JPH1079330A - Manufacture of thin film semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a thin film semiconductor, having excellent crystallizability, easily and accurately at low cost by a method wherein a porous layer is formed on the surface of a semiconductor substrate, a semiconductor film is grown thereon, and the porous layer is exfoliated from the semiconductor substrate. SOLUTION: A porous layer 12 is formed on the surface of a semiconductor substrate 11 by anodizing the surface of the semiconductor substrate 11. An Si semiconductor film 13 is formed on the porous layer 12 by epitaxially growing. External force is applied to between the semiconductor substrate 11 and a supporting substrate 61 in the direction which pulls apart them. Separation is made on the highly porous layer 12 or in its vicinity, and the semiconductor film 13, where an integrated circuit is formed, is exfoliated from the semiconductor substrate 11 together with the supporting substrate 61. Accordingly, a flexible semiconductor film 13, which is formed in deposition on the flexible substrate 61, is formed and a thin film semiconductor can be produced in high volume at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single semiconductor device comprising a semiconductor element such as a thin film transistor, or a semiconductor integrated circuit (IC) comprising a plurality of semiconductor elements.
The present invention relates to a method for manufacturing a thin film semiconductor that can constitute various semiconductor devices such as an IC card and a solar cell.

[0002]

2. Description of the Related Art Single semiconductor devices, semiconductor integrated circuits, and ICs
To configure various semiconductor devices such as cards and solar cells, the thickness of the devices should be made sufficiently small to reduce the size of the equipment. For example, in a solar cell, the conversion efficiency of light-electricity should be increased, or the thickness should be further reduced. This makes it possible to simplify the assembling of various devices and to increase the benefits in use.

[0003]

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing a thin-film semiconductor which can easily and reliably obtain a thin-film semiconductor at low cost from the above-mentioned objects.

[0004]

In a method of manufacturing a thin film semiconductor according to the present invention, a step of changing the surface of a semiconductor substrate to a porous layer, a step of forming a semiconductor film on the porous layer, and a step of A step of removing the porous film from the semiconductor substrate via the porous layer and a step of removing the porous film remaining on the semiconductor substrate of the porous layer by etching are employed.

According to the manufacturing method of the present invention described above, a porous layer is formed on the surface of a semiconductor substrate, a semiconductor film is formed thereon, and the semiconductor film is formed by utilizing a decrease in strength of the porous layer. Since the thin film semiconductor is formed by separating the semiconductor film from the base, the thickness can be controlled by the thickness of the semiconductor film. Therefore, the thickness can be made sufficiently thin, for example, a flexible thin film semiconductor.

According to the manufacturing method of the present invention, a semiconductor thin film is formed on a porous layer formed on a surface of a semiconductor substrate,
This is separated by a porous layer, and in the present invention, the semiconductor substrate used for the production of the thin film semiconductor by the above-described method is again subjected to the same method to repeat the semiconductor film, It is used as a semiconductor substrate for producing a thin film semiconductor. That is, the above-described peeling of the semiconductor film is performed on the porous layer, and the peeling is performed at the interface between the porous layer and the semiconductor substrate in the thickness direction (the interface with the semiconductor substrate is not made porous). In the case where the semiconductor layer is separated within the porous layer irrespective of the mode in which the semiconductor layer is separated in the porous layer, the porous layer is formed on the separated surface of the semiconductor substrate after the semiconductor film is separated. However, in this case, in the method of the present invention, since the porous film remaining on the semiconductor substrate side is removed by etching, when the semiconductor substrate is used again, Even in the case where the semiconductor substrate surface itself is changed to a porous layer, the porous film is removed and the semiconductor substrate surface is made to have a surface with excellent crystallinity. It can be formed as a porous layer having a predetermined porosity with good realizability, and the semiconductor film formed thereon can be formed with a stable and reproducible semiconductor film having the desired characteristics, and therefore a thin film semiconductor. can do.

Therefore, according to the manufacturing method of the present invention, a thin-film semiconductor can be manufactured easily and reliably in mass production and at low cost.

[0008]

Embodiments of the present invention will be described.
In the present invention, the porous layer is formed by changing the surface of the semiconductor substrate by, for example, anodization. This porous layer is a porous layer composed of two or more layers having different porosity from each other. Then, a semiconductor film is epitaxially grown on the surface of the porous layer, and a circuit element or an integrated circuit is formed thereon. Thereafter, the epitaxial semiconductor film is peeled off from the semiconductor substrate via the porous layer to manufacture a target thin film semiconductor device.

On the other hand, the remaining semiconductor substrate is repeatedly used in the above-mentioned production of the thin film semiconductor. In particular, in the present invention, the porous layer remaining on the semiconductor substrate prior to the reuse thereof is used. A step of removing the porous film for removing the film by etching is performed.

