JPH10326759A - Formation of thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing SOI substrate which is helpful in elimination of resources and reducing the cost and, at the same time, a method for manufacturing low-cost photoelectric conversion device by saving resources such as the solar battery, etc., by which substrates can be separated completely by using a porous Si layer and the need of strong adhesion between the substrates and a jig can be eliminated. SOLUTION: In a method for forming Si thin film, Si thin layers are formed by separating the nonporous Si layer 2 and less porous Si layer 4 of a substrate, in which a porous Si layer 3 is formed on the nonporous Si layer 2 and the less porous Si layer 4 is formed on the layer 3, are separated by using the layer 3. At this point, the side face of the substrate is irradiated with a laser beam 13. Then, an SOI substrate is manufactured from separated substrates 4, 7, and 6 and the nonporous Si layer 2 is again utilized for the manufacturing process of the SOI substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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]

2. Description of the Related Art An integrated circuit fabricated on a substrate having an SOI (semiconductor-on-insulator) structure has various advantages over an integrated circuit fabricated on a normal Si wafer. For example, dielectric isolation is easy, high integration is possible, radiation resistance is excellent, stray capacitance is reduced and high speed is possible, well process can be omitted, latch-up can be prevented, and fully depleted type by thinning Since a field effect transistor can be formed, high speed and low power consumption can be achieved.

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
s. Lett. vol. 64, 2108 (1994). (A) of FIG.
17E and FIGS. 17A to 17D show this manufacturing process. In the figure, 1 and 5 are Si wafers, 2 is a non-porous Si layer,
Reference numeral 3 denotes a porous Si layer, 4 denotes an epitaxial Si layer, 6 denotes a single crystal Si layer, and 7 denotes a Si oxide layer. First, FIG.
As shown in FIG. 16A, a Si wafer 1 serving as a device substrate is prepared, and the
A substrate having a porous Si layer 3 on the surface of a non-porous Si layer 2 as shown in FIG. Then, an epitaxial Si layer 4 is formed on the surface of the porous Si layer 2 as shown in FIG.

On the other hand, as shown in FIG. 16 (d), a Si wafer 5 serving as a support substrate is prepared, and the surface thereof is oxidized.
6 (e), the surface of the single crystal Si layer 6 is
A substrate is prepared. Then, the substrate (2, 3, 4) produced in FIG. 16C is turned over, and the epitaxial Si layer 4 is placed on the substrates 6 and 7 produced in FIG. 16E as shown in FIG. The silicon oxide layer 7 is opposed to the silicon oxide layer 7 as shown in FIG.
The epitaxial Si layer 4 and the Si oxide layer 7 as shown in FIG.
And bonding both substrates together. Then, FIG.
As shown in (c), the non-porous Si layer 2 is mechanically removed from the non-bonding surface side by gliding, and the porous Si layer 3 is removed.
To expose. Thereafter, the porous Si layer 3 is removed by wet etching with an etchant for selectively etching the porous Si layer 3 as shown in FIG. Then, an SOI substrate having an extremely uniform thickness of the epitaxial Si layer 4 serving as a semiconductor layer of the SOI substrate can be obtained.

In manufacturing a substrate having an SOI structure, the manufacturing method described above uses the substrate shown in FIG.
Since the non-porous Si layer 2 is removed by grinding when forming the substrate (c), a single SOI substrate is prepared for the substrate 1 to be the non-porous layer 2 and the porous layer 3. You need one card each time. For this reason, Japanese Patent Laid-Open No. 7-302
No. 889 proposes to use the non-porous Si layer 2 many times in the manufacturing process of the SOI substrate. In other words, in converting the substrate of FIG. 17B into the substrate of FIG. 17C, a tensile force, a crushing force, a shearing force, or the like is applied to the substrate of FIG. 17B, or the porous Si layer 3 is cured. Using a method such as inserting a tool into the porous Si layer 3
4, 7, 6, and 2, which are OI substrates, are separated. Then, the remaining non-porous Si layer 2 is transferred to the Si wafer 1 shown in FIG.
It is used many times.

