JP5360127B2 - Thin film semiconductor manufacturing method - Google Patents

Description

  The present invention provides a thin film semiconductor that can constitute a single semiconductor device made of a semiconductor element such as a thin film transistor, or various semiconductor devices such as a semiconductor integrated circuit (IC), an IC card, and a solar cell made of a plurality of semiconductor elements. Related to the method.

  To configure various semiconductor devices such as a single semiconductor device, a semiconductor integrated circuit, an IC card, and a solar cell, the thickness of the device is sufficiently reduced to reduce the size of the device. For example, in a solar cell, It is possible to increase the conversion efficiency or make it flexible by reducing the film thickness, thereby simplifying the assembly of various devices and improving the convenience of use.

Conventionally, as a method of manufacturing a thin film semiconductor, the surface of a Si single crystal substrate is made porous, a non-porous single crystal Si layer is formed on the porous Si, and then the Si support substrate and the single crystal Si layer are insulated layers. A method is known in which an SOI substrate is manufactured by laminating with porous Si and then separating with porous Si (see Patent Document 1).

Japanese Patent Laid-Open No. 7-302889

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

The method of the thin film semiconductor manufacturing present invention, a semiconductor substrate surface, so it so varied in three steps comprising sequentially increasing the current density in anodizing stages, and a porous surface layer of, under said surface layer A porous layer having an intermediate porosity layer having a higher porosity than the surface layer, and a surface layer inside the intermediate porosity layer and a high porosity layer having a higher porosity than the intermediate porosity layer. A step of changing to a layer. Then, after the surface of the formed porous layer is annealed in an oxygen atmosphere, there are a number of processes in which the surface is annealed in a hydrogen atmosphere. Furthermore, the method includes a step of forming an epitaxial semiconductor film on the porous layer and a step of peeling the epitaxial semiconductor film from the semiconductor substrate in the porous layer.

  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 on the porous layer, and the semiconductor film is peeled off from the semiconductor substrate by utilizing a decrease in strength in the porous layer. And since a thin film semiconductor is comprised by the peeled semiconductor film, since the thickness can be controlled by the thickness of a semiconductor film, this can be sufficiently thin, for example, can be comprised as a flexible thin film semiconductor.

Therefore, according to the manufacturing method of the present invention, it is possible to manufacture a thin film semiconductor easily and reliably at a low cost with mass production.

According to the above-described manufacturing method of the present invention, a porous layer is formed on the surface of a semiconductor substrate, a semiconductor film is grown on the porous layer, and the thin film having excellent crystallinity is peeled off from the semiconductor substrate in the porous layer. the semiconductor easily, reliably, Ru can be produced inexpensively.

It is process drawing (the 1) of one experimental example of this invention method. A to D are sectional views of the respective steps. It is process drawing (the 2) of one experimental example of this invention method. EH is sectional drawing of each process. It is process drawing (the 1) of the other experiment example of this invention method. A and B are sectional views of the respective steps. It is process drawing (the 2) of the other experiment example of this invention method. C and D are sectional views of the respective steps. It is process drawing (the 3) of the other experiment example of this invention method. EF is sectional drawing of each process. It is process drawing (the 4) of the other experiment example of this invention method. It is a block diagram of an example of the anodizing apparatus which enforces the method of this invention.

An embodiment of the present invention will be described.
In the present invention, the surface of the semiconductor substrate is changed by, for example, anodization to form a porous layer. This porous layer is a porous layer composed of two or more layers having different porosities. 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. After which the epitaxial semiconductor film via the porous layer, to produce a thin film semiconductors of interest is peeled from the semiconductor body.

On the other hand, remaining semiconductor body is Ru are used repeatedly in the production of thin film semiconductor described above again, particularly in the present invention, the porous layer prior to its reuse, the porous film remaining semiconductor body A step of removing the porous film to be etched away is performed.

  The step of removing the porous film remaining on the semiconductor substrate can be performed by etching with chemicals and subsequent electrolytic etching by anodization. As a chemical for this etching, a mixed solution of hydrofluoric acid, a mixed solution of hydrofluoric acid and acetic acid, or a mixed solution of hydrofluoric acid and hydrogen peroxide can be used.

  In addition, the semiconductor substrate that has been repeatedly used to reduce its thickness can 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 a layer having a high porosity is formed on the side close to the semiconductor substrate that is not made porous, that is, on the inner side.

  Further, 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, and the intermediate porosity. A high-porosity layer that is formed in the 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, and has a higher porosity than the intermediate porosity layer can be formed.

  In the anodization for forming the porous layer, a step of anodizing the surface of the semiconductor substrate at a low current density and a step of anodizing at a high current density are performed thereafter.

  Further, in anodizing, the step of anodizing the surface of the semiconductor substrate at a low current density, the step of anodizing at an intermediate low current density slightly higher than the low current density, and the anodizing at a higher current density than this step. Process.

  Further, in the anodization, the anodization at the high current density can intermittently energize the high current density.

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

  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 anodizing step, the composition of the electrolytic solution can be changed when changing the current density.

  After forming the porous layer, it is preferable to heat in a hydrogen gas atmosphere. Moreover, it is preferable to thermally oxidize a porous layer before the heating process in hydrogen gas atmosphere after forming a porous layer.

