JPH1187752A - Solar battery, manufacture thereof and photolithography mask therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To complete photolithographic process for forming a resist film in a single process to reduce a manufacturing cost by patterning a transparent conductive film together with a metal electrode and an a-Si film in first etching and patterning the metal electrode and the a-Si film in second etching. SOLUTION: Etching is done using a stepped film 10 to pattern a transparent electrode 10 together with a laminated a-Si film 3 and a metal electrode 4. An ashing process for removing the resist film stops when a thin resist film 10b is eliminated. The resist film at a part 10a remains as a resist film 10'. The resist film 10' is used to perform etching again and pattern the a-Si film 3 and the metal electrode 4 simultaneously. A protective film 6 is printed between elements to prevent short-circuiting between adjacent transparent electrodes 2 or between the transparent electrode 2 and the metal electrode 4, and conductive paste is applied to connect the metal electrode 4 of the element A with the transparent electrode 2 of the element B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solar cell having an electrode and an amorphous silicon film laminated on a substrate.

[0002]

2. Description of the Related Art A solar cell formed by laminating an electrode and a PIN-junction amorphous silicon film on a substrate has an electromotive force of about 0.4 to 0.5 V during operation. For example, when used as a power supply for an electronic wristwatch, one element has insufficient voltage to operate the circuit. Therefore, a structure is obtained in which a plurality of solar cell elements (for example, four) are arranged on a substrate and these elements are connected in series to obtain an added electromotive force.

FIG. 3F schematically shows a cross section of one structure of a solar cell. In this solar cell, a transparent conductive film 2 is formed on a glass substrate 1 and a P-I-N junction type amorphous silicon film (abbreviated as a-Si film) 3 is formed thereon. A metal electrode 4 is formed thereon. The photovoltaic power generated in the a-Si film by the incident light from below the substrate 1 is:
It can be extracted from the transparent conductive film 2 and the metal electrode 4 sandwiching the a-Si film. Figure 3 shows the laminated structure on the substrate.
(F) is separated into right and left at substantially the center, and both sides thereof form another solar cell element region. For convenience, the left side will be referred to as element A and the right side will be referred to as element B. The metal electrode 4 of the element A and the transparent conductive film 2 of the element B are connected,
Thus, the two elements are connected in series.

[0004] The metal electrode 4 of the adjacent element and the transparent conductive film 2 are similarly electrically conductively connected to each other at a position outside the range of FIG. 3 (F), so that a plurality of solar cell elements formed on the substrate 1 can be formed. They are connected in series to form a solar cell having a desired electromotive force.

A method for manufacturing such a solar cell will be briefly described with reference to FIG. In FIG. 3A, the transparent conductive film 2 on the substrate 1 is formed by forming a SnO ₂ film by, for example, a CVD method, and a resist film 7 for etching the transparent conductive film 2 is formed by photolithography (hereinafter, referred to as “photolithography”). "Photolithography").

Referring to FIG. 3B, the transparent conductive film 2 other than the portion masked by the resist film 7 is removed by etching to perform patterning. Thereafter, the resist film 7 is stripped. Thus, the transparent conductive film 2 has a required electrode shape.

[0007] In FIG. 3 (C), CV is placed on the transparent conductive film 2.
The a-Si film 3 is laminated by the method D, and a resist film 8 for etching the a-Si film 3 is formed again by photolithography.

In FIG. 3D, etching is performed again to pattern the a-Si film 3, and the resist film 8 is peeled off. Thereby, the a-Si film 3 has a required shape.

In FIG. 3E, the transparent conductive film 2 and a-Si
A metal film to be the metal electrode 4 is formed on the film 3 by sputtering, and a resist film 9 for etching these is formed.
Is formed by a third photolithography.

In FIG. 3F, a third etching is performed to pattern the metal electrode 4, and the resist film is stripped. As a result, the laminated structure on the substrate has a required shape, and each region becomes a solar cell element. As described above, the metal electrode 4 of the element A and the transparent conductive film 2 of the element B are conductively connected. Thus, the element A and the element B are connected in series.

The elements outside the range shown in the figure are similarly configured, and the plurality of solar cell elements formed on the substrate 1 are connected in series and generate a combined electromotive force. After this,
The solar cell is completed by, for example, applying a protective film on the upper surface.

[0012]

In the conventional method for manufacturing a solar cell as described above, etching is performed three times. That is, etching of the transparent conductive film 2 in FIG. 3B, etching of the a-Si film 3 in FIG. 3D, and etching of the metal electrode 4 in FIG. Since a resist film is formed by photolithography prior to each etching,
Photolithography is also performed three times. Three types of masks having different patterns are required for the photolithography. If photolithography can be performed only once, the manufacturing process can be shortened and only one type of mask can be used, resulting in a significant reduction in manufacturing cost. The present invention makes it possible to simplify such a manufacturing method.

