Formation of thin film

The present invention relates to a method for forming a thin film used for an SOI substrate or a photoelectric conversion device such as a solar cell or an area sensor.

[0002] Conventional Techniques An integrated circuit made on a substrate having an SOI (semiconductor-on-insulator) structure has various advantages over an integrated circuit made on a normal Si wafer. For example, 1 Dielectric separation is easy and high integration is possible, 2 Excellent resistance to radiation, 3 Stray capacitance is reduced and high speed is possible, 4 Well process can be omitted. 5 Latch-up can be prevented, 6 Completely depleted field effect transistor can be formed by thinning, so speed and power consumption can be reduced.

[0003] As a manufacturing method for providing a substrate having this SOI structure, US Pat. No. 5,371,037 and Applied Physics Letters, Vol. 64, p. 2108 (T.Yonehara et.al., Appl.Phys.Lett.vol.64, There is a method as disclosed in 2108 (1994). (a)-(e) in FIG. 16 and (a)-(d) in FIG. 17 represent this manufacturing process. In the figure, 1 and 5 Is a Si wafer, 2 is a non-porous Si layer, 3 is a porous Si layer, 4 is an epitaxial Si layer, 6 is a single crystal Si layer, and 7 is an oxide Si layer. A Si wafer 1 to be a device substrate is prepared, and the Si wafer 1 is anodized to prepare a substrate having the porous Si layer 3 on the surface of the non-porous Si layer 2 as shown in FIG. 16 (b). Then, as shown in FIG. 16 (c), the epitaxial Si layer 4 is formed on the surface of the porous Si layer 2.

[0004] On the other hand, a Si wafer 5 to be a support substrate is prepared as shown in FIG. 16 (d), the surface thereof is oxidized, and Si oxide is formed on the surface of the single crystal Si layer 6 as shown in FIG. 16 (e). A substrate with layer 7 is prepared. Then, the substrate (2,3,4) produced in FIG. 16 (c) is turned over, and the epitaxial Si layer 4 is formed on the substrates 6 and 7 produced in FIG. 16 (e) as shown in FIG. 17 (a). The Si oxide layer 7 is faced with each other, and the epitaxial Si layer 4 and the Si oxide layer 7 are bonded to each other as shown in FIG. 17 (b), and both substrates are bonded together. Then, as shown in FIG. 17 (c), the non-porous Si layer 2 is mechanically removed from the non-junction surface side by gliding to expose the porous Si layer 3. Then, the porous Si layer 3 is removed as shown in FIG. 17 (d) by performing wet etching with an etching solution that selectively etches the porous Si layer 3. Then, an SOI substrate having an extremely uniform film thickness of the epitaxial Si layer 4 which is the semiconductor layer of the SOI substrate can be obtained.

[0005] In producing a substrate having an SOI structure, the manufacturing method described above is performed by grinding the non-porous Si layer 2 in order to change the substrate of FIG. 17 (b) to the substrate of FIG. 17 (c). Since it is removed, one substrate 1 to be the non-porous layer 2 and the porous layer 3 is required for each production of one SOI substrate. Therefore, Japanese Patent Application Laid-Open No. 7-302889 proposes to use the non-porous Si layer 2 many times in the manufacturing process of the SOI substrate. That is, when changing from the substrate of FIG. 17 (b) to the substrate of FIG. 17 (c), a tensile force, a crushing force, a shearing force, etc. are applied to the substrate of FIG. 17 (b), or the porous Si layer 3 is cured. Separate 4, 7, 6 and 2 which will be the SOI substrate in the porous Si layer 3 by using a method such as inserting a jig. Then, the remaining non-porous Si layer 2 is used many times as the Si wafer 1 shown in FIG. 16 (a).

