JP2002217438A - Manufacture of thin-film semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing thin-film semiconductor element which can easily transfer a semiconductor element, such as a solar battery and can improve the manufacturing yield. SOLUTION: Porous silicon layers 3, 6 are formed to both surfaces of a single crystal silicon substrate 5 by anode formation method and thereby a compression stress of these porous silicon layers 3, 6 is applied to both surfaces of a single-crystal silicon substrate 5. An epitaxial film 4 is formed on the surface of porous silicon layer 3 through the epitaxial growth. In this case, with existence of the porous silicon films 3, 6, natural removal of the epitaxial film 4 from the single-crystal silicon substrate 5 is controlled, because the bending moment on the epitaxial film 4 can be almost removed. Thereafter, a solar battery element can be manufactured by removing the photoelectric converting part, consisting of the epitaxial film 4 from the single-crystal silicon substrate 5 at the separation layer 3A in the porous silicon layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film semiconductor device such as a solar cell device, and more particularly to a method for transferring a semiconductor device to another substrate after forming the semiconductor device on a semiconductor substrate via a release layer. The present invention relates to a method for manufacturing a thin film semiconductor device including a step.

[0002]

2. Description of the Related Art In recent years, a solar cell element using a single crystal silicon thin film has been manufactured by, for example, the following method. First, after forming a porous (porous) silicon layer including a release layer having a low tensile strength on a single crystal silicon substrate,
A single-crystal silicon thin film is formed on the porous silicon layer, and a main body (photoelectric conversion unit) of the solar cell element is formed on the single-crystal silicon thin film. Further, after a plastic film is adhered to the element body, the element body is separated from the single crystal silicon substrate by applying a tensile force to the porous silicon layer (Japanese Patent Application Laid-Open No. H8-213645). Thus, the element body is transferred to the plastic film side, and by using this method, a flexible solar cell element formed on a plastic film, a paper sheet, or the like can be obtained.

[0003]

However, in the above-mentioned manufacturing method, in order to facilitate the transfer of the element body, that is, the peeling from the single crystal silicon substrate, the peel strength of the peeling layer in the porous silicon layer should be as small as possible. What is necessary is just to make it small. However, if the tensile strength of the release layer becomes too small, the element body may be removed before the transfer step, that is, during the manufacturing step of the element body following the release layer (for example, an oxidation step, a diffusion step, or a metal sputtering step). A phenomenon occurs in which the substrate is spontaneously separated from the single crystal silicon substrate.

In order to prevent such a spontaneous peeling phenomenon from occurring, the tensile strength of the peeling layer may be made relatively high.
In this case, for example, a plastic film may be separated from the element body before the element body is separated from the single crystal silicon substrate in the separation layer portion, and there is a problem that the production yield of the element body is reduced. .

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of manufacturing a thin film semiconductor device in which a semiconductor device such as a solar cell can be easily transferred and a manufacturing yield can be improved. It is in.

[0006]

A method of manufacturing a thin film semiconductor device according to the present invention comprises forming a first porous semiconductor layer for peeling on one surface of a semiconductor substrate having two opposing surfaces, and a semiconductor substrate. Forming a second porous semiconductor layer on the other surface of the semiconductor device, forming a semiconductor element on the first porous semiconductor layer, bonding a transfer substrate to the semiconductor element, And transferring to the transfer substrate side by peeling off at the first porous semiconductor layer portion.

In the method for manufacturing a thin film semiconductor device according to the present invention, in a step before forming a semiconductor device on the first porous semiconductor layer, a second porous semiconductor layer is formed on the opposite surface of the semiconductor substrate. I have. Accordingly, the stress on both sides of the semiconductor substrate is balanced, and the occurrence of bending moment on the semiconductor substrate and the layer on which the semiconductor element is formed is suppressed, thereby preventing the semiconductor element from spontaneously peeling off from the semiconductor substrate. Is transferred to the transfer substrate side.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but before that, the background to the present invention will be described.