[0013]

According to the present invention, a resist film formed by photolithography includes a thin portion and a thick portion. First, a transparent conductive film on the substrate,
The a-Si film and the metal electrode film are all laminated, and photolithography is performed on the film to form a resist film having two different thicknesses as described above. Etching using this,
All the laminates on the substrate are commonly patterned. Next, the resist film is removed by plasma (so-called ashing). At this time, the resist film is not completely removed, but ashing proceeds to reduce the thickness of the resist film. Stop ashing at any stage. Then, etching is performed again using the remaining resist film, and then the metal electrode and the a-Si film are patterned. In other words, the transparent conductive film is patterned together with the metal electrode and the a-Si film by the first etching, and the metal electrode and the a-Si film are patterned by the second etching. With this, conventional 3
The photolithography process for forming the resist film, which has been performed once, can be performed only once.

In the method of forming a resist film having a step with a thickness as described above, the present invention uses characteristic means. In photolithography for forming a resist film, when a resist agent is applied to the surface of the laminated body on the substrate and the resist surface is exposed using a mask by an exposure device, for example, if the resist agent is cured by exposure, the exposed portion is a resist. Since the agent is hardened and the unexposed portion is not so, the unexposed portion is washed away during development, and the resist agent in the exposed portion remains as a mask for etching. In this case, portions of the mask pattern that are exposed to the resist agent are transparent, and portions that are not exposed are shielded from light. However, in the present invention, since a thick portion and a thin portion are provided in the resist film as described above, the mask for exposure used in the present invention completely shields light from the portion without the resist film, and the portion where the resist film is thickened is transparent. In this case, a portion where the resist film is thinned is formed as a kind of mesh by mixing a light-transmitting pattern and a light-shielding pattern having fine dimensions smaller than the resolution of the exposure apparatus. When exposure is performed through such a combination of fine patterns, since each pattern is equal to or less than the resolution of the exposure apparatus, the pattern is not transferred to the resist material as it is, but is exposed with an insufficient amount of light. Therefore, only part of the thickness of the resist material is hardened and remains after development, and the remaining portion of the thickness flows away, so that this portion becomes a thin resist film.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a procedure for manufacturing a solar cell according to the present invention. 1A, a transparent conductive film 2, an a-Si film 3, and a metal electrode 4 are sequentially laminated on a substrate 1,
A resist film 10 is formed thereon by photolithography.
In the resist film on the element A side, only the thick part 10a is visible, whereas on the element B side, the thick part 10a and the thin part 10b are visible. No resist film is provided at the position 11. Here, the case of using a resist agent that is cured by exposure will be described. As a mask used for photolithography, a portion 10a where the resist film is thickened is made transparent, and a portion 11 where no resist film is formed is masked. The portion 10b where the resist film is thinned is a mixture of the fine patterns of the light transmitting portion and the light shielding portion as described above.

FIG. 2 shows an example of a mask pattern, in which the reference numerals of the corresponding portions in FIG. 1A are given, and the portions 10a on both sides corresponding to the thick resist film are formed by the light transmitting portion and the resist film. The portion 11 not provided is a light-shielding portion, and the portion 10b having a thin resist film is provided with a fine light-transmitting pattern and a light-shielding pattern alternately in a grid pattern. One side of the fine pattern is smaller than the resolution of the exposure apparatus. For example, if the resolution is 10 μm, one side of the pattern is 5 μm.
And so on. When exposure is performed using such a pattern, the pattern is not transferred to the resist agent, the amount of light is insufficient, insufficient exposure is performed, and the thickness of the cured layer of the resist agent is smaller than that of a completely transparent portion such as 10a. Is reduced, and the resist agent that has been insufficiently cured by the development after exposure is removed, resulting in a thin resist film 10b as shown in FIG. 1 (A). Various fine mask patterns such as stripes and grids other than those shown in FIG. 2 are possible, and the resist film thickness is controlled by appropriately selecting the area ratio between the light-transmitting portion and the light-shielding portion. When the resist material has a property opposite to that of this example and a non-photosensitive portion is cured, the arrangement of the light transmitting portion and the light shielding portion of the mask is naturally reversed.

In FIG. 1B, etching is performed using the stepped resist film 10, and the transparent conductive film 2 is patterned together with the laminated a-Si film 3 and metal electrode 4.

FIG. 1C shows an ashing step for removing the resist film. For this, plasma is used, and as the ashing proceeds, the thickness of each of the resist films 10a and 10b decreases, but instead of removing the entire resist film,
Ashing is stopped when the thin resist film 10b is gone. As a result, the thickness of the resist film in the portion 10a is smaller than before, but remains as the resist film 10 '.

In FIG. 1D, etching is performed again using the remaining resist film 10 'as described above, and a-
The Si film 3 and the metal electrode 4 are simultaneously patterned. Thereafter, the resist film 10 'is peeled off.

In FIG. 1 (E), a protective film 6 is printed between the elements formed as described above to form a short circuit between the electrodes, that is, a short circuit between the transparent conductive films 2 of adjacent elements or the same. The conductive paste 5 is applied so as to prevent the short circuit between the transparent conductive film 2 and the metal electrode 4 in the element and to straddle the protective film 6, thereby connecting the metal electrode 4 of the element A and the transparent conductive film 2 of the element B. The same connection is made outside the illustrated range, and a plurality of solar cell elements formed on the substrate 1 are connected in series to generate a combined electromotive force. Thereafter, a solar cell is completed by, for example, applying a protective film on the upper surface.

