having a thickness of about 50 nm was formed (FIG. 8D). Thus, the porous layer 12 is formed by laminating the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H.

Also in the porous layer 12 thus formed, the porosity between the high porosity layer 12H and the intermediate porosity layer 12M and the substrate 11 is greatly different, so that the porosity is large at these interfaces and near the interfaces. Distortion is applied, and the strength near this becomes extremely weak.

After the formation of the porous layer 12 in this manner, annealing is performed at normal pressure S, as described in the second embodiment.
The surface layer 12S of the porous layer 12 is smoothed by performing the process in an H ₂ atmosphere in an i-epitaxial growth apparatus, and the porous layer 12
The strength is weakened near the interface between the inner middle porosity layer 12M and the high porosity layer 12H.

Thereafter, in the normal pressure Si epitaxial growth apparatus where annealing was performed in the same manner as in Example 2, Si
Was epitaxially grown for 17 minutes to form an epitaxial semiconductor film 13 of single crystal Si having a thickness of about 5 μm (FIG. 8E).

Also in this case, for example, PET
Adhesion of sheet (not shown), epitaxial semiconductor film 1
The target thin film semiconductor 23 is obtained by peeling off the semiconductor substrate 11 of FIG. 2 (FIG. 8F).

[Embodiment 9] In this embodiment, a method similar to that of Embodiment 2 is used, but an oxidizing step is performed prior to heat treatment of the porous layer 12 in an H ₂ atmosphere. This will be described with reference to FIGS. In this embodiment, as in the second embodiment, boron B
Is doped, and the specific resistance is, for example, 0.01 to 0.02 Ωc.
wafer-like semiconductor substrate 1 of single crystal Si
1 was prepared (FIG. 4A).

Using the anodizing apparatus having a two-tank structure described in FIG. 1, an electrolytic solution of HF: C ₂ H ₅ OH = 1: 1 was injected into both the first and second tanks 1A and 1B. .
Then, a current was applied by the DC power supply 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solutions of the electrolytic solution tanks 1A and 1B in a dark place.

First, a current was applied at a current density of 1 mA / cm ² for 8 minutes to form a surface layer 12S (FIG. 4B). After the current supply was once stopped, a current density of 7 mA / cm ² was supplied for 8 minutes to form an intermediate porosity layer 12M under the surface layer 12S (FIG. 4).
C). Furthermore, after the current supply was once stopped, 200 mA / cm ²
For 3 seconds, the high porosity layer 1 in the intermediate porosity layer 12M.
2H, a surface layer 12S and an intermediate porosity layer 12M.
Then, the porous layer 12 is formed by the high porosity layer 12H (FIG. 4D).

After that, in this embodiment, an oxidation treatment step is performed. This oxidation treatment is performed in an oxygen atmosphere at 400
By dry oxidation heating to ° C. By this treatment, the inside of the porous layer 12 is oxidized, and it is possible to prevent a large structural change from occurring in the porous layer even by a subsequent heat treatment, that is, annealing in an H ₂ atmosphere.
It is possible to effectively avoid the effect of the strain generated near the interface of 2H on the surface layer 12S.

Thereafter, in the same manner as in Example 2, the substrate 11 is heat-treated in an H ₂ atmosphere by a normal-pressure Si epitaxial growth apparatus, followed by epitaxial growth of Si (FIG. 5A). The target thin film semiconductor 23 is obtained by attaching and detaching the substrate (FIG. 5B).

[Embodiment 10] In this embodiment, the case where the concentration of the electrolytic solution is changed in the anodization of the porous layer 12 is described. This case will be described with reference to FIGS. Also in this embodiment, boron B is doped at a high concentration and the specific resistance is 0.01 to 0.5.
A wafer-like semiconductor substrate 11 made of single-crystal Si having a thickness of 02 Ωcm was prepared (FIG. 4A).

Also in this case, the anodization was performed in a dark place using the anodizing apparatus having the two-tank structure described with reference to FIG. 1. In this case, HF: C ₂ H was added to the first tank 1A. _Five
An electrolytic solution of OH = 2: 1 was injected, and H 2 was introduced into the second tank 1B.
F: An electrolytic solution of C ₂ H ₅ OH = 1: 1 was injected, a Si substrate was sandwiched between these electrolytic solution tanks, and a Pt electrode 3A provided as an electrode in each of the electrolytic solution tanks 1A and 1B.
And a current was passed between 3B.

First, current was applied at a current density of 1 mA / cm ² for 8 minutes. This gives a porosity of 16% and a thickness of 1.7
A μm surface layer 12S was formed (FIG. 4B). The energization was stopped once, and the energization was performed at 7 mA / cm ² for 8 minutes. As a result, an intermediate porosity layer 12M having a porosity of 26% and a thickness of 6.3 μm was formed (FIG. 4C).

Next, in this embodiment, the first tank 1
The concentration of the electrolytic solution of A was changed to HF: C ₂ H ₅ OH = 1: 1. Then, the current density was increased to 200 mA / cm ^2, and energization was performed for 3 seconds. By doing so, the porosity is about 60% and the thickness is about 0.5 μm in the intermediate porosity layer 12M.
Was formed (FIG. 4D). Thus, the porous layer 12 formed by superimposing the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H is formed.

Thereafter, in the same manner as in Example 2, the substrate 11 is heat-treated in an H ₂ atmosphere by a normal-pressure Si epitaxial growth apparatus, followed by epitaxial growth of Si (FIG. 5A), and the supporting substrate by a PET sheet. A thin film semiconductor 23 is obtained by attaching and detaching (not shown) and peeling (FIG. 5B).

In this embodiment, the HF concentration is increased on the surface side of the porous layer 12, that is, in the formation of the surface layer 12S and the intermediate porosity layer 12M. Thus, the HF concentration of the electrolytic solution is increased. Then, the porosity of the porous layer is reduced, and in this case, a porous layer having an extremely small diameter is formed on the surface of the porous layer 12. The epitaxial semiconductor film is formed as a film having excellent crystallinity.

In this case, in forming the high porosity layer 12H, if the HF concentration of the electrolytic solution is high, a sufficient porosity cannot be obtained with a current density of 200 mA / cm ² and an electric current of about 3 seconds. However, in this embodiment, since the HF concentration of the electrolytic solution is reduced in forming the high porosity layer 12H, the high porosity layer 12H having a sufficiently high porosity can be generated.

[Embodiment 11] This embodiment is also a case where the concentration of the electrolytic solution is changed in the anodization of the porous layer 12. This will be described with reference to FIGS. Also in this example, a wafer-like semiconductor substrate 11 made of single crystal Si doped with boron B at a high concentration and having a specific resistance of 0.01 to 0.02 Ωcm was prepared (FIG. 6A).

Also in this embodiment, the first tank 1A is formed using the two-tank anodizing apparatus described with reference to FIG.
HF: C ₂ H ₅ OH = 2: 1 electrolytic solution is injected into the second tank 1B, and HF: C ₂ H ₅ OH = 1: 1 electrolytic solution is injected into the second tank 1B. And 1B, the Si substrate was sandwiched, and a current was passed between Pt electrodes 3A and 3B provided as electrodes in the respective electrolytic solution tanks 1A and 1B in a dark place.

First, current was applied at a current density of 1 mA / cm ² for 8 minutes. As a result, a surface layer 12S having a porosity of about 14% and a thickness of about 2.0 μm was formed (FIG. 6B). The energization was temporarily stopped, and the energization was performed at 7 mA / cm ² for 6 minutes. Thus, porosity of about 20%, the first intermediate porosity layer 12M ₁ having a thickness of approximately 6.4μm is formed (FIG. 6C).

