JPH11219948A - Method of forming coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an even film thickness for a coating film and high processing precision of the coating film and to form the void-free coating film by a method wherein a coating material is begun to feed on a substrate from a discharge needle in the rotation of a low speed lower than specified for the substrate and processes for increasing the number of rotation of the substrate more than specified for the substrate while the coating material is fed are repeated more than two times. SOLUTION: This diagram is one example of process diagrams for forming a coating film by a spin coating method, the abscises of the diagram show the time and the ordinates of the diagram show the number of rotation. A silicon wafer, which is used as a substrate, is installed on a spin coater and the wafer is rotated for the number of rotation of 100 rpm. While the wafer is rotated, a coating material is begun to drip on the wafer. After two seconds from the dripping, the number of rotation is increased up to 3000 rpm or thereabouts. After about 15 seconds from the increase, the dripping is stopped. After that, the number of rotation is again decreased down to 100 rpm, the coating material is dripped on the wafer and after about two seconds from the dripping, the number of rotation of the wafer is increased up to about 2300 rpm. After that, the rotation of the wafer is left as it is to extend the coating material on the surface of the wafer by a centrifugal force for about 20 minutes and at the same time, the excessive coating material is made to scatter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a coating film used as a chip component of an electronic element such as an IC or a sensor.

[0002]

2. Description of the Related Art Coating films typified by polyimide have excellent electrical insulation and heat resistance and are therefore used as moisture-proof coatings or electrical insulation coatings on various electronic devices such as ICs and sensors. Conventionally, such a coating film is mostly formed using a liquid coating material at the final stage of the chip process as overcoating of the chip, and it is not necessary to pay much attention to the film thickness distribution.

[0003]

However, in recent years, with the increase in the density of electronic elements, there has been an increasing demand for high insulation inside the electronic element chip. There are many situations where the use of such materials is considered. For example, an interlayer insulating film such as between wirings is formed at an intermediate stage of a chip manufacturing process, and a coating film having a thickness of several μm to several tens μm is used. Furthermore, when trying to form a fine pattern in micron units by a photo process using a photoresist,
In order to achieve precise processing accuracy, it is important to form a flat coating film with high uniformity of the film thickness.

When a coating film is formed from a liquid coating material at an intermediate stage of a device manufacturing process, a spin coater is usually used. In this method, while rotating a base material such as a semiconductor wafer at a predetermined speed, a coating material is dropped from a thin nozzle called a discharge needle near the center thereof,
Thereafter, the base material is rotated at a speed of several thousand revolutions / minute (hereinafter referred to as rpm) or more, and excess coating material is blown off to obtain a target coating film. The film thickness and its distribution mainly depend on the rotation speed and time, the amount of liquid to be discharged, the temperature of the liquid,
It is determined by the temperature and humidity of the application environment.

FIG. 3 shows an example of a process diagram according to a conventional spin coating method, in which the horizontal axis represents time and the vertical axis represents rotation speed. First, the coating material is dropped from the discharge needle while rotating the wafer at a rotation speed of 100 rpm, and the wafer surface is almost covered with the coating material. After stopping the dropping, increase the rotation speed of the wafer to about 2500 rpm,
Excessive coating material is blown off by centrifugal force to form a coating film having a desired thickness.

FIG. 4 shows a viscosity of 2.4 × 10 ⁻³ m ² / s (2
400 centistokes) of polyimide resin
FIG. 4 is a film thickness distribution chart after spin coating on a 25 mm Si wafer surface under the conditions of FIG. 3 and heat treatment at 150 ° C.
There is a thick part almost at the center of rotation, a thin part near one half of the radius, and thicker around. A fluctuation of about ± 6.5% is observed in a coating film having a thickness of about 9.5 μm.

Unlike a general resist having low viscosity,
As described above, when the coating material having a high viscosity such as polyimide is used, when the rotation speed at the time of dropping is lowered, the spread of the coating material during the rotation of the base material is poor, and the film thickness near the center of the base material becomes thick and slightly away from the center. There is a tendency that the film thickness of the portion where it is bent becomes thin. In general, the distance between the tip of the discharge needle and the substrate is 2
When the substrate is rotated while dropping from such a height, the dropping tip is pulled by the spreading coating material, and the dropping position is off center. In some cases, this may cause the coating material to not spread uniformly on the substrate surface.
On the other hand, when the rotation speed at the time of dropping is increased, bubbles are generated in the coating material, and voids may remain even after heat treatment.
In the case of using for a semiconductor or the like, it is not preferable that bubbles are present in the coating film because it causes discharge.

