JPH0345529B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resist coating method, and particularly to a photoresist coating method in a semiconductor device manufacturing process.

In the manufacturing process of this conductor device, before the semiconductor device is completed, a photoresist process is performed in which a photoresist is applied onto a substrate to form a thin film of photoresist, and then exposed to light to form a predetermined pattern. Usually performed several times.

Conventionally, the photoresist coating method has been as follows: First, the substrate to be coated is placed on a rotating table of a spinner, a small amount of photoresist is dropped onto the surface of the substrate, and the rotating table is rotated several hundred revolutions per minute. By rotating at a low speed, the photoresist is spread over the entire surface of the substrate, and excess photoresist is shaken off and removed.
A method has been used in which the film thickness is made uniform and the film thickness is controlled by high-speed rotation at 5000 revolutions/minute.

However, when it is desired to increase the film thickness of the photoresist, by lowering the high-speed rotation speed and increasing the film thickness using the coating method described above, the film thickness of the photoresist increases at a period of about 100 μm on the surface of the substrate. There is a periodic change of several hundred angstroms, resulting in uneven film thickness. This film thickness unevenness is called striation.

Generally, when a photoresist is developed into a predetermined pattern, the photoresist that remains has a trapezoidal cross section, so the thicker portion of the photoresist film has a larger area covered by the photoresist. Therefore, when the above-mentioned striation occurs, the pattern dimensions of the semiconductor device will vary. For example, variations in gate length of MOS transistors cause variations in threshold voltage V _T . In the case of a solid-state image sensor, fixed pattern noise occurs in a reproduced image due to variations in the threshold voltage V _T based on variations in the area of the photodiode and variations in the gate length.

The present invention provides a photoresist coating method for suppressing the occurrence of the above-mentioned striations and obtaining a thick photoresist film having a uniform thickness.

In the present invention, photoresist is dropped onto the surface of a substrate, the photoresist is spread over the surface of the substrate by rotating at low speed, and then the substrate is rotated at high speed for a short period of time to shake off excess photoresist at once. Finally, there is a method of making the film thickness uniform by rotating at a medium speed between the low speed rotation and the high speed rotation.

Examples of the photoresist coating method of the present invention will be described below.

First, a silicon substrate was placed on a rotating table, and while the silicon substrate was kept stationary, a photoresist was dropped for 2 seconds. Next, the silicon substrate was rotated together with the rotating table for 1 second at a rotation speed of 300 rotations/minute, and then for 1 second at a rotation speed of 5000 rotations/minute.
The silicon substrate was rotated for 25 seconds and then at a rotation speed of 2000 revolutions/minute for 25 seconds.
In this way, results were obtained in which the photoresist film thickness was 155 μm and the film thickness variation width was 50 Å.

The above-mentioned low speed rotation is 200 to 600 rotations/min.
About 3 seconds is preferable. If the rotation speed is too high or the rotation time is too long, part of the photoresist will wrap around the back side of the substrate. Further, the high speed rotation is preferably 4000 to 8000 revolutions/minute for less than 2 seconds. In order to suppress the width of variation in film thickness to 100 Å or less, it is necessary to rotate at least 4000 times. If the time is too long, the film thickness will become thin. The medium speed rotation is preferably 1000 to 5000 revolutions/minute for about 10 to 30 seconds. The film thickness can be determined by appropriately selecting the rotation speed within this rotation speed range.

As described in detail above, the resist coating method of the present invention involves spreading the photoresist over the entire surface of the substrate by rotating at a low speed, then rotating at a high speed for a short time, and finally rotating at a medium speed to make the film thickness uniform. This is a resist coating method, and according to this method, a uniform photoresist film with extremely small striations can be formed even if the film is thick.

Claims (1)

[Claims] 1. After dropping the resist solution onto the surface of the substrate placed on the rotary table, the substrate is rotated 200 to 600 times.
a first spin coating step of rotating the substrate for 1 to 3 seconds at 4000 to 8000 rotations/minute; a second spin coating step of rotating the substrate at 4000 to 8000 rotations/minute for 1 to 2 seconds;
A resist coating method in which a third spin coating step of rotating for 10 to 30 seconds at a lower speed than the second step of 1000 to 5000 rotations/min is performed successively.