Manufacture of electrode for solar cell

Description: TECHNICAL FIELD [Detailed description of the invention] (Industrial application field) The present invention relates to a manufacturing method for an electrode of a solar cell, particularly one having a structure in contact with a substrate in a dot shape. (Conventional technique) In a normal solar cell, a comb-shaped electrode is arranged on the surface of the light receiving surface, but on the contact surface between the metal of the electrode and the silicon substrate, the surface recombination speed is large and the efficiency is reduced. In order to reduce the contact area between the electrode metal and the silicon substrate, a large number of dot-like holes are made in the antireflection film on the surface of the substrate, and these are connected by a metal film by the vacuum vapor deposition method and the lift-off method to generate electric power. There is a way to collect it. In order to reduce the series resistance and improve the efficiency, the surface of the electrode is thickened by applying a dent. An example of the process of forming an electrode having a structure in contact with a conventional substrate in a dot shape is shown below. FIGS. 5 (a) and 5 (b) show a plan view of the surface 2 of the silicon substrate 1 with the antireflection film 3 applied, and a cross-sectional view of the X5-X5. A PN junction for photoelectric conversion is formed inside the silicon substrate 1. Next, a resist pattern 4 having a large number of punctate small holes 4-1 is formed on the surface of the antireflection film 3. The plan view at this time is FIG. 6 (a), and the cause of the x6-x6 cross section is the same figure (b). In the figure (a), more small holes 4-1 are formed in the upper part than in the lower part, because a wide electrode for connecting a ninth connection for extracting a current to the outside is provided in the upper part. When a large number of dot-shaped small holes 3-1.3-1 ... are formed in the antireflection film 3 by etching or the like and the resist is removed, as shown in the plan view of FIG. The X7 sectional view is the same figure (b). A groove 5-1.5 that connects the small holes 3-1.3-1 ... in order to form an electrode that is formed as described above and connects the nine small holes 3-1 3-1 ... The plan view of FIG. 8A is shown with a resist pattern for connecting electrodes having -1 .... FIG. 6) is a cross-sectional view of the xg-Xg, and the cause of the cross-sectional view of Yg-Yg is the same figure (c). Next, by performing vacuum deposition and lift-off on this surface, as shown in FIG. 9 (a), a metal layer 6 connecting the small holes 3-1.3-1 .... Is formed. A metal layer 7 is also formed on the back surface of the silicon substrate 1. This will be the other electrode. The figure (b) is a cross-sectional view of xg -xg, and the figure (e) is a cross-sectional view of yg-yg. Next, as shown in FIG. 10 (a), the surfaces of the metal layers 6 and 7 are covered with the metal film 8 by a metal film to be thickened. The Xl0-xto cross-sectional view is the same figure (b), and the YIO-Y 1G cross-sectional view is the same figure (c). (Problems to be solved by the invention) In the conventional method as described above, the resist pattern is formed twice by forming the ninth resist pattern for removing the antireflection film in dots and forming the resist pattern for forming the electrodes connecting the dots. Needed to form. In addition, advanced technology is required to align each resist pattern with high accuracy. Further, in order to reduce the series resistance and improve the efficiency, it is necessary to apply a mesh on this electrode, which leads to an increase in man-hours and a decrease in yield. (Means to solve the problem) In the present invention, in order to eliminate the above-mentioned problem, the antireflection film is removed in dots, and then the resist is formed in the removed portion without removing the resist, and then a punctate electrode that becomes the core of the metal is formed. Is removed, and a metal layer connecting the punctate electrodes is formed by resisting. (Action) By forming the resist pattern once, the antireflection film can be removed in dots and a dot electrode can be formed in that part, which greatly shortens the process and makes it possible to connect the substrate and electrodes with a simple operation. The contact area can be reduced. By appropriately selecting the width or diameter of the punctate electrodes, the core of the Mecki layer can be formed, so that a metal layer connecting these punctate electrodes can be formed by Metuki. (5! Example) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in the plan view of FIG. 1 (a) and the Xl-xl sectional view thereof ('b), the surface 2 of the silicon substrate 1 having the PN junction is provided with antireflection! [3. There is. This is the same as in FIGS. 5 (a) and 5 (b). As the antireflection film 3, an insulating coating such as A / 20B, TiO2, Ta205 ° SiOx, and Si8N4 is used. As shown in FIG. 2A , a resist pattern having a large number of point-like small holes 41.4-1 ... Is formed on the surface of these antireflections 11! 3 . This resist pattern is created by the well-known 7-Otoresist technique. The x2-x2 cross-sectional view of the figure (a) is the figure (b). Next, the antireflection film 3 corresponding to the small holes 4-4.4-1 ... Is removed in dots by acid treatment, and a metal film is formed by vacuum deposition without removing the resist, and then the resist and unnecessary. When the metal film is removed, as shown in the plan view of Fig. 3 (a), a point-shaped electrode protruding from the surface of the antireflection film 30 in the portion corresponding to the small holes 4-1 4-1 ... You can get 9,9 .... FIG. 6B is a cross-sectional view taken along the line xB-xB of FIG. The height of the dotted electrodes 9, 9 ... Can be the height from the surface of the silicon substrate 1 to the surface of the resist before it is removed. Metal N7 is also vapor-deposited at this time and becomes a back electrode. When the metal to be squeezed is spread around the many point-shaped electrodes 9 ° 9 ... formed in this way as the core, the metal to be squeezed spreads in the lateral direction as well as the thickness direction. The point-shaped electrodes 9.9 ... Can be connected by appropriately adjusting the above. ! jx46 (a) is a plan view of the state of being meshed in this way, and 8 is a mesh metal. The figure (b) is the X4-X4 cross-sectional view of the figure (a), and the figure (c) is the cause of the y4-Y4 cross-section of the figure (a). The state in which the metal 8 spreads laterally as well as the thickness direction and connects the point-shaped electrodes 9 ° 9, ... Is shown. In the above embodiment, the electrode 9 is described as having a point shape, but it does not have to have the same vertical and horizontal dimensions, and may have an arbitrary shape. The formation of the metal film to be the electrode is not limited to vacuum vapor deposition, and a means such as the Metsuki method, which has ohmic contact with the silicon substrate and has adhesive force, can be used. Further, GaAs or other semiconductors can be used instead of the silicon substrate. (Effect of the invention) By using both the resist pattern for removing the antireflection film and the resist pattern for forming and connecting dots, the work process can be shortened. Therefore, an electrode having a structure in contact with a conventional substrate is formed. Compared to the method, the cost can be reduced. If the mesh is made thicker, it spreads widely in the lateral direction around the point-shaped electrode, so that the density of the point-shaped electrode can be reduced, and therefore the contact area between the substrate and the electrode can be reduced. It is effective for large high-efficiency solar cells that need to be thickened.

[Simple explanation of drawings] FIGS. 1 (a), (b), 211 (a), (b), 3 (a), and (b) are drawings showing the steps of an embodiment of the present invention, and in each of 6 (a). ) Is a plan view, and Jia) is a cross-sectional view. Figure 4 (a). (b) and (c) are the final stages thereof, (a) is a plan view, and (b) and (C) are cross-sectional views having different cut surfaces. FIG. 5 (a). Can), FIGS. 6 (a), 6 (b), 7 (a), and (b) are plan views and cross-sectional views of each step of the conventional steps, respectively. Fig. 8 (a), (b), (c), Fig. 9 (a), (b), (e), and Fig. 10 (a), (b), (c) are the above-mentioned steps, respectively. It is the plan view of each process which follows and the cross-sectional view which is different from the cut surface.