On the other hand, solar cells using amorphous Si as a structure suitable for a large area are currently the mainstream.
From the viewpoints of conversion efficiency and life, single-crystal Si and polycrystalline Si solar cells have also attracted attention. Japanese Patent Application Laid-Open No. H8-213645 discloses a method for providing a thin-film solar cell at low cost. In this method, as shown in FIG.
A porous Si layer 3 is formed thereon, and ap ⁺ -type Si layer 21, a p-type Si layer 22, and an n ⁺ -type Si
Layer 23 is epitaxially grown. n ⁺ type Si layer 23
After the protective film 30 is formed thereon, the jig 31 is bonded to the back surface of the Si wafer 1 and the jig 32 is bonded to the surface of the protective film 30 with an adhesive 34. Next, the jigs 31 and 32 are pulled in opposite directions to mechanically break the porous Si layer 3, and the solar cell layers 21, 22 and 23 are separated from the Si wafer 1. The solar cell layers 21 and
No. 2,23 is disclosed between two plastic substrates to produce a flexible thin film solar cell. Among them, it discloses that the Si wafer 1 can be used many times. Before applying a tensile force, the porous S
It discloses that a partial flaw 33 is formed on the side wall of the i-layer 3.

[0007]

In manufacturing an SOI substrate, the method disclosed in Japanese Patent Application Laid-Open No. 7-302889 can reduce the cost by using a Si wafer many times. However, this method is not sufficient in terms of reproducibility.

On the other hand, in a solar cell, Japanese Patent Laid-Open No.
In the manufacturing method as disclosed in Japanese Patent No. 3645, it is not always possible to cleanly separate the porous Si layer. For this reason, cracks often occur in the epitaxial layer, and the yield decreases. In addition, since this method pulls and separates the porous Si layer, it requires a strong adhesive force between the jig and the single-crystal Si layer, and is not suitable for mass production.

An object of the present invention is to provide a method of manufacturing a photoelectric conversion device such as a solar cell, which is advantageous in terms of cost, has excellent separation capability, and has a reproducibility that enables effective use of earth resources by using wafers without waste. It is to provide a high way.

[0010]

The inventors of the present invention have made intensive efforts to solve the above-mentioned problems, and have obtained the following inventions. That is, the method for forming a thin film according to the present invention includes a method in which the non-porous layer has a porous layer on the non-porous layer, and the non-porous layer has a smaller porosity than the porous layer on the porous layer. In the method of forming a thin film, in which the layer having a small porosity is separated and formed by the porous layer, the separation is performed by irradiating a laser beam from the side surface of the substrate to the center of the substrate. I do.

Here, it is desirable that the separation is performed by focusing the laser beam on the side surface of the porous layer and expanding the porous layer. Preferably, the porous layer on the non-porous layer is formed by anodizing a Si wafer. Here, the non-porous layer on the side not in contact with the porous layer may be brought into close contact with a vacuum chuck, and a small tensile force may be transmitted from the vacuum chuck to the substrate.

In the present invention, it is preferable that the laser beam is an excimer laser. Further, the laser light is
Irradiation may be performed on a plurality of portions of the porous layer, or the laser light may be narrowed down linearly using a cylindrical lens, and the linear laser light may be irradiated along the porous layer.

Preferably, the layer having a small porosity is formed by epitaxial growth on the porosity. Here, after bonding the epitaxial layer and a support substrate having an insulating layer on at least the surface, separation at the porous layer is performed, the porous layer remaining on the epitaxial layer is removed, and the epitaxial layer is It is preferable that the insulating layer be a semiconductor layer and a base insulating layer of an SOI substrate, respectively. At this time, the support substrate having the insulating layer on at least the surface is preferably a substrate obtained by oxidizing the surface of a Si wafer. Further, an insulating layer is formed on the surface of the epitaxial layer, and after bonding to a supporting substrate, separation is performed at the porous layer, and the porous layer remaining on the epitaxial layer is removed. The insulating layer can be a semiconductor layer and a base insulating layer of the SOI substrate, respectively. At this time, the support substrate is
The substrate may be a substrate obtained by oxidizing the surface of a Si wafer or a quartz substrate.

The low-porosity layer may be formed by performing anodization at a lower current density when forming the porous layer than when forming the porous layer. At this time, after bonding the low-porosity layer and the support substrate, separation at the porous layer may be performed, and the low-porosity layer may be used as a photoelectric conversion layer of a photoelectric conversion device. At this time, the photoelectric conversion layer may be an epitaxial layer. These substrates and layers are desirably formed of silicon.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 to 8 of the present invention will be described. The first to fourth embodiments are modes for manufacturing an SOI substrate, and the fifth to seventh embodiments are modes for manufacturing a photoelectric conversion device such as a solar cell or an area sensor. Embodiment 8
Is a mode in which ion implantation is used as a method for forming a layer serving as a separation portion. The present invention is not limited to each embodiment, but also includes a combination of the embodiments.

Embodiment 1 is a mode of manufacturing an SOI substrate, and uses laser light to separate a wafer SOI substrate to be reused by a porous layer.

