JPS6164364A - Method for forming coating film - Google Patents

Abstract

PURPOSE:To uniformly a film to the entire surface region to a plate shaped substrate having various shapes, in spreading a coating solution by rotation, by rotating the substrate at a low speed at first and subsequently rotating said substrate at a high speed before stopping the same instantaneously. CONSTITUTION:A substrate 1 is mounted on a rotary shaft 2 and begins to rotate at a low speed at first while a coating solution is dripped on the substrate 1. Whereupon, the solution is spread to the circumference by centrifugal force and, at the spread point of time, the substrate 1 is rapidly changed over to high speed rotation to fly the unnecessary solution and, thereafter, rotation is stopped instantaneously. By this method, a coating film can be uniformly formed to the entire surface region of the plate shaped substrate having various shapes.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for forming a coating film on the surface of a plate-shaped substrate by rotating it.

<Prior art> For example, a single-crystal silicon solar cell uses a P-type silicon semiconductor substrate, forms a film doped with N-type impurities on its surface, and heat-treats the silicon substrate covered with the film to add the above-mentioned properties to the surface. A PN junction for photoelectric conversion is created by diffusing N-type impurities.

The film doped with N-type impurities is not only used to form a PN junction, but in recent years, materials have been used that can produce, for example, titanium oxide through a reaction during heat treatment and become an antireflection film. The heel material is supplied as a solution in which an N-type impurity and a titanium compound are dissolved in a volatile solvent, and the solution is applied to form a film on the silicon surface. When the coating film is formed, a method is adopted in which the silicon substrate is rotated to spread the dropped coating liquid over the silicon substrate surface. When the silicon substrate has a circular shape, a uniform coating film can be formed relatively easily over the entire substrate area by spreading the coating liquid by rotation as described above. However, for wafers that are deviated from circular shapes, such as squares or rectangles, if the same conventional spin coating method is applied, the film thickness will be different between the corners and the center, which may reduce photoelectric conversion efficiency in solar cells, etc. was there.

<Object of the Invention> The present invention has been made in consideration of the above-mentioned conventional coating film forming method, and it is possible to form a uniform thick film even on the surface of a plate-shaped substrate having a shape different from a circular one. A coating film forming method is provided.

<Implementation row> In FIG. 1, a P-type silicon single crystal semiconductor substrate 1 cut into a square or rectangle is mounted on a rotating shaft 2 whose rotational speed can be adjusted, and rotation is applied. The rotation at the start of the operation starts at low speed rotation as shown by the solid line in FIG. The coating liquid 3 is dropped onto the surface of the silicon substrate 1 before the rotation starts or during a period of low speed rotation. The dropped coating liquid 1
- is spread around by the centripetal force accompanying the rotation, and a coating film is formed on the entire surface of the silicon substrate 1.

Once the coating C3 has been spread on the substrate surface by the above-mentioned low-speed rotation, it is then rapidly rotated at a high speed (e.g., 3000 rpm).
pm). For example, the period of high-speed rotation is α5 s.
Although it is a short period of time such as ec, during this period, unnecessary coating liquid is scattered, the thickness of the coating film to be produced is determined, and the solvent is further dried. After a period of high-speed rotation, the rotation is stopped instantaneously and the coating liquid is subjected to a heat treatment process.The titanium compound dissolved in the organic solvent of the coating liquid 3r/i dropped onto the substrate 1 is an N-type impurity. The solution also contains phosphorus, and the number of revolutions and time during the formation of the coating film can vary depending on the concentration of the solution. The concentration of the solution is lowered to increase volatility, shorten the high speed period, and prevent solution buildup around the substrate.

For comparison, the time change of the conventional coating film forming process is shown in the second graph.
Indicated by a broken line in the figure.

In this embodiment, shown by the solid line in FIG. 2, after the coating liquid is spread over the substrate surface by low-speed rotation, high-speed rotation is instantaneously brought about, and also instantaneously when stopping from high-speed rotation.

After the coating film is formed through the above steps, the heat-treated silicon substrate has a KPN junction formed on the substrate surface, and a solar cell substrate whose surface is covered with an anti-reflection film made of titanium oxide is obtained.

When the surface of the solar cell substrate was observed, it was found that the solar cell according to this example was able to obtain an optimal film thickness as an antireflection film, that is, a blue interference color over the entire surface of the substrate. However, in the solar cell substrate that underwent the process shown by the solid line, non-uniformity of the film was observed in the corners of the rectangle, etc. A conversion efficiency higher by about 2.5% was obtained than in the step shown by the broken line in the figure.

Effects> As described above, according to the present invention, by controlling the rotational movement when spreading the coating liquid by rotation, it is possible to apply not only circular substrates but also circular substrates.
A coating film can be uniformly created over the entire surface of a plate-shaped substrate with a shape that deviates from a circle.

[Brief explanation of the drawing]

Fig. 1 is a semiconductor substrate mounting diagram used to explain the present invention;
The figure is a time chart for comparing and explaining the operation of one embodiment of the present invention and the conventional operation. 01: Semiconductor substrate, 2
: Rotating shaft, 3: Coating liquid.

Claims (3)

[Claims] (1) In a method of forming a volatile coating film on the surface of a plate-shaped substrate, the plate-shaped substrate is mounted on a rotating shaft, and then a coating liquid is dropped onto the plate-shaped substrate, and the coating liquid is applied over the entire surface of the plate-shaped substrate by slow rotation. A coating film forming method characterized by spreading, then rapidly rotating at high speed and stopping instantly to form a uniform coating film on the surface of a plate-shaped substrate. (2) The coating film forming method according to claim 1, wherein the plate-like substrate has a shape deviated from a circle. (3) The coating film forming method according to claim 2, wherein the plate-like substrate is a silicon wafer cut into a rectangular shape, and the coating film is an antireflection film covering the surface of the silicon substrate.