Next, the concentration of the electrolytic solution in the first tank 1A was
HF: C ₂ H ₅ OH was changed to 1: 1. Then, electricity was supplied again at 7 mA / cm ² for 2 minutes. In this way, about 26% porosity, the second intermediate porosity layer 12M ₂ having a thickness of approximately 1.7μm is formed (FIG. 6D).

Thereafter, the energization was temporarily stopped, and the concentration of the electrolytic solution in the first tank 1A was further adjusted to HF: C ₂ H ₅ OH = 1:
The concentration was changed to 1.5 to further lower the concentration of the electrolytic solution. In this state, the current density was increased to 200 mA / cm ² and 2
Energization was performed for seconds. In this way, the second intermediate porosity layer 12M _2, about 60% porosity, thickness of about 0.5μm
Was formed (FIG. 6E). Thus, the porous layer 12 was formed by overlapping the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H.

Thereafter, in the same manner as in Examples 2 and 3, etc., the substrate 11 is heat-treated in an H ₂ atmosphere by a normal pressure Si epitaxial growth apparatus,
i to form an epitaxial semiconductor film 13 by epitaxial growth (FIG. 7A).
The target thin film semiconductor 23 is obtained by peeling the semiconductor substrate 11 from the semiconductor substrate 11 (FIG. 7B). Also in this example, the porous layer attached to the thin film semiconductor 23 was removed by etching.

In this embodiment, the first and second intermediate porosity layers 12M ₁ and 12M ₂ are formed, and in forming the second intermediate porosity layer 12M ₂ , the concentration of the electrolytic solution is reduced. Since the concentration of the electrolytic solution was lowered in the formation of the high porosity layer 12H, the porosity was increased stepwise from the surface layer 12S toward the high porosity layer 12H, so that the strain caused by the high porosity layer 12H was increased. Can be effectively mitigated on the surface of the porous layer 12, and the crystallinity of the epitaxial semiconductor film 13 epitaxially grown on the porous layer 12 can be further improved.

In addition, in the anodization of the high porosity layer 12H, since the concentration of the electrolytic solution was further reduced, the fragility of the high porosity layer 12H could be further increased, and the separation, that is, The peelability of the epitaxial semiconductor film 13 can be improved.

[Embodiment 12] In this embodiment, the epitaxial semiconductor film, that is, the thin film semiconductor has a multilayer structure, in this example, a p ⁺ -p ^-- n ⁺ structure. 9 and 10 show a process chart of this embodiment.
Also in this example, a wafer-like semiconductor substrate 11 made of single crystal Si doped with boron B at a high concentration and having a specific resistance of, for example, 0.01 to 0.02 Ωcm was prepared (FIG. 9A).

Also in this case, the first and second anodizing apparatuses having the two-tank structure described with reference to FIG.
HF: C ₂ H ₅ OH = 1: 1 in both tanks 1A and 1B
Pt electrodes 3A and 3 are immersed and placed in the electrolytic solutions of the electrolytic solution tanks 1A and 1B in a dark place.
A current was passed between B by the DC power supply 2.

First, current was applied at a current density of 1 mA / cm ² for 8 minutes to form a surface layer 12S (FIG. 9B). After the current supply was stopped once, current supply was performed at a current density of 7 mA / cm ² for 8 minutes to form an intermediate porosity layer 12M (FIG. 9C). Further, after the current supply was once stopped, 200 mA / cm ² was supplied for 3 seconds.
In this way, a high porosity layer 12H was formed in the intermediate porosity layer 12M (FIG. 9D). Thus, the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H
Thus, the porous layer 12 is formed.

After the formation of the porous layer 12 in this manner, the annealing is performed at normal pressure S, as described in the second embodiment.
The surface layer 12S of the porous layer 12 is smoothed by performing the process in an H ₂ atmosphere in an i-epitaxial growth apparatus, and the porous layer 12
The strength is weakened near the interface between the inner middle porosity layer 12M and the high porosity layer 12H.

Thereafter, in the annealed normal pressure Si epitaxial growth apparatus, epitaxial growth using SiH ₄ gas and B ₂ H ₆ gas was performed for 2 minutes, and the first epitaxial growth was performed using p ⁺ Si doped with boron B at a high concentration. Semiconductor layer 13
1 was formed (FIG. 10A).

Next, by changing the flow rate of the B ₂ H ₆ gas,
i-epitaxial growth was performed for 17 minutes to form a second semiconductor layer 132 of low-concentration boron-doped p ^- Si (FIG. 10B).

[0177] Then, by supplying PH ₃ gas in place of B ₂ H ₆ gas, p ^- on the epitaxial semiconductor layer 132,
Third epitaxial semiconductor film 13 of n ⁺ Si by performing high concentration phosphorus-doped Si epitaxial growth for 2 minutes
3 is formed (FIG. 10C). Thus, the p ⁺ -p ^-- n ⁺ composed of the first to third semiconductor layers 131 to 133 is provided.
A semiconductor film 13 having a structure is formed.

Thereafter, the semiconductor film 13 is peeled off from the base 11 in the same manner as in the above-described embodiments to obtain the desired thin film semiconductor 23 (FIG. 10D). Also in this example, the porous layer attached to the thin film semiconductor 23 was removed by etching. The thin film semiconductor 23 having the p ⁺ -n ^-- p ⁺ three-layer structure can constitute a solar cell.

[Embodiment 13] In this embodiment, in the manufacturing method of Embodiment 12, the semiconductor film 13 is
s to form an epitaxial semiconductor film. That is, in this case, in the steps of FIGS. 9A to 9D, the same steps as those of the twelfth embodiment are employed, and thereafter, the epitaxial semiconductor film 13 is formed.
In the epitaxial growth of TMGa, trimethyl gallium (TMGa) and AsH ₃
Using the above as a source gas, heteroepitaxial growth was performed at a substrate temperature of 720 ° C. for 1 hour using a normal pressure MOCVD apparatus to form an epitaxial semiconductor film 13 of GaAs having a thickness of about 3 μm.

Thereafter, the epitaxial semiconductor film 13 was separated from the semiconductor substrate 11 to obtain a thin film semiconductor 23 of the epitaxial semiconductor film 13.

[Embodiment 14] In this embodiment, a solar cell is manufactured. 11 to 14 show the process diagrams. In this embodiment, an epitaxial semiconductor film having a p ⁺ -p ^-- n ⁺ three-layer structure is formed in the same manner as in the twelfth embodiment. That is, also in this example, a wafer-like semiconductor substrate 11 made of single crystal Si doped with boron B at a high concentration and having a specific resistance of, for example, 0.01 to 0.02 Ωcm was prepared.

Also in this case, the first and second anodizing apparatuses having the two-tank structure described with reference to FIG.
HF: C ₂ H ₅ OH = 1: 1 in both tanks 1A and 1B
Was injected, and a current was applied by the DC power supply 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solutions of the electrolytic solution tanks 1A and 1B.

First, current was applied at a current density of 1 mA / cm ² for 8 minutes to form a surface layer 12S (FIG. 11A). After the current supply was once stopped, current supply was performed at a current density of 7 mA / cm ² for 8 minutes to form an intermediate porosity layer 12M (FIG. 11B). Furthermore,
After the current supply was stopped once, 200 mA / cm ² was supplied for 3 seconds. Thus, a high porosity layer 12H was formed in the intermediate porosity layer 12M (FIG. 11C). Thus, the porous layer 12 in which the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H are laminated is formed.