[0008] In view of the above problems, an object of the present invention is to provide a method of forming a coating film capable of realizing precise processing accuracy with a uniform film thickness and having no voids.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method of forming a coating film on a substrate by supplying a fluid coating material while rotating the substrate. The process of starting to supply the coating material from the discharge needle at the following low-speed rotation and increasing the rotation speed to 2000 rpm or more while supplying the coating material is repeated twice or more.

[0010] High-speed rotation of 2000 rpm or more is necessary to uniformly spread the liquid coating material by centrifugal force and to make the film thickness uniform. However, 1000r from the beginning
When the coating material is dropped at a high rotation speed exceeding pm, the coating material is blown off and bubbles are generated at the moment when the dropped coating material comes into contact with the base material, and remain in the coating film. If dropping is started during low-speed rotation of 1000 rpm or less and then high-speed rotation is performed, generation of bubbles is small. Furthermore, by repeatedly dropping at a low speed, bubbles generated earlier can be eliminated. In addition, a single drop causes a thick portion near the center of rotation, but by repeating the drop, the thick portion is smoothed and the film thickness distribution is averaged. As an upper limit, if the rotation speed is too high, for example, exceeding 10,000 rpm, the film thickness will not be sufficient.

If a process of rotating the coating material at a high speed for a short time after stopping the supply of the coating material is provided, the film thickness can be adjusted by the rotating speed and time during the process. The distance between the tip of the discharge needle that drops the coating material and the base material is
It may be in the range of 1 to 10 mm. The distance is 10
If the thickness exceeds mm, in the case of a coating material having a high viscosity, the dropping position of the coating material coming out of the discharge needle may be largely shifted from the center of the rotating base material. Also, 1
If it is set to less than mm, the coating material adheres to the outer periphery of the discharge needle, and the amount of dripping becomes unstable. Between 1 and 10
When the distance is set in the range of mm, the drop position of the coating material coming out of the discharge needle does not largely deviate from the center of the rotating substrate, and the distribution of the coating film becomes uniform.

The coating material contains an organic solvent such as liquid polyimide and has a kinematic viscosity of 1 × 10 ^{−4 to} 5 × 1.
It is important that it is in the range of 0 ^-3 m ² / s. Even with such a large viscosity, by repeating dropping,
The thick portion is smoothed, and the film thickness distribution is averaged. 5
A coating material having a high kinematic viscosity of 10 ⁻² m ² / s or more is not suitable for spin coating. In the case of a material having a low kinematic viscosity of 1 × 10 ⁻⁴ or less, it is not necessary to adopt this method.

[0013]

[Embodiment] FIG. 1 is an example of a process diagram by a spin coating method according to the present invention, in which the horizontal axis represents time and the vertical axis represents rotation speed. A silicon wafer having a diameter of 125 mm serving as a substrate is set on a spin coater and rotated at a rotation speed of 100 rpm. Polyimide used as a coating material from the discharge needle while rotating the wafer (Polyimide KI manufactured by Shin-Etsu Chemical Co., Ltd.)
S1001, start dropping kinematic viscosity 2.4 × 10 ⁻³ m ² / s). Approximately 2 seconds after the start of dropping, the number of rotations of the wafer is increased to 30.
At about 00 rpm, the coating material is spread on the wafer surface by centrifugal force. The drop amount of the coating material is about 1.5 g. After about 15 seconds, the dripping is stopped, and the rotation is continued for about 35 seconds to blow off excess coating material. Thereafter, the number of revolutions is again reduced to 100 rpm, and the coating material is dropped from the discharge needle while rotating the wafer. After about 2 seconds, the number of revolutions of the wafer is increased to about 2300 rpm. After the dropping of about 1.5 g, the dropping is stopped, the rotation is kept as it is, and the coating material is spread on the wafer surface by centrifugal force for about 20 seconds, and the excess coating material is scattered. Depending on the number of rotations and time, a coating film having a desired thickness is obtained.