[0006] On the other hand, solar cells that use amorphous Si as a structure suitable for a large area are currently the mainstream, but single crystal Si and polycrystalline Si solar cells are also attracting attention from the viewpoint of conversion efficiency and life. There is. Japanese Unexamined Patent Publication No. 8-213645 discloses a method for providing a thin-film solar cell at low cost. In this method, as shown in FIG. 18, a porous Si layer 3 is formed on the Si wafer 1, and a solar cell layer is formed on the porous Si layer 3.⁺ Type Si layer 21, p type Si layer 22 and n⁺ The mold Si layer 23 is epitaxially grown. n⁺ After forming the protective film 30 on the mold Si layer 23, the jig 31 is adhered to the back surface of the Si wafer 1 and the jig 32 is also adhered to the front surface of the protective film 30 with the adhesive 34. Next, the porous Si layer 3 is mechanically broken by pulling the jigs 31 and 32 in opposite directions, and the solar cell layers 21, 22 and 23 are separated from the Si wafer 1. Then, it discloses that the solar cell layers 21, 22, and 23 are sandwiched between two plastic substrates to manufacture a flexible thin-film solar cell. In this, it is disclosed that the Si wafer 1 can be used many times. It also discloses that the side wall of the porous Si layer 3 is partially scratched 33 by a mechanical method or irradiation with a laser beam before applying a tensile force.

[0007] [Problems to be Solved by the Invention] In manufacturing an SOI substrate, the method disclosed in Japanese Patent Application Laid-Open No. 7-302889 can reduce costs by using Si wafers many times. it can. However, this method is also not sufficient in terms of reproducibility.

[0008] On the other hand, in a solar cell, it is not always possible to cleanly separate the porous Si layer by the manufacturing method as described in JP-A-8-213645. Therefore, cracks often occur in the epitaxial layer, and the yield is reduced. Further, since this method pulls and separates the porous Si layer, a strong adhesive force is required between the jig and the single crystal Si layer, which is not suitable for mass production.

[0009] An object of the present invention is that even in a method for manufacturing a photoelectric conversion device such as a solar cell, the cost is advantageous, the separation ability is excellent, and the reproducibility that the earth's resources can be effectively used by using the wafer without waste. To provide a high way.

[Means for Solving the Problems] Therefore, as a result of diligent efforts by the present inventor to solve the above problems, the following inventions have been obtained. That is, in the method for forming a thin film of the present invention, a substrate having a porous layer on a non-porous layer and a layer having a smaller porosity than the porous layer on the porous layer.<u style="single">Is prepared, and a laser beam is irradiated from the side surface of the substrate along the porous layer to allow the porous layer to absorb the laser light, whereby the substrate is separated by the porous layer.</u>It is characterized by that.

[0011] Further, the method for forming a thin film of the present invention is a substrate having a defect layer internally by ion implantation.<u style="single">Is prepared, and a laser beam is irradiated from the side surface of the substrate along the defect layer to allow the defect layer to absorb the laser light, whereby the substrate is separated by the defect layer.</u>It is characterized by that.

[Embodiments of the Invention] Hereinafter, embodiments 1 to 8 of the present invention will be described. Embodiments 1 to 4 are a form of manufacturing an SOI substrate, and embodiments 5 to 7 are a form of manufacturing a photoelectric conversion device such as a solar cell or an area sensor. The eighth embodiment is a form in which ion implantation is used as a method for forming a layer to be a separation site. The present invention is not limited to each embodiment, but also includes a combination of the respective embodiments.

[0016] The first embodiment is a mode in which an SOI substrate is manufactured, and laser light is used to separate the wafer SOI substrate to be reused by a porous layer.

[0017] The laser beam irradiates the side surface (end surface) of the plate-shaped substrate horizontally with respect to the front surface and the back surface of the substrate, and adjusts the intensity of the laser beam so that the laser beam reaches the vicinity of the center of the substrate.

[0018] The laser beam is applied to a relatively brittle layer such as a highly porous layer formed in the substrate or a defect layer due to microbubbles, and is absorbed there.

The layer that has absorbed the laser beam becomes even more brittle, and the substrate is separated into two sheets with the layer as a boundary.

The laser light irradiation method will be described in detail in the following embodiments.