The semiconductor substrate is formed thereon, that is, depending on the semiconductor film formed on the porous layer on the surface of the semiconductor substrate, for example, a semiconductor substrate made of Si single crystal, polycrystal, SiGe, GaAs, GaP or the like is used. 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 the semiconductor substrate. If a compound semiconductor is epitaxially grown on this porous layer, for example, a lattice mismatch can be made smaller than when a compound semiconductor is epitaxially grown on a Si semiconductor substrate, so that a thin film compound semiconductor having good crystallinity can be obtained. Can be formed. In any of the semiconductor substrates such as SiGe, GaAs, and GaP, the porous layer can be formed on the surface by anodizing.

  Various shapes can be adopted as the shape of the semiconductor substrate. For example, various shapes such as a wafer shape, that is, a disk shape, or a cylindrical ingot formed by pulling a single crystal having a curved substrate surface can be used.

The semiconductor substrate can be constituted by a semiconductor substrate doped with n-type or p-type impurities, or a semiconductor substrate not containing impurities. However, when anodizing is performed, it is preferable to use a low specific resistance semiconductor substrate so-called p ⁺ Si substrate doped with a high concentration of p-type impurities. When a p ⁺ -type Si substrate is used as the semiconductor substrate, a p-type impurity such as boron B is doped to about 10 ¹⁹ atoms / cm ³ and the resistance is about 0.01 to 0.02 Ωcm. It is desirable to use it. When the p ⁺ -type Si substrate to anodization, elongated elongated micropores substantially vertically to the substrate surface is formed, for porous quality of keeping the crystallinity, desirably porous layer is formed.

Such crystalline remains porous quality of porous layer was maintained, the semiconductor film is epitaxially grown. The semiconductor film may be constituted by a semiconductor film of a single layer may be a two or more layers of the multilayer semiconductor film.

  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 joined to the semiconductor substrate, and the support substrate and the epitaxial semiconductor film are bonded. Then, the epitaxial semiconductor film can be peeled from the semiconductor substrate together with the supporting substrate through a porous layer formed on the semiconductor substrate.

  The support substrate is not limited to a flexible sheet, but can be constituted by a glass substrate, a resin substrate, or a flexible or rigid so-called rigid transparent printed substrate on which a required printed wiring is made, for example.

  A porous layer composed of two or more layers having different porosities is formed on the surface of the semiconductor substrate. The outermost porous layer is formed as a dense porous layer having a relatively small porosity so that an epitaxial semiconductor film can be satisfactorily grown on the porous layer, and the inner side of the surface layer That is, on the lower layer side, by forming a porous layer having a relatively high porosity along the substrate surface, the mechanical strength is lowered by increasing the porosity of the porous layer itself, or the lattice constant between this porous layer and others is reduced. The layer is weakened by strain based on the difference, and the epitaxial semiconductor film can be easily peeled off, that is, separated in this layer. For example, it is possible to form a porous layer that is weak enough to be separated by application of ultrasonic waves.

  The layer formed on the inner side of the surface of the porous layer with the increased porosity becomes easier as the porosity increases. However, if the porosity is too high, the above-described epitaxial semiconductor film may be peeled off. In addition, peeling may occur or the porous layer may be damaged. Therefore, the porosity of the layer having a large porosity is set to 40% or more and 70% or less.

  In addition, when a layer having a high porosity is formed in the porous layer, the strain increases as the porosity increases. When the influence of this strain reaches the surface layer of the porous layer, the surface layer is cracked. There is a risk of generating it. Further, when the influence of strain occurs on the surface of the porous layer in this way, crystal defects are generated in the semiconductor film epitaxially grown thereon. Therefore, the porous layer has a higher porosity than the surface layer as a buffer layer to relieve strain between the layer with high porosity and the surface layer with low porosity. Thus, an intermediate porosity layer having an intermediate porosity with a low porosity is formed. By doing so, the porosity of the high-porosity layer is increased to such an extent that the above-described epitaxial semiconductor film can be reliably peeled off, and an epitaxial semiconductor film having excellent crystallinity can be formed. .

The above-mentioned anodization of the surface of the semiconductor substrate is performed by a known method, for example, surface technology Vol. 46, no. 5, pp. 8-13, 1995 [Anodic conversion of porous Si]. That is, for example, it can be performed by the double cell method whose schematic configuration is shown in FIG. In this method, an electrolytic solution tank 1 having a two-tank structure 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 disposed between both tanks 1A and 1B, and each one of a pair of platinum electrodes 3A and 3B connected to a DC power source 2 is disposed in both tanks 1A and 1B. Is done. In the first and second tanks 1A and 1B of the electrolytic solution tank 1, for example, an electrolytic solution 4 containing hydrogen fluoride HF and ethanol C ₂ H ₅ OH, or hydrogen fluoride HF and methanol CH ₃ OH, respectively. In the first and second tanks 1A and 1B so that both surfaces of the semiconductor substrate 11 are in contact with each other, and both electrodes 3A and 3B are placed in the electrolyte solution 4. Immersion arrangement. Then, the DC power source 2 is connected between the electrodes 3A and 3B with the electrode 3A side immersed in the electrolytic solution 4 in the tank 1A on the surface side where the porous layer of the semiconductor substrate 11 is to be formed as the negative electrode side. Energization is performed. In this way, power is supplied with the semiconductor substrate 11 side as the anode side and the electrode 3A as the cathode side, whereby the surface of the semiconductor substrate facing the electrode 3A side is eroded and becomes porous.

  When this two-cell method is used, it is not necessary to deposit the ohmic electrode on the semiconductor substrate, and the introduction of impurities from the ohmic electrode into the semiconductor substrate is avoided.