[0010] The step of removing the porous film remaining on the semiconductor substrate by etching can be carried out by etching with a chemical and subsequent electrolytic etching by anodization. This etching chemical is a mixture of hydrofluoric and nitric acid,
Alternatively, a mixed liquid of hydrofluoric nitric acid and acetic acid, or a mixed liquid of hydrofluoric nitric acid and hydrogen peroxide can be used.

The semiconductor substrate which has been repeatedly used and has a reduced thickness can be used as a thin film semiconductor itself.

In the step of forming the porous layer, a layer having a low porosity is formed facing the surface thereof, and a layer having a high porosity is formed on the side closer to the non-porous semiconductor substrate, that is, on the inner side.

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; It is possible to form a high porosity layer having a higher porosity than the intermediate porosity layer, formed in the intermediate porosity layer or at the lower layer of the intermediate porosity layer, that is, at the interface with the semiconductor substrate that has not been made porous. it can.

In the anodization for forming the porous layer,
The step of anodizing the surface of the semiconductor substrate at a low current density is followed by the step of anodizing at a high current density.

Further, in the anodization, 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 slightly higher than the low current density, and a step of further anodizing at a higher current density. And a step of anodizing.

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

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

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 the current density is changed, the composition of the electrolytic solution can also be changed.

After forming the porous layer, it is preferable to heat in a hydrogen gas atmosphere. Further, it is preferable to thermally oxidize the porous layer after the porous layer is formed and before the heating step in a hydrogen gas atmosphere.

The semiconductor substrate is formed, for example, in accordance with the semiconductor film formed on the porous layer on the surface of the semiconductor substrate, for example, Si single crystal, polycrystal, SiG or the like.
A semiconductor substrate of e, GaAs, GaP or the like can be used. For example, in the case of forming a thin film semiconductor using a compound semiconductor, a compound semiconductor substrate is used as a semiconductor substrate. When a compound semiconductor is epitaxially grown on this porous layer, a lattice mismatch can be reduced as compared with, for example, the case where a 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.
In any of the semiconductor substrates made of SiGe, GaAs, GaP or the like, a porous layer can be formed on the surface by performing anodization.

The shape of the semiconductor substrate can take various configurations. For example, various shapes such as a wafer shape, a disk shape, or a columnar ingot obtained by pulling a single crystal having a curved base surface can be used.

Further, the semiconductor substrate is an n-type or p-type
A semiconductor substrate doped with impurities, or
And a semiconductor substrate. Only
However, when performing anodization, p-type impurities are doped at a high concentration.
So-called "p"⁺Si group
It is preferred to use a body. As this semiconductor substrate, p ⁺
When a p-type impurity is used, for example, boron
B is about 10¹⁹atoms / cm^ThreeDoped to the extent that its resistance
Use a Si substrate having a thickness of about 0.01 to 0.02 Ωcm.
Is desirable. And this p⁺Anodizing of Si substrate
Then, a fine hole elongated in a direction almost perpendicular to the substrate surface
Is formed and becomes porous while maintaining the crystallinity.
A better porous layer is formed.

A semiconductor film is epitaxially grown on the porous layer while maintaining the crystallinity. This semiconductor film can be composed of a single-layer semiconductor film or a multi-layer semiconductor film of two or more layers.

As described above, the semiconductor film epitaxially grown on the semiconductor substrate is peeled off from the semiconductor substrate. Prior to the peeling, for example, a support substrate such as a flexible resin sheet is bonded on the semiconductor film to form a contact with the support substrate. After the integration with the epitaxial semiconductor film, the epitaxial semiconductor film and the supporting substrate can be peeled off 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 printed substrate on which required printed wiring is formed. is there.

On the surface of the semiconductor substrate, 2 having different porosity are used.
A porous layer composed of at least two layers is formed. The outermost porous layer is formed as a dense porous layer having a relatively small porosity, so that an epitaxial semiconductor film can be favorably grown on the porous layer. That is, on the lower layer side, by forming a porous layer having a relatively high porosity along the surface of the substrate, the mechanical strength is reduced due to its own high porosity, or the lattice constant between this porous layer and the other is reduced. Weakened by the strain based on the difference, peeling of the epitaxial semiconductor film in this layer,
That is, separation can be easily performed. For example, it is possible to form a porous layer that is weak enough to be separated by application of ultrasonic waves.

In a layer having a higher porosity formed inside the surface of the porous layer, the larger the porosity is, the easier the above-mentioned peeling becomes. However, if the porosity is too large, the above-mentioned epitaxial semiconductor film may be damaged. Before peeling treatment, or peeling may cause damage to the porous layer,
The porosity of the layer having the large porosity is 40% or more and 7% or more.
0% or less.

When a layer having a high porosity is formed on the porous layer, the strain increases as the porosity increases. If the strain affects 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 above-mentioned 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 facing the electrode 3A is eroded and becomes porous.

According to the two-tank cell method, it is not necessary to form an ohmic electrode on the semiconductor substrate, and the introduction of impurities from the ohmic electrode into the semiconductor substrate is avoided.