After the formation of the porous layer 12, annealing is performed in a normal pressure Si epitaxial growth apparatus in an H ₂ atmosphere by the same method as described in the second embodiment. By doing so, the surface layer 12S of the porous layer 12 is made smooth, and the intermediate porosity layer 12M inside the porous layer 12 is
The strength is weakened near the interface with the high porosity layer 12H.

Thereafter, in the annealed normal pressure Si epitaxial growth apparatus, epitaxial growth using SiH ₄ gas and B ₂ H ₆ gas was performed for 2 minutes to obtain a thickness of 0.5 mm.
μm of p doped with boron ¹⁹ to 10 ¹⁹ atoms / cm ^3
+ First Si layer 131 is formed, and then B
By changing the flow rate of ₂ H ₆ gas, Si epitaxial growth was performed for 17 minutes, and boron B having a thickness of 5 μm was 10 ¹⁶ at.
forming a second semiconductor layer 132 of low-concentration p ^- Si doped to oms / cm ³ , and further replacing P _{2 with} B ₂ H ₆ gas;
By supplying H ₃ gas and performing epitaxial growth for 2 minutes, phosphorus P is formed on the p ⁻ semiconductor layer 132 by 10 ¹⁹ atoms / cm 2.
³ to form a third semiconductor layer 133 of n ⁺ Si doped at a high concentration,
A semiconductor film 13 having ap ⁺ -p ^-- n ⁺ structure made of 33 was formed (FIG. 12A).

Next, in this embodiment, the semiconductor film 1
An SiO ₂ film, that is, a transparent insulating film 16 is formed on the surface 3 by thermal oxidation, and pattern etching is performed by photolithography to form an opening 16W for making contact with an electrode or a wiring (FIG. 12B). This opening 16
W can be formed in parallel with each other in a stripe shape extending in a direction perpendicular to the sheet of the drawing while maintaining a required interval. With the SiO ₂ film thus formed,
It is possible to minimize carrier generation and recombination at the interface.

Then, a metal film is vapor-deposited on the entire surface, and pattern etching is performed by photolithography to form electrodes or wirings 17 on the light receiving surface side in the stripe-shaped openings 1.
6W (FIG. 13A). The metal film forming the electrode or the wiring 17 is, for example, a 30 nm thick T
An i-film, Pd with a thickness of 50 nm, and Ag with a thickness of 100 nm are sequentially deposited, and a multilayer structure film formed by subjecting this to Ag plating can be used. Then 4
Annealing was performed at 00 ° C. for 20 to 30 minutes.

On the other hand, on a transparent substrate 18 made of, for example, a flexible resin sheet, a flexible printed circuit board 20 in which wiring 19 of a required circuit is formed is arranged and the printed circuit board 20 is formed with an insulating film 16. And overlaid on the semiconductor film 13 with a transparent and insulating adhesive 21. At this time, the wiring 19 and the electrode or the wiring 17 to be connected to each other are made to abut each other, and solder is interposed between them so that electrical connection is made (FIG. 13).
B). At this time, the strength of the adhesive 21 was slightly higher than the separation strength of the porous layer.

Thereafter, an external force is applied to separate the semiconductor substrate 11 and the printed circuit board 20 from each other. In this manner, the semiconductor substrate 11 and the semiconductor film 13 are separated from each other at or near the fragile high porosity layer 12H of the porous layer 12, and the thin film semiconductor 23 on which the semiconductor film 13 is bonded is formed on the printed circuit board 20. Is obtained (FIG. 14A).

In this case, the porous layer 12 remains on the back surface of the thin-film semiconductor 23, and a silver paste is applied on the porous layer 12, and a metal plate is further joined to form the other back electrode 24. In this manner, the printed circuit board 20 p ⁺ -p ^{- -}
A solar cell on which the thin film semiconductor 23 having the n ⁺ structure is formed (FIG. 14B). In this case, the metal electrode 24
Functions also as an element layer protective film on the back surface of the solar cell.

In the fourteenth embodiment, a flexible printed circuit board is integrated with a solar cell, which can also have a flexible structure. However, the solar cell is mounted on a rigid substrate such as a glass substrate. An integrated configuration can also be used.

Next, an example in which the anodizing conditions for forming a high porosity layer serving as a separation layer of the porous layer in the method of manufacturing a thin film semiconductor or a solar cell are changed will be described.

[Embodiment 15] Description will be made with reference to the process charts of FIGS. 15 and 16. Also in this case, the second embodiment
Similarly, the boron B-doped resistivity is 0.01 to
A semiconductor substrate 11 made of single-crystal Si of 0.02 Ωcm is prepared (FIG. 15A).

For the semiconductor substrate 11, an anodizing apparatus having a two-tank structure described with reference to FIG. 1 was used, and HF: C ₂ H ₅ OH was used as an electrolytic solution in the first and second layers 1A and 1B.
1: 1 was injected. A current was applied by the DC power supply 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solution of each layer 1A and 1B in a dark place.

First, current was supplied at a current density of 1 mA / cm ² for 8 minutes. Thus, the surface layer 12S having a low porosity was formed (FIG. 15B). After the current is stopped once, 7mA / c
m ² for 8 minutes. Thus, the intermediate porosity layer 1
2M was formed (FIG. 15C). Further, after the current supply was once stopped, in this example, current supply was performed at 90 mA / cm ² for 5 seconds. By doing so, the intermediate porosity layer 1
A high porosity layer 12H was generated within 2M (FIG. 15D).
Thereafter, energization was performed at 7 mA / cm ² for 8 minutes. In this way, the surface layer 12S, the intermediate porosity layer 12M,
The porous layer 12 composed of the high porosity layer 12H is formed.

Thereafter, the same annealing as in Example 2 was performed, and epitaxial growth of Si was performed on the porous layer 12 for 17 minutes to form an epitaxial semiconductor film 13 of single-crystal Si having a thickness of about 5 μm (FIG. 16A). .

Then, the epitaxial semiconductor film 13 and
An external force is applied to the semiconductor substrate 11 in a direction in which they are separated from each other. By doing so, the epitaxial semiconductor film 13 becomes
The thin film semiconductor 23 is obtained by being separated at or near the high porosity layer 12H of the porous layer 12 (FIG. 16B).

[Embodiment 16] This will be described with reference to the process chart of FIG. Also in this case, similarly to the sixth embodiment, the boron B-doped specific resistance is 0.01 to 0.02 Ωc.
A semiconductor substrate 11 made of m single crystal Si is prepared (FIG. 1).
7A).

For the semiconductor substrate 11, an anodizing apparatus having a two-tank structure described with reference to FIG. 1 was used, and HF: C ₂ H ₅ OH was used as an electrolytic solution in each of the first and second layers 1A and 1B.
1: 1 was injected. A current was applied by the DC power supply 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solution of each layer 1A and 1B in a dark place.

First, current was applied at a current density of 1 mA / cm ² for 8 minutes. Thus, a low porosity surface layer 12S was formed (FIG. 17B). After the current is stopped once, 7mA / c
m ² for 8 minutes. Thus, the intermediate porosity layer 1
2M was formed (FIG. 17C). Further, after the energization is once stopped, in this embodiment, 30 mA / cm ² , 15 mA
The energization was performed for seconds. In this way, a high porosity layer 12H was generated below the intermediate porosity layer 12M.
D). Thereafter, energization was performed at 7 mA / cm ² for 8 minutes. Thus, the surface layer 12S and the intermediate porosity layer 1
Porous layer 12 formed by laminating 2M and high porosity layer 12H
Is formed.

