JPH10308520A - Manufacture of semiconductor thin film and solar battery using the semiconductor thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the effective photoelectric conversion efficiency and to make the manufacturing cost inexpensive by separating the structure, wherein at least a plurality of columnar structures formed in a semiconductor crystal base material, a part of the semiconductor base material containing a porous layer and a supporting substrate are laminated as the constituent elements. SOLUTION: Light 3, which is applied at the time of anodization reaction, is irradiated from the rear surface of an n-type (100) Si crystal base substance 1 or base material, and the anodization reaction is performed. The anodization conditions are largely changed instantly, and a layer 4 having the large porous degree is formed by the relatively short-time reaction. B-doped glass 5 is applied. A p-type diffused layer 6 is formed in an n-type Si layer 11 through an ordinary diffusing process. After the B-doped glass 5 is removed, a (p) electrode 7 is attached. Furthermore, a grass plate a is bonded. The layer having columnar holes 2 is mechanically removed from the n-type (100) Si crystal base substance 1 of the base material as a unitary body together with the glass plate 8. The layer 4 having the large porous degree can be separated with a breaking plane 40 as the boundary since the layer 4 is mechanically weak.

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 semiconductor thin film laminated on a supporting substrate, and a solar cell using the semiconductor thin film.

[0002]

2. Description of the Related Art Effective energy conversion from sunlight to electricity using a semiconductor is a technical issue that should be emphasized in the future from the viewpoint of creating clean energy in consideration of the global environment. Among various semiconductor materials, silicon (Si) semiconductors, which are safe, inexpensive and have high energy conversion efficiency, are important as one of the key players in energy demand, which is expected to increase further in the future. Has been put to practical use. Therefore, Si will be described below as a typical example of a conventional solar cell and a method of manufacturing the same. With the dramatic spread of photovoltaic power generation expected in the future, there is a concern that the demand for battery materials will be enormous. There is a demand for a solar cell structure that maintains photoelectric conversion efficiency. As a method of manufacturing such a resource-saving Si solar cell, (1) a Si thin film having a desired thickness is cut out (ie, sliced) from a single crystal or polycrystalline bulk crystal, or (2) A step of integrally peeling a Si thin film having a desired thickness from a similar crystal in a state of being bonded to a supporting substrate, or (3) depositing a Si thin film layer on a predetermined substrate, or a combination of these methods After that, there is a method of successively performing various known processes required for manufacturing a solar cell.

[0003]

The method of the above (1) is as follows.
There is a problem in the uniformity of the thickness of the Si thin film to be cut. In addition, in the step of bonding the cut thin film to any substrate, particularly when the film thickness is 100 μm or less, there is a problem that handling is difficult and the production yield is reduced. As one of the above methods (2), there has been a method of injecting proton ions into a single crystal or a polycrystal bulk crystal, and peeling off a Si thin film by utilizing the generated defects. It was difficult to recover the defect sufficiently to leave no defects. Further, in the above method (3), a polycrystalline Si thin film having an amorphous or small grain size previously deposited on a substrate is not converted into a Si thin film having a large grain size by various methods such as heat treatment. ,
Thereby, a method of obtaining a relatively efficient solar cell was attempted. In this case, although a desired thin film can be formed,
The cost required for depositing the Si film and the cost required for various accompanying heat treatments are relatively high, which has been a practical problem. Furthermore, it is difficult to sufficiently suppress the manufacturing cost of the solar cell by a method in which these methods (1) to (3) are appropriately combined.

It is an object of the present invention to solve the problem of uniformity of film thickness in the above method (1), the problem of defect recovery in the above method (2), and the problem of cost reduction in the above method (3). To provide a method of manufacturing a semiconductor thin film having the same effective photoelectric conversion efficiency as a thick single crystal silicon solar cell of about several hundred μm and a low manufacturing cost, and to provide a solar cell using the semiconductor thin film. is there.

[0005]

Means for Solving the Problems In order to achieve the object of the present invention, the present invention is configured as described in the claims. That is, according to the present invention, as described in claim 1, the first semiconductor crystal is contained in the semiconductor crystal base material.
A first step of forming a plurality of columnar structures from the main surface to another second main surface, and a second step of forming a porous layer in the semiconductor crystal base material by anodization; A structure in which a part of a semiconductor crystal base material including the porous layer and the columnar structure and a support substrate are laminated as at least constituent elements,
Forming a semiconductor thin film having the columnar structure penetrating through the thin film on the support substrate by peeling the semiconductor thin film from the base material of the semiconductor crystal. is there. According to a second aspect of the present invention, in the method for manufacturing a semiconductor thin film according to the first aspect, the first step and the second step are performed by using a semiconductor crystal base material remaining after the third step. A method of manufacturing a semiconductor thin film including a step of repeating a step and a third step to obtain a plurality of semiconductor thin films. According to a third aspect of the present invention, there is provided a semiconductor thin film solar cell using a semiconductor thin film manufactured by the method of manufacturing a semiconductor thin film according to the first or second aspect as at least a photoelectric conversion layer of the solar cell. It is assumed that.

