JPH03250671A - Semiconductor photoelectric converting device and its manufacture - Google Patents

Abstract

PURPOSE:To make contact resistivity of an electrode extremely low by providing a laser-processed opening of a specific width through an anti-reflection film formed on a light receiving face and providing a surface electrode made of metal so that it is in contact with a semiconductor layer inside the opening. CONSTITUTION:A fine line opening groove 1 of width of 100mum or less is formed on oxide films 2, 3 on the surface of a substrate 10 by means of laser beam scanning. An Ni-plated film 6 is formed by using electroless plating solution on the entire surface at the light receiving side of the substrate 10 formed with the opening groove 1. The entire substrate 10 after the treatment is put into acetone and subjected to ultrasonic vibration so as to dissolve and remove a resist film 4. After the Ni-plated film 6 on the resist film 4 is also removed by lift-off, it is subjected to heat treatment in a nitrogen atmosphere to have the Ni-plated film 6 annealed and Ni silicide formed on an interface with the substrate 10. Then electroless Cu plating solution is used to form a Cu-plated film 7 selectively only on an electrode to have a surface electrode completed.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a semiconductor photoelectric conversion device with a large fill factor (FF) and conversion efficiency Cη) and a method for manufacturing the same.

<Prior Art> A conventional method for manufacturing a solar cell is as follows. That is, as shown in the structural diagram of FIG. 4, an N+ type scattering layer 11 is formed by POC on a P type silicon substrate 10, and an oxide film 3 of 5i02 film is formed thereon as a passivation film. Further, a TiO2 film 2 as an antireflection film is formed thereon. Then, remove the N diffusion layer on the back side and print and bake the aluminum paste to create JBSFCP”)
Form layer 12. Next, a fired penetrating metal paste 14 is printed on the surface of the TiO2 film 2, and this metal paste is fired to form the Ti0z film 2 and the Sin.

An electrode on the light-receiving surface side that penetrates the film 8 and contacts the N + g diffusion layer 11 is formed. Formation of electrodes by such Nuclean printing method is described, for example, in Takateru Tsuji: Solar Cells, Power Publishing, p. 75, published July 28, 1980.

<Problems to be Solved by the Invention> One way to improve the conversion efficiency of semiconductor photoelectric conversion devices such as solar cells and illumination meters is to reduce the contact area of the surface electrode formed on the light receiving surface. That is, on the light-receiving surface of the semiconductor photoelectric conversion device, which is the surface of the diffusion layer, a non-light-receiving portion is formed due to the surface electrode. The surface of the light-receiving part, which has no surface electrode other than the non-light-receiving part, is covered with a film of oxide such as 5IO2, and a passivation treatment is applied to reduce the recombination rate of minority carriers on this surface, thereby increasing the photoelectric conversion efficiency. Preventing decline. On the other hand, at the contact portion between the non-light-receiving portion of the surface electrode and the diffusion layer on the surface of the substrate, the recombination rate of minority carriers was extremely high, reducing the charge conversion efficiency.

Therefore, the area of the contact portion of this electrode is made as small as possible, and the relatively passivated light-receiving area is increased.
In addition, it is necessary to reduce the mechanical adverse effect of the surface electrode on the semiconductor surface.

Furthermore, in order to increase the amount of light incident on the light-receiving surface, it is possible to reduce the occupation rate of the surface electrode with respect to the light-receiving surface.

However, in general, in semiconductor photoelectric conversion devices in which surface electrodes are printed and fired electrodes by screen printing of a metal paste, the viscosity of the metal paste depends on the technology used.
Due to the characteristics of the paste such as adhesiveness and the pattern accuracy of the screen mask, the limit was to reduce the electrode occupancy to 3 to 4 inches.

Therefore, the limit was to reduce the contact area to 3 to 4%.

Therefore, the present applicant irradiated the surface of the anti-reflection film formed on the surface of the semiconductor photoelectric conversion device with short wavelength laser light to form fine dots, and determined the positions where electrodes were to be formed, including the portions of the dots. proposed a method of printing and firing electrode materials to form surface electrodes. (Patent application 1198881' filed on May 12, 1989 - Method for manufacturing solar cells)
).

According to the above electrode forming method, the surface portion of the anti-reflection film that has not been processed by the laser beam acts as a barrier against the penetration of the metal paste during firing, reducing the contact area of the electrode and passivating it. This further improves the effectiveness of FIG. 3 is a schematic cross-sectional view showing the electrode manufacturing process by printing and firing the metal paste by laser processing.