Thereafter, the same annealing as in Example 2 was performed, and epitaxial growth of Si was performed on the porous layer 12 for 17 minutes to form a semiconductor film 13 of single-crystal Si having a thickness of about 5 μm (FIG. 17E).

Then, the epitaxial semiconductor film 13 and
An external force was applied to the semiconductor substrate 11 in a direction to separate them from each other. However, in this case, the semiconductor film 13 may not always be able to be separated from the semiconductor substrate 11 satisfactorily.

[Embodiment 17] This will be described with reference to the process chart of FIG. Also in this case, similarly to the sixth embodiment, the boron B-doped specific resistance is 0.01 to 0.02 Ωc.
A semiconductor substrate 11 made of m single crystal Si is prepared (FIG. 1).
8A).

Using the two-tank anodizing apparatus described with reference to FIG. 1 for the semiconductor substrate 11, the first and second layers 1A and 1B are used as electrolytic solutions of HF: C ₂ H ₅ OH =
1: 1 was injected. An electric current was applied by the DC power supply 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solution of each layer 1A and 1B.

First, current was supplied at a current density of 1 mA / cm ² for 8 minutes. Thus, a low porosity surface layer 12S was formed (FIG. 18B). After the current is stopped once, 7mA / c
m ² for 8 minutes. Thus, the intermediate porosity layer 1
2M was formed (FIG. 18C). Further, after the current supply was once stopped, in this example, current supply was performed at 80 mA / cm ² for 5 seconds. By doing so, the intermediate porosity layer 1
2M and below the intermediate porosity layer 12M, that is, the semiconductor substrate 1
The high porosity layers 12H were generated at the interface with the surface 1 (FIG. 18D). Thereafter, energization was performed at 7 mA / cm ² for 8 minutes. Thus, the porous layer 12 is formed by laminating the surface layer 12S, the intermediate porosity layer 12M, the high porosity layer 12H, the intermediate porosity layer 12M, and the high porosity layer 12H.

Thereafter, the same annealing as in Example 2 was performed, and epitaxial growth of Si was performed on the porous layer 12 for 17 minutes to form an epitaxial semiconductor film 13 of single-crystal Si having a thickness of about 5 μm (FIG. 18E). .

Then, the epitaxial semiconductor film 13 and
An external force is applied to the semiconductor substrate 11 in a direction in which they are separated from each other. By doing so, the epitaxial semiconductor film 13 becomes
Separated by one of the high porosity layers 12H of the porous layer 12, a thin film semiconductor made of the epitaxial semiconductor film 13 was obtained.

As described above, the sixth embodiment (FIG. 8), the fifteenth embodiment (FIGS. 15 and 16), and the sixteenth embodiment (FIG. 1)
7), Example 17 (FIG. 18) and Example 5 (FIG. 8) clearly show the selection of the amount of electricity for the anodization and the manner of energization in the formation of the high porosity layer 12H. Thus, the position at which the high porosity layer 12H is formed changes. For example, an anodizing electrolytic solution is prepared by using HF: C ₂ H ₅ OH = 1: 1.
When it is set to about 40 to 70 mA / cm ² , the high porosity layer 1
2H can be formed at the lowermost layer of the porous layer, that is, at the interface of the semiconductor substrate 11, and in a high current range of 90 mA / cm ² or more, for example, about 300 mA / cm ² or less, the intermediate porosity on the surface side from the interface is higher. It could be formed in layer 12M. Even in the high current range, when the current is intermittently supplied for a short time, the intermediate porosity layer 1
It can be formed at the interface with the lowermost semiconductor substrate 11 of 2M. And the selection of the formation position of this high porosity layer,
It was confirmed that the design could be performed with good reproducibility.

Further, an embodiment of a method for manufacturing a solar cell according to the present invention will be described. [Embodiment 18] In this embodiment, the terminals can be easily derived from the light-receiving surface side electrode, that is, the conductive wires can be easily derived. This will be described with reference to FIGS. 11, 12, 19, and 20. Also in this example, the same steps as those described in Example 14 with reference to FIGS. 11A to 11C, 12A and 12B, and 13A were employed. Also in this embodiment, p ⁺
An epitaxial semiconductor film having a -p ^-- n ⁺ three-layer structure is formed. That is, a wafer-like semiconductor substrate 11 made of single-crystal Si doped with boron B at a high concentration and having a specific resistance of, for example, 0.01 to 0.02 Ωcm was prepared.

Also in this case, the first and second anodizing apparatuses having the two-tank structure described with reference to FIG.
HF: C ₂ H ₅ OH = 1: 1 in both tanks 1A and 1B
Was injected, and a current was applied by the DC power supply 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solutions of the electrolytic solution tanks 1A and 1B.

First, current was applied at a current density of 1 mA / cm ² for 8 minutes to form a surface layer 12S (FIG. 11A). After the current supply was once stopped, current supply was performed at a current density of 7 mA / cm ² for 8 minutes to form an intermediate porosity layer 12M (FIG. 11B). Furthermore,
After the current supply was stopped once, 200 mA / cm ² was supplied for 3 seconds. Thus, a high porosity layer 12H was formed in the intermediate porosity layer 12M (FIG. 11C). Thus, the porous layer 12 including the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H is formed.

After the formation of the porous layer 12, annealing is performed in a normal pressure Si epitaxial growth apparatus in an H ₂ atmosphere by the same method as described in the second embodiment. By doing so, the surface layer 12S of the porous layer 12 is made smooth, and the intermediate porosity layer 12M inside the porous layer 12 is
The strength is weakened near the interface with the high porosity layer 12H.

After that, the annealed normal-pressure Si epitaxial growth apparatus was subjected to epitaxial growth using SiH ₄ gas and B ₂ H ₆ gas for 2 minutes to obtain a thickness of 0.5 mm.
μm of p doped with boron ¹⁹ to 10 ¹⁹ atoms / cm ³
Forming a first epitaxial semiconductor layer 131 of ⁺ Si, and then changing the flow rate of the B ₂ H ₆ gas and performing Si epitaxial growth for 17 minutes to obtain a boron nitride of 5 μm in thickness of 10 ¹⁶ atoms / cm 2 Lightly doped p ^- S doped to ³
i, forming a second epitaxial semiconductor layer 132, and further supplying PH ₃ gas instead of B ₂ H ₆ gas,
Epitaxial growth is performed for 2 minutes to form a third epitaxial semiconductor layer 133 of n ⁺ Si doped with phosphorus P at a high concentration of 10 ¹⁹ atoms / cm ³ on the p ⁻ epitaxial semiconductor film 132, ~ P ⁺ -p ^-- n ⁺ composed of third epitaxial semiconductor layers 131 to 133
An epitaxial semiconductor film 13 having a structure was formed (FIG. 12).
A).

Next, in this embodiment, a SiO ₂ film, that is, a transparent insulating film 16 is formed on the epitaxial semiconductor film 13 by surface thermal oxidation, and pattern etching is performed by photolithography to make contact with an electrode or a wiring. The opening 16W to be formed is formed (FIG. 12).
B). The openings 16W can be formed in parallel with each other in a stripe shape extending in a direction perpendicular to the paper surface in the drawing while maintaining a required interval. The Si thus formed
The O ₂ film makes it possible to minimize carrier generation and recombination at the interface.