(Embodiment 1) FIG. 1 is a diagram showing a separation method of the present embodiment. In the figure, the same reference numerals as those in FIGS. 16 and 17 represent the same ones. 10 is a lens, 11 is an optical microscope, 12 is a vacuum chuck, and 13 is a laser beam. LS is a laser light source and ATL is an article before separation, and each layer consists of 2, 3, 4, 7, and 6. The side wall of the porous layer 3 is irradiated with laser light. The laser light source LS is an excimer laser such as XeCl, KrF, ArF that can output a large output, and its output is 300 mJ / cm.² ~ 1J / cm² Is desirable. Especially desirable is 500mJ / cm² Degree. Since the laser light of the excimer laser is ultraviolet light, the lens 10 is made of quartz or fluorite that transmits ultraviolet light, and the irradiation area of the laser light 13 can be narrowed down to a width of 0.1 μm by this optical system. The optical microscope 11 is provided as needed and is used to confirm whether the laser beam 13 can correctly irradiate the porous layer 3 having a thickness of 0.1 μm to 30 μm. Here, the porous layer 3 is more brittle and more easily separated than the non-porous layer 2 which does not have a porous structure and the epitaxial layer 4 which is a layer having a small porosity. Therefore, the laser beam 13 does not have to be strictly irradiated only to the porous layer 3. As the light source LS that emits the laser beam 13, it is desirable to use a high-power excimer laser device, but an Ar laser, a YAG laser, or the like may be used separately. In order to promote separation, a liquid such as water, alcohol, or IPA (isopropyl alcohol) in the pores of the porous layer 3 may be injected or adsorbed. Since these liquids have a larger coefficient of thermal expansion than solids such as Si, the expansion of the liquids promotes separation.

[0022] The vacuum chuck 12 as a substrate holder has a region in which gas enters, and is brought into contact with the outside of the non-porous layer 2 and the single crystal layer 6 to remove the gas inside before separation. The substrate ATL, which is an article of the above, can be fixed. In this embodiment, the vacuum chuck 12 can rotate about the center of the substrate, and the laser beam 13 can be applied to all the side walls of the porous layer 3. The vacuum chuck 12 may be used only for fixing and rotating the substrate, but in order to facilitate separation, a minute tensile force may be applied from the vacuum chuck 12 to the substrate. The laser beam reaches from the side wall of the porous layer 3 to the vicinity of the center of the substrate ATL. The light-absorbing porous layer becomes even more brittle and the substrate ATL can be separated without destroying the non-porous portion.

As a result of the above separation steps, as shown in FIG. 2, the porous layer 3 can separate the substrates 4, 7, and 6 on the side to be the SOI substrate and the substrate 2 to be reused. In FIG. 2, the porous portion 3'remains on the surface (separation surface) of each substrate, but if the porous layer 3 is made sufficiently small in film thickness in the anodization process, it is substantially separated. After that, it is also possible to prevent the porous portion 3'from remaining on one or both substrates.

[0024] A thin film forming method by the wafer separation method shown in FIG. 1 will be described.

[0025] First, the bonded substrate is prepared. FIG. 3 is a cross-sectional view of an apparatus for anodizing a Si wafer. In the figure, 1 is a Si wafer, 27 is a hydrofluoric acid-based etching solution stored in a container RV, 28 is a positive metal electrode, and 29 is a negative metal electrode. The Si wafer 1 to be anodized is preferably p-type, but n-type may be used if the resistance is low. Further, even an n-type Si wafer can be easily made porous by irradiating it with light to form holes. As shown in FIG. 3, a voltage is applied between the two electrodes with the positive electrode 28 on the left and the negative electrode 29 on the right so that the electric field in the etching solution caused by this voltage is applied in the direction perpendicular to the surface of the Si wafer 1. When both electrodes and the wafer are parallel to each other, the Si wafer 1 is made porous from the negative electrode 29 side. Concentrated hydrofluoric acid (49% HF) is used as the hydrofluoric acid-based etching solution 27. Since bubbles are generated from the Si wafer 1 during the anodization, it is advisable to add alcohol as a surfactant to the liquid 27 for the purpose of efficiently removing the bubbles.

[0026] As the alcohol, methanol, ethanol, propanol, isopropanol and the like are desirable. Further, instead of adding the surfactant, an anodization may be carried out while stirring using a stirrer.

[0027] The thickness of the layer to be made porous is preferably 0.1 μm to 30 μm.