This figure 3 (al) indicates that the p-type silicon substrate 10 has a p
+ A diffusion layer 12 is formed, and a back electrode 18 is formed on almost the entire surface thereof using A) or the like. On the surface of the substrate 10, an n1 diffusion layer 11 is formed, and a passivation oxide film 3 such as 5402 and an antireflection film are laminated and coated. This anti-reflection film needs to be laminated in this order: TiO2 film 2, SnO, and film 9. A short wavelength laser spot light is irradiated from the surface of this antireflection film to form a minute hole 1' that penetrates at least the Snow film 9. Next, as shown in Fig. 2 [b], metal bake 14 was applied to the surface electrode formation area including the opening part of hole 1' by 7 clean printing, followed by baking at about 600°C). This is shown in Figure 2 (c
It is l. As a result of this firing, the metal paste 14 is hardened and an electrode is formed which penetrates through the oxide film layers 2 and 3 and connects to the surface of the substrate 10.

However, the method proposed above still has the following problems.

First of all, since the screen printing method is used to form the light-receiving surface electrode, the contact area can be reduced, but the electrode occupation rate is still 3.
The limit is to lower it to ~4%.

Second, the contact resistance between the electrode made of fired metal paste and the n10 diffusion layer on the substrate surface is large, and when the electrode area is reduced, the series resistance increases and the FF decreases.

Thirdly, at the same time as firing the metal paste, a heating process of approximately 600° C. is required in order to connect the composition of the metal paste to the substrate through an oxide film such as an antireflection film.

Fourth, since the electrode is formed by penetrating the oxide film with metal paste as mentioned above, it is necessary to have a double anti-reflection film structure with different penetration characteristics, such as 5N02 and TiO2. etc.

Therefore, the present invention aims to solve the above problems.

Means for Solving the Problem> In order to achieve the above object, the present invention provides an anti-reflection film formed on a light-receiving surface with a laser-processed opening having a width of 100 μm or less penetrating the anti-reflection film. , provides a semiconductor photoelectric conversion device characterized in that a surface electrode made of metal is provided so as to be in contact with the semiconductor layer within the opening.

The present invention also provides a method for forming an opening that penetrates the anti-reflection film by irradiating the surface of the anti-reflection film formed on the light-receiving surface with a short-wavelength laser beam, and forming a surface electrode forming portion including the opening. Provided is a method for manufacturing a semiconductor photoelectric conversion device, characterized in that a surface electrode is formed by depositing an electrode material on the semiconductor photoelectric conversion device.

It is preferable that the short wavelength laser beam has a wavelength that is absorbed by the surface of the antireflection film and reflected by the semiconductor substrate.

The above-mentioned deposition is preferably carried out at a low temperature, and it is more preferable to use a metallizing method or a vapor deposition method.

<Function> In the semiconductor photoelectric conversion device of the present invention, electrodes are formed directly from metal through a very small opening of 1/100 μm or less that completely penetrates the antireflection film formed by laser processing. For example, compared to the contact resistivity (on the order of 10"Ω・12) when a conventional silver paste permeates an anti-reflection film and is connected to an n-diffusion layer, N1
The contact resistivity (10
Since the contact resistivity of the surface electrode can be made extremely low (on the order of -'Ω·-), the characteristics of the semiconductor photoelectric conversion device, particularly the FF characteristics, can be improved.

Furthermore, the method of the present invention can produce laser light with a short wavelength, and this short wavelength light hardly transmits through the material used for the antireflection film of a typical semiconductor photoelectric conversion device. It is absorbed on the surface and converted into heat, which is instantaneously evaporated by the energy of the incident laser beam, allowing the formation of fine lanons or an opening pattern consisting of a large number of continuous dots directly on the antireflection film. The depth of the opening in the above anti-reflection film is determined by the energy intensity of the irradiated laser beam,
Alternatively, since it can be controlled by a simple method such as the number of times of irradiation, the electrode contact area can be easily changed as desired.

Furthermore, by creating a resin pattern in the shape of the surface electrode on the anti-reflection film before irradiating the laser beam,
Electrode metal films such as Ni and Ti coated by deposition methods such as plating and vapor deposition can be processed by lift-off, reducing the margin for alignment and minimizing the electrode occupancy, improving short-circuit current. can be done.

Furthermore, since the openings are created using laser light, problems that occur when the openings are created using photoetching techniques do not occur. In other words, when forming electrodes by creating minute openings in the semiconductor surface anti-reflection film and passivation film using photo-etching technology used in semiconductor microfabrication, the materials of the anti-reflection film and passivation film are The etching method and etching time vary depending on the etching and film thickness, and it takes time to find the appropriate processing and etching conditions.In addition, for polycrystalline silicon substrates aimed at lowering costs, the surface of the substrate is not coated with texture T treatment. Since fine irregularities of several tens of micrometers are formed, there is no problem that it is difficult to form a precise pattern by photoetching, making it impractical.

Furthermore, if the electrode is deposited by a metallizing method or a vapor deposition method, the deposition process can be performed at a low temperature and the semiconductor layer will not be adversely affected by heat.