Then, a metal film is vapor-deposited on the entire surface and pattern etching is performed by photolithography to obtain a required pattern, in this example, a stripe-shaped opening 16W.
A striped electrode or wiring 17 is formed along (FIG. 13A, FIG. 19A). This electrode or wiring 17
Can be composed of a multilayer structure film formed by sequentially depositing, for example, a 30-nm-thick Ti film, a 50-nm-thick Pd, and a 100-nm-thick Ag, and further performing Ag plating thereon. . After that, at 400 ° C for 20 ~
Annealing was performed for 30 minutes.

Next, in this embodiment, a conductive wire 41, in this embodiment, a metal wire is joined along the stripe-shaped electrodes or wirings 17 along these, respectively, and a transparent adhesive 21 is placed thereon. Thereby, the transparent substrate 42 is joined (FIG. 19B). The connection of the conductive line 41 to the electrode or the wiring 17 can be performed by soldering. And
One end or both ends of each of the conductive lines 41 is longer than the electrode or the wiring 17 and is led out.

Thereafter, an external force for separating the semiconductor substrate 11 and the transparent substrate 42 from each other is applied. This way,
The semiconductor substrate 11 and the epitaxial semiconductor film 13 are separated at or near the fragile high porosity layer 12H of the porous layer 12, and the thin film semiconductor 23 with the epitaxial semiconductor film 13 bonded to the transparent substrate 42 is obtained. (FIG. 20
A).

In this case, the porous layer 12 remains on the back surface of the thin-film semiconductor 23. A silver paste is applied on the porous layer 12, and a metal plate is further joined to form the other back electrode 24. In this manner, the printed circuit board 20 p ⁺ -p ^{- -}
A solar cell on which the thin film semiconductor 23 having the n ⁺ structure is formed (FIG. 20B). This metal electrode 24 also functions as an element layer protective film on the back surface of the solar cell.

In the solar cell formed in this manner, the light-receiving-side electrode or wiring 17 is covered with the transparent substrate 42, but is electrically led to the outside by the conductive wire 41. The electrical connection with the outside is easily made. Further, for example, as in the above-described embodiment,
That is, since the conductive line 41 is led out from each of the plurality of electrodes or wirings 17 that are in contact with the active portion of the solar cell, the series resistance of the solar cell can be sufficiently reduced.

Further, since the conductive wire 41 is led out as described above, when a plurality of solar cells are connected to each other,
This connection can be easily made. Next, an embodiment in which a plurality of solar cells are connected to each other on a common substrate to form an array will be described.

[Embodiment 19] FIGS. 21 and 22 show process charts of this embodiment. Since the same steps as those of Embodiment 18 are employed up to the step of FIG. The description of the steps overlapping with those of the eighteenth embodiment will be omitted.
In FIGS. 21 and 22, parts corresponding to those in FIGS. 19 and 20 are denoted by the same reference numerals, and redundant description is omitted.

However, in this embodiment, the surface of the porous layer 12 was the same as that shown in FIG. 19B.
Is formed thereon, and an epitaxial semiconductor film 13 having ap ⁺ -p ^-- n ⁺ structure is formed thereon. An electrode or wiring 17 is contacted to a predetermined portion of the epitaxial semiconductor film 13, and a conductive line 41 is
Are prepared, and a plurality of semiconductor substrates 11 to which a common transparent substrate 42
Glue to Also in this case, the ends of the plurality of conductive wires 41 are led out from each semiconductor substrate 11 (FIG. 21).
A).

Thereafter, an external force is applied to each of the semiconductor substrates 11 and the common transparent substrate 42 in a direction of separating them from each other. In this way, the fragile high porosity layer 12H of the porous layer 12 is formed.
Alternatively, the semiconductor substrate 11 and the semiconductor film 13 are separated in the vicinity thereof, and the thin film semiconductors 23 of the semiconductor films 13 are arranged and formed on the common transparent substrate 42 (FIG. 21).
B).

The porous layer 12 remains on the back surface of each of the thin film semiconductors 23. A silver paste is applied on the porous layer 12, and a metal plate is joined to form the other back electrode 24. In this manner, the active portion of the solar cell is formed on the common transparent substrate 42 by the thin film semiconductor 23 having the p ⁺ -p ^-- n ⁺ structure, and the light receiving surface side electrode or the wiring 1 is formed.
7 are formed, and a plurality of solar cell elements S having electrodes 24 formed on the back surface are arranged and formed (FIG. 21C).

Then, one end of the conductive wire 41 is soldered to a required electrode 24, and an insulating material 43 such as a resin is filled between the solar cell elements to achieve mutual insulation (FIG. 22A). In this case, the free end of the conductive wire 41 on the light receiving surface side of the solar cell element S to be mutually connected to the outside of the insulating material 43 is led out, and this free end is connected to, for example, the back electrode 24 of the adjacent solar cell element S. Connected by soldering or the like.

A plurality of interconnected solar cell elements S
The free ends of the first and last conductive lines 41 are led out, and the transparent substrate 42 side is exposed to the outside to cover each solar cell S and form a protective insulating layer 44 by resin molding or the like. Cover. In this way, the plurality of solar cell elements S are arranged on the common transparent substrate 42, and constitute a solar cell connected in series with each other (FIG. 22B). Needless to say, incident light such as sunlight on the solar cell is emitted from the transparent substrate 42 side.

In each of the above examples, the conductive wire 41
Is not limited to a metal wire, and may be constituted by, for example, a strip-shaped metal wire.

The transparent substrate 42 can be formed of a rigid substrate such as a glass substrate or a flexible substrate formed of a resin sheet. In the case of using a flexible substrate as described above, the entire solar cell can be configured flexibly.

In the case where the solar cell is manufactured in this manner, the conductive wires can be led out from the respective electrodes 17 irrespective of the fact that the transparent substrate is disposed on the light receiving surface. The series resistance can be reduced, and the connection of the conductive line is mechanically strong and stable in a state formed on the semiconductor substrate 11 before being separated as a thin-film solar cell. In this state, the mass production can be performed reliably and easily, and a plurality of solar cells can be easily connected to each other by conducting the conductive wires.

In FIGS. 21 and 22, only two solar cell elements S are shown, but it goes without saying that two or more solar cell elements S can be arranged and connected.

When the porous layer 12 is left on the back surface of the thin film semiconductor in the solar cell, the porous layer 1
2. If the semiconductor substrate 11 has a high impurity concentration, and if the semiconductor substrate 11 also has a high impurity concentration and there is a problem of absorbing photovoltaic power, it can be removed by, for example, etching. Next, an embodiment of a method for manufacturing a light emitting device according to the present invention will be described.

[Embodiment 20] Description will be made with reference to FIGS. In this example, a p-type Si single crystal semiconductor substrate 11 was prepared (FIG. 25A). One of the main faces is n
The n-type semiconductor layer 101 was formed by diffusing the phosphorus of the type impurity (FIG. 25B).

Using the anodizing apparatus shown in FIG. 1, anodizing is performed by applying a current of 50 mA / cm ² for 30 minutes under light irradiation, and the surface of the semiconductor layer 101 has a relatively high porosity. to form a first high porosity layer 12H ₁ (FIG. 25
C). Next, 7 mA / cm ² ,
Anodization was performed by applying a current for 10 minutes to obtain an intermediate porosity of 12
M is formed to a depth that crosses the semiconductor layer 101 (FIG. 25).
D). Next, similarly, 200 mA /
forming cm ^2, 7 seconds anodizing the performed second as a separating layer of high porosity layer 12H ₂ to intermediate porosity layer 12M (Fig. 25E).

