JPH04340217A - Resist coating method - Google Patents

Abstract

PURPOSE:To obtain even patterns into high quality semiconductor wafers with high precision by a method wherein the resist dripped on the semiconductor wafer is emitted with sound waves so as to coat the wafers with resist uniform in film thickness. CONSTITUTION:A speaker 14 to be a sound wave transmitter is provided above the cup 9 of a resist coating device 4. The cup 9 is lowered to mount a semiconductor wafer 1 on a chuck 6 and then the cup 9 is lifted to shift a resist solution discharging nozzle 7 to the position above the semiconductor wafer 1 so that specific amount of resist solution R may be dripped on the semiconductor wafer 1 from a resist solution feeder 8. Next, when the chuck 6 is turned in order to spread the resist solution R on the whole surface of the semiconductor wafer 1 by the centrifugal force, the speaker 14 is actuated to transmit the sound waves for bringing the semiconductor wafer 1 into contact with the resist solution R. Through these procedures, the semiconductor wafer 1 can be coated with the resist solution R uniform in film thickness without striation at all thereby enabling the semiconductor wafer 1 in high quality to be formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resist coating process for semiconductor manufacturing, and more particularly to a coating method for uniformly coating a resist.

0002

[Prior Art] Conventionally, in a pattern forming process for forming a thin film electronic circuit pattern on a semiconductor wafer, a resist film coated in a thin film form on the semiconductor wafer is exposed to light through a mask on which a desired pattern is formed, and then developed. to form a negative or positive resist pattern. Thereafter, this resist pattern is used as a mask to perform etching to form a desired electronic circuit pattern on the underlying thin film, and then the resist used as a mask is removed. When applying resist onto a semiconductor wafer in this process, the resist film thickness is related to the precision of the resist pattern, so it must be applied uniformly. A spin coater is often used, which performs coating by rotating and extending the coating to the peripheral area.

However, the resist solvent is easily vaporized, and in order to form a uniform resist film, it must be applied within a short time after being dropped. Therefore, 20 semiconductor wafers
When attempting to perform spin coating in a short time by rotating at a high speed of 00 to 3000 revolutions per minute, the resist 2 is applied in a radial wavy manner with different thicknesses in the radial direction of the semiconductor wafer 1, as shown in FIG. So-called striation 3 occurs. Therefore, a resist pattern formed by a resist film coated with a non-uniform thickness has been formed into a non-uniform pattern.

0004

[Problem to be Solved by the Invention] Therefore, in order to prevent the occurrence of striations, a resist solvent atmosphere is formed in a cup surrounding a mounting table on which a semiconductor wafer 1 is mounted and rotates at high speed, thereby preventing vaporization of the resist. Coating is performed by controlling the rotation speed of the semiconductor wafer (Japanese Patent Laid-Open No. 50-68)
No. 475, JP-A-56-52745, JP-A-57-7
No. 6835, JP-A-58-206124, JP-A-59
-50525, JP-A-60-10248, JP-A-6
1-29125), adding a surfactant to the resist solution to speed up the stretching of the resist solvent (Japanese Unexamined Patent Publication No. 1-29125)
No. 74621), reducing the temperature of the resist solution to suppress vaporization of the resist solvent (Japanese Patent Application Laid-open No. 60-1601)
No. 4, JP-A-60-235130, JP-A-60-86
(No. 542), or the semiconductor wafer was not subjected to hydrophobizing treatment before resist coating, so that the resist solution was easily stretched.

However, even with these treatments, as the diameter of semiconductor wafers has increased, it has not been possible to cope with semiconductor wafers having a diameter of 8 inches, for example, and it has not been possible to prevent the occurrence of striations. The present invention has been made in order to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a resist coating method for semiconductor wafers that can coat a resist with a uniform film thickness without causing striations even on large-diameter semiconductor wafers. With the goal.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the resist coating method of the present invention includes a method for coating the semiconductor wafer by rotating a semiconductor wafer onto which a resist has been dropped and coating the semiconductor wafer surface with the resist. The resist applied dropwise onto the wafer is coated with a uniform thickness by irradiating the resist with sound waves.

[0007]

[Operation] Generally, when a rotating body with a plane is rotated around the vertical axis of this plane, a laminar region and a turbulent region of air are generated on this plane, and furthermore, sound waves are generated on the plane of this rotating body. It is known that by irradiation, the area where air turbulence occurs can be moved to an area remote from the center of rotation. Therefore, when applying this fact to spin-coat a resist onto a semiconductor wafer, a sound wave is irradiated onto the resist liquid dropped onto the semiconductor wafer, which has a kinematic viscosity close to that of air. As a result, the area where the resist liquid level is disturbed can be moved away from the center of the semiconductor wafer, that is, to the outside of the semiconductor wafer, and since the area above the semiconductor wafer becomes a laminar region, the resist liquid level will not be disturbed. It can be applied to a uniform film thickness.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the resist coating method of the present invention is applied to a resist coating apparatus for semiconductor wafers will be described with reference to the drawings. The resist coating device 4 shown in FIG. 1 mounts and fixes the semiconductor wafer 1 by vacuum suction or the like, and includes a chuck 6 having a disc-shaped upper surface fixed to the rotating shaft of a motor 5. A resist liquid discharge nozzle 7 is provided above the chuck 6 and connected to a moving mechanism (not shown), so that it can be retracted from above the chuck 6 to a position outside the peripheral edge of the semiconductor wafer 1. The resist liquid discharge nozzle 7 is connected to a resist liquid supply system 8 equipped with a filter, a bellows pump, a suckback valve, and the like. A cup 9 is provided around the chuck 6 to prevent excess resist liquid shaken off from the periphery of the rotating semiconductor wafer 1 during resist application from scattering around. The cup 9 is movable up and down, and when loading/unloading the semiconductor wafer 1, it is lowered from the illustrated position to expose the chuck 6 from the upper center of the cup 9, facilitating loading/unloading. Further, at the bottom of the cup 9, there is a drain port 11 connected to a waste liquid treatment device 10, and the resist liquid splashed from the periphery of the rotating semiconductor wafer 1 hits the inner wall of the cup 9, bounces off, and adheres to the semiconductor wafer 1 again. An exhaust port 13 is provided which is connected to an exhaust device 12 to generate a gas flow toward the lower part of the cup 9 to prevent the cup 9 from leaking.