The laser beam is applied to the side (end face) of the plate-like substrate horizontally toward the front and back surfaces of the substrate, and the intensity of the laser beam is adjusted so that the laser beam also reaches near the center of the substrate.

The laser beam is applied to a relatively fragile layer such as a layer having a large porosity or a defect layer due to microbubbles formed in the substrate, and is absorbed there.

The layer that has absorbed the laser beam becomes even more brittle, and the substrate is separated into two pieces by the layer.

The method of irradiating a laser beam will be described in detail in the following embodiments.

(Embodiment 1) FIG. 1 is a diagram showing a separation method of this embodiment. In the figure, the same reference numerals as those in FIGS. 16 and 17 denote the same components. 10 is a lens, 11 is an optical microscope, 12
Denotes a vacuum chuck, and 13 denotes a laser beam. LS is a laser light source, ATL is an article before separation, and each layer 2, 3, 4,
It consists of 7 and 6. The side wall of the porous layer 3 is irradiated with laser light. The laser light source LS has a large output, XeCl, Kr.
An excimer laser such as F or ArF, whose output is 3
00 mJ / cm ^{2 to 1} J / cm ² is desirable. Particularly desirable is about 500 mJ / cm ² . Since the laser light of the excimer laser is ultraviolet light, the lens 10 is made of quartz or fluorite that transmits ultraviolet light.
The irradiation area of the laser light 13 can be reduced to a width of 0.1 μm. The optical microscope 11 is provided as needed, and is used to confirm whether the laser beam 13 has been correctly irradiated on the porous layer 3 having a thickness of 0.1 μm to 30 μm. Here, the porous layer 3 is fragile and easily separated as compared with the non-porous layer 2 having no porous structure or the epitaxial layer 4 having a low porosity. Therefore, the laser beam 13 does not have to be strictly applied only to the porous layer 3. As the light source LS that emits the laser light 13, it is desirable to use a high-output excimer laser device.
A laser, a YAG laser or the like may be used. 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, expansion of the liquid promotes separation.

Vacuum chuck 12 as a substrate holder
Is to fix the substrate ATL, which is an article before separation, by contacting the non-porous layer 2 and the outside of the single-crystal layer 6 with the inside of which the gas enters, and removing the gas inside. Can be. In the present embodiment, the vacuum chuck 12 is rotatable around 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 a small tensile force may be applied to the substrate from the vacuum chuck 12 to facilitate separation. The laser light is emitted from the side wall of the porous layer 3 to the substrate ATL.
To the vicinity of the center of. The porous layer that has absorbed light becomes more brittle, and the substrate ATL can be separated without destroying the non-porous portion.

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

A method of forming a thin film by the method of separating a wafer shown in FIG. 1 will be described.

First, a bonded substrate is prepared. FIG.
1 is a sectional view of an apparatus for anodizing a Si wafer.
In the drawing, 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 of a p-type, but may be of an n-type if the resistance is low. Also, n
Even if the Si wafer of the mold is irradiated with light to form holes, it can be easily made porous. 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 an electric field in the etching solution caused by this voltage is applied in a direction perpendicular to the surface of the Si wafer 1. When both electrodes and the wafer are parallel, the negative electrode 29 of the Si wafer 1
It is made porous from the side. As the hydrofluoric acid-based etchant 27, concentrated hydrofluoric acid (49% HF) is used. During the anodization, bubbles are generated from the Si wafer 1. For the purpose of efficiently removing the bubbles, alcohol as a surfactant may be added to the liquid 27.

As the alcohol, methanol, ethanol, propanol, isopropanol and the like are desirable.
Also, instead of adding a surfactant, use a stirrer,
Anodization may be performed while stirring.

The thickness of the layer to be made porous is 0.1 μm to 3 μm.
It is good to set it to 0 μm.

For the negative electrode 29, it is desirable to use a material that does not corrode with a hydrofluoric acid solution, for example, gold (Au), platinum (Pt), or the like. The positive electrode 28 may be a generally used metal material, but is preferably a material that does not corrode with hydrofluoric acid. The current density at which anodization is performed is a maximum of several hundred mA / cm ² , and the minimum value is 0 mA.
It is not good. The current density is set so that a high-quality epitaxial Si layer is formed on the formed porous Si layer, and the porous Si layer facilitates separation by separation. Specifically, when the current density of porous Si is large during anodization, the density of Si in the porous Si layer becomes small. Therefore, the larger the current density, the larger the volume of the hole,
The porosity (porosity; porosity is defined as the ratio of the volume of pores to the total volume of the porous layer) increases. The porous Si layer has many pores inside the Si layer, but its single crystallinity is maintained. Therefore, it is possible to epitaxially grow a single crystal Si layer on the porous Si layer.