  The structure of the porous layer to be formed changes considerably depending on the selection of conditions in this anodization, and this changes the crystallinity and peelability of the above-described epitaxial semiconductor film formed thereon.

In order to form a porous layer composed of two or more layers having different porosities, a multi-step anodizing method having two or more steps with different current densities is employed in the anodizing treatment. Specifically, in order to produce a relatively dense porous layer having a low porosity on the surface, that is, a fine pore having a small diameter, first, the first anodization is performed at a low current density. Since the film thickness of the porous layer is proportional to time, the anodization is performed in a time period that achieves a desired film thickness. Thereafter, if the second anodization is performed at a considerably high current density, a porous layer having a high porosity and a high porosity is formed below the porous layer having a low porosity formed first. That is, the porous layer having a low low a Kutomo porosity low porosity quality layer, a high porosity high porosity layer is formed.

  In this case, a large strain is generated in the vicinity of the interface between the porous layer having a low porosity and the porous layer having a high porosity due to the difference in lattice constant between the two. When this strain exceeds a certain value, the porous layer separates into two. Therefore, if a porous layer is formed under an anodizing condition in the vicinity of the boundary condition of whether or not separation due to this strain or mechanical strength due to porosity will occur, it will be grown on this porous layer. A semiconductor film such as an epitaxial semiconductor film can be easily separated through this porous layer.

In this case, the first anodization with 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 (49% HF solution, When ethanol is a 95% solution (volume ratio) (hereinafter the same), it is performed for several minutes to several tens of minutes at a low current density of about 0.5 to ¹⁰ mA / cm ² . 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 two-stage anodization described above, the strain generated in the highly porous layer inside the porous layer becomes considerably large. Therefore, the influence of this strain extends to the surface of the porous layer. As described above, the generation of cracks and the possibility of generating crystal defects in the epitaxial semiconductor film formed thereon are caused. Therefore, the porous layer has a higher porosity than the surface layer as a buffer layer to relieve the distortion generated between the surface layer having a low porosity and the high porosity layer. An intermediate porosity layer having a lower porosity is formed. Specifically, the first anodization with a low current density is first performed, then the second anodization with a slightly higher current density than the first anodization is performed, and then the third anode with a much higher current density than those. Perform chemical conversion. The conditions for the first anodization are not particularly limited. For example, when 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 is used as the electrolytic solution, the first anodizing condition is 0. .5~3mA / cm ² less than about, about the current density of the second anodization example 3~20mA / cm ^2, current density of the third anodization, for example, is preferably carried out at 40~300mA / cm ² approximately. For example, when anodization is performed at a current density of 1 mA / cm ² , the porosity is about 16%, and when anodization is performed at a current density of 7 mA / cm ² , the porosity is about 26% and a current of 200 mA / cm ² . When anodizing is performed at a density, the porosity is about 60 to 70%. When epitaxial growth is performed on the anodized porous layer, an epitaxial semiconductor film with good crystallinity can be formed.

Further, as described above, when anodizing with three stages of current density is performed, the surface layer with low porosity formed by the first anodizing maintains the low porosity as it is, and the porosity formed by the second anodizing is maintained. A slightly higher intermediate porosity layer, i.e., a buffer layer, is formed inside the surface layer, i.e., at the interface between the surface layer and the non-porous semiconductor substrate. It becomes a two-layer structure with a layer. The principle of the high-porosity layer having a high porosity formed by the above-mentioned third anodization is unknown, but if the current density is about 90 mA / cm ² or more, the intermediate layer formed by the second anodization It is formed in the porosity layer, that is, in the intermediate portion in the thickness direction of the intermediate porous layer.

  Further, in the formation of the intermediate porosity layer, the anodization for forming the intermediate porosity layer is performed in a multi-stage or gradually under, for example, a condition in which the current density is changed, whereby a low porosity surface layer, a high porosity layer, An intermediate porosity layer is formed in which the porosity is increased stepwise or inclined from the surface layer toward the high porosity layer. In this way, the strain between the surface layer and the high porosity layer is further relaxed, and an epitaxial semiconductor film with good crystallinity can be epitaxially grown more reliably.

  By the way, the separation surface can be formed by applying a large strain due to the difference in lattice constant at the interface between the release layer having a large porosity performed last and the buffer layer having a low porosity performed immediately before. If the device is devised when anodizing is performed, the separation surface is more easily separated. It is the last anodization with a high current density. For example, it is not energized for a period of 3 seconds, but after an energization for 1 second, the anodization is temporarily stopped and left for about 1 minute after the required time has elapsed. After that, the anodization is stopped by energizing for 1 minute at the same or different high current density, and after leaving the required time, for example, after leaving for about 1 minute, the energization is again performed for 1 second at the same or different high current density. This is a method of intermittently energizing to stop the anodization. When an appropriate anodization condition is selected using this method, a release layer is formed at the interface with the semiconductor substrate, that is, the lowermost surface of the porous layer, and the separation surface is the inside of the intermediate porous layer, that is, the buffer layer as described above. Instead, they are separated at the interface of the porous layer with the semiconductor substrate. The surface of the semiconductor substrate side is electropolished.

  In this case, the highly porous layer where distortion occurs in the porous layer and the surface are separated as much as possible, and the buffer effect by the intermediate porosity layer is maximized, and the epitaxial semiconductor has good crystallinity. A film can be formed. In addition, since the intermediate porous layer is formed only on the surface side in this way, the entire thickness of the porous layer can be reduced, and the consumption thickness of the semiconductor substrate for forming this porous layer is reduced. Therefore, the number of repeated use of the semiconductor substrate can be increased.