Cup 9 of such resist coating device 4
A speaker 14, which is a sound wave generator, is provided above. Note that this speaker 14 is connected to a sound wave generator (not shown). The sound waves generated from the speaker 14 are transmitted through the air, and are irradiated onto the resist liquid R dropped on the semiconductor wafer 1 on the chuck 6 while the chuck 6 rotates and stretches the resist liquid R.

A coating method for coating the resist liquid R onto the semiconductor wafer 1 using such a resist coating device 4 will be explained. The cup 9 is lowered from the position shown in FIG. 1, and the semiconductor wafer 1 is placed on the chuck 6 by a transport device (not shown). Next, when the cup 9 is raised to the position shown in the figure, the resist liquid discharge nozzle 7 is moved to above the center of the semiconductor wafer 1, and a predetermined amount of the resist liquid R is supplied from the resist liquid supply system 8.
is dropped onto the semiconductor wafer 1. Then, when the chuck 6 is rotated and the resist solution R is stretched over the entire surface of the semiconductor wafer 1 by centrifugal force, the speaker 14 is activated to generate sound waves and apply them to the resist solution R on the semiconductor wafer 1.

If the radius of the rotating disk is much larger than the thickness of the layer of air that the disk moves in contact with, then the relationship between the angular velocity ω of the tip of the moving fluid, the radius of rotation r, and the kinematic viscosity ν of the fluid The Reynolds number is known as a numerical value that indicates . The Reynolds number R is expressed as R=γ2ων-1. Here, r: radius of rotation on the disk, ω: speed of the tip of the moving air, ie, angular velocity of the rotating body, ν: kinematic viscosity of the fluid. Experiments have shown that if the Reynolds number R is smaller than a certain value, the upper surface of the fluid layer on the rotating disk is a flat laminar region, and when it is larger than a certain value, the upper surface of the fluid layer on the rotating disk becomes a turbulent region with unevenness. confirmed by. Such a relationship is common to resists having a kinematic viscosity of 20 cp, which is similar to that of air, which has a kinematic viscosity of 15 to 16 cp at room temperature. Then, a sound wave with a frequency of 630 Hz is applied in order to shift the region having this Reynolds number to a point greater than the radius of the semiconductor wafer. The sound waves are, for example, sine waves, rectangular waves, triangular waves, sawtooth waves, or composite waves of these, and can be selected as appropriate depending on the actual process.
The output intensity is also set to an optimal value.

[0012] Here, the above-mentioned Reynolds number and the transition of the laminar region will be explained in detail. The value of the Reynolds number R takes various values depending on the values of the variables on the right side of the above equation. For example, angular velocity ω=2π・100 (rad/sec) [60
00RPM], resist kinematic viscosity ν=20・10−6
(m2/sec) and the rotation radius of the boundary position between the laminar region and the turbulent region confirmed during rotation under these conditions is r = 0.09
5(m), R=2.83·105.

It has been experimentally confirmed that when the Reynolds number is smaller than this value, it is in a laminar region, and when it is larger, it is in a turbulent region. Therefore, using the R value as a guide, the state at any position on the rotating disk can be expressed as
This can be known by finding the ds number. In other words,
Under the above rotation conditions, if the radius of rotation r is smaller than 0.095 m, it is a laminar region, and the radius of rotation r is 0.095 m.
A larger area becomes a turbulent region. Therefore, in order to coat a resist film of uniform thickness over the entire surface of a large-diameter semiconductor wafer without generating striations, it is sufficient to apply the resist film in a laminar region.

On the other hand, the growth of turbulent flow in laminar flow can be suppressed by irradiating sound waves toward the surface of the rotating disk during rotation.
It has been found that as a result, the Reynolds number can be increased. Therefore, if the angular velocity ω and kinematic viscosity ν of the rotating body are constant due to the spin coating conditions, the Reynolds number increases, which means that the rotation radius r, that is, the radius of the laminar region can be increased from R=r2ων-1. For example, Reyn
When the olds number R=3.2, r=0.180 (m), and it becomes possible to make the entire surface of an 8-inch (10 cm) diameter semiconductor wafer a laminar region.

[0015] By applying sound waves transmitted by air to the rotating resist solution in this way, the generation of turbulence in the resist waves can be shifted to a radius larger than the semiconductor wafer, so that the resist film is free from striations. The coating can be applied uniformly without the occurrence of. The above explanation is an explanation