The selection of the conditions for the anodization significantly changes the structure of the porous layer to be formed, whereby the crystallinity and releasability of the above-described epitaxial semiconductor film formed thereon are reduced. Change.

In order to form a porous layer composed of two or more layers having different porosity, a multi-stage anodization method having two or more steps having different current densities is employed in the anodization treatment.
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, when the second anodization is performed at a considerably high current density, a high porosity high porous layer is formed below the low porosity porous layer formed first. 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, a large strain is generated near the interface between the low porosity porous layer and the high porosity porous layer due to the difference in the lattice constant between the two. When this distortion exceeds a certain value, the porous layer separates into two. Therefore, if the porous layer is formed under anodizing conditions near the boundary condition of whether separation due to this strain or separation due to decrease in mechanical strength due to porosity occurs or not, growth on this porous layer A semiconductor film, for example, an epitaxial semiconductor film, can be easily separated via the 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 HF: C ₂ H ₅ OH = 1: 1 (HF is 49%). % Solution and ethanol in a 95% solution (by volume) (the same applies hereinafter) at a low current density of about 0.5 to ¹⁰ mA / cm ² for several minutes to several tens of 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 first and second anodizations described above, since the strain generated in the highly porous layer inside the porous layer becomes considerably large, the influence of the strain extends to the surface of the porous layer. In this case, as described above, cracks occur,
There is a risk 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 HF: C ₂ H ₅ OH = 1: 1 as an electrolytic solution.
When using, about 0.5 to less than 3 mA / cm ² , the second
The current density of the anodization is, for example, about 3 to ²⁰ mA / cm ² , and the current density of the third anodization is, for example, 40 to 300 m
It is preferable to carry out at about A / cm ² . For example, 1 mA /
When anodizing is performed at a current density of ² cm ² , the porosity is about 16
% Of, when the anodization at a current density of 7 mA / cm ^2, a porosity of about 26%, when the anodization at a current density of 200 mA / cm ^2, the porosity becomes about 60% to 70%. 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 surface layer having a low porosity formed by the first anodization maintains the low porosity as it is and is formed by the second anodization. The intermediate porosity layer, which has a somewhat higher porosity, that is, the buffer layer is formed inside the surface layer, that is, at the interface between the surface layer and the non-porous semiconductor substrate, and the porous layer is It has a two-layer structure with an intermediate porosity layer. The principle of the high porosity layer having a high porosity formed by the third anodization is not known, but if the current density is about 90 mA / cm ² or more, the intermediate layer formed by the second anodization may be used. It is formed in the porosity layer, that is, at an intermediate portion in the thickness direction of the intermediate 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 where 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 can be formed by a large strain caused by a difference in lattice constant at the interface between the release layer having the highest porosity and the buffer layer having the low porosity performed immediately before the separation layer. If a device is devised during the last anodization, the separation surface can be more easily separated. It is the last high current density anodization,
For example, instead of energizing for a constant time of 3 seconds, after energizing for 1 second, anodizing is temporarily stopped, and after a required time elapses, for example, left for about 1 minute, the same or different high current density is applied again. Anodization is stopped by energizing for
Further, after a required time elapses, for example, after being left for about 1 minute, the current is applied again at the same or different high current density for 1 second to stop the anodization. When an appropriate anodizing condition is selected using this method, a release layer is formed at the interface with the semiconductor substrate, that is, at the lowermost surface of the porous layer, and the separation surface is formed inside the intermediate porous layer, that is, the buffer layer as described above. Instead, they are separated at the interface between the porous layer and the semiconductor substrate. Then, the semiconductor substrate side surface is electropolished.

In this case, the surface of the highly porous layer where the distortion occurs in the porous layer is maximally separated from the surface, and the buffer effect of the intermediate porosity layer is maximized.
An epitaxial semiconductor film having good crystallinity can be formed. In addition, since the intermediate porous layer is formed only on the surface side, the overall thickness of the porous layer can be reduced, and the consumption thickness of the semiconductor substrate for forming the porous layer is reduced. This makes it possible to increase the number of times the semiconductor substrate is repeatedly used.

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.

Further, in order to epitaxially grow a semiconductor with good crystallinity on the porous layer, it is desired to reduce 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 performing anodization, it is preferable to perform the anodization in a dark place where light is blocked. This means that when you illuminate,
This is because irregularities increase on the surface of the porous layer, and it becomes difficult to obtain an epitaxial semiconductor film having good crystallinity.

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, contrary to the above, 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 the 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, usually 8 μm.
m. 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.

It is preferable to anneal the porous layer before forming the semiconductor film on the porous layer. The annealing may be a heat treatment in a hydrogen gas atmosphere, that is, a hydrogen annealing. When performing this hydrogen annealing, the natural oxide film formed on the surface of the porous layer can be completely removed, and oxygen atoms in the porous layer can be removed as much as possible, so that the surface of the porous layer becomes smooth. Thus, an epitaxial semiconductor film having good crystallinity can be formed. At the same time, the strength of the interface between the high porosity layer and the intermediate porosity layer can be further reduced by this pretreatment, and the epitaxial semiconductor film can be more easily separated from the substrate. 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, the semiconductor is epitaxially grown on the surface of the porous layer as described above. 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, 700C to 1100C.