[0006] The present invention is directed to a first aspect.
As a typical example, in the case of n-type Si, a method of forming a hole having a constant diameter using anodization in which conditions such as current are controlled is used for the formation of a columnar structure in Si in the step of However, in the case of p-type Si, it is performed by a method of making a specific region in a plane formed by a photo process or the like porous. Then, when the columnar structure reaches a desired depth, the anodization conditions are appropriately changed and / or the properties such as the conduction type of the Si crystal are controlled in the film thickness direction. The change in the anodization conditions was the starting point, and the Si crystal portion having the columnar structure formed a layer structure advantageous for peeling off as a thin film in a later step (second step). A third structure in which a laminated structure obtained by bonding (joining) a Si crystal having a columnar structure obtained through the steps and a supporting substrate prepared separately from the Si crystal to peel off the Si crystal. Depending on the process,
An object of the present invention is to provide a method of manufacturing a semiconductor thin film in which a Si thin film having a columnar structure penetrating the thin film is formed on a support substrate. By employing such a method for manufacturing a semiconductor thin film, there is an effect that an inexpensive semiconductor thin film having a uniform thickness, no defects, and no defects can be obtained. According to a second aspect of the present invention, in the method of manufacturing a semiconductor thin film according to the first aspect, the first step, the second step, and the second step are performed by using a semiconductor crystal base material remaining after the third step. By repeating the step 3 to obtain a semiconductor thin film including a step of obtaining a plurality of semiconductor thin films, there is an effect that a semiconductor thin film having a uniform thickness and no defect can be manufactured at a lower cost. Further, as described in claim 3, the semiconductor thin film manufactured by the method for manufacturing a semiconductor thin film according to claim 1 or 2 is used as a semiconductor thin film solar cell at least as a photoelectric conversion active layer of the solar cell. As a result, there is an effect that a semiconductor thin-film solar cell having the same effective photoelectric conversion efficiency as a conventional thick single-crystal silicon solar cell having a thickness of about several hundred μm and having a large area and being inexpensive can be realized.