However, epitaxial S without stacking faults
In order to form the i-layer, the porosity of the porous Si layer in contact with the epitaxial Si layer is preferably smaller. On the other hand, in order to facilitate separation of the device substrate and the SOI substrate from the porous Si layer as a boundary, it is preferable that the porosity of the porous Si layer is large. That is, ideally, the outermost surface side of the porous Si layer has low porosity, and the side of the porous Si layer near the non-porous Si layer has high porosity. FIG. 4 is a sectional view showing an ideal shape of the porous Si layer. Porous Si
A porous Si layer 3a having a low porosity is formed on the surface side of the layer 3, and a porous Si layer 3b having a high porosity is formed on the non-porous Si layer side of the porous Si layer 3. In order to form this structure, anodize at a small current density at the beginning of the anodization of the portion 3a, and anodize at a large current density at the subsequent anodization of the portion 3b. . With this structure, the separation surface of the substrate can be specified as 3b,
Further, an epitaxial Si layer having no stacking fault can be formed on the porous Si layer 3a. This epitaxial Si layer is preferably grown by molecular beam epitaxy, plasma CVD, low pressure CVD, optical CVD, bias sputtering, liquid phase epitaxy, etc., especially at low temperature.

According to the method described above, FIG.
As shown in FIG. 5, an Si wafer 1 is prepared, and its surface is made porous as shown in FIG. Thus, the Si wafer 1 changes to a structure in which the porous Si layer 3 is stacked on the non-porous Si layer 2.

Next, as shown in FIG.
A non-porous epitaxial Si layer 4 having a low porosity is formed on the i-layer 3.

Next, if necessary, the surface of the epitaxial Si layer 4 is thermally oxidized to form a 0.05 μm to 2 μm thick Si oxide layer 8 as shown in FIG.

The above is the processing before bonding on the substrate PW side called a prime wafer, a bond wafer, or a device substrate.

The processing on the side of the substrate HW called a handle wafer, a base wafer or a support substrate is as follows.

A Si wafer is prepared and, if necessary, its surface is thermally oxidized to a thickness of 0.05 μm to 3 μm.
An i film is formed on the surface.

Next, the steps of bonding and separating 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 Adhere at room temperature.

Thereafter, the oxidized Si layer 8 and the oxidized Si oxide are
The layer 7 is firmly bonded to form an article ATL composed of a bonded substrate as shown in FIG.

Next, the vacuum chuck 1 of the apparatus shown in FIG.
In FIG. 2, the bonded article ATL having the structure shown in FIG. 6B is mounted, and while the article ATL is rotated, the side of the article ATL is focused on the portion of the porous Si layer 3 and excimer laser light is applied. Is irradiated. Excimer laser light is applied to the entire porous Si layer and absorbed.

In this way, as shown in FIG.
The W-side non-porous Si layer 2 is separated from the substrate HW. At this time, the epitaxial Si layer 4 has been transferred to the surface of the substrate HW.

Porous S destroyed by absorption of laser light
The i-layer 3 is composed of the non-porous Si layer 2 side and the epitaxial Si layer.
It may remain on at least one of the layers 4 side. FIG. 6 (c) shows a state in which it remains only on the epitaxial Si layer 4 side.

When the porous Si layer 3 remains, the substrate H
The porous Si layer 3 remaining on the W side is removed by selective etching. At the time of selective etching, if the electroless wet chemical etching is performed using hydrofluoric acid as an etching solution, a mixed solution of hydrofluoric acid and alcohol, or a mixed solution of hydrofluoric acid and hydrogen peroxide water, porous Si Layer is non-porous Si
Etched more than layers. In particular, when a mixed solution of hydrofluoric acid and an aqueous solution of hydrogen peroxide is used, the selective etching ratio of the porous Si layer to the non-porous Si layer is 10 to 10 ⁵
Becomes Thus, the epitaxial Si layer 4 having a uniform thickness remains on the surface of the substrate HW as shown in FIG. Thus, a very uniform SOI substrate of the semiconductor layer 4 on the insulating layer is obtained.

The decomposed non-porous layer 2 is used again as a prime wafer to produce another SOI substrate.

Further, in the process of manufacturing the SOI substrate of the present embodiment,
The supporting substrate may be a completely insulating substrate such as a glass or quartz substrate. FIG. 7 is a diagram illustrating 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. And the support base H
The quartz substrate 9 serving as W and the silicon oxide layer 8 face each other,
As shown in FIG. 7B, the quartz substrate 9 and the Si oxide layer 8 are closely adhered to each other, and the Si oxide layer 8 and the quartz substrate 9 are firmly bonded by anodic bonding, pressing, heat treatment or a combination thereof. I do.