In any of the above-described hydrogen annealing and the epitaxial growth of the semiconductor, a method of heating the semiconductor substrate to a predetermined substrate temperature may be a so-called susceptor heating method, or a method in which a current is directly applied to the semiconductor substrate itself. An electric heating method of flowing and heating can be employed.

The semiconductor film 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, using a single crystal Si semiconductor substrate, Si or a compound semiconductor such as GaAs, or a silicon compound, for example, Si _1-y Ge _y is epitaxially grown on a porous layer formed on the surface thereof, or a combination thereof is appropriately laminated. And various other types of epitaxial growth.

The semiconductor film has n
Type or p-type impurities can be introduced. Alternatively, after the semiconductor film is formed, 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.

Also, the thickness of the semiconductor film can 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.

The surface of the epitaxial semiconductor film obtained as described above has some irregularities. The surface of the epitaxial film is exposed to a photoresist in, for example, a photolithography process performed in a process of forming a circuit element or an integrated circuit on the semiconductor film. When inconveniences such as a decrease in mask alignment accuracy of the exposure apparatus occur, it is preferable to polish the semiconductor film surface. In this case, the porous layer is brittle,
Since the porous layer is weak, the polishing is performed without imposing a load on the porous layer.

Next, in forming a semiconductor device, a circuit element or an integrated circuit is formed on a semiconductor film. For example, DRAM (Dynamic Random Access Memory)
And CMOS (Complementary Matal Oxide Semiconduc
tor) or the like, or an integrated circuit combining these elements. These circuit elements or integrated circuits can be generally formed by general semiconductor manufacturing techniques. All circuits that can be formed on a semiconductor substrate by using, for example, a diffusion furnace, an ion implantation apparatus, an exposure apparatus, a CVD (chemical vapor deposition) apparatus, a sputtering apparatus, a cleaning apparatus, a dry etching apparatus, and an epitaxial growth apparatus. It can be applied to an element or an integrated circuit. Further, as the circuit element or the integrated circuit, for example, each semiconductor element such as a diode and a transistor, a digital or analog
For example, a solar cell can be configured irrespective of its type, such as C or flash memory.

As described above, it is preferable that the entire thin film semiconductor device in which the circuit element or the integrated circuit is formed on the semiconductor film is covered with the insulating layer.

After the circuit element or the integrated circuit is formed as described above, a supporting substrate is bonded to the semiconductor film, that is, the thin film semiconductor device. The type of the support substrate is not limited, such as a resin substrate, a glass substrate, a metal substrate, and a ceramic substrate. For example, the IC card may be configured by being attached to a flexible substrate, a cover sheet, or the like that configures the IC card. Also on the support substrate,
A circuit element or an integrated circuit can also be formed, and can be constituted by a printed board or the like. The method of bonding the support substrate includes, for example, an adhesive, solder,
Bonding with an adhesive material or the like can be performed, and the bonding strength is a bonding strength equal to or higher than the peeling strength through the porous layer performed later, that is, a bonding strength that does not break the bonding by the force required for peeling. A bonding agent is used which has such an adhesive strength that the supporting substrate and the semiconductor film are integrated and the semiconductor film can be peeled off from the semiconductor substrate.

After the support substrate and the semiconductor film have been integrated in this manner, the porous layer is separated from the semiconductor substrate by internal destruction. In a porous layer having a highly porous layer, this separation is easily separated by the highly porous layer.

In some cases, a porous layer may remain on the surface of the semiconductor film thus peeled off from the semiconductor substrate, and this porous layer may be polished,
This is removed by etching or the like. Further, it may be as it is without being removed. Alternatively, a protective film may be attached or a protective substrate such as a resin substrate may be bonded to protect the peeled surface.

The thin film semiconductor manufactured as described above or a semiconductor device using the same has a circuit element or an integrated circuit formed on a thin film semiconductor made of a semiconductor film formed by extremely thin epitaxial growth, and utilizes the characteristics of being flexible and thin. For example, the present invention can be applied to electronic devices such as portable devices and the like, such as IC cards, and is adapted to recent light and thin.

On the other hand, the surface of the separated semiconductor substrate is polished and reused. For example, the thickness of the substrate consumed for manufacturing one thin-film semiconductor device is about 3 to 20 μm. Therefore, the thickness consumed even for ten times of repeated use is about 30 to 200 μm. Therefore, an expensive single-crystal semiconductor substrate can be repeatedly used, so that the method of the present invention
A thin-film semiconductor device can be manufactured at extremely low cost and low energy. If epitaxial growth is performed on the surface of the semiconductor substrate, the same semiconductor substrate can be used forever, and a thin-film semiconductor device can be manufactured at lower cost and lower energy.

Next, an embodiment of the present invention will be described.
However, the invention is not limited to this embodiment.