The method for producing a semiconductor thin film and the semiconductor thin film solar cell according to the present invention are not limited to a Si thin film, but include an amorphous Si layer formed on a Si base material crystal, or a group II-VI or III. -In a compound semiconductor layer including -V group, a columnar structure is formed in the semiconductor layer, a porous layer for separation is formed in a lower Si base material crystal, and a layer having the columnar structure, Separately from the base material crystal, by peeling off the laminated structure by bonding to a prepared supporting substrate, an amorphous Si layer or a compound semiconductor film including II-VI group, III-V group, etc. Can be realized. Further, the semiconductor thin film formed by the present invention is not only useful as a solar cell element, but also applicable to a case where the semiconductor thin film generally functions as a semiconductor element formed in the thin film. For a method of forming a hole in a conventional n-type Si, see, for example, Journal of the Electrochemical Society, Vol. 137 (1990), pp. 653--659 [V.
ical Society, vol. 137, 653-659 (1990)]. By appropriately setting the bias voltage, the light irradiation wavelength, the photoconductive current, the anodization time, and the like during the anodization for an n-type Si crystal having an appropriate resistivity, a hole having a constant diameter can be formed at a depth of 400 μm. There is a disclosure that it can be formed up to this point. However, although the hole is formed only by the technique of the above-mentioned literature, it was impossible to constitute a solar cell element composed of a thin film having a thickness of 400 μm or less. The formation of the columnar structure in the semiconductor thin film of the present invention applies the above-described hole forming technique, and at the stage when the hole reaches a desired depth, causes an anodization reaction under significantly different conditions from the hole forming reaction. As a result, instead of the conventional formation reaction in the film thickness direction (ie, formation of holes), the formation reaction is performed mainly in the direction of the film surface, thereby forming a porous structure. It can be a high quality layer. The layer having high porosity formed under the Si layer including the plurality of holes is formed by the Si layer including the upper holes.
It is mechanically weaker than the layer and the lower Si crystal part, and has a structure advantageous in that the Si crystal part having holes in a later step is peeled off as a thin film. When a columnar structure is formed in p-type Si, the following features of the anodization reaction are used. That is, when the Si crystal is not irradiated with light, the n-type S
Anodization reaction of p-type Si occurs more actively than i. Therefore, after appropriately arranging the n-type and p-type regions in the Si crystal, only the p-type region formed in a columnar shape is made porous by anodizing, and the anodizing conditions are changed as in the case of the n-type Si. Thus, a structure in which a layer having high porosity is formed is obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for producing a semiconductor thin film having a hole-shaped columnar structure formed by an anodizing step and the production of a solar cell element using the semiconductor thin film will be described below in more detail. <Embodiment 1> FIGS. 1A to 1E are schematic views showing steps of manufacturing a semiconductor thin film exemplified in this embodiment and a solar cell element using the semiconductor thin film.
In FIG. 1A, reference numeral 1 denotes an n-type (100) Si crystal base material of a base material. Do it. In order to form a hole having a certain diameter, the light 3
Irradiation is preferably performed using a filter that cuts light having a wavelength of 800 nm or more. By appropriately setting the anodizing conditions, a columnar hole 2 having a depth of 30 μm and a diameter of 1 μm could be formed. Regarding the arrangement of the columnar holes 2 in the Si crystal plane, the Si crystal substrate 1
If a small concave surface (pit) is formed on the surface of the substrate by a method such as photolithography, it is possible to form a hole having a constant diameter depending on anodizing conditions by using the concave surface as a starting point. Subsequently, as shown in FIG. 1 (b), anodizing conditions such as bias were instantaneously changed greatly, and a layer 4 having high porosity was formed by a relatively short reaction. Next, B (boron) -doped glass 5 was applied as shown in FIG. As shown in FIG. 1D, a p-type diffusion layer 6 is formed in the n-type Si layer 11 through a normal diffusion process, and after the B-doped glass 5 is removed, the p-type diffusion layer 6 is removed.
The electrode 7 was attached, and a glass plate 8 serving as a supporting substrate of the solar cell was further attached. For bonding the glass plate 8 and the p-electrode 7, it is preferable to use an appropriate heat-resistant adhesive. After bonding the glass plate 8, the layer having the columnar holes 2 could be mechanically separated from the base n-type (100) Si crystal base 1 integrally with the glass plate 8. Further, the layer 4 having high porosity is also mechanically fragile as described above, so that the fracture surface 4
Peeling was possible at 0. In addition, at the time of peeling, the breakage could be more suitably performed by adding a chemical treatment or a heat treatment of dipping in a solution such as an acid to promote the peeling. After peeling, the porous layer 41 remaining on the columnar hole layer side was removed by etching. Further, the base material n-type (100) Si crystal substrate 1 remaining after peeling
Was reused after removing the porous layer 42 near the fracture surface 40. As shown in FIG. 1 (e), the solar cell was formed by sequentially forming an antireflection film 9 for solar light and an n-electrode 10 on the separated structure. Note that Si around the columnar hole 2 is in a state where the strain accompanying the hole formation is accumulated and easily oxidized, and the oxide film 1 is formed in the process from immediately after the hole formation to the formation of the n-electrode.
2 are formed. From the viewpoint of the characteristics of the solar cell, the oxide film 12 and the antireflection film 9 are effective in preventing surface recombination of photogenerated carriers. In the case where the p-electrode 7 is a transparent electrode, in FIG. 1E, a part of the light incident from the top is the columnar hole 2, the p-electrode 7, and the glass plate 8 serving as a support substrate.
And a solar cell having a so-called see-through function (a function of partially transmitting light) is also possible. The arrangement, depth and diameter of the columnar holes 2 can be adjusted by controlling the anodizing conditions, and for example, the degree of see-through can be changed.

<Embodiment 2> FIGS. 2 (a) to 2 (e)
It is a schematic diagram which shows the process of manufacturing the semiconductor thin film illustrated in this Embodiment and the solar cell element using the semiconductor thin film. In FIG. 2A, reference numeral 21 denotes a base material p-type (1
00) Si crystal substrate. After screen printing of the mask 22, hydrogen ion implantation is performed, and after removing the mask 22, annealing at 400 ° C.
An n-type region 23 is formed in a part of the region according to the implantation energy. Then, when anodization is performed, as shown in FIG. 2B, the columnar structure 20 which is made porous without being ion-implanted and remains p-type and the p-type region 2 which is made porous thereunder are formed.
4 are formed. Next, in order to form a bond, FIG.
As shown in (c), P (phosphorus) -doped glass 25 was applied, and heat treatment for n-type diffusion was performed. With heat treatment,
The implanted hydrogen diffuses out of the Si crystal substrate 21 and dissipates, and P diffuses from the P-doped glass layer 25 to form an n-type layer 26 as shown in FIG.
The n-type region 23 becomes the original p-type. P-doped glass 2
After removing 5, an n-electrode 27 was attached, and a glass plate 28 serving as a supporting substrate of the solar cell was further adhered [FIG.
(D)]. Next, in the same manner as in Embodiment 1, the Si thin layer including the columnar structure was peeled off. The remaining base material p-type (10
0) The Si crystal substrate 21 was reused. As shown in FIG. 2E, the surface of the exfoliated Si thin layer was etched with an alkaline solution to enhance the antireflection effect, thereby forming an inverted pyramid-shaped surface 30. Antireflection film 31, p electrode 3
2 were sequentially laminated and heat-treated to produce a solar cell.
Si in the peripheral portion of the porous p-type region 24 was oxidized in the process of manufacturing the solar cell to become a columnar oxidized region 29.
The oxidation of the porous p-type region 24 may be intentionally and positively performed at an appropriate stage during the manufacturing process of the solar cell.