In general, in a method of manufacturing a solar cell device by applying a tensile force to a porous silicon layer to separate an element body made of an epitaxial film or the like from a single crystal silicon substrate, a solar cell element is formed on the single crystal silicon substrate. Before the step of growing an epitaxial film (single-crystal silicon film) on the surface of the porous silicon layer, the natural oxide film formed on the surface of the porous silicon layer is removed, and the surface of the porous silicon layer is removed. It is necessary to perform a high-temperature hydrogen annealing treatment in order to close the holes formed in the substrate.
However, due to this high-temperature hydrogen annealing,
Since the porous silicon layer itself is recrystallized, the surface area in the porous silicon layer is rapidly reduced, voids having a structure such as an octahedron or a tetrahedron are formed, and the porous silicon layer is formed. , Volume contraction occurs. In this state, when an epitaxial film is grown on the surface of the porous silicon layer, this corresponds to a kind of heteroepitaxial growth, so that stress is generated between the porous silicon layer and the epitaxial film. .

[0010] Here, the present inventors cooled the single crystal silicon substrate on which the epitaxial film was grown from high temperature to room temperature, and then peeled the epitaxial film from the single crystal silicon substrate in the porous silicon layer. As a result, as shown in FIG. 1, each of the epitaxial film 1 and the porous silicon film 2 was convexly curved. As a result, stress (tensile stress) that curves convexly in the epitaxial film 1 and stress (compressive stress) that curves concavely are generated in the porous silicon layer 2 after peeling. I understood.

Based on the above results, as shown in FIG. 2, the release layer 3A serving as a starting point of the release of the porous silicon layer 3 is formed.
In the state before the epitaxial film 4 is separated from the single crystal silicon substrate 5, the single crystal silicon substrate 5, the porous silicon layer 3 and the epitaxial film 4 have the compressive stress of the porous silicon layer 3 and the single crystal silicon substrate 5 It is expected that a bending moment due to the tensile stress is applied and the epitaxial film 4 is deformed so as to be concave. From this, in particular, in order to easily peel off the epitaxial film 4 from the single crystal silicon substrate 5, the peeling layer 3A having a small tensile strength is replaced with the porous silicon layer 3A.
When formed inside, the above bending moment becomes a factor when the epitaxial film 4 is spontaneously peeled off from the single crystal silicon substrate 5 during the subsequent manufacturing process.

In order to reduce the bending moment, the present inventor has not only formed the porous silicon film 3 on one surface of the single crystal silicon substrate 5 as shown in FIG. The porous silicon layer 5 was also formed on the surface of the substrate. This is because the porous silicon layers 3, 6
This is because if the compressive stress is applied to both surfaces of the single crystal silicon substrate 5, the bending moment for the single crystal silicon substrate 5 and the epitaxial film 4 formed in a later step can be almost eliminated. Hereinafter, a method for manufacturing a solar cell element, which is an example of a thin-film semiconductor element, based on such a concept will be described.

FIGS. 4 and 5 illustrate a method of manufacturing a solar cell element according to an embodiment of the present invention. First, as shown in FIG. 4A, a semiconductor substrate 11 for forming a main body of a solar cell element is prepared. The semiconductor substrate 11 is doped with, for example, a p-type impurity such as boron and has a concentration of about 0.01 Ω · cm to 0.02 Ω · c.
A single crystal silicon substrate having a specific resistance in the range of m is used. Next, as shown in FIG.
The porous silicon layer 12 having a thickness of, for example, about 8 μm is formed on one surface (rear surface) of the substrate 1 by anodizing using the anodizing apparatus described below.

FIG. 6 shows a schematic configuration of the anodizing apparatus. This anodizing apparatus includes an anodizing tank 30. In the anodizing tank 30, two anodizing electrodes 32 and 33 made of, for example, platinum (Pt) connected to a power supply 31 are provided to face each other. Here, after the semiconductor substrate 11 is disposed between the anodizing electrodes 32 and 33 in the anodizing tank 30 by a support (not shown), the anodizing is performed on the back surface side of the semiconductor substrate 11. A DC voltage is applied from the power supply 31 using the anodized electrode 32 as an anode and the anodized electrode 33 as a cathode. Examples of the anodizing solution contained in the anodizing tank 30 include hydrogen fluoride (HF) and ethanol (C ₂ H ₅ OH):
1 electrolytic solution is used. The current density for anodization is, for example, about 7 mA / cm ² , and the anodization time is, for example, about 8
Minutes.