When the manufacturing method according to the present invention shown in FIG. 1 is compared with the conventional manufacturing method shown in FIG. 3, the conventional methods shown in FIGS.
The resist film is formed by photolithography three times in (E), and etching is performed three times in FIGS. (B), (D), and (F). On the other hand, in the present invention, a resist film is formed by photolithography only once in FIG. Although etching is performed twice in FIGS. 1B and 1D in the present invention, FIGS. 3B, 3D and 3D in the conventional manufacturing method are used.
While the etching step of FIG. 3F is separated by the steps of FIGS. 3C and 3E, which are film formation and photolithography, in the present invention, the etching step of FIG. 1B and FIG. Only the ashing step (C) is interposed therebetween, and there is no film formation or photolithography step. Both etching and ashing are the same kind of processes of removing the surface layer of the substrate using plasma, and the processes of FIGS. 1B, 1C, and 1D are
It is possible to carry out continuously by simply switching the type and concentration of gas while keeping the substrate in the same processing tank. Therefore, the manufacturing method of the present invention requires about 3 steps compared to the conventional method.
It can be said that it becomes 1 /. Conventionally, a different mask was required for each of the three photolithography steps. However, in the present invention, the number of photolithography steps is one and only one type of mask is required. This also reduces the cost.

In FIG. 1E, a protective film 6 is formed between the devices A and B.
Is provided, a conductive paste 5 is applied, and the metal electrode 4 of the element A is provided.
FIG. 3F shows a structure for connecting the transparent conductive film 2 of the element B with the transparent conductive film 2 of the element B.
Was not found in the conventional solar cell. This is because in the conventional structure of FIG. 3F, the end of the transparent conductive film 2 of the element A is covered with the a-Si film 3 and separated from the metal electrode 4 of the element A and the transparent conductive film 2 of the element B. This is because there is no need to provide a protective film to insulate the device, and the required connection between the metal electrode 4 of the device A and the transparent conductive film 2 of the device B can be obtained through film formation and patterning. In the solar cell of the present invention, the end of the transparent conductive film 2 of the element A is not covered with the a-Si film 3, and the metal electrode 4 of the element A and the transparent electrode of the element B may be formed depending on film formation and patterning. Since the connection of the conductive film 2 cannot be obtained, a conductive paste is used, which is a structure unique to the present invention.

In the above embodiment, the case where the present invention is applied to a solar cell formed on a transparent glass substrate has been described. However, the substrate is formed by using an opaque insulating plate or a metal plate coated with an insulating material. The solar cell can be configured by reversing the order of the body, and the present invention is naturally applicable to such a solar cell.

[0024]

As described above, the present invention provides a method of manufacturing a solar cell by laminating an electrode or an amorphous silicon film on a substrate by performing photolithography utilizing the resolution of an exposure apparatus. The photolithography process, which has been performed three times in the past, can be reduced to one time, and only one type of mask, which has conventionally required three types, is sufficient.
In addition, the etching which has been performed three times in the past can be performed substantially in a form close to one step. As described above, according to the present invention, the number of steps and the number of masks for manufacturing a solar cell can be reduced to one third, and the manufacturing cost can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a solar cell according to the present invention and a method for manufacturing the same.

FIG. 2 shows a mask used for photolithography in the present invention.
It is an example of a pattern.

FIG. 3 is a cross-sectional view showing a conventional solar cell and a method for manufacturing the same.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 transparent conductive film 3 a-Si film 4 metal electrode 5 conductive paste 6 protective film 7, 8, 9, 10 resist film

Claims (4)

[Claims] In a solar cell having a transparent conductive film, an amorphous silicon film, and a metal electrode formed on a substrate, a protective film is provided between adjacent solar cell elements to insulate the electrodes, and the protective film is formed. A solar cell in which solar cells are connected in series by connecting electrodes on both sides of a protective film with a conductive paste applied on the other side. 2. A method of manufacturing a solar cell by forming a transparent conductive film, an amorphous silicon film, and a metal electrode on a substrate, comprising: forming a resist film having a stepwise thickness for patterning a laminate on the substrate. A method for manufacturing a solar cell, comprising forming a pattern, removing the resist film until the thin portion disappears after the first etching, and performing the next etching using the resist film remaining as the thick portion. 3. The method for manufacturing a solar cell according to claim 2, wherein a mask having a pattern in which a light-transmitting portion and a light-shielding portion having dimensions smaller than the resolution of the exposure device are mixed is used, so that the thickness is graded. A method for manufacturing a solar cell, wherein a resist film is formed by one photolithography. 4. A mask used for photolithography in the method of manufacturing a solar cell according to claim 3, wherein the mask has a pattern in which light-transmitting portions and light-shielding portions having dimensions smaller than the resolution of an exposure device are mixed. Mask to do.