Next, the two substrates are separated using a laser beam in the same manner as described above. The transferred epitaxial Si layer 4 and porous Si layer 3 remain on the quartz substrate 9 (FIG. 7C). Further, the remaining porous Si layer 3 is selectively removed by the method described above. Thus, an SOI having a non-porous single-crystal Si thin film on a quartz substrate 9
A substrate is obtained (FIG. 7D).

Further, in the step of manufacturing the SOI substrate of the present embodiment, a Si wafer is used as a support substrate, and an Si oxide layer is formed on the epitaxial Si layer on the device substrate side without forming an Si oxide layer on the Si wafer side. Thus, an insulating layer having an SOI structure can be formed. FIG. 8 illustrates this step. The device substrate in the upper part of FIG. 8A is manufactured in the same manner as the method described with reference to FIG. And S
Surface of single crystal Si layer 5 made of i-wafer and Si oxide layer 8
The surface of the single crystal Si layer is
The surface of layer 8 is brought into close contact and bonded. At this time, the oxidized Si layer 8 and the single-crystal Si layer 5 may be strongly bonded by anodic bonding, pressurization, heat treatment, or a combination thereof.
Thus, the article ATL is obtained as shown in FIG.

Then, using the apparatus shown in FIG. 1, the article ATL is separated at the porous Si layer 3 and the non-porous single-crystal Si layer 5 is provided on the non-porous Si layer 5 side as the supporting substrate HW. The epitaxial Si layer 4 made of is transferred. At this time, FIG.
In the case where the porous Si layer 3 remains on the epitaxial Si layer 4 on the support substrate HW as shown in (c), if the porous Si layer is selectively removed by the method described above, An SOI substrate as shown in FIG. 8D is obtained.

(Embodiment 2) Embodiment 2 is a mode of manufacturing an SOI substrate, and uses an excimer laser for separating a Si wafer to be reused and a substrate to finally become an SOI substrate by a porous Si layer. . At this time, the excimer laser light is focused to one point, the substrate is fixed, and the laser light is scanned to perform separation.

FIG. 9 is a view showing the separation step of the present embodiment. Reference numeral 14 denotes a guide which can scan 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 ones as described in FIG. In the present embodiment, the outside of the single-crystal Si layer 6 and the non-porous Si layer 2 constituting the article ATL are fixed by the chuck 12. Then, the laser beam 13 of the excimer laser device is focused on one point of the side wall of the porous Si layer 3 by the lens 10 and irradiated. At the same time that the lens 10 is scanned by the guide 14, the laser beam 13 is also scanned, and the SOI substrate composed of the layers 4, 7, and 6 is separated from the substrate 2 reused in the manufacturing process by the porous Si layer 3. To separate. Other steps and materials to be used are the same as those in the first embodiment.

Embodiment 3 Embodiment 3 is a mode of manufacturing an SOI substrate, and uses an excimer laser to separate a reused Si wafer and an SOI substrate by a porous Si layer. At this time, the light of the excimer laser is linearly stopped down by a cylindrical lens, and the laser light is irradiated along the porous Si layer.

FIG. 10 is a view showing the separation step of the present embodiment, and 15 is a cylindrical lens. Other part numbers represent the same ones as described in FIG. The cylindrical lens 15 can focus the laser light 13 in a straight line running vertically. Therefore, the side wall of the porous Si layer 3 having a small thickness of 0.1 μm to 30 μm can be efficiently irradiated with the laser beam. In addition, a cylindrical lens 1
Alternatively, laser irradiation may be performed at a linear focus using a toic lens instead of 5 in accordance with 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 In Embodiment 4, an SOI substrate is manufactured, and an excimer laser is used to separate a reused Si wafer and an SOI substrate by a porous Si layer. At this time, the light of the excimer laser is linearly stopped down 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 beams, and the laser beam 13 is linearly narrowed down along the porous Si layer 3 using four cylindrical lenses 15 to form a porous film from four directions. Irradiate the Si layer. In the present embodiment, the outside 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) Embodiment 5 is a mode of manufacturing a solar cell. FIG. 12 is a diagram illustrating a process until a photoelectric conversion layer that converts light into electricity is formed. 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 anodizing method as described with reference to FIG. Then, Figure 1
As shown in FIG. 2B, a substrate having the porous Si layer 3 on the non-porous Si layer 2 of the wafer 1 is obtained. And FIG.
As shown in (c), an epitaxial Si layer serving as the photoelectric conversion layer 18 is formed on the porous Si layer 3 by a method such as molecular beam epitaxial growth, plasma CVD, low pressure CVD, optical CVD, bias sputtering, and liquid phase growth. Formed. Thus, 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. For this reason, the epitaxial Si layer is composed of an n ⁺ layer on the porous Si layer 3, a p ⁻ layer thereon, and a p ⁺ layer thereon.
It has a PN junction in which ⁺ layers are stacked.