[Embodiment 1] FIGS. 1 and 2 show a process chart of this embodiment. First, a wafer-shaped semiconductor substrate 11 made of single-crystal Si doped with boron at a high concentration and having a specific resistance of, for example, 0.01 to 0.02 Ωcm) was prepared (FIG. 1A). . Then, the surface of the semiconductor substrate 11 was anodized 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,
A semiconductor substrate 11 made of single crystal Si was placed between the first and second tanks 1A and 1B, and HF: C ₂ H ₅ OH = 1: 1 was injected into both tanks 1A and 1B. A DC power source 2 is connected between the Pt electrodes 3A and 3B immersed in the electrolytic solution 4 of the electrolytic solution tanks 1A and 1B.
Caused the current to flow.

First, the current density was set to a low current of 1 mA / cm ² , and the current was applied for 8 minutes. As a result, a surface layer 12S having fine pores with a small diameter, forming a porous layer having a dense porosity of 16% and a thickness of 1.7 μm was formed (FIG. 1B). If the micropores on the surface of the porous layer are small, the surface of the porous layer becomes flatter and smoother by the H ₂ annealing performed later, and the crystallinity of the Si epitaxial semiconductor film epitaxially grown later on the porous layer is further improved. effective. Thereafter, the energization is temporarily stopped. Next, the current density was set to 7 mA / cm ² and energization was performed for 8 minutes. By doing so, under the surface layer 12S,
An intermediate porosity layer 12M having a porosity of 26% and a thickness of 6.3 μm having a higher porosity than this surface layer was formed.
C). Thereafter, the energization is stopped again. Next, the current density was increased to 200 mA / cm ² , and energization was performed for 3 seconds. By doing so, the porosity of about 60%, which is higher than the surface layer 12S and the intermediate porosity layer 12M, is sandwiched between the intermediate porosity layer 12M, that is, from above and below, by the intermediate porosity layer 12M. Thus, a high porosity layer 12H having a thickness of about 0.05 μm is formed (FIG. 1D). Thus, the porous layer 12 including the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H is formed.

In the porous layer 12 thus formed, since the porosity of the intermediate porosity layer 12M and the porosity of the high porosity layer 12H are largely different, a large strain is generated at these interfaces and near the interfaces. The strength becomes extremely weak. However, this distortion is caused by the presence of the intermediate porosity layer 12M between the high porosity layer 12H and the surface layer 12S, which acts as a buffer and causes the surface of the porous layer to be greatly affected by the distortion. Can be reduced. Therefore, the influence of the strain on the crystallinity of the epitaxial growth performed later on the porous layer can be effectively avoided.

Thereafter, in a normal-pressure Si epitaxial growth apparatus in which epitaxial growth is performed later, the semiconductor substrate 11 having the porous layer 12 is placed in an H ₂ atmosphere for 1 hour.
Heating at 100 ° C., ie, annealing was performed. In this annealing, the temperature was raised from room temperature to 1100 ° C. over about 20 minutes, and annealing was performed at 1100 ° C. for about 30 minutes. By the H ₂ annealing, the surface layer formed by the small holes having a small diameter becomes flat and smooth. At the same time, inside the porous layer 12, the separation strength was further reduced near the interface between the intermediate porosity layer 12M and the high porosity layer 12H.

Thereafter, Si was epitaxially grown on the porous layer 12, that is, on the surface layer 12S, in a normal-pressure Si epitaxial growth apparatus subjected to H ₂ annealing to form a Si semiconductor film 13 (FIG. 2E). This epitaxial growth is performed at the annealing temperature of 110 in the H ₂ atmosphere.
The temperature was lowered from 0 ° C. to 1030 ° C., and Si epitaxial growth using SiH ₄ gas was performed for 17 minutes. Thus, the Si layer having excellent crystallinity and a thickness of about 5 μm is formed on the porous layer 12.
The epitaxial semiconductor film 13 was formed.

At this time, the Si epitaxial semiconductor film 1
3. If the surface has irregularities, this surface is polished. The high porosity layer 12H has the above-described strain and a weak force to prevent the porosity of the layer from becoming frost columnar and weakened with a high porosity so that the separation strength is very weak. Was polished. Thereby, the surface of the epitaxial semiconductor film 13 became flatter. By doing so, for example, mask alignment of the exposure apparatus can be performed with higher accuracy.

The semiconductor film 13 is separated from the semiconductor substrate 11. First, a support substrate 61 made of a PET (polyethylene terephthalate) sheet is bonded onto the semiconductor film 13 via an adhesive 60 (FIG. 2F).

The bonding strength of the support substrate 61 at this time is set to a strength higher than the separation strength of the porous layer 12 from the semiconductor substrate 11, that is, an adhesion strength that does not cause separation of the support substrate 61 during separation.