[0234] On the high porosity layer 12H ₁ on the surface, and parallel arrangement formed by the stripe electrodes 102, for example, Au deposition extending in a direction perpendicular to the paper surface in FIG. 26 for example (FIG. 26A). A transparent adhesive 103 is applied to the surface of the base 11 on which the electrodes 102 are formed (FIG. 26B), and a transparent substrate 104 is attached (FIG. 26C).

Next, using the second high porosity layer 12H ₂ as a separation layer, the surface of the semiconductor substrate 11 to which the transparent substrate 104 is bonded is separated from the substrate 11 to form the light emitting element substrate 111 (FIG. 26D). The substrate 111 thus configured is a p-type semiconductor layer 105 formed by the intermediate porosity layer 12M obtained by making the p-type semiconductor substrate 11 porous.
When, p-n by the high porosity layer 12H ₁ of p-type formed in the formed n-type surface of the semiconductor layer 101 on top of this
With bonding.

On the back surface (separation surface) of the substrate 111, a stripe-shaped back surface electrode 106 of, for example, an Au vapor-deposited layer is formed similarly to the stripe-shaped electrode 102 (FIG. 2).
7A). The transparent adhesive 103 is applied to the surface of the substrate 111 on which the electrodes 106 are formed (FIG. 27B), and the transparent substrate 104 is joined (FIG. 27C). The substrate 111 is, for example,
The target light-emitting element 107 is obtained (FIG. 28B). Thus the light emitting element constituted by a so-called EL, as indicated by the arrows in FIG. 28B, although light is emitted, the main emission unit, the high porosity layer 12H _1, and the its luminous efficiency is high. This the active layer, due to the fact that the superlattice structure is composed of high porosity layer 12H ₁ is sufficiently thin. In the above embodiment, the semiconductor layer 101 is formed by diffusion of an impurity. However, the semiconductor layer 101 can be formed by ion implantation of an impurity, by an epitaxially grown semiconductor layer, by solid phase growth, CVD, or the like. .
The semiconductor layer 101 is not limited to being formed over the entire surface, but may be formed at a predetermined portion by selective diffusion, ion implantation, or the like. In addition, the semiconductor substrate 11 can be an n-type, and the luminous efficiency can be increased by using a high-resistance substrate. Further, when the substrate 111 is separated after being thermally oxidized in an oxygen atmosphere, a blue shift of an emission wavelength, that is, a shorter wavelength can be achieved.

In each of the above-described examples, the semiconductor film 3 is separated from the semiconductor substrate 11 by applying an external force to separate the semiconductor film 3 from each other. In some cases, the semiconductor film 3 can be separated by ultrasonic vibration.

In each of the above examples, in the anodization,
When a large current is applied or a long time is applied, a semiconductor, for example, Si may be separated from the substrate side, and this Si dust may adhere to the electrolytic solution tank. In this case, unnecessary semiconductor chips such as Si can be removed by etching by injecting hydrofluoric nitric acid into the tank instead of the electrolytic solution after the substrate 11 is taken out. In each of the above-described examples, the two-tank structure shown in FIG. 2 is used as an anodizing apparatus. However, the anodizing apparatus having a single-tank structure described with reference to FIG. 29 can be used.

In each of the examples described above, the semiconductor film 13 is formed by epitaxial growth. However, as described above, the semiconductor film 13 can be formed by a polycrystalline layer, an amorphous layer, or a mixture of these. It is.
When a silicon Si film is formed as the semiconductor film 13, a chlorine-based gas such as SiCl ₄ or SiH is used as a source gas for supplying Si in order to obtain a Si film having excellent surface smoothness.
Film formation by Cl ₃ , Si ₂ H ₂ Cl ₂ or the like is preferable. For example, in order to generate fine irregularities on the surface in order to increase the light receiving efficiency as in a solar cell, etching with HCl is performed before forming the semiconductor film. After that, the silane-based gas S
It is preferable to perform damping by iH ₄ , S ₂ H _6, or the like.

According to the manufacturing method of the present invention described above, the semiconductor substrate has a porous layer formed on the surface, a semiconductor film is formed thereon, and the semiconductor layer is peeled off. However, after the above-described formation and peeling of the semiconductor film, the formation of the porous layer, the formation and peeling of the semiconductor film are repeated again by polishing the surface of the semiconductor substrate. And can be used at low cost because it can be used repeatedly. If the semiconductor substrate is thinned by repeated use, the semiconductor substrate itself can be used as a thin film semiconductor, and for example, a solar cell can be manufactured. Therefore, since the semiconductor substrate can be used almost without waste without being finally invalidated, the cost can be reduced.

In addition, a semiconductor film having a thickness commensurate with the reduced thickness is formed on a semiconductor substrate having a reduced thickness by manufacturing a thin film semiconductor or a solar cell. By repeatedly manufacturing the solar cell, the same semiconductor substrate can be permanently used, so that the solar cell can be manufactured at lower cost and lower energy.

According to the manufacturing method of the present invention, after a supporting substrate such as a printed board is joined to the semiconductor film to integrate the substrate and the semiconductor film, the substrate is peeled off from the semiconductor substrate together with the epitaxial semiconductor film. There is no limitation on the type of the substrate, and a thin film single crystal can be formed on a substrate such as a metal plate, ceramic, glass, resin, etc., which has never been considered by common sense of conventional semiconductor technology. Or a solar cell can be formed.

In the case where a semiconductor layer is simply epitaxially grown on a porous layer having a single porosity, a porous layer serving as a nucleus for crystal growth is required to improve the crystallinity of the semiconductor film. Since it is necessary to reduce the porosity of, the current density is reduced after anodizing,
It is necessary to increase the HF mixture ratio of the electrolytic solution. However, when the porosity is reduced as described above, the porous layer becomes hard, and it becomes difficult to separate the epitaxial semiconductor film. So, in order to increase the porosity to weaken the separation strength,
For example, when the current density is increased and the HF mixture ratio of the electrolytic solution is reduced among the anodization conditions, in this case, separation is facilitated, but crystallinity of the epitaxial semiconductor film is extremely deteriorated. However, as described above, by reducing the porosity of the surface portion of the porous layer and forming a porous layer having a two-sided property that the porosity inside the porous layer is large, the porous layer is formed. An epitaxial semiconductor film can be favorably formed thereon, and the epitaxial semiconductor film can be easily separated. For example, it is also possible to form a weak porous layer that can be easily separated by ultrasonic waves.

The high porosity layer formed on the porous layer is
The larger the porosity, the easier the peeling is, but the larger the strain, and the influence is exerted on the surface layer of the porous layer. For this reason, cracks may occur in the surface layer. In addition, when performing epitaxial growth, it causes defects in the epitaxial semiconductor film. In contrast, as described above, between the very high porosity layer and the low porosity surface layer, as a buffer layer to alleviate the strain generated from these layers, a slightly higher porosity than the surface layer By forming the intermediate porosity layer, a high-quality epitaxial semiconductor film that can be easily peeled off can be formed.

Further, according to the present invention, in anodization at a high current density, a current can be intermittently passed to form a high porosity layer on the porous layer at the semiconductor substrate side interface or in the vicinity thereof. Therefore, the surface and the highly porous layer serving as the release layer can be separated to the maximum, so that the buffer layer can be made thinner, and the thickness of the porous layer can be reduced by that much, and the consumption of the semiconductor substrate in the thickness decreasing direction can be reduced. Can be reduced,
The cost can be further reduced.