<Examples> Example 1 A first example of the present invention will be described below with reference to FIG. 1.

FIG. 1 (al, fb) and fc) are 8 schematic cross-sectional views showing each step of a first embodiment of forming a surface electrode of a semiconductor photoelectric conversion device according to the present invention.

FIG. 1(a) shows that a p-n junction is formed by forming an n+ diffusion layer 11 on the surface of a p-type silicon substrate 10 on which a photoelectric conversion device is to be fabricated, and then a p-n junction is formed on the surface of the n+ diffusion layer 11. , a photoresist film 4 is formed on the oxide film 3 of 150A, 5ioz, which becomes a passivation layer, and a 500-layer TiO film 2, which becomes an anti-reflection film. 371E-width 50μm at intervals
This electrode pattern portion accounts for 1.4% of the light-receiving area of the substrate. ), furthermore, the silicon substrate 10 processed as described above is set in a nutage that can be precisely moved in the X-Y direction, and a short wavelength laser beam [for example, Xe
C) with a laser with a wavelength of s o s nm) at 25X25
When irradiating the non-formed part of the resist film 4 with a spot focused to .mu.m, the energy intensity is about 4 J/a when the output of the laser light source is sufficiently large.
The Oz film 2 and the oxide film 3 can be simultaneously evaporated and removed, and a fine line-shaped opening groove 1 with a width of 25 μm is formed in the oxide films 2 and 8 on the surface of the substrate 10 by scanning with a laser beam.

With this strength, @2.8 can be selectively removed.

Note that on the back surface of the silicon substrate 11 described above, a p-soil layer 12 which becomes a BSF layer and a back electrode 13 are formed.

The following Fig. 1 (bl) shows that approximately 20 OA of Ni was applied to the entire surface of the light-receiving side of the substrate 10 in which fine line-shaped opening grooves l as shown in I\il were formed using a commercially available electroless plating solution. A state in which a plating film 6 has been formed is shown.

This Ni plating film 6 covers the opening groove 1 and the resist film 4.
Covers all surfaces.

Subsequently, as shown in FIG. 1 (cl), the entire substrate 10 after the processing steps described above is placed in acetone and subjected to ultrasonic vibration.
After dissolving and removing the resist film 4 and removing the Ni plating film 6 on the resist film 4 by lift-off, the entire processed substrate 10 is placed in a nitrogen atmosphere for 2 hours.
A heat treatment is performed at 50° C. for 80 minutes to anneal the @EN 1 plating film 6 to form Ni silicide at the interface with the substrate 10 to improve the electrical bonding state. Subsequently, by using a commercially available electroless Cu coating liquid, a Cu coating/J coating film 7 with a thickness of about 5 μm was selectively formed only on the electrode of the Ni plating film 6 formed in the inebriated state. This shows the completed state of the surface electrode.

In the embodiment of the semiconductor photoelectric conversion device formed by the method of the present invention described above, the contact area between the n+ diffusion layer 11 on the surface of the substrate 10 and the N1...ki@6 of the electrode metal layer is 0.0% of the total light receiving area. 7
%, the surface electrode occupies a much smaller contact area than conventional surface electrodes.

Example 2 A second example of the present invention will be described below with reference to FIG.

FIGS. 1A, 1B, and 1C are schematic cross-sectional views showing each step of a second embodiment of forming a surface electrode of a semiconductor photoelectric conversion device according to the present invention.

In FIG. 1 ia), the steps up to the formation of the opening groove 1 having a width of 25 μm were performed in the same manner as in Example 1.

FIG. 2(b) shows that kg/p d /
Each layer is made of 5μ steel 1500A/T i laminated vapor deposited film 8
It shows a state in which it is formed to have a thickness of 800A. Note that Ti is in contact with the n+ diffusion layer 11.

Subsequently, as shown in FIG. 2, after the above steps, the bAg/pd/Ti vapor deposited film 8 was removed by ultrasonic cleaning in acetone, and then heated at 415°C for 30 minutes in a nitrogen-free environment. The surface electrode is shown completed by heat treatment in an ambient atmosphere.

In this embodiment, the occupation rate of the contact area between the n+ diffusion layer 11 and the electrode metal is 0.7 inches, which is much smaller than that of the conventional method.

In this embodiment, the surface electrode was formed by a list-off method using a resist, but the surface electrode may be formed by vapor deposition using a metal mask without using a resist.

Examples of the present invention have been shown above using Examples 1 and 2, but
The surface electrodes obtained by the above two examples both exhibit similar good properties as shown below. Note that since there was no difference in the following characteristics between Examples 1 and 2, one data is shown using these as the surface electrodes of this example.