[0028] It is desirable to use a material such as gold (Au) or platinum (Pt) that is not eroded by the hydrofluoric acid solution for the negative electrode 29. The positive electrode 28 may be a generally used metal material, but a material that is not eroded by hydrofluoric acid is preferable. The maximum current density for anodization is several hundred mA / cm.² And the minimum value does not have to be 0. The current density is set so that a high-quality epitaxial Si layer can be formed on the formed porous Si layer, and the porous Si layer can be easily separated by separation. Specifically, in the case of porous Si, when the current density is high during anodization, the density of Si in the porous Si layer becomes low. Therefore, the larger the current density, the larger the volume of the pores, and the larger the porosity (porosity is defined as the ratio of the volume of the pores to the total volume of the porous layer). The porous Si layer has many pores inside the Si layer, but its single crystallinity is maintained. Therefore, it is possible to epitaxially grow the single crystal Si layer on the upper part of the porous Si layer.

[0029] However, in order to form the epitaxial Si layer without stacking defects, the porosity of the porous Si layer in contact with the epitaxial Si layer should be small. On the other hand, in order to facilitate the separation between the device substrate and the SOI substrate with the porous Si layer as a boundary, it is preferable that the porous Si layer has a large porosity. That is, the ideal shape is that the outermost surface side of the porous Si layer has a small porosity, and the side of the porous Si layer close to the non-porous Si layer has a large porosity. FIG. 4 is a cross-sectional view showing the ideal shape of this porous Si layer. A porous Si layer 3a having a small porosity is formed on the surface side of the porous Si layer 3, and a porous Si layer 3b having a large porosity is formed on the non-porous Si layer side of the porous Si layer 3. In order to form this structure, the anodic formation of the 3a part is performed with a small current density at the beginning, and the anodic formation of the later 3b part is performed with a large current density. .. With this structure, the separation surface of the substrate can be specified as 3b, and an epitaxial Si layer without stacking defects can be formed on the porous Si layer 3a. The epitaxial Si layer is preferably grown at low temperature by methods such as molecular beam epitaxial growth, plasma CVD, reduced pressure CVD, optical CVD, bias sputtering method, and liquid phase growth method.

[0030] According to the method described above, the Si wafer 1 is prepared as shown in FIG. 5 (a), and the surface thereof is made porous as shown in FIG. 5 (b). In this way, the Si wafer 1 changes to a structure in which the porous Si layer 3 is laminated on the non-porous Si layer 2.

Next, as shown in FIG. 5 (c), a non-porous epitaxial Si layer 4 as a layer having low porosity is formed on the porous Si layer 3.

Next, if necessary, the surface of the epitaxial Si layer 4 is thermally oxidized as shown in FIG. 5 (d) to form the Si oxide layer 8 having a thickness of 0.05 μm to 2 μm.

[0033] The above is the process before bonding on the PW side of the substrate, which is called a prime wafer, a bond wafer, or a device substrate.

[0034] The processing on the substrate HW side, which is called the handle wafer, the base wafer, or the support substrate, is as follows.

[0035] A Si wafer is prepared, and the surface thereof is thermally oxidized as needed to form a Si oxide film having a thickness of 0.05 μm to 3 μm on the surface.

Next, the bonding and separation steps of the substrates will be described with reference to FIG.

As shown in FIG. 6A, the surface of the Si oxide layer 8 on the epitaxial Si layer 4 of the substrate PW and the surface of the Si oxide layer 7 of the substrate HW are opposed to each other, and the surfaces are opposed to each other. Adhere at room temperature.

[0038] After that, the Si oxide layer 8 and the Si oxide layer 7 are firmly bonded to each other by anodic bonding, pressurization, heat treatment, or a combination thereof, and from the bonded substrate as shown in FIG. 6 (b). Form the article ATL.

Next, the bonded article ATL having the structure shown in FIG. 6 (b) is mounted on the vacuum chuck 12 of the apparatus shown in FIG. 1, and while rotating the article ATL, the side surface of the article ATL is porous. Focus on the part of the quality Si layer 3 and irradiate it with excimer laser light. The excimer laser light irradiates and absorbs the entire porous Si layer.

[0040] Thus, as shown in FIG. 6 (c), the non-porous Si layer 2 on the substrate PW side is separated from the substrate HW. At this time, the epitaxial Si layer 4 is transferred to the surface of the substrate HW.