Next, an external force is applied between the semiconductor substrate 11 and the support substrate 61 in a direction to separate them. In this way, separation occurs at or near the high porosity layer 12H of the porous layer 12 having a low strength as described above, and the semiconductor film 13 on which the integrated circuit is formed together with the support substrate 61 from the semiconductor substrate 11 is formed. Peeled off (FIG. 2G).

In this manner, the flexible substrate 6
For example, a flexible semiconductor film 13 having a thickness of, for example, 5 μm is formed.

In this case, a porous film having a thickness of 5 μm is formed on the separation surface of the semiconductor substrate 11 from the semiconductor film 13 due to the remaining porous layer 12 recrystallized by annealing in the H ₂ atmosphere. 22 are present.

The porous film 2 remaining on the semiconductor substrate 11
2 is removed by etching. The etching of the porous film 22 is performed by using a chemical such as hydrofluoric nitric acid, that is, hydrofluoric acid HF.
The semiconductor substrate 11 is immersed in an etching solution of a mixed solution of water, nitric acid HNO ₃ and water H ₂ O. Thus, the porous film 22 is removed by etching (FIG. 2H).

Further, the semiconductor substrate 11 is subjected to electrolytic polishing using the anodizing apparatus shown in FIG. In this case, both tanks 1A and 1B have HF: C
An electrolytic solution with ₂ H ₅ OH = 1: 2 is injected. And, 200 mA / cm ² between the Pt electrodes 3 A and 3 B,
Energization was performed for 15 seconds. At this time, the surface of the semiconductor substrate 11 was electrolytically polished, and a surface having good crystallinity was exposed on the substrate surface.

As described above, the semiconductor substrate 11 on which the surface having good crystallinity is exposed is reused, and the semiconductor substrate 11 shown in FIG.
2 are repeated to obtain a plurality of thin film semiconductors.

[Embodiment 2] In this embodiment, the surface layer 12S is formed on the surface of the semiconductor substrate 11 by the same method as that of the embodiment 1 and employing the steps described with reference to FIGS. 1A to 1D.
Then, the porous layer 12 in which the high porosity layer 12H is formed is formed in the intermediate porosity layer 12M.

In this example, after the formation of the porous layer 12, annealing was performed at 400 ° C. for one hour in an oxygen atmosphere using a diffusion furnace. By this treatment, the inside of the porous layer 12 is oxidized, and H
_{(2) A} large structural change can be prevented from occurring in the porous layer even by annealing in an atmosphere.
It is possible to more effectively avoid the effect of the strain generated near the interface of 2H on the surface layer 12S.

Thereafter, as in the first embodiment, annealing is performed in an H ₂ atmosphere by a normal pressure Si epitaxial growth apparatus, and then a 5 μm-thick semiconductor film having excellent crystallinity is formed by Si epitaxial growth as in the first embodiment. 13 were formed (FIG. 2E).

Also in this case, when the surface of the Si epitaxial semiconductor film 13 has irregularities, this surface is polished. The high porosity layer 12H has the above-described strain and a weak force to prevent the porosity of the layer from becoming frost columnar and weakened with a high porosity so that the separation strength is very weak. Was polished. Thereby, the surface of the epitaxial semiconductor film 13 became flatter. By doing so, for example, mask alignment of the exposure apparatus can be performed with higher accuracy.

The semiconductor film 13 is separated from the semiconductor substrate 11 by the same method as in the first embodiment. (FIGS. 2F and 2
G).

In this manner, as in the first embodiment, a flexible semiconductor film 13 having a thickness of, for example, 5 μm and formed on the flexible substrate 61 is formed.

Also in this case, a 5 μm-thick porous film is formed on the separation surface of the semiconductor substrate 11 from the semiconductor film 13 due to the remaining porous layer 12 recrystallized by annealing in the H ₂ atmosphere. The membrane 22 is present.

Thereafter, in this embodiment, the porous film 22 remaining on the semiconductor substrate 11 is converted into an etching solution by a mixed solution of hydrofluoric acid, hydrogen peroxide H ₂ O ₂ and water H ₂ O. The substrate 11 is removed by etching by dipping (FIG. 2H).

Then, the semiconductor substrate 11 is subjected to electrolytic polishing by using the anodizing apparatus shown in FIG. In this case, both tanks 1A and 1B have HF: C
An electrolytic solution with ₂ H ₅ OH = 1: 2 is injected. And, 200 mA / cm ² between the Pt electrodes 3 A and 3 B,
Energization was performed for 15 seconds. At this time, the surface of the semiconductor substrate 11 was electrolytically polished, and a surface having good crystallinity was exposed on the substrate surface.

As described above, the semiconductor substrate 11 on which the surface with good crystallinity is exposed is reused, and a similar process is repeated. Thus, a plurality of thin film semiconductors can be obtained.

Next, an embodiment of the present invention for producing a solar cell will be described.

[Embodiment 3] Referring to FIGS. 3 and 4, this embodiment will also be described with reference to FIGS. 1A to 1D.
The surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12
A porous layer 12 of H is formed. Then, annealing was performed in an H ₂ atmosphere similar to that described in Example 1, and thereafter, the semiconductor film 13 was epitaxially grown (FIG. 3A). The semiconductor film 13 in this embodiment has a p ⁺ -p
⁻ −n ^{+ It has a} three-layer structure.