[0010]

As described above, the method of manufacturing a semiconductor thin film of the present invention and the thin-film solar cell using the semiconductor thin film of the present invention have a film thickness of about 10 μm, which is difficult to realize by the above-mentioned conventional method (1). A thick thin-film Si crystal can be easily produced. Further, in the above-mentioned conventional method (2), it is difficult to recover an injection defect to such an extent that there is no problem in the solar cell characteristics. However, in the present invention, a Si crystal part which does not participate in the anodization reaction is basically used. No problem arises because the original crystal structure with few defects is maintained. This is because the method of the present invention is a single crystal or a polycrystalline Si having a large grain size of about several cm or more, which was difficult to achieve by the above-mentioned conventional method (3).
This means that a thin film can be realized while maintaining the crystallinity of the base material. Further, it is not necessary to use an expensive apparatus such as an ion implantation apparatus, and a large-area thin film can be processed in a short time with a simple anodizing apparatus. In the case of a thin film of a single crystal (or a polycrystal having a large particle size that can be regarded as a single crystal), the recombination of carriers at the crystal grain boundaries, which has been a problem in the above-mentioned conventional method (3), having a small particle size. The conventional thick (several hundreds) because there is no reduction in efficiency due to leakage current
(approximately μm) The same effective photoelectric conversion efficiency as that of a Si single crystal solar cell can be obtained. Further, since the remaining base material Si crystal can be reused after the peeling step, it is an advantageous method in terms of saving Si resources. There is an effect that about 50 or more 10-μm-thick Si single-crystal solar cells can be manufactured from one standard 6-inch Si single-crystal wafer.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for manufacturing a semiconductor thin film exemplified in Embodiment 1 of the present invention and a process for manufacturing a solar cell using the semiconductor thin film.

FIG. 2 is a process chart showing a method for manufacturing a semiconductor thin film exemplified in Embodiment 2 of the present invention and a process for manufacturing a solar cell using the semiconductor thin film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... n-type (100) Si crystal base material 2 ... columnar hole 3 ... light irradiated at the time of anodization reaction 4 ... layer with large porosity 5 ... B-doped glass 6 ... p-type diffusion layer 7 ... p-electrode 8 ... Glass plate 9 serving as a support substrate 9 ... Anti-reflection film 10 ... N-electrode 11 ... N-type Si layer 12 ... Oxide film 20 ... Porosified columnar structure 21 ... Base material p-type (100) Si crystal base 22 ... Mask 23 ... n-type region 24 ... porous p-type region 25 ... P-doped glass 26 ... n-type layer 27 ... n-electrode 28 ... glass plate 29 ... columnar oxidized region 30 ... inverted pyramid surface 31 ... antireflection film 32 p-electrode 40 fracture surface 41 porous layer remaining on columnar hole layer 42 porous layer near fracture surface

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeshi Yamada 3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A semiconductor crystal base material comprising:
A first step of forming a plurality of columnar structures from the main surface to another second main surface, a second step of forming a porous layer in the semiconductor crystal base material by anodization, By peeling a structure in which the porous layer and a part of the semiconductor crystal base material including the columnar structure and a support substrate are laminated at least as constituent elements from the semiconductor crystal base material,
A third step of forming a semiconductor thin film having the columnar structure penetrating the thin film on the support substrate. 2. The method of manufacturing a semiconductor thin film according to claim 1, wherein the first, second, and third steps are repeated using a semiconductor crystal base material remaining after the third step. Performing a step of obtaining a plurality of semiconductor thin films. 3. A solar cell, wherein the semiconductor thin film manufactured by the method for manufacturing a semiconductor thin film according to claim 1 or 2 is used at least as a photoelectric conversion layer of the solar cell.