Then, the surface of the p ⁺ layer of the photoelectric conversion layer 18 epitaxially grown and the back metal electrode 16 formed in advance on the surface of the plastic substrate 17 are bonded and joined.

Thereafter, the vacuum chuck 12 is moved to the non-porous Si
The laser light 13 from the excimer laser device is focused on the porous Si layer 3 by using the lens 10 so as to be in close contact with the outside of the layer 2,
Irradiate. FIG. 13 illustrates a mode in which the laser light is focused to one point by a lens, but the laser light may be applied in any manner described in the first to fourth embodiments. Then, FIG.
In such a porous Si layer, the substrate HW that will eventually become a solar cell and the substrate PW that will become a Si wafer to be reused in the manufacturing process can be separated.

Thereafter, as shown in FIG. 15A, a mesh surface metal electrode 19 is formed on the surface of the photoelectric conversion layer 18. Next, the wiring 24 is connected to the front metal electrode 19 and the back metal electrode 16, and the protective layer 20 is formed on the front metal electrode 19. FIG. 15B is a cross-sectional view taken along line AA ′ of FIG. The photoelectric conversion layer 18 includes an n ⁺ layer 23, a p layer 22, and a back metal electrode 16 in contact with the front metal electrode 19 from above.
Is formed of ap ⁺ layer 21 in contact with. In FIG. 15, the surface metal electrode 19 is illustrated as being meshed so as to transmit light, but this may be replaced with a transparent electrode such as ITO. In addition, since the back metal electrode 16 also has a function 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 with a metal material with high reflectance.

According to this embodiment, since a single Si wafer can be used to form a number of single-crystal thin-film solar cells, the conversion efficiency,
Excellent in terms of life, manufacturing cost, and the like. In addition, since the porous Si layer is irradiated with laser light to cause thermal absorption of the porous Si layer to cause thermal expansion of the porous Si layer and to cause distortion of the crystal to separate the substrate, a strong pulling force is not required. For this reason, since a strong adhesive force is not required between the substrate and the jig or the like, it is excellent in terms of manufacturing cost.

(Embodiment 6) Embodiment 6 is a mode of manufacturing a solar cell as in Embodiment 5. In the fifth embodiment, the photoelectric conversion layer 18 is constituted by an epitaxial Si layer formed on the porous Si layer 3. On the other hand, in the sixth embodiment, a porous Si layer having a small porosity is used as the photoelectric conversion layer 18 as it is. Embodiment 1 describes that the porosity of the porous Si layer can be changed by changing the current density in the anodizing step. That is, if the current density flowing from the electrode 28 to the electrode 29 is increased in the anodization step described with reference to FIG. 3, the porosity of the porous Si layer formed on the Si wafer 1 increases, and the current concentration decreases. It explains that the porosity becomes smaller if it is done. When the surface of the p ⁺ -type Si wafer 1 is made porous using this phenomenon, the current density is reduced and the porous S
An i-layer is formed, and a porous Si layer 3b having a high porosity is formed below and above the non-porous Si layer 2. P, which forms an n-type on the outermost surface of the porous Si layer 3a having a small porosity,
Donor ions such as As are ion-implanted and used for a part of a photoelectric conversion layer having a pn junction with a small-porosity porous Si layer.

Thereafter, similarly to the one shown in FIG. 13, the porous Si layer having a small porosity as the photoelectric conversion layer and the back metal electrode 16 are bonded. Other steps are the same as in the fifth embodiment. In this embodiment, since a single Si wafer can form solar electric fields of several single crystal thin films,
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 lower than in the fifth embodiment. Also, the photoelectric conversion layer 18
Is made of a porous Si layer having a small porosity, so that single crystallinity is maintained, and light is appropriately scattered in the pores, so that the conversion efficiency is high.