  As described above, by selecting the anodizing conditions, a large strain can be applied to the separation surface, and the influence of this strain can be prevented from being applied to the epitaxial growth surface of the semiconductor film.

  Further, in order to perform semiconductor epitaxial growth on the porous layer with good crystallinity, it is desired to reduce the micropores that become seeds for crystal growth on the surface layer of the porous layer. As one of means for reducing the micropores in the surface layer as described above, there is a method of increasing the HF concentration in the electrolytic solution in anodizing. That is, in this case, first, 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 lowered, and finally anodization with a high current density is performed. By doing so, the fine pores of the surface layer can be made finer, 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 peeled off satisfactorily.

The change of the electrolytic solution in the anodization of the porous layer is, for example, in the formation of the surface layer, by performing anodization using an electrolytic solution such as HF: C ₂ H ₅ OH = 2: 1 as the electrolytic solution, In the formation of the intermediate porosity layer as a layer, anodization using an electrolytic solution with a slightly lower HF concentration, for example, an electrolytic solution with HF: C ₂ H ₅ OH = 1: 1 is performed, and further a high porosity layer is formed. In the method, the HF concentration of the electrolytic solution is further reduced, and anodization at a high current density is performed using an electrolytic solution of HF: C ₂ H ₅ OH = 1: 1 to 1: 2, for example.

  In the formation of the porous layer described above, when the current density is changed from the formation of the surface layer to the formation of the intermediate porosity layer, the anodization is temporarily stopped and then energization for the next anodization is started. It can also be carried out by changing the current density continuously without stopping anodization, that is, without stopping energization.

  Moreover, when performing anodization, it is preferable to carry out in the dark place which blocked light. This is because when the light is irradiated, the surface of the porous layer becomes uneven, making it difficult to obtain an epitaxial semiconductor film with good crystallinity.

  The anodized porous silicon layer 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 the light emission efficiency. Further, when oxidized, a blue shift occurs in the wavelength. Further, the semiconductor substrate may be p-type or n-type, but is preferably a high-resistance substrate that does not introduce impurities.

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

  Moreover, it is preferable to anneal the porous layer prior to forming the semiconductor film on the porous layer. This annealing can include heat treatment in a hydrogen gas atmosphere, that is, 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, and the surface of the porous layer becomes smooth. An epitaxial semiconductor film having good crystallinity can be formed. At the same time, the pretreatment can further weaken the strength of the interface between the high porosity layer and the intermediate porosity layer, 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 about 950 ° C. to 1150 ° C., for example.

  In addition, if the porous layer is oxidized at a low temperature before hydrogen annealing, the inside of the porous layer is oxidized, so that a large structural change occurs in the porous layer even if thermal annealing is performed in a hydrogen gas atmosphere. Absent. That is, it becomes difficult for the strain from the release layer to be transmitted to the surface of the porous layer, and a high-quality crystalline epitaxial semiconductor film can be formed. In this case, the low-temperature oxidation can be performed in a dry oxidation atmosphere at 400 ° C. for about 1 hour, for example.

  Then, as described above, the semiconductor is epitaxially grown on the porous layer surface. In the epitaxial growth of this semiconductor, since the porous layer formed on the surface of the single crystal semiconductor substrate is porous, it maintains its crystallinity, so that it can be epitaxially grown on this porous layer. The epitaxial growth on the surface of the porous layer can be performed, for example, at a temperature of 700 ° C. to 1100 ° C., for example, by a CVD method.

In both of the above-described hydrogen annealing and semiconductor epitaxial growth, a method of heating the semiconductor substrate to a predetermined substrate temperature can be a so-called susceptor heating method, or heating by direct current flow to the semiconductor substrate itself. It is also possible to adopt an electric heating method or the like.

The semiconductor film is grown on a porous layer can also be a multi-layer semiconductor film by lamination of a plurality of semiconductor layers may be a single layer semiconductor film. The semiconductor film may be the same material as the semiconductor substrate or a different material. For example, a single crystal Si semiconductor substrate is used, and a compound semiconductor such as Si or GaAs, or a silicon compound such as Si _1-y Ge _y is epitaxially grown on a porous layer formed on the surface thereof, or a combination thereof is appropriately laminated. Various epitaxial growths can be performed.

  Further, n-type or p-type impurities can be introduced into the semiconductor film during the growth. Alternatively, after the semiconductor film is formed, impurities can be introduced over the entire surface 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.

  Further, the thickness of the semiconductor film can be appropriately selected according to the use of the thin film semiconductor. For example, when the 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 a slight unevenness, and an exposure apparatus for exposing the photoresist in a photolithography process, for example, performed in the process of forming a circuit element or an integrated circuit on the semiconductor film. In the case where inconvenience such as a decrease in the accuracy of mask alignment occurs, it is preferable to polish the surface of the semiconductor film. In this case, since the porous layer is fragile and weak, weak polishing is performed so as not to burden the porous layer.

  Next, in the case of configuring a semiconductor device, a circuit element or an integrated circuit is formed on a semiconductor film. For example, a semiconductor element such as DRAM (Dynamic Random Access Memory) or CMOS (Complementary Matal Oxide Semiconductor) or an integrated circuit combining these elements is formed. These circuit elements or integrated circuits can usually be obtained by general semiconductor manufacturing techniques. For example, all circuits that can be formed on a semiconductor substrate using a diffusion furnace, ion implantation apparatus, exposure apparatus, CVD (chemical vapor deposition) apparatus, sputtering apparatus, cleaning apparatus, dry etching apparatus, epitaxial growth apparatus, etc. It can be applied to an element or an integrated circuit. In addition, as a circuit element or an integrated circuit, for example, each semiconductor element such as a diode or a transistor, a digital or analog IC, a flash memory, or the like can be used, for example, a solar cell.