[0041] The porous Si layer 3 destroyed by the absorption of the laser beam may remain on at least one of the non-porous Si layer 2 side and the epitaxial Si layer 4 side. FIG. 6 (c) shows that it remains only on the epitaxial Si layer 4 side.

[0042] When the porous Si layer 3 remains, the porous Si layer 3 remaining on the substrate HW side is removed by selective etching. At the time of selective etching, when hydrofluoric acid-free wet chemical etching is performed using a mixed solution of hydrofluoric acid, hydrofluoric acid and alcohol, or a mixed solution of hydrofluoric acid and hydrogen peroxide solution, porous Si The layer is etched more than the non-porous Si layer. In particular, when a mixed solution of hydrofluoric acid mixed with hydrogen peroxide solution was used, the selective etching ratio of the porous Si layer to the non-porous Si layer was ~ 10.⁵ Will be. Thus, as shown in FIG. 6D, the epitaxial Si layer 4 having a uniform thickness remains on the surface of the substrate HW. In this way, an extremely uniform SOI substrate of the semiconductor layer 4 on the insulating layer can be obtained.

[0043] The decomposed non-porous layer 2 is used again as a prime wafer in order to prepare yet another SOI substrate.

[0044] Further, in the process of producing the SOI substrate of this embodiment, the support substrate can be a completely insulated substrate such as a glass or quartz substrate. FIG. 7 is a diagram showing a manufacturing process of an SOI substrate when a quartz substrate is used as a support substrate. The device substrate PW in the upper part of FIG. 7A is manufactured in the same manner as the method described with reference to FIG. Then, the quartz substrate 9 as the support base HW and the Si oxide layer 8 are faced to each other, and the quartz substrate 9 and the Si oxide layer 8 are brought into close contact with each other as shown in FIG. 7 (b), and anodic bonding, pressurization, heat treatment or these are performed. The Si oxide layer 8 and the quartz substrate 9 are firmly bonded by the combined method.

Next, both substrates are separated by using a laser beam in the same manner as described above. The transferred epitaxial Si layer 4 and the porous Si layer 3 remain on the quartz substrate 9 ((c) in FIG. 7). Further, the residual porous Si layer 3 is selectively removed by the method described above. In this way, an SOI substrate having a non-porous single crystal Si thin film on the quartz substrate 9 is obtained ((d) in FIG. 7).

[0046] Further, in the step of producing the SOI substrate of this embodiment, a Si wafer is used as the support substrate, and the Si oxide layer is formed on the epitaxial Si layer on the device substrate side without forming the Si oxide layer on the Si wafer side. By doing so, an insulating layer having an SOI structure can be formed. FIG. 8 illustrates this process. The upper device substrate of FIG. 8 (a) is manufactured in the same manner as described with reference to FIG. Then, the surface of the single crystal Si layer 5 made of a Si wafer and the surface of the Si oxide layer 8 face each other, and the surface of the single crystal Si layer and the surface of the Si oxide layer 8 are brought into close contact with each other to be bonded. At this time, it is preferable to firmly bond the Si oxide layer 8 and the single crystal Si layer 5 by anodic bonding, pressurization, heat treatment, or a combination of these methods. In this way, the article ATL is obtained as shown in FIG. 8 (b).

Then, using the apparatus shown in FIG. 1, the article ATL is separated at the porous Si layer 3 as a boundary, and the non-porous single crystal Si is placed on the non-porous Si layer 5 side which is the support substrate HW. The epitaxial Si layer 4 composed of the above is transferred. At this time, if the porous Si layer 3 remains on the epitaxial Si layer 4 on the support substrate HW as shown in FIG. 8 (c), the porous Si layer is selected by the above-mentioned method. If it is removed as shown in FIG. 8 (d), an SOI substrate as shown in FIG. 8 (d) can be obtained.

(Embodiment 2) The second embodiment is a mode for manufacturing an SOI substrate, and an excimer laser is used to separate a reusable Si wafer and a substrate to be finally an SOI substrate with a porous Si layer. .. At this time, the light of the excimer laser is focused on one point, the substrate is fixed, and the laser light is scanned to perform separation.