(Embodiment 7) Embodiment 7 is a mode of manufacturing an area sensor. In this embodiment, a single-crystal thin-film photoelectric conversion layer is formed from a Si wafer as in the fifth and sixth embodiments. Then, an optical sensor is two-dimensionally arranged on the photoelectric conversion layer, and a matrix wiring is provided. For the matrix wiring, for example, a column wiring is provided instead of arranging the front metal electrode 19 in FIG. 15, and a row wiring is provided instead of arranging the rear metal electrode 16 in FIG. According to the present embodiment, since a plurality of single-crystal thin film area sensors can be formed from one Si wafer, they are excellent in terms of exchange efficiency, life, manufacturing cost, enlargement of area, and the like.

(Embodiment 8) First, as one substrate, S
Prepare an i-wafer.

Next, the Si wafer is set in an ion implantation apparatus, and hydrogen ions or rare gas ions are implanted into the entire surface of the Si wafer so as to reach a certain depth. Thus, Si
A defect layer by microbubbles is formed inside the wafer.

On the other hand, another Si wafer is prepared as a supporting 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.

An article made of the bonded wafer thus formed is irradiated with an excimer laser beam in the vicinity of a defect layer formed by microbubbles on the side face of the article by a method as shown in FIGS. Light is absorbed by the defect layer to make the defect layer more brittle and separate the two wafers.

Thus, the single crystal Si layer on the defect layer of the Si wafer as one substrate is transferred onto the silicon oxide film on the other substrate.

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

Although the above description has been made with reference to the case of a Si wafer separately, the present invention relates to SiGe, Ge, Si
The present invention is also applicable to other semiconductors such as C, GaAs, and InP.

[0069]

According to the present invention, the laser light is irradiated from the side of the substrate not only to the periphery of the substrate but also to the porous layer near the center, and the porous layer absorbs the laser light, so that the Si layer can be easily formed. Many single crystal thin films Si can be obtained from the substrate. In addition, since laser light without impurities is used for the separation, the obtained Si thin film has a high quality. Therefore, the quality of the SOI substrate itself becomes high. Further, when manufacturing the SOI substrate, since the materials can be used without waste, it is possible to provide a low-cost and low-resource manufacturing method. In addition, the quality of the photoelectric conversion device itself is improved. Further, even when the photoelectric conversion device is manufactured, the materials can be used without waste, so that it is possible to provide a low manufacturing cost and resource saving manufacturing method.

[Brief description of the drawings]

FIG. 1 shows a first embodiment in which a porous Si layer is irradiated with a laser beam.
FIG.

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

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

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

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

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

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

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

FIG. 9 is a second embodiment in which a porous Si layer is irradiated with a laser beam.
FIG.

FIG. 10 is a diagram illustrating a separation step of Embodiment 3 in which a porous Si layer is irradiated with laser light.

FIG. 11 is a view illustrating a separation step of Embodiment 4 in which a porous Si layer is irradiated with laser light.

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

FIG. 13 shows a separation step of Embodiment 5 in which a porous Si layer is irradiated with laser light.

FIG. 14 is a diagram illustrating 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 illustrating a manufacturing process of an SOI substrate.

FIG. 17 is a diagram illustrating a manufacturing process of the SOI substrate.

FIG. 18 is a view illustrating a conventional method of manufacturing a solar cell.

[Explanation of symbols]

1,5 Si wafer 2 Non-porous Si layer 3 Porous Si layer 4 Epitaxial Si layer 6 Single crystal Si layer 7,8 Si oxide layer 9 Quartz substrate 10 Lens 11 Optical microscope 12 Vacuum chuck 13 Laser beam 14 Guide 15 Cylindrical lens Reference Signs List 16 back 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 etchant 28 positive electrode 29 negative electrode 30 protective film 31, 32 cure Tool 33 wound

Claims (31)