  As described above, the thin film semiconductor device in which a circuit element or an integrated circuit is formed on a semiconductor film is preferably covered entirely with an insulating layer.

Thus, by forming a circuit element or an integrated circuit, the semiconductor film, i.e. a thin film semiconductor device, bonding the supporting substrate. The support substrate is not limited in its type 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 or a cover sheet that constitutes the IC card. Further, a circuit element or an integrated circuit can also be formed on the support substrate, and can be constituted by a printed circuit board or the like. This support substrate bonding method can be performed by, for example, bonding with an adhesive, solder, adhesive, or the like, and the bonding strength is equal to or higher than the peeling strength through the porous layer performed later, that is, the force required for peeling. Therefore, the bonding strength is such that the bonding does not break, and a bonding agent is used which exhibits an adhesive strength that can be used to integrate the supporting substrate and the semiconductor film and peel the semiconductor film from the semiconductor substrate.

  Thus, after integrating a support substrate and a semiconductor film, a porous layer is peeled from this by a destruction inside. This peeling is easily separated in the porous layer having the highly porous layer.

  A porous layer may remain on the peeled surface of the semiconductor film thus peeled from the semiconductor substrate, and this porous layer is removed by polishing, etching or the like, if necessary. To do. Further, it may be left 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 peeling surface.

  A thin film semiconductor manufactured as described above or a semiconductor device using the thin film semiconductor has a circuit element or an integrated circuit formed on a thin film semiconductor by an extremely thin epitaxial growth, and is flexible and thin. For example, it can be applied to an electronic device such as an IC card and a portable device, and is adapted to lightness, thinness and smallness in recent years.

  On the other hand, the separated semiconductor substrate is used again after its surface is polished. For example, since the thickness of the substrate consumed for manufacturing one thin film semiconductor device is about 3 to 20 μm, the thickness consumed even after 10 repeated uses is about 30 to 200 μm. Therefore, since an expensive single crystal semiconductor substrate can be used repeatedly, the method of the present invention can manufacture a thin film semiconductor device with extremely low cost and low energy. If the epitaxial growth for the amount consumed on the surface of the semiconductor substrate is performed, the same semiconductor substrate can be used permanently, and a thin film semiconductor device can be manufactured at low cost and low energy.

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

[ Experimental Example 1]
1 and 2 show process diagrams of this experimental example . First, a wafer-like 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 experimental example , anodization was performed using the two-tank structure anodizing apparatus described in FIG. That is, the semiconductor substrate 11 made of single crystal Si was disposed 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. Then, a current was passed by the DC power source 2 between the Pt electrodes 3A and 3B immersed in the electrolytic solutions 4 of the electrolytic solution tanks 1A and 1B.

First, the current density was set to a low current of 1 mA / cm ² and this was energized for 8 minutes. As a result, a surface layer 12S constituting a porous layer having fine pores with a small diameter, 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 subsequent H ₂ annealing, and the crystallinity of the Si epitaxial semiconductor film that grows epitaxially on the surface 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. Thus, an intermediate porosity layer 12M having a porosity of 26% and a thickness of 6.3 μm was formed under the surface layer 12S (FIG. 1C). Thereafter, the energization is stopped again. Next, the current density was increased to 200 mA / cm ² and energization was performed for 3 seconds. In this way, the porosity of about 60% of the porosity higher than that of the surface layer 12S and the intermediate porosity layer 12M so as to be sandwiched 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). In this way, the porous layer 12 is formed by the surface layer 12S, the intermediate porosity layer 12M, and the high porosity layer 12H.

  The porous layer 12 thus formed has a large difference in porosity between the intermediate porosity layer 12M and the high porosity layer 12H, so that a large strain is generated at these interfaces and in the vicinity of the interfaces, and the strength in the vicinity thereof is extremely high. Weakens. However, this strain acts as a buffer due to the presence of the intermediate porosity layer 12M between the high porosity layer 12H and the surface layer 12S, and the surface of the porous layer is greatly affected by this strain. The effect of distortion can be mitigated. Therefore, this strain can effectively avoid the influence of the epitaxial growth performed later on the porous layer on the crystallinity.

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 was heated at 1100 ° C., that is, annealed in an H ₂ atmosphere. 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 this H ₂ annealing, the surface layer by the fine holes having a small diameter becomes flat and smooth. At the same time, in the porous layer 12, the separation strength became even weaker in the vicinity of the interface between the intermediate porosity layer 12 </ b> M and the high porosity layer 12 </ b> H.

Thereafter, Si was epitaxially grown on the porous layer 12, that is, on the surface layer 12S in the atmospheric pressure Si epitaxial growth apparatus subjected to H ₂ annealing to form the Si semiconductor film 13 (FIG. 2E). In this epitaxial growth, the temperature was lowered from the annealing temperature of 1100 ° C. to 1030 ° C. in the previous H ₂ atmosphere, and Si epitaxial growth using SiH ₄ gas was performed for 17 minutes. As a result, a Si epitaxial semiconductor film 13 having excellent crystallinity and a thickness of about 5 μm was formed on the porous layer 12.