The silicon wafer thus obtained is heated on a hot plate at 150 ° C. for 90 seconds to evaporate the solvent.
A coating film having a thickness of about 10 μm was obtained. FIG. 2 is a film thickness distribution diagram of the polyimide film after the above heat treatment.
The measurement was performed with an optical film thickness meter. A thick portion near the center of rotation as shown in FIG. 4 according to the conventional method is not seen.
The thin part near the half radius is also shallow and uniform throughout. ± 9.5 μm coating film
It can be seen that the variation was about 2.6%, and the variation was reduced to less than half of the conventional method. This is presumably because the thick portion near the rotation center, which occurred in the first drop, was dissolved during the second drop. In addition, almost the same results were obtained with a stylus-type film thickness meter.

The first dripping may cause some bubbles, but the bubbles disappear by the second low-speed rotation, and no bubbles are generated even at the high-speed rotation. After the temperature was once lowered to room temperature, it was again set on a spin coater, and a positive resist AZ6130 manufactured by Hoechst Co. was applied at a predetermined rotation speed and time (3000 rpm, 20 seconds). 90 ° C on a hot plate set to
Heated for seconds. Then, irradiation was performed at 300 mJ / cm ² with i-line using an exposure machine (mask aligner). Thereafter, development was performed using an alkaline developer NMD-3 manufactured by Tokyo Ohka Co., Ltd. At this time, the coating material not covered with the photoresist is also removed. After the development, the resist was immersed in acetone as a solvent to remove the resist, and further cured by heating at 350 ° C. for 1 hour.

Since the thickness of the coating film after curing is almost proportional to the thickness before curing, the obtained film has a thickness of 5 ± 0.
12 μm, and the line and space 15 μm ± 0.
A fine pattern of 5 μm could be formed uniformly over the entire surface of the wafer. In this embodiment, the coating material was dropped twice.However, the coating material may be dropped three or more times.The number of drops, the number of high-speed rotations after the supply of the coating material is stopped, and the time are used to reduce the film thickness. Can be adjusted.

According to the method of the present invention, dripping does not have to be performed over the entire surface of the substrate as in the prior art, which leads to a reduction in the amount used. The substrate may be, for example, a wafer that has been processed, another semiconductor wafer, a metal substrate, or the like, in addition to the silicon wafer of the above embodiment.

[0018]

As described above, according to the present invention, a high-viscosity coating material is supplied from a discharge needle at a low speed of 1000 rpm or less, and the rotation speed is increased to 2000 rpm or more while supplying the coating material. By repeating the raising step twice or more, a coating film having a uniform film thickness can be formed, and the generation of bubbles is suppressed, so that the chip can be used as an internal component. As a result, precise processing accuracy can be realized, the degree of freedom in the configuration of the electronic element increases, and the possibilities expand.

It is also effective to form a coating film having a more uniform thickness by setting the distance between the tip of the discharge needle for dropping the coating material and the base material within the range of 1 to 10 mm.

[Brief description of the drawings]

FIG. 1 is a diagram of a coating process according to an embodiment of the present invention.

FIG. 2 is a diagram showing a film thickness distribution of a coating film formed under the conditions of FIG.

FIG. 3 is a diagram of a conventional coating process.

FIG. 4 is a diagram showing a film thickness distribution of a coating film formed under the conditions of FIG. 3;

Claims (5)

[Claims] In a method of forming a coating film on a substrate by supplying a fluid coating material while rotating the substrate, the coating material is supplied from a discharge needle at a low speed of 1000 rpm or less. And a step of repeating the step of increasing the rotation speed to 2000 rpm or more while supplying the coating material two or more times. 2. The method according to claim 1, wherein the high-speed rotation is performed for a short time after the supply of the coating material is stopped. 3. The method for forming a coating film according to claim 1, wherein the distance between the tip of the discharge needle for dropping the coating material and the substrate is in the range of 1 to 10 mm. 4. The coating material according to claim 1, wherein the coating material contains an organic solvent, and has a kinematic viscosity in a range of 1 × 10 ^{−4 to} 5 × 10 ⁻³ m ² / s. The method for forming the coating film according to the above. 5. The method according to claim 4, wherein the coating material is a liquid polyimide.