[Claims] 1. The non-porous layer and the layer having a low porosity of a substrate having a porous layer on the non-porous layer and a layer having a lower porosity than the porous layer on the porous layer. Wherein the separation is performed by irradiating the substrate with a laser beam from the side surface of the substrate to the center of the substrate. 2. The method for forming a thin film according to claim 1, wherein the separation is performed by focusing a laser beam on a side surface of the porous layer and expanding the porous layer. 3. The method according to claim 1, wherein the porous layer on the non-porous layer is formed by anodizing a Si wafer. 4. The method for forming a thin film according to claim 1, wherein the laser light is applied to a plurality of portions of the porous layer. 5. The non-porous S not in contact with the porous layer
2. The method of forming a thin film according to claim 1, wherein the back surface of the i-layer is brought into close contact with a vacuum chuck, and a small tensile force is transmitted from the vacuum chuck to the substrate. 6. The method according to claim 1, wherein the laser beam is an excimer laser beam. 7. The method for forming a thin film according to claim 1, wherein the laser light is linearly converged using a cylindrical lens, and the linear laser light is irradiated along the porous layer. 8. The method according to claim 3, wherein the low-porosity layer is a non-porous epitaxial layer formed by epitaxial growth on the porous layer. 9. After bonding the non-porous epitaxial layer and the supporting substrate with an insulating layer interposed therebetween, separation is performed at the porous layer, and the non-porous epitaxial layer is left on the non-porous epitaxial layer. 9. The method of forming a thin film according to claim 8, wherein the porous layer is removed, and the non-porous epitaxial layer and the insulating layer are used as a semiconductor layer and a base insulating layer of an SOI substrate, respectively. 10. The method for forming a thin film according to claim 9, wherein the supporting substrate is a substrate obtained by oxidizing a surface of a Si wafer, and the insulating layer is the oxidized surface. 11. An insulating layer is formed on the surface of the non-porous epitaxial layer, and after bonding to a supporting substrate, separation is performed at the porous layer and the insulating layer remains on the non-porous epitaxial layer. The method of forming a thin film according to claim 8, wherein the porous layer is removed, and the non-porous epitaxial layer and the insulating layer are used as a semiconductor layer and a base insulating layer of an SOI substrate, respectively. 12. The method according to claim 11, wherein the support substrate is a quartz substrate. 13. The method according to claim 11, wherein the supporting substrate is a substrate obtained by oxidizing a surface of a Si wafer. 14. The thin film according to claim 3, wherein the layer having a small porosity is formed by performing anodization having a smaller current density when forming the porous layer when anodizing the Si wafer. Method. 15. The method according to claim 8, wherein after bonding the low-porosity layer and the supporting substrate, separation is performed at the porous layer, and the low-porosity layer is used as a photoelectric conversion layer of a photoelectric conversion device. A method for forming a thin film according to claim 14. 16. The method according to claim 1, wherein the non-porous layer, the porous layer, and the low-porosity layer are each made of silicon. 17. By focusing the laser beam on a side surface of the porous layer and expanding the porous layer,
The method according to claim 16, wherein the separation is performed. 18. The method according to claim 18, wherein the porous layer on the non-porous layer is made of Si.
17. The method for forming a thin film according to claim 16, wherein the thin film is formed by anodizing a wafer. 19. The method for forming a thin film according to claim 16, wherein the laser light is applied to a plurality of portions of the porous layer. 20. The non-porous back surface which is not in contact with the porous layer is brought into close contact with a vacuum chuck, and a small tensile force is transmitted from the vacuum chuck to the substrate.
7. The method for forming a thin film according to 6. 21. The method according to claim 16, wherein the laser light is an excimer laser light. 22. The method for forming a thin film according to claim 16, wherein the laser beam is squeezed linearly using a cylindrical lens, and the linear laser beam is irradiated along a porous layer. 23. The method according to claim 18, wherein the low-porosity layer is a non-porous epitaxial layer formed by epitaxial growth on the porous layer. 24. After bonding the epitaxial layer and a support substrate having an insulating layer on at least the surface, separation is performed at the porous layer, and the porous layer remaining on the epitaxial layer is removed. 24. The method according to claim 23, wherein the epitaxial layer and the insulating layer are a semiconductor layer and a base insulating layer of an SOI substrate, respectively. 25. The method for forming a thin film according to claim 24, wherein the support substrate having an insulating layer on at least the surface is a substrate obtained by oxidizing the surface of a Si wafer. 26. An insulating layer is formed on the surface of the epitaxial layer and bonded to a supporting substrate. Then, separation is performed at the porous layer, and the porous layer remaining on the epitaxial layer is removed. 24. The method of forming a thin film according to claim 23, wherein the layer and the insulating layer are a semiconductor layer and a base insulating layer of an SOI substrate, respectively. 27. The method according to claim 26, wherein the support substrate is a quartz substrate. 28. The method according to claim 26, wherein the supporting substrate is a substrate obtained by oxidizing a surface of a Si wafer. 29. The thin film according to claim 18, wherein the low-porosity layer is formed by performing anodization at a lower current density during the anodization of the Si wafer than when forming the porous layer. Method. 30. The method according to claim 18, wherein after bonding the low-porosity layer and the supporting substrate, separation is performed at the porous layer, and the low-porosity layer is used as a photoelectric conversion layer of a photoelectric conversion device. A method for forming a thin film according to claim 29. 31. A method for forming a thin film, comprising: irradiating a side surface of a substrate having a defect layer by ion implantation with laser light to separate the substrate at the defect layer.