Further, in the method of the present invention, in the anodization at a low current density, the current is gradually increased so that the porosity of the buffer layer between the surface layer of the porous layer and the release layer increases as going inside. When formed so as to increase gradually, the function of the buffer layer can be further improved.

The porous layer can be easily formed by performing anodization in an electrolytic solution containing hydrogen fluoride and ethanol or a mixed solution of hydrogen fluoride and methanol. In this case, when changing the current density of anodization, by changing the composition of this electrolytic solution,
The adjustment range of the porosity is further increased.

[0248] Irradiation of light during the anodization significantly causes irregularities on the surface of the porous layer, thereby deteriorating the crystallinity of the epitaxial semiconductor film. In a dark place, the unevenness can be reduced or avoided, and an epitaxial semiconductor film having good crystallinity can be formed.

By heating in a hydrogen gas atmosphere after the formation of the porous layer, the surface of the surface layer of the porous layer becomes smooth, and an epitaxial semiconductor film having good crystallinity can be formed. did it. Also, after the porous layer is formed, before the heating step in a hydrogen gas atmosphere, the inside of the porous layer is oxidized by thermally oxidizing the porous layer. Even if it is applied, since a large structural change hardly occurs in the porous layer and distortion from inside is hardly transmitted to the surface of the porous layer, an epitaxial semiconductor film having good crystallinity can be formed.

Further, by using a single crystal of silicon as the semiconductor substrate, a single crystal silicon thin plate used for a solar cell can be manufactured. Furthermore, as a semiconductor substrate, one doped with boron at a high concentration is made porous while maintaining a crystalline state during anodization,
A high quality epitaxial semiconductor film can be formed.

According to the manufacturing method of the present invention, for example, a solar cell can be easily manufactured by, for example, epitaxially growing two or more semiconductor films on the surface of the porous layer.

In the case of manufacturing a solar cell, for example, an insulating film is formed on the surface of the multilayer epitaxial semiconductor film, and an electrode is further formed thereon, thereby generating carriers at the interface with the epitaxial semiconductor film. Current can be extracted from the epitaxial semiconductor film while minimizing recombination and recombination.

Further, according to the method of the present invention, by bonding a transparent printed circuit board to the electrode surface of a solar cell, the substrate on which the circuit for the solar cell is wired can be integrated with the solar cell. The integration of a printed circuit board and a thin-film single-crystal solar cell, which has never been considered in the field of semiconductor technology, can be facilitated.

The solar cell manufactured according to the present invention can be formed thinly, that is, flexibly, by using, for example, single crystal Si as an epitaxial semiconductor film. Therefore, a solar cell having a certain degree of flexibility can be obtained by selecting a supporting substrate and the like. Can be. Therefore, it can be installed on a window glass with a solar cell formed on a glass surface, a roof of a solar car, or the like.

Further, since the single crystal is excellent in photoelectric conversion efficiency, the amount of power generation per unit area is superior to that of conventional amorphous silicon. Moreover, since it is manufactured with low energy, the years of energy recovery can be greatly reduced.

[0256]

According to the method for manufacturing a thin film semiconductor of the present invention described above, a large area thin film semiconductor can be manufactured easily and at low cost. Further, a thin film semiconductor having excellent crystallinity can be easily and inexpensively manufactured. Further, according to the method for manufacturing a solar cell of the present invention, a highly efficient solar cell having excellent crystallinity in a large area and being sufficiently thin can be manufactured at low cost. Thus, the cost reduction results in a shortened energy recovery life.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of an anodizing apparatus for performing a method of the present invention.

FIG. 2 is a process diagram (part 1) of one embodiment of the method of the present invention. A to C are cross-sectional views of each step.

FIG. 3 is a process diagram (part 2) of one embodiment of the method of the present invention. A to D are cross-sectional views of the respective steps.

FIG. 4 is a process chart (part 1) of another embodiment of the method of the present invention. A to C are cross-sectional views of each step.

FIG. 5 is a process diagram (part 2) of another embodiment of the method of the present invention. A and B are cross-sectional views of the respective steps.

FIG. 6 is a process chart (1) of another embodiment of the method of the present invention. AE are cross-sectional views of each step.

FIG. 7 is a process diagram (part 2) of another embodiment of the method of the present invention. A and B are cross-sectional views of the respective steps.

FIG. 8 is a process chart of another embodiment of the method of the present invention. A ~
F is a cross-sectional view of each step.

FIG. 9 is a process chart (part 1) of another embodiment of the method of the present invention. A to D are cross-sectional views of the respective steps.

FIG. 10 is a process chart of another embodiment of the method of the present invention (part 2).
It is. A to D are cross-sectional views of the respective steps.

FIG. 11 is a process chart of another embodiment of the method of the present invention (part 1).
It is. A and B are cross-sectional views of the respective steps.

FIG. 12 is a process chart of another embodiment of the method of the present invention (part 2).
It is. A and B are cross-sectional views of the respective steps.

FIG. 13 is a process chart of another embodiment of the method of the present invention (part 3).
It is. A and B are cross-sectional views of the respective steps.

FIG. 14 is a process chart of another embodiment of the method of the present invention (part 4).
It is. A and B are cross-sectional views of the respective steps.

FIG. 15 is a process chart of another embodiment of the method of the present invention (part 1).
It is. A to D are cross-sectional views of the respective steps.

FIG. 16 is a process chart of another embodiment of the method of the present invention (part 2).
It is. A and B are cross-sectional views of the respective steps.

FIG. 17 is a process chart of another embodiment of the method of the present invention. A
1 to E are cross-sectional views of the respective steps.

FIG. 18 is a process chart of another embodiment of the method of the present invention. A
1 to E are cross-sectional views of the respective steps.

FIG. 19 is a process chart of another embodiment of the method of the present invention (part 1).
It is. A and B are cross-sectional views of the respective steps.

FIG. 20 is a process chart of another embodiment of the method of the present invention (part 2).
It is. A and B are cross-sectional views of the respective steps.

FIG. 21 is a process chart of another embodiment of the method of the present invention (part 1).
It is. A to C are cross-sectional views of each step.

FIG. 22 is a process chart of another embodiment of the method of the present invention (part 2).
It is. A and B are cross-sectional views of the respective steps.

FIG. 23 is a schematic view of a micrograph of a main part of a porous layer before heat treatment in the method of the present invention.

FIG. 24 is a schematic view of a micrograph of a main part after heat treatment of a porous layer in the method of the present invention.

FIG. 25 is a process chart of another embodiment of the method of the present invention (part 1).
It is. A to E are cross-sectional views of the respective steps.

FIG. 26 is a process chart of another embodiment of the method of the present invention (part 2).
It is. A to D are cross-sectional views of the respective steps.

FIG. 27 is a process chart of another embodiment of the method of the present invention (part 3).
It is. A to C are cross-sectional views of the respective steps.

FIG. 28 is a process chart of another embodiment of the method of the present invention (part 4).
It is. A and B are cross-sectional views of each of the steps.

FIG. 29 is a configuration diagram of another example of the anodizing apparatus for performing the method of the present invention.