FIG. 9 is a diagram showing the separation process of the present embodiment, and FIG. 14 is a guide capable of scanning along the circumference while focusing on the side surface of the article ATL for separating the position of the lens 10. is there. Other part numbers represent the same as those described in FIG. In this embodiment, the chuck 12 fixes the outside of the single crystal Si layer 6 and the non-porous Si layer 2 constituting the article ATL. Then, the laser beam 13 of the excimer laser apparatus is narrowed down to one point on the side wall of the porous Si layer 3 by the lens 10 and irradiated. Then, at the same time as scanning the lens 10 with the guide 14, the laser beam 13 is also scanned, and the SOI substrate composed of layers 4, 7, and 6 and the substrate 2 reused in the manufacturing process are separated by the porous Si layer 3. Separate into. Other steps, materials used, and the like are the same as in the first embodiment.

(Embodiment 3) The third embodiment is a mode for manufacturing an SOI substrate, and an excimer laser is used to separate the reused Si wafer and the SOI substrate with a porous Si layer. At this time, the light of the excimer laser is linearly focused by a cylindrical lens, and the laser light is irradiated along the porous Si layer.

[0051] FIG. 10 is a diagram showing the separation process of the present embodiment, and FIG. 15 is a cylindrical lens. Other part numbers represent the same as those described in FIG. The cylindrical lens 15 can focus the laser beam 13 in a straight line running vertically. Therefore, the side wall of the porous Si layer 3 having a thin film thickness of 0.1 μm to 30 μm can be efficiently irradiated with the laser beam. Further, a toyc lens may be used instead of the cylindrical lens 15 to irradiate the laser with a linear focal point according to the curved surface of the side wall of the porous Si layer 3. Other steps are the same as in the first embodiment.

(Embodiment 4) The fourth embodiment is a mode for manufacturing an SOI substrate, and an excimer laser is used to separate the reused Si wafer and the SOI substrate with a porous Si layer. At this time, the light of the excimer laser is linearly focused by a cylindrical lens, and the laser light is irradiated along the porous Si layer. At this time, as shown in FIG. 11, the laser beam 13 is separated into four, and the laser beam 13 is linearly focused along the porous Si layer 3 using four cylindrical lenses 15 to be porous from four directions. Irradiate the Si layer. In this embodiment, the outsides of the single crystal Si layer 6 and the non-porous Si layer 2 are fixed by the chuck 12. Other steps are the same as in the first embodiment.

(Embodiment 5) The fifth embodiment is a mode for manufacturing a solar cell. FIG. 12 is a diagram showing a process up to forming a photoelectric conversion layer that converts light into electricity. First, as shown in FIG. 12A, a p-type Si wafer 1 is prepared, and the surface of the Si wafer 1 is made porous by the same anodization method as described with reference to FIG. Then, as shown in FIG. 12B, a substrate having the porous Si layer 3 on the non-porous Si layer 2 of the wafer 1 is formed. Then, as shown in FIG. 12 (c), the epitaxial Si layer to be the photoelectric conversion layer 18 is formed on the porous Si layer 3 by molecular beam epitaxial growth, plasma CVD, reduced pressure CVD, optical CVD, bias sputtering method, and liquid phase deposition. Form by a method such as law. In this way, one substrate PW is obtained.

Since the epitaxial Si layer is used as a photoelectric conversion layer, it is epitaxially grown while adding a dopant. Therefore, the epitaxial Si layer is n on the porous Si layer 3.⁺ Layer, p on it^- Layer, and p on top of it⁺ It has a PN junction with laminated layers.

[0055] Then, p of the photoelectric conversion layer 18 that has been epitaxially grown.⁺ The front surface of the layer and the back surface metal electrode 16 preliminarily formed on the surface of the plastic substrate 17 are bonded and joined.

[0056] After that, the vacuum chuck 12 is brought into close contact with the outside of the non-porous Si layer 2, and the laser beam 13 from the excimer laser apparatus is focused on the porous Si layer 3 using the lens 10 and irradiated. Although FIG. 13 illustrates a form in which the laser beam is focused on one point by a lens, the method of irradiating the laser beam may be any of the forms described in the first to fourth embodiments. Then, in the porous Si layer as shown in FIG. 14, the substrate HW which will be the final solar cell and the substrate PW which will be the Si wafer to be reused in the manufacturing process can be separated.