Epitaxial growth of this semiconductor film 13
Is H_Two Atmospheric pressure Si epitaxy annealed in atmosphere
SiH_FourGas and B_TwoH₆With gas
Epitaxial growth was performed for 3 minutes, and boron B was 10
¹⁹atoms / cm^ThreeP doped in ⁺First semiconducting silicon
A body layer 131 is formed, and then B_TwoH₆Change gas flow
Then, perform Si epitaxial growth for 10 minutes,
B is 10¹⁶atoms / cm^ThreeLightly doped p^-S
i to form a second semiconductor layer 132, _Two H₆
PH instead of gas_ThreeSupply gas and epitaxial growth
Go for 4 minutes, p^-Epitaxial semiconductor layer 132
On top, phosphorus P is 10¹⁹atoms / cm^ThreeHighly doped
N⁺Forming a third semiconductor layer 133 of Si,
From the first to third epitaxial semiconductor layers 131 to 133
Becomes p⁺-P^--N⁺A semiconductor film 13 having a structure was formed.

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. 3B). This opening 16W
Can be formed in parallel with each other in the form of stripes extending in a direction perpendicular to the plane of the drawing while maintaining a required interval. With the SiO ₂ film formed in this way, 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. 4C). The metal film forming the electrode or the wiring 17 is, for example, a 30 nm thick Ti film.
It can be constituted by a multilayer structure film formed by sequentially depositing a film, Pd having a thickness of 50 nm, and Ag having a thickness of 100 nm, and further performing Ag plating thereon. Then 40
Annealing was performed at 0 ° C. for 20 to 30 minutes.

Next, in this embodiment, a conductive wire 41, in this embodiment, a metal wire is bonded on the striped electrodes or wirings 17 along these, respectively, and a transparent adhesive 21 is placed thereon. Thereby, the transparent substrate 42 is joined (FIG. 4D). Conductivity 4 to electrode or wiring 17
1 can be joined by soldering. These conductive wires 41 have one end or the other end longer than the electrode or the wiring 17 and are 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. 5
E).

In this case, the porous layer 12 remains on the back surface of the thin-film semiconductor 23, and a silver paste is applied thereon and a metal plate is further joined to form the other back electrode 24. Thus, the transparent substrate 42 has p ⁺ -p ^-- n ⁺
A solar cell on which the thin film semiconductor 23 having the structure is formed is configured (FIG. 5F). 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 as described above, the light-receiving-side electrode or the wiring 17 is covered with the transparent substrate 42, but is electrically led to the outside through 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.

Then, the solar cell, ie, the semiconductor film 13
The same etching and electrolytic etching as in Example 1 are performed on the semiconductor substrate 11 from which the semiconductor substrate 11 has been peeled off. That is, the porous film 22 is removed by etching with hydrofluoric nitric acid, and the semiconductor substrate 11 is further subjected to electrolytic polishing using the anodizing apparatus shown in FIG.
In this case, both tanks 1A and 1B are both HF: C ₂ H
An electrolytic solution with ₅ OH = 1: 2 is injected. And P
A current of 200 mA / cm ² was applied between the t electrodes 3A and 3B for 15 seconds. At this time, the surface of the semiconductor substrate 11 was electropolished, and a surface having good crystallinity was exposed on the substrate surface (FIG. 6).

In this manner, a plurality of solar cells can be obtained by repeating the steps of forming the semiconductor film 13 as described above on the semiconductor substrate 11 on which the surface having good crystallinity is exposed.

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

In each of the above examples, in the anodization,
When the current density is large, or when the semiconductor, for example, Si is peeled off due to long-time energization, and Si scraps are generated due to this, and adhere to the inside of the device, for example, an electrolytic solution tank, the semiconductor substrate 11 is taken out. By injecting the hydrofluoric-nitric acid solution into the tank, unnecessary deposits of Si can be dissolved and removed. Further, the apparatus for performing anodization is not limited to the example shown in FIG. 7, and an apparatus for immersing a semiconductor substrate in a single-tank structure can be used.

In addition, a semiconductor substrate having a thickness reduced by manufacturing a thin film semiconductor or a solar cell is epitaxially grown on a semiconductor having a thickness commensurate with the reduced thickness. By repeatedly performing the above, 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 described above, the semiconductor substrate has a porous layer formed on the surface, the semiconductor is epitaxially grown thereon, and the semiconductor layer is peeled off. Although only the thickness is consumed, after the formation and peeling of the epitaxial semiconductor film described above, the surface of the semiconductor substrate is removed by etching and electrolytic etching.
Can be repeatedly used to produce a plurality of thin-film semiconductors of interest, that is, thin-film half-type, for example, flexible semiconductor devices.