Next, the other surface (front surface) of the semiconductor substrate 11
Then, a porous silicon layer 13 having a thickness of, for example, about 8 μm is formed by anodization using the above-described anodizing apparatus.
FIG. 7 is for explaining anodization at the time of forming the porous silicon layer 13. Here, the polarities of the anodized electrodes 32 and 33 are reversed so that anodization is performed on the surface side of the semiconductor substrate 11, the anodized electrode 32 is used as a cathode, the anodized electrode 33 is used as an anode, and a DC voltage is supplied from the power supply 31. Is applied. The anodization is performed, for example, in three stages. That is, for example, in the first stage, about 1
mA / cm ² current density at about 8 minutes, in the second stage, about 7 mA / cm ² current density at about 8 minutes, in the third stage,
Anodization is performed at a current density of about 200 mA / cm ² for several seconds. This anodization can be performed in two steps or in four steps.
You may make it perform in steps or more.

After the porous silicon layers 12 and 13 are formed on both surfaces of the semiconductor substrate 11, the holes existing on the surfaces of the porous silicon layers 12 and 13 are closed by hydrogen annealing. Next, as shown in FIG. 4 (C), epitaxial growth is performed, and for example, about 10
A p-type epitaxial film (single crystal silicon film) 14 having a thickness of μm is formed.

During such hydrogen annealing and epitaxial growth, a release layer 13A having the lowest tensile strength is formed in the porous silicon layer 13.
However, during the manufacturing process of the solar cell element, the p-type epitaxial film 14 and the like serve as the release layer 13A.
It has a tensile strength that does not cause partial or complete peeling from 1.

Subsequently, as shown in FIG. 4D, an n-type impurity is diffused into the epitaxial film 14 by, for example, ion implantation to form an n-type layer 14A.
Form a bond. After the anti-reflection film 15 is formed on the surface of the epitaxial film 14, the surface electrode 16 is formed as an anode and the surface electrode 17 is formed as a cathode, for example, by screen printing.

After the photoelectric conversion unit 10A is formed as described above, a film 18 made of, for example, plastic is prepared as shown in FIG.
8 on the surface side of the photoelectric conversion unit 10A (the porous silicon film 13
Is adhered to the surface on which no is formed) using, for example, an adhesive made of EVA (ethylene vinyl acetate).
After this bonding, as shown in FIG. 5B, the photoelectric conversion unit 10A is separated from the semiconductor substrate 11 at the separation layer 13A and transferred to the film 18. At the time of this peeling, for example, a tensile stress is generated between the semiconductor substrate 11 and the film 18. After this peeling, the porous silicon layer 13B remaining on the back surface side (peeling surface side) of the photoelectric conversion unit 10A is removed by, for example, etching.

If the porous silicon layer 13C remaining on the front surface side (peeling surface side) of the semiconductor substrate 11 and the porous silicon film 12 formed on the back surface side of the semiconductor substrate 11 are removed by, for example, etching, Semiconductor substrate 1
1 can be used again as a substrate for forming a solar cell element, and the manufacturing cost of the solar cell element can be reduced.

After removing the porous silicon layer 13B,
As shown in FIG. 5C, a film 20 made of, for example, plastic on which the light reflection plate 19 is formed is prepared, and this film 20 is placed on the back side of the photoelectric conversion unit 10A, for example, by E.
Adhesion is performed using an adhesive made of VA. As described above, the solar cell element 10 having the photoelectric conversion unit 10A is manufactured. Note that a transparent plastic film without a light reflecting plate may be used instead of the film 20, and such a configuration enables photoelectric conversion by light incident from the back surface side of the solar cell element 10. Since the plastic film is bonded after the above-described peeling is performed, a flexible or thin plastic film may be used.

Incidentally, the solar cell element expands in a high temperature state due to the irradiation of sunlight in the daytime in summer, for example, but contracts in a low temperature state in the nighttime in winter. Due to such a change in the temperature state, a tensile stress or a compressive stress is generated in the solar cell element, and in particular, a thin-film solar cell element may be broken. However,
If plastic films of the same type and approximately the same thickness are used as plastic films adhered to the front and back surfaces of the photoelectric conversion unit of the thin-film solar cell element, the same level of stress is applied to both surfaces of the photoelectric conversion unit. As they are applied, these stresses cancel each other. As a result, it is possible to minimize the destruction of the solar cell element.