  At this time, if the surface of the Si epitaxial semiconductor film 13 is uneven, this surface is polished. The high-porosity layer 12H has the above-described strain and is made into a frost column shape with a high porosity, so that it is weakened and the separation strength is very weak. Polishing was performed. As a result, the surface of the epitaxial semiconductor film 13 became flatter. By doing in this way, it can perform with higher precision, for example in mask alignment of an exposure apparatus.

  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 adhesive strength of the support substrate 61 at this time is set to a strength stronger than the separation strength from the semiconductor substrate 11 by the porous layer 12, that is, an adhesive strength that does not cause the support substrate 61 to be peeled off during the separation.

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

  In this way, the flexible semiconductor film 13 having a thickness of, for example, 5 μm and formed on the flexible substrate 61 is formed.

In this case, a porous film 22 having a film thickness of 5 μm is present 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 described above. To do.

The porous film 22 remaining on the semiconductor substrate 11 is removed by etching. In the etching of the porous film 22, the semiconductor substrate 11 is immersed in an etching solution of a chemical, in this example, hydrofluoric acid, that is, a mixture of hydrofluoric acid HF, nitric acid HNO _3, and water H ₂ O. In this way, the porous film 22 is removed by etching (FIG. 2H).

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

  In this manner, the semiconductor substrate 11 having a surface with good crystallinity is reused, and the steps described with reference to FIGS. 1 and 2 described above are repeated, whereby a plurality of thin film semiconductors can be obtained.

[ Experiment 2]
Also in this experimental example , the process described in FIGS. 1A to 1D is performed in the same manner as in experimental example 1, and the surface layer 12S and the intermediate porosity layer 12M are formed on the surface of the semiconductor substrate 11 with a high porosity. The porous layer 12 formed with the rate layer 12H is formed.

In this experimental example , after the porous layer 12 was formed, annealing was performed at 400 ° C. for 1 hour in an oxygen atmosphere using a diffusion furnace. 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 the subsequent annealing in the H ₂ atmosphere, and the vicinity of the interface of the high porosity layer 12H. Can more effectively avoid the influence of the distortion generated on the surface layer 12S.

Thereafter, as in Experimental Example 1 , annealing in an H ₂ atmosphere is performed by an atmospheric pressure Si epitaxial growth apparatus, and then the semiconductor film 13 having a good crystallinity with a thickness of 5 μm is formed by Si epitaxial growth as in Experimental Example 1. (FIG. 2E).

  Even in this case, if the surface of the Si epitaxial semiconductor film 13 is uneven, this surface is polished. The high-porosity layer 12H has the above-described strain and is made into a frost column shape with a high porosity, so that it is weakened and the separation strength is very weak. Polishing was performed. As a result, the surface of the epitaxial semiconductor film 13 became flatter. By doing in this way, it can perform with higher precision, for example in mask alignment of an exposure apparatus.

The semiconductor film 13 is separated from the semiconductor substrate 11 by the same method as in Experimental Example 1. (FIG. 2F, FIG. 2G).

In this manner, the flexible semiconductor film 13 having a thickness of, for example, 5 μm and formed on the flexible substrate 61 is formed in the same manner as in Experimental Example 1 .

Even in this case, the porous film 22 having a film 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 described above. Exists.

Thereafter, in this experimental example , the porous substrate 22 remaining on the semiconductor substrate 11 is used as an etching solution containing hydrofluoric acid, hydrogen peroxide H ₂ O ₂ , and water H ₂ O. Etching is removed by dipping (FIG. 2H).

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

  In this manner, a plurality of thin film semiconductors can be obtained by reusing the semiconductor substrate 11 having a surface with good crystallinity and repeating the same process.

Next, an experimental example in the case of manufacturing a solar cell according to the present invention will be described.

[ Experimental Example 3]
Will be described with reference to FIGS. 3-4, also in this experimental example, take the steps shown in FIG 1A~D by the same method as Experimental Example 1, by anodizing the surface of the semiconductor substrate 11, the surface layer The porous layer 12 is formed by 12S, the intermediate porosity layer 12M, and the high porosity layer 12H formed therein. Then, annealing in the same H ₂ atmosphere as the method described in Experimental Example 1 was performed, and then the semiconductor film 13 was epitaxially grown (FIG. 3A). The semiconductor film 13 in this experimental example has a p ⁺ -p ⁻ −n ⁺ three-layer structure.

The epitaxial growth of the semiconductor film 13 is performed by performing epitaxial growth using SiH ₄ gas and B ₂ H ₆ gas for 3 minutes in an atmospheric pressure Si epitaxial growth apparatus that has been annealed in an H ₂ atmosphere, so that boron B is 10 ¹⁹ atoms / First semiconductor layer 131 made of p ⁺ Si doped in cm ³ is formed, and then the flow rate of B ₂ H ₆ gas is changed and Si epitaxial growth is performed for 10 minutes, so that boron B is 10 ¹⁶ atoms / low concentration doped cm ^{3 p} - a second semiconductor layer 132 is formed by Si, and supplies PH ₃ gas in place of the more _B 2 _{H 6} gas, by performing epitaxial growth for 4 minutes, p ^- epitaxial On the semiconductor layer 132, the third semiconductor layer 1 of n ⁺ Si doped with phosphorus P at a high concentration of 10 ¹⁹ atoms / cm ^3. 33 was formed, and the semiconductor film 13 having a p ⁺ -p ⁻ −n ⁺ structure composed of the first to third epitaxial semiconductor layers 131 to 133 was formed.