Table 1 shows the surface electrode according to this example and the patent application 1-
A comparison of the shape and various characteristics of the surface electrode semiconductor photoelectric conversion device proposed in No. 119888 will be shown below.

Table 1 Comparison table between this example and conventional example In the above table, JSC is short circuit current, η is the conversion efficiency (sunlight).

From Table 1, it can be seen that the increase in short-circuit current and open circuit voltage due to the surface electrode of this example is due to the improvement in the passivation effect due to the reduction in the electrode occupation rate with respect to the light-receiving surface and the electrode contact area. Furthermore, although the contact area occupancy rate of the electrode was significantly reduced to 0.7, which is approximately half of the open circuit voltage, the contact resistance of the surface electrode according to the present example was This semiconductor photoelectric conversion device O
Greatly improves FF, resulting in improved conversion efficiency (η)
I was able to improve this by 1.5 points.

The surface electrode of the semiconductor photoelectric conversion device of this embodiment described above does not require heat treatment of the metal paste to penetrate the anti-reflection film, unlike the surface electrode of the previous proposal, so it is possible to heat the metal paste at 600° C. after attaching the electrode material. There is no need for a process of heating to a certain extent, and it is possible to prevent the occurrence of distortion due to the heat treatment process after bonding various materials. Furthermore, when connecting the electrodes by penetrating the anti-reflection film with the electrode material described above, a two-layer structure combining 5n02 and TiO3, which have different penetration characteristics, is used.
There are no restrictions on the structure of the antireflection film, such as the need to form a 02 film.

The aperture processing in the anti-reflection film for forming the surface electrode according to this example uses a focused laser beam with a short wavelength, so the aperture can be formed with finer processing than in the example, and the contact area of the electrode can be further significantly reduced. Moreover, even if the electrode contact area is reduced as described above, the contact resistance (ratio) can be made sufficiently small, so this will not cause an increase in series resistance or a decrease in FF.

The formation of minute openings in the anti-reflection film using the laser beam described above can also be done with an irradiation energy of about J/-2 if a short wavelength laser source with an appropriate output is focused and irradiated into a minute spot. Since an aperture can be formed in the reflective film, it is possible to scan the ME short-wavelength laser spot at a high speed (about several meters per second), resulting in a fast processing speed and fewer steps involved in this process. Therefore, productivity can be increased.

Although the present invention has been described above with reference to examples, the present invention is not limited to the examples, and the gist of the present invention is to form fine openings in an antireflection film and to connect metal electrodes directly to a semiconductor. If it is a surface electrode for depositing a film, the metal to be deposited first is not limited to Ni or Ti, but metals with the same effect such as W may be used, and the deposition method may be not only electroless plating but also evaporation or It may also be deposited by, for example, suba-talling. Further, the anti-reflection film is not limited to the Sn02 film or the TiO2 film, and an anti-reflection film such as an In03 film or a combination thereof may also be used.

<Effects of the Invention> In the present invention, a semiconductor photoelectric conversion device efficiently forms a minute opening by irradiating the anti-reflection film on the surface with a laser beam condensing groove, and then forms a surface electrode directly deposited on the substrate. By forming the electrode, the electrode contact resistivity can be made extremely low. Therefore, without increasing the series resistance of the charging conversion device, the electrode occupation rate of the surface electrode with respect to the light receiving surface,
The area occupied by contact with the substrate can be reduced, short-circuit current and open circuit voltage can be increased compared to conventional devices, and FF and conversion efficiency η can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the surface electrode manufacturing process of the first embodiment of the present invention, FIG. 2 is a schematic cross-sectional view showing the surface electrode manufacturing process of the second example of the present invention, and FIG. FIG. 4 is a schematic cross-sectional view showing the previously proposed surface electrode manufacturing process, and is a structural diagram of a conventional surface electrode. 1...Opening groove, 2...TiO□ film, 3: Oxide film, 4...
・・Resist film, 6-・-Ni plating film, 7-=Cu
Membrane film, 8...Ag/pd/Ti vapor deposited film, 10...
・Substrate, 11...n10 diffusion layer.

Claims (1)

[Claims] 1. The antireflection film formed on the light receiving surface has a width of 100 μm.
A semiconductor photoelectric conversion device characterized in that the following laser-processed opening is provided through the antireflection film, and a surface electrode made of metal is provided in the opening so as to be in contact with the semiconductor layer. 2. The surface of the anti-reflection film formed on the light-receiving surface is irradiated with short-wavelength laser light to form an opening that penetrates the anti-reflection film, and electrode material is applied to the surface electrode formation area including the opening. A method for manufacturing a semiconductor photoelectric conversion device, comprising forming a surface electrode by depositing. 3. The method of manufacturing a semiconductor photoelectric conversion device according to claim 2, wherein the deposition is performed by a plating method or a vapor deposition method.