After that, as shown in FIG. 15A, a surface metal electrode 19 on a mesh is formed on the surface of the photoelectric conversion layer 18. Next, the wiring 24 is connected to the front surface metal electrode 19 and the back surface metal electrode 16, and the protective layer 20 is formed on the front surface metal electrode 19. FIG. 15 (b) is a cross-sectional view taken along the line AA'of FIG. 15 (a). The photoelectric conversion layer 18 is in contact with the surface metal electrode 19 from above n⁺ P in contact with layer 23, p layer 22, back metal electrode 16⁺ It is composed of layer 21. In FIG. 15, the surface metal electrode 19 is shown to be meshed so as to transmit light, but this may be replaced with a transparent electrode such as ITO. Further, since the back surface metal electrode 16 also functions as a back reflector that returns the light transmitted through the photoelectric conversion layer 18 without being absorbed to the photoelectric conversion layer 18, it is desirable to form the back metal electrode 16 with a metal material having a large reflectance. ..

[0058] Since this embodiment can form a number of single crystal thin film solar cells from one Si wafer, it is excellent in terms of conversion efficiency, life, manufacturing cost, and the like. Further, since the substrate is separated by irradiating a laser beam and absorbing it into the porous Si layer to cause thermal expansion of the porous Si layer and causing distortion of the crystal, a strong tensile force is not required. Therefore, it is excellent in terms of manufacturing cost because it does not require a strong adhesive force between the substrate and the jig.

(Embodiment 6) The sixth embodiment is also the same as the fifth embodiment in that the solar cell is manufactured. In the fifth embodiment, the photoelectric conversion layer 18 is composed of an epitaxial Si layer formed on the porous Si layer 3. On the other hand, in the sixth embodiment, the porous Si layer having a small porosity is used as it is as the photoelectric conversion layer 18. In the first embodiment, it is explained that the porosity of the porous Si layer can be changed by changing the current density in the anodization step. That is, in the anodization step described with reference to FIG. 3, if the current density flowing from the electrode 28 to the electrode 29 is increased, the porosity of the porous Si layer formed on the Si wafer 1 is increased and the current concentration is decreased. It is explained that the porosity is also reduced. Using this phenomenon, p⁺ When making the surface of the mold Si wafer 1 porous, the current density is reduced to form a porous Si layer with low porosity, and the porosity with high porosity is formed below and above the non-porous Si layer 2. Form Si layer 3b. Then, ions that serve as donors such as P and As that form n-type are ion-implanted on the outermost surface of the porous Si layer 3a having a small porosity to form a photoelectric conversion layer having a small porous Si layer pn junction. Used for some.

[0060] After that, in the same manner as shown in FIG. 13, the porous Si layer having a small porosity, which is the photoelectric conversion layer, and the back surface metal electrode 16 are bonded together. Other steps are the same as in the fifth embodiment. Since this embodiment can form a number of single crystal thin film solar electrodes from one Si wafer, it is excellent in terms of conversion efficiency, life, manufacturing cost, and the like. Further, since there is no epitaxial growth step, the manufacturing cost is further smaller than that of the fifth embodiment. Further, since the photoelectric conversion layer 18 is made of a porous Si layer having a small porosity, the single crystal property is maintained, and light scattering is appropriately caused in the pores, so that the conversion efficiency is high.

(Embodiment 7) The seventh embodiment is a mode in which an area sensor is manufactured. In this embodiment, a photoelectric conversion layer of a single crystal thin film is formed from a Si wafer as in the fifth and sixth embodiments. Then, the optical sensor is two-dimensionally arranged on the photoelectric conversion layer, and the matrix wiring is provided. For the matrix wiring, for example, in FIG. 15, column wiring is provided instead of arranging the front surface metal electrode 19, and row wiring is provided instead of arranging the back surface metal electrode 16. Since this embodiment can form a number of single crystal thin film area sensors from one Si wafer, it is excellent in terms of replacement efficiency, life, manufacturing cost, and large area.

(Embodiment 8) First, a Si wafer is prepared as one of the substrates.

[0063] Next, the Si wafer is installed in an ion implantation apparatus, and hydrogen ions or rare gas ions are ion-implanted on the entire surface of the Si wafer so as to reach a certain depth. In this way, a defect layer due to microbubbles is formed inside the Si wafer.