Next, in this experimental example , an SiO ₂ film, that is, a transparent insulating film 16 is formed on the semiconductor film 13 by surface thermal oxidation, and an opening 16W for making contact with an electrode or wiring by performing pattern etching by photolithography is provided. Form (FIG. 3B). The openings 16W can be formed in parallel with a stripe shape extending in a direction orthogonal to the paper surface in the drawing while maintaining a required interval. With the SiO ₂ film thus formed, it is possible to minimize the generation of carriers and recombination at the interface.

  Then, a metal film is deposited on the entire surface, and pattern etching by photolithography is performed to form electrodes or wirings 17 on the light receiving surface side along the stripe-shaped openings 16W (FIG. 4C). The metal film forming this electrode or wiring 17 is a multilayer formed by, for example, sequentially depositing a Ti film with a thickness of 30 nm, Pd with a thickness of 50 nm, and Ag with a thickness of 100 nm, and further performing Ag plating thereon. It may be constituted by a structural film. Thereafter, annealing was performed at 400 ° C. for 20 to 30 minutes.

Next, in this experimental example , a conductive wire 41, a metal wire in this experimental example , are joined to the striped electrodes or wirings 17 along these, respectively, and a transparent adhesive 21 is used on the conductive wire 41. The substrate 42 is bonded (FIG. 4D). Bonding of the conductive member 41 to the electrode or the wiring 17 can be performed by soldering. These conductive wires 41 are led out outward by making one end or the other end longer than the electrode or wiring 17.

  Thereafter, an external force is applied to the semiconductor substrate 11 and the transparent substrate 42 to separate them from each other. In 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 in which the epitaxial semiconductor film 13 is bonded on the transparent substrate 42. A semiconductor 23 is obtained (FIG. 5E).

In this case, although 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 bonded to form the other back electrode 24. In this manner, a solar cell is formed in which the thin film semiconductor 23 having the p ⁺ -p ⁻ -n ⁺ structure is formed on the transparent substrate 42 (FIG. 5F). The metal electrode 24 also functions as an element layer protective film on the back surface of the solar cell.

In the solar cell thus formed, the light receiving side electrode or the wiring 17 is covered with the transparent substrate 42, but the electrical external derivation from this is performed by the conductive wire 41. Can be easily connected. Further, for example, as in the above-described experimental example, the conductive line 41 is derived from each of the plurality of electrodes or wirings 17 that are in contact with the epitaxial semiconductor film 13, that is, the active part of the solar cell. Thus, the series resistance of the solar cell can be made sufficiently small.

Then, the same etching and electrolytic etching as in Experimental Example 1 are performed on the solar cell, that is, the semiconductor substrate 11 from which the semiconductor film 13 has been peeled off. That is, the porous film 22 is removed by etching with hydrofluoric acid, and the semiconductor substrate 11 is electropolished using the anodizing apparatus shown in FIG. In this case, an electrolytic solution in which HF: C ₂ H ₅ OH = 1: 2 is injected into both tanks 1A and 1B. Then, energization was performed at 200 mA / cm ² for 15 seconds between the Pt electrodes 3A and 3B. At this time, the surface of the semiconductor substrate 11 was electrolytically polished, and a surface with good crystallinity was exposed on the surface of the substrate (FIG. 6).

In this manner, the semiconductor substrate 11 to be surface crystallinity is exposed, repeatedly form Naruko degree or the like of the same semiconductor film 13 and described above, it is possible to obtain a plurality of solar cells.

  In each of the above-described examples, the epitaxial semiconductor film is peeled off from the semiconductor substrate 11 by applying an external force that separates the epitaxial semiconductor films from each other. However, in some cases, the epitaxial semiconductor film can be peeled off by ultrasonic vibration.

In each of the examples described above, when the current density is large in the anodization or when the semiconductor, for example, Si is peeled off due to a long-time energization, the silicon waste is generated and adhered to the electrolytic solution tank, etc. in the apparatus. , after removal of the semiconductor substrate 11, it is possible to dissolve and remove the deposits unwanted Si by injection of hydrofluoric nitric acid solution in the bath. The apparatus for performing anodization is not limited to the example of FIG. 7, and an apparatus for immersing a semiconductor substrate in a single tank structure can be used.

  In addition, the above-described thin film solar cell is repeatedly manufactured by epitaxially growing a semiconductor having a thickness corresponding to the reduced thickness on a semiconductor substrate whose thickness is reduced by manufacturing the thin film semiconductor and the solar cell. By doing so, since the same semiconductor substrate can be used permanently, a 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 is formed with a porous layer on the surface, the semiconductor is epitaxially grown on the semiconductor layer, and the semiconductor substrate is peeled off. However, since the surface of the semiconductor substrate is removed by etching and electrolytic etching after the formation and peeling of the epitaxial semiconductor film described above, the target thin film semiconductor is repeatedly used again. That is, since a plurality of various thin-film semiconductor devices, for example, flexible semiconductor devices, can be manufactured, it can be manufactured at low cost.

  Further, although the semiconductor substrate 11 is thinned 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 thickness reduction. You can also. Further, when the thickness is not compensated when the thickness is not compensated, the semiconductor substrate itself can be used as a thin film semiconductor, and for example, a solar cell can be manufactured. Therefore, the semiconductor substrate can be used almost without waste without finally becoming ineffective, and this can also reduce the cost.

  In the production method of the present invention, when electrolytic etching is finally performed, the next porous layer 12 forming step can be performed continuously thereafter.

