JPS5916333A - Resist coating method - Google Patents

Abstract

PURPOSE:To enable to form a uniform film of small striation even with a thick film thickness by a method wherein photo resist is expanded over the entire surface of a substrate at low speed spinning, thereafter rotated for a short time at high speed spinning, and finally the film thickness is made uniform at medium speed spinning. CONSTITUTION:The Si substrate is placed on a spinning base, and then the photo resist is dripped for two seconds while the Si substrate is made still. Next, the Si substrate is rotated together with above-mentioned spinning base at the rotary speed of 300rev/min, successively rotated for a second at the rotary speed of 5,000rev/min, and further rotated for 25sec at the rotary speed of 2,000rev/ min. Thus, the result that the photo resist film thickness is 155mum and the dispersion width for the film thickness is 50Angstrom is obtained. The low speed spinning is preferable at approx. 200-600rev/min for 1-3sec, and the high speed spinning within 4,000-8,000rev/min.

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, the photoresist process of coating a photoresist on a substrate to form a thin film of photoresist and exposing it to form a predetermined pattern is performed before the semiconductor device is completed. 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 then the rotating table is rotated several hundred times for 7 minutes. By rotating at low speed, the photoresist is spread over the entire surface of the substrate, and
Cut off and remove excess photoresist, then 3
A method is used in which the film thickness is made uniform and controlled by high speed rotation of 000 to 5000 revolutions/minute.

However, when it is desired to increase the film thickness of the photoresist, if the coating method described above is used and the number of rotations of the high-speed rotation is lowered to increase the film thickness, the film thickness of the photoresist will be increased at a period of about 100μ7n on the surface of the substrate. Periodically, hundreds of changes occur, resulting in uneven film thickness.

This film thickness unevenness is called striation.

Generally, when a photoresist is developed into a predetermined pattern, the cross section of the remaining photoresist is trapezoidal, so the thicker the photoresist film is, the larger the dimension covered by the photoresist becomes. Therefore, when the striations occur, the pattern dimensions of the semiconductor device will vary. For example, MOS)
Variations in the gate lengths of transistors cause variations in threshold voltage VT. In the case of a solid-state image sensor, fixed pattern noise occurs in a reproduced image due to variations in the threshold voltage (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 IJ any and obtaining a thick photoresist film having a uniform film 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.

The photoresist coating method of the present invention was carried out below. A silicon substrate was placed on a rotary table, and photoresist No. 11 was dropped for 2 seconds while the silicon substrate was kept stationary. Next, the Noricon board was rotated together with the turntable for 1 second at a rotation speed of 300 revolutions/minute, then the Noricon board was rotated for 1 second at a rotational speed of 6000 revolutions/minute, and then at 2000 revolutions/minute. It was rotated for 25 seconds at a rotating speed. In this way, the photoresist film thickness was 165μ7n.
The result was that the width of variation in film thickness was 508.

Note that the low speed rotation is 200 to 600 revolutions/minute and 1 to 500 rpm.
About 3 seconds is preferable. If the rotation speed is too high or the rotation time is too long, a portion of the first resist will curl onto the back surface of the substrate. Well, the high speed rotation is 40QO ~ 8
It is preferable that the rotation speed be within 2 seconds at o○○ revolutions/minute. In order to suppress the width of variation in film thickness to 1008 or less, it is necessary that the rotation speed be 4000 or more. 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 uniformizing the film thickness by rotating at a medium speed. This is a resist coating method, and according to this method, a photoresist film with a uniform thickness and extremely small striations can be formed even if the film is thick.

Claims (1)

[Claims] A step of dropping a resist onto the surface of a substrate placed on a rotating table, a step of rotating the substrate at a first rotation speed, and a step of rotating the substrate at a second rotation speed sufficiently higher than the first rotation speed. A resist coating method comprising: rotating the substrate; and rotating the substrate at a third rotation speed between the first rotation speed and the second rotation speed.