[0064] On the other hand, another Si wafer is prepared as a support substrate, the surface is oxidized, and the surface of the Si wafer having the defect layer due to the microbubbles is bonded and heat-treated.

[0065] The article made of the bonded wafer thus formed is irradiated with excimer laser light in the vicinity of the defect layer due to the microbubbles on the side surface of the article by the method as shown in FIGS. Light is absorbed by the defect layer to make the defect layer even more brittle and separate the two wafers.

[0066] The single crystal Si layer thus on the defective layer of the Si wafer, which is one substrate, is transferred onto the silicon oxide film of the other substrate.

The formation of microbubbles by ion implantation described above is described in detail in US Pat. No. 5,374,564.

Although the above has been described separately for the case of a Si wafer, the present invention can be applied to other semiconductors such as SiGe, Ge, SiC, GaAs, and InP other than Si.

[Effectiveness of the Invention] According to the present invention, it is easy to irradiate not only the periphery of the substrate but also the porous layer near the center from the side surface of the substrate so that the porous layer absorbs the laser beam. In addition, many single crystal thin film Sis can be obtained from the Si substrate. Moreover, since the laser beam without impurities is used for the separation, the obtained Si thin film is of good quality. Therefore, the quality of the SOI substrate itself is also high. Further, when manufacturing the SOI substrate, since the material can be used without waste, it is possible to provide a resource-saving manufacturing method at a low manufacturing cost. Moreover, the quality of the photoelectric conversion device itself is also improved. Further, since the material can be used without waste when manufacturing the photoelectric conversion device, it is possible to provide a resource-saving manufacturing method at a low manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a separation step of the first embodiment in which a porous Si layer is irradiated with a laser beam.

FIG. 2 is a diagram showing a substrate after separation.

FIG. 3 is a diagram showing a manufacturing process of an SOI substrate using a Si wafer as a base according to the first embodiment.

FIG. 4 is a diagram showing a manufacturing process of an SOI substrate using a Si wafer as a base according to the first embodiment.

FIG. 5 is a diagram showing a manufacturing process of an SOI substrate using a quartz substrate as a base according to the first embodiment.

FIG. 6 is a diagram showing a manufacturing process of an SOI substrate using a Si wafer as a base according to the first embodiment.

FIG. 7 is a diagram showing a manufacturing process of another SOI substrate.

FIG. 8 is a diagram showing a manufacturing process of another SOI substrate.

FIG. 9 is a diagram showing a separation step of the second embodiment in which a porous Si layer is irradiated with a laser beam.

FIG. 10 is a diagram showing a separation step of the third embodiment in which a porous Si layer is irradiated with a laser beam.

FIG. 11 is a diagram showing a separation step of the fourth embodiment in which a porous Si layer is irradiated with a laser beam.

FIG. 12 is a diagram showing a process of manufacturing a single crystal Si solar cell.

FIG. 13 shows a separation step of the fifth embodiment in which a porous Si layer is irradiated with a laser beam.

FIG. 14 is a diagram showing a substrate after separation.

FIG. 15 is a perspective view (a) and a cross-sectional view (b) of a single crystal Si solar cell.

FIG. 16 is a diagram showing a manufacturing process of an SOI substrate.

FIG. 17 is a diagram showing a manufacturing process of an SOI substrate.

FIG. 18 is a diagram showing a method of manufacturing a conventional solar cell.

[Code description] 1,5 Si wafer 2 Non-porous Si layer 3 Porous Si layer 4 Epitaxial Si layer 6 Single crystal Si layer 7,8 Oxidized Si layer 9 Quartz substrate 10 Lens 11 Optical microscope 12 Vacuum chuck 13 Laser light 14 Guide 15 Cylindrical lens 16 Back side metal electrode 17 Plastic substrate 18 Photoelectric conversion layer 19 Metal electrode 20 Protective film 21 p⁺ Layer 22 p Layer 23 n⁺ Layer 24 Wiring 27 Hydrofluoric acid-based etching solution 28 Positive electrode 29 Negative electrode 30 Protective film 31,32 Jig 33 Scratch