As described above, in the present embodiment, in the manufacturing process of the solar cell element, the porous silicon layers 12, 13 are formed on both surfaces of the semiconductor substrate 11 to compress the porous silicon layers 12, 13. A bending moment due to stress is hardly generated. Therefore, even if the release layer 13A having a small tensile strength is formed on the porous silicon layer 13 on the side where the photoelectric conversion unit 10A is formed, the photoelectric conversion unit 10A and the like are removed from the semiconductor substrate 11 during the manufacturing process of the solar cell element. Almost no spalling occurs. Therefore, the yield can be improved and a solar cell element using the single crystal silicon thin film can be manufactured. In addition, by making almost no bending moment due to the compressive stress of the porous silicon layer,
A solar cell element using a large-area semiconductor substrate can be easily manufactured.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment.
Various modifications are possible. For example, both the front and back surfaces of the semiconductor substrate before anodization may have been subjected to polishing or etching. Alternatively, the surface of the semiconductor substrate on which the epitaxial film is grown may have been subjected to polishing or etching, and the surface on which the epitaxial film has not been grown may be a lap surface.

[0025]

As described above, according to the method of manufacturing a thin film semiconductor device of the present invention, the first porous semiconductor layer for peeling is formed on one surface of a semiconductor substrate having two opposing surfaces. A second porous semiconductor layer is formed on the other surface of the semiconductor substrate, a semiconductor element is formed on the first porous semiconductor layer, and a transfer substrate is adhered to the semiconductor element. Is transferred to the transfer substrate side by peeling off the first porous semiconductor layer portion, so that the semiconductor element can be prevented from spontaneously peeling off from the semiconductor substrate during the manufacturing process as much as possible. Can be improved.

[Brief description of the drawings]

FIG. 1 is a view for explaining a porous silicon layer and an epitaxial film after being separated from a single crystal silicon substrate in a manufacturing process of a solar cell element.

FIG. 2 is a view for explaining a bending moment with respect to an epitaxial film before being separated from a single crystal silicon substrate in a manufacturing process of a solar cell element.

FIG. 3 is a view for explaining a bending moment due to a compressive stress of a porous silicon layer formed on both surfaces of a single crystal silicon substrate by anodization in a manufacturing process of a solar cell element.

FIG. 4 is a cross-sectional view for explaining a method for manufacturing a solar cell element which is a thin-film semiconductor element according to one embodiment of the present invention.

FIG. 5 is a cross-sectional view for describing a step that follows the step of FIG.

6 is a diagram showing a schematic configuration of an anodizing apparatus used in the anodizing step shown in FIG.

FIG. 7 is a view for explaining anodizing when forming a porous silicon film using the anodizing apparatus shown in FIG. 6;

[Explanation of symbols]

1,4,14 ... epitaxial film, 2,3,6,12,
13, 13B, 13C ... porous silicon layer, 3A, 13
A: release layer, 5: single crystal silicon substrate, 10: solar cell element, 10A: photoelectric conversion unit, 11: semiconductor substrate, 14A
... n-type layer, 15 ... antireflection film, 16, 17 ... surface electrode,
18, 20: film, 19: light reflecting plate, 30: anodizing tank, 31: power supply, 32, 33: anodizing electrode.

Claims (8)

[Claims] A step of forming a first porous semiconductor layer on one surface of a semiconductor substrate having two opposing surfaces and a second porous semiconductor layer on the other surface of the semiconductor substrate; Forming a semiconductor element on the first porous semiconductor layer; bonding a transfer substrate to the semiconductor element; and exfoliating the semiconductor element at the first porous semiconductor layer portion. Transferring to the transfer substrate side. 2. The method according to claim 1, wherein the semiconductor substrate is made of single crystal silicon. 3. The method according to claim 1, wherein the first and second porous semiconductor layers are formed in an anodizing bath by an anodizing method. 4. After forming one of the first porous semiconductor layer and the second porous semiconductor layer, the polarity of the electrode of the anodization tank is reversed to form the other. 4. The method according to claim 3, wherein a porous semiconductor layer is formed. 5. The method according to claim 1, wherein a plastic film is used as the transfer substrate. 6. The method for manufacturing a thin film semiconductor device according to claim 1, wherein a peeling layer having a low local strength is locally formed at an intermediate portion in a thickness direction of said first porous semiconductor layer. 7. The method for manufacturing a thin film semiconductor device according to claim 1, further comprising a step of bonding a plastic film to a separation surface of the semiconductor device after peeling the semiconductor device from the semiconductor substrate. Method. 8. The method according to claim 7, wherein a film having a light reflecting plate is used as the plastic film.