The thickness of the semiconductor substrate 11 is reduced by forming the porous layer. The thickness of the semiconductor substrate 11 is compensated by epitaxially growing a semiconductor having a thickness corresponding to the decrease in the thickness. You can also do so. Also, when not compensating for the thickness,
When the thickness is reduced, 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 the manufacturing method of the present invention, when the electrolytic etching is finally performed, the subsequent step of forming the porous layer 12 can be continuously performed.

According to the above-described manufacturing method, after the supporting substrate 42 is joined to the semiconductor film 13 to integrate the substrate and the epitaxial semiconductor film, the substrate is peeled off from the semiconductor substrate together with the epitaxial semiconductor film. The method can be adopted, there is no limitation on the type of this substrate, flexible printed circuit board, rigid printed circuit board, metal plate, ceramic, glass, resin, etc., which could not be considered at all by conventional common sense of semiconductor technology A thin film single crystal semiconductor can be formed over such a substrate, or a solar cell can be formed.

When the semiconductor layer is simply grown epitaxially on a porous layer having a single porosity, the semiconductor film may have good crystallinity in order to improve the crystallinity. Since it is necessary to reduce the porosity of the layer, the current density is lowered 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, according to the method described above, the porosity of the surface portion of the porous layer is reduced to form a porous layer having a two-sided property that the porosity inside the porous layer is large. 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. However, in the above-described method, an intermediate porous layer having a somewhat higher porosity than the surface layer is provided between the very high porosity layer and the low porosity surface layer as a buffer layer for relaxing the strain generated from these layers. By forming the index layer, a high-quality epitaxial semiconductor film which is easy to peel off can be formed.

In the anodization at a high current density in the above-described method, when a current is intermittently applied, a high porosity layer can be formed on the porous layer at the semiconductor substrate side interface or in the vicinity thereof. In this case, 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 thinned, the thickness of the porous layer can be reduced accordingly, and the thickness of the semiconductor substrate can be reduced. The consumption in the down direction can be reduced, and the cost can be further reduced.

In anodization at a low current density,
When the current is gradually increased, when the porosity of the buffer layer between the surface layer of the porous layer and the release layer is gradually increased toward the inside, the function of the buffer layer is further improved. be able to.

The porous layer can be easily formed by performing the 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.

By avoiding light irradiation during anodization, the occurrence of irregularities on the surface of the porous layer 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.

[0113]

According to the manufacturing method of the present invention described above, a crystal layer is formed by forming a porous layer on the surface of a semiconductor substrate, growing a semiconductor film thereon, and peeling the semiconductor layer from the semiconductor substrate in the porous layer. Although it is possible to easily, reliably and inexpensively produce a thin film semiconductor having excellent properties, the present invention further provides that the remaining semiconductor substrate can be reused by removing the porous layer. Thus, the semiconductor substrate can be effectively used, and can be configured at a lower cost.

[Brief description of the drawings]

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

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

FIG. 3 is a process diagram (part 1) of another embodiment of the method of the present invention. A and B are cross-sectional views of the respective steps.

FIG. 4 is a process diagram (part 2) of another embodiment of the method of the present invention. C and D are sectional views of the respective steps.

FIG. 5 is a process diagram (part 3) of another embodiment of the method of the present invention. EF are cross-sectional views of each step.

FIG. 6 is a process diagram (part 4) of another embodiment of the method of the present invention.

FIG. 7 is a configuration diagram of an example of an anodizing apparatus for performing the method of the present invention.

[Explanation of symbols]

Reference Signs List 11 semiconductor substrate, 12 porous layer, 12M intermediate porosity layer, 12H high porosity layer, 13 semiconductor film, 131
1st semiconductor film, 132 2nd semiconductor film, 133 3rd semiconductor film, 41 conductive lines, 42 transparent substrate

Claims (6)

[Claims] A step of converting a semiconductor substrate surface into a porous layer; a step of forming a semiconductor film on the porous layer; and a step of peeling the semiconductor film from the semiconductor substrate via the porous layer. A step of removing the porous film remaining on the semiconductor substrate of the porous layer by etching with a chemical agent. 2. The method according to claim 1, wherein an electrolytic etching by anodization is performed after the step of removing the porous film remaining on the semiconductor substrate by etching. 3. The method according to claim 4, wherein the chemical is a mixed solution of hydrofluoric nitric acid, a mixed solution of hydrofluoric nitric acid and acetic acid, or a mixed solution of hydrofluoric nitric acid and hydrogen peroxide. A method for manufacturing a thin film semiconductor. 4. The method according to claim 1, wherein the semiconductor film formed on the porous layer is an epitaxial semiconductor film. 5. The method according to claim 1, wherein after forming a circuit element or an integrated circuit on the semiconductor film, a step of separating the semiconductor film from the semiconductor substrate via the porous layer is performed. Method of manufacturing a thin film semiconductor. 6. The semiconductor substrate according to claim 1, wherein said semiconductor substrate is Si, SiGe, G
2. The method according to claim 1, wherein the method is based on one of aAs and GaP.