[Explanation of symbols]

Reference Signs List 11 semiconductor substrate, 12 porous layer, 12M, 12
M ₁ , 12M ₂ middle porosity layer, 12H high porosity layer,
12H ₁ first high porosity layer, 12H ₂ second high porosity layer, 13 semiconductor film, 131 first semiconductor film, 13
2 second semiconductor film, 133 third semiconductor film, 14,
103 adhesive, 15 support substrate, 16 insulating film, 16
W opening, 23 thin film semiconductor, 17 electrodes or wiring, 18 transparent substrate, 19 wiring, 20 printed circuit board, 21 adhesive, 23 thin film semiconductor, 24 electrodes, 4
1 conductive wire, 42 transparent substrate, 43 insulating material, 44 protective insulating layer, 101, 105 semiconductor layer, 102, 106
Electrode, 107 light emitting element

Claims (31)

[Claims] A step of forming a porous layer composed of two or more layers having different porosity by changing a surface of a semiconductor substrate; a step of growing a semiconductor film on a surface of the porous layer; Separating the semiconductor film from the semiconductor substrate via the porous layer. A step of forming a first porous layer by changing a surface of the semiconductor substrate; and forming the first porous layer in the first porous layer or at an interface between the first porous layer and the semiconductor substrate. Forming a second porous layer having a higher porosity than the first porous layer; forming a semiconductor film on the surface of the first porous layer; Separating the semiconductor substrate from the semiconductor substrate via the porous layer. 3. The method according to claim 1, wherein the semiconductor film is an epitaxially grown film. 4. The method according to claim 2, wherein said semiconductor film is an epitaxially grown film. 5. The method according to claim 1, wherein in the step of forming the porous layer, a layer having a low porosity is formed on the surface, and a layer having a high porosity is formed on the inner side near the semiconductor substrate. Method of manufacturing a thin film semiconductor. 6. In the step of forming the porous layer, a surface layer having a low porosity; an intermediate porosity layer having a higher porosity than the surface layer between the surface layer and the semiconductor substrate; 2. The thin film semiconductor according to claim 1, wherein a high porosity layer having a higher porosity than the intermediate porosity layer is formed in the layer or at an interface between the intermediate porosity layer and the semiconductor substrate. Method. 7. The thin film semiconductor according to claim 1, wherein the step of forming the porous layer is an anodizing step of forming the porous layer by anodizing the surface of the semiconductor substrate. Production method. 8. The method according to claim 1, wherein the step of forming the porous layer includes a step of anodizing the surface of the semiconductor substrate at a low current density, and a step of subsequently anodizing the surface of the semiconductor substrate at a high current density. The manufacturing method of the thin film semiconductor according to the above. 9. The step of forming the porous layer includes: a step of anodizing the surface of the semiconductor substrate at a low current density; a step of anodizing at an intermediate low current density higher than the low current density; 2. The method of manufacturing a thin film semiconductor according to claim 1, wherein: 10. The method of manufacturing a thin film semiconductor according to claim 8, wherein in the anodization step at a high current density in the step of forming the porous layer, a current is intermittently passed. 11. The thin film semiconductor according to claim 9, wherein the current density is gradually or stepwise increased in the anodization step at the intermediate low current density in the step of forming the porous layer. Method. 12. The thin film semiconductor according to claim 7, wherein the anodization in the step of forming the porous layer is performed in an electrolytic solution containing hydrogen fluoride and ethanol or hydrogen fluoride and methanol. Manufacturing method. 13. The thin film according to claim 7, wherein in the anodization step in the step of forming the porous layer, the current density of the anodization is changed and the composition of the electrolytic solution is changed. Semiconductor manufacturing method. 14. The method according to claim 7, wherein in the anodizing step in the step of forming the porous layer, the anodizing is performed in a dark place. 15. The method according to claim 1, further comprising, after the step of forming the porous layer, a heat treatment step of heating in a hydrogen gas atmosphere. 16. The thin film according to claim 15, further comprising a step of thermally oxidizing the porous layer between the step of forming the porous layer and the step of heating in a hydrogen gas atmosphere. Semiconductor manufacturing method. 17. The method according to claim 1, wherein the semiconductor substrate is a single crystal silicon substrate. 18. The method according to claim 1, wherein the semiconductor substrate is doped with boron (B) at a high concentration. 19. The method according to claim 1, wherein the semiconductor film to be grown on the surface of the porous layer is a multilayer semiconductor film having two or more semiconductor layers. Method. 20. A semiconductor device comprising: a step of bonding a substrate to the semiconductor film; and a step of peeling the semiconductor film from the semiconductor substrate in a state where the substrate and the semiconductor film are integrated. A method for manufacturing a thin film semiconductor according to claim 1. 21. A step of forming a porous layer composed of two or more layers having different porosity by changing the surface of a semiconductor substrate, and forming at least an active portion of a solar cell on the surface of the porous layer. A method for manufacturing a solar cell, comprising: a step of forming a multilayer semiconductor film to be constituted; and a peeling step of peeling the multilayer semiconductor film from a semiconductor substrate via the porous layer. 22. The method according to claim 21, wherein the multilayer semiconductor film is an epitaxial semiconductor film. 23. The multi-layer semiconductor film having a high impurity concentration of p
22. The method for manufacturing a solar cell according to claim 21, comprising a type semiconductor layer, a p-type semiconductor layer having a lower impurity concentration than the type semiconductor layer, and an n-type semiconductor layer. 24. A method comprising: forming an insulating film on a surface of the multilayer semiconductor film; and forming an electrode connected to the multilayer semiconductor film through a contact window formed in the insulating layer. The method for manufacturing a solar cell according to claim 21. 25. A step of bonding a transparent printed substrate to the surface on which the electrodes are formed, and a step of integrally peeling the printed substrate together with the multilayer semiconductor film from the semiconductor substrate via the porous layer. The method for manufacturing a solar cell according to claim 21, comprising: 26. A step of forming an electrode or a wiring on a predetermined portion of the multilayer semiconductor film formed on the surface of the semiconductor substrate, a step of bonding a conductive wire to the electrode or the wiring, and thereafter, Joining the semiconductor substrate on a transparent substrate such that the free ends of the conductive wires are led out to the outside on the side where the conductive wires are joined; and then peeling off the multilayer semiconductor film from the semiconductor substrate. 22. The method for manufacturing a solar cell according to claim 21, wherein a step is performed. 27. A plurality of semiconductor substrates each having the multilayer semiconductor film formed thereon and having a conductive line bonded to an electrode or a wiring formed at a predetermined portion thereof, wherein each of the plurality of semiconductor substrates has a conductive line bonded to the electrode or the wiring. 22. The method according to claim 21, further comprising: bonding the free end of the conductive wire to a common transparent substrate so that the free end of the conductive wire is led out; 3. The method for manufacturing a solar cell according to 1. 28. A porous structure comprising two or more layers including a porous layer constituting a light emitting portion on the surface side of a semiconductor substrate by changing the surface of the semiconductor substrate and a separation layer having a high porosity inside the substrate. A method for manufacturing a light-emitting element, comprising: forming a layer; and removing a porous layer constituting the light-emitting portion from the semiconductor substrate via the separation layer. 29. The porous layer constituting the light emitting section is pn
The method according to claim 28, further comprising a junction, wherein the pn junction is formed by impurity diffusion. 30. After the formation of the porous layer, the method further includes the step of forming an impurity-containing semiconductor film on the porous layer, wherein the porous layer constituting the light emitting section and the impurity-containing porous layer are formed. The method according to claim 28, wherein a pn junction is formed. 31. The method according to claim 28, further comprising a step of forming an electrode on the porous layer and a step of forming an electrode on the back surface of the porous layer after the peeling step.
A method for manufacturing the light-emitting element according to the above.