Further, according to the manufacturing method described above, on the semiconductor film 13, after integrating the substrate and the epitaxial semiconductor layer by bonding a supporting substrate 42, a substrate with an epitaxial semiconductor film, a method for peeling the semiconductor body Since there are no restrictions on the type of this substrate, flexible printed circuit boards, rigid printed circuit boards, metal plates, ceramics, glass, resins, etc., which have never been considered by conventional common sense in semiconductor technology A thin film single crystal semiconductor can be formed on a substrate, or a solar cell can be formed.

In addition, when a method of epitaxially growing a semiconductor layer on a porous layer having a single porosity is used, in order to improve the crystallinity of the semiconductor film, the porosity of the porous layer serving as the nucleus of crystal growth it is necessary to reduce the rate, against the anodization, to lower the current density, it is necessary to increase the HF mixing ratio of the electrolytic solution. However, when the porosity is lowered as described above, the porous layer becomes hard and separation of the epitaxial semiconductor film becomes difficult. Therefore, in order to increase the porosity in order to weaken the separation strength, for example, if the current density is increased and the HF mixing ratio of the electrolytic solution is reduced in the anodizing conditions, separation is facilitated in this case. The crystallinity of the epitaxial semiconductor film is extremely deteriorated. However, when the above-described method is used, 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. The epitaxial semiconductor film can be satisfactorily formed thereon, and the epitaxial semiconductor film can be easily separated. For example, it is possible to form a porous layer that is weak enough to be easily separated by ultrasonic waves.

Further, the high porosity layer formed on the porous layer becomes easier to peel off as the porosity increases, but the strain is large, and the influence is exerted on the surface layer of the porous layer. Therefore, there is a crack occurs in the surface layer. In addition, when performing epitaxial growth, it causes a defect in the epitaxial semiconductor film. However, in the above-described method, an intermediate porosity having a slightly higher porosity than the surface layer is used as a buffer layer that relieves strain generated from these layers between the layer having a very high porosity and the surface layer having a low porosity. By forming the rate layer, it is possible to form a high-quality epitaxial semiconductor film that is easy to peel off.

  Further, in the anodization at a high current density in the above method, when the current is intermittently passed, a high porosity layer can be formed in the porous substrate side interface or in the vicinity thereof, In this case, the surface and the highly porous layer serving as the peeling layer can be separated as much as possible, so that the buffer layer can be thinned, and accordingly the thickness of the porous layer is reduced, and the thickness of the semiconductor substrate is reduced. Consumption can be reduced, and the cost can be further reduced.

  In addition, when anodizing at a low current density, by gradually increasing the current, the porosity of the buffer layer between the surface layer and the release layer of the porous layer is gradually increased toward the inside. Can further improve the function of the buffer layer.

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

  Further, if the irradiation of light during anodization is avoided, the generation 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.

  Further, by forming the porous layer and then heating in a hydrogen gas atmosphere, the surface of the surface layer of the porous layer became smooth, and an epitaxial semiconductor film having good crystallinity could be formed. In addition, after the porous layer is formed and before the heating step in the hydrogen gas atmosphere, the porous layer is thermally oxidized to oxidize the inside of the porous layer. Even if applied, it is difficult for a large structural change to occur in the porous layer, and strain from the inside is hardly transmitted to the surface of the porous layer, so that an epitaxial semiconductor film with good crystallinity can be formed.

  DESCRIPTION OF SYMBOLS 11 Semiconductor substrate, 12 Porous layer, 12M Middle porosity layer, 12H High porosity layer, 13 Semiconductor film, 131 1st semiconductor film, 132 2nd semiconductor film, 133 3rd semiconductor film, 41 Conductive line, 42 Transparent substrate

Claims (6)

The surface of the semiconductor substrate is changed in three stages so that the current density of the anodization treatment is increased in order, and the porosity is gradually increased compared to the surface layer formed under the surface layer and the surface layer. Changing to a porous layer formed with a large intermediate porosity layer, and the surface layer inside the intermediate porosity layer and a high porosity layer having a higher porosity than the intermediate porosity layer ;
Annealing the surface of the porous layer in an oxygen atmosphere and then annealing in a hydrogen atmosphere;
Forming an epitaxial semiconductor film on the porous layer;
Peeling the epitaxial semiconductor film from the semiconductor substrate in the porous layer. A method for producing a thin film semiconductor.   2. The method of manufacturing a thin film semiconductor according to claim 1, wherein an epitaxial semiconductor layer is formed on the semiconductor substrate, and the porous layer is formed on the epitaxial semiconductor layer on the semiconductor substrate by the anodizing treatment.   2. The thin film according to claim 1, wherein in the step of forming the porous layer, intermittent energization that repeats energization and stop of the surface of the semiconductor substrate is performed in the last anodizing treatment of the step of forming the porous layer. Semiconductor manufacturing method.   2. The thin film according to claim 1, wherein in the step of forming the porous layer, the HF concentration in the electrolytic solution that performs the first anodizing treatment is higher than the HF concentration in the electrolytic solution that performs the subsequent anodizing treatment. Semiconductor manufacturing method.   2. The thin film semiconductor device according to claim 1, wherein in the step of forming the porous layer, a layer having a low porosity is formed on a surface side of the semiconductor substrate, and a layer having a high porosity is formed on the inner side of the semiconductor substrate. Production method.   The method for manufacturing a thin film semiconductor according to claim 1, wherein a support substrate is bonded onto the epitaxial semiconductor film, and the epitaxial semiconductor film is peeled from the semiconductor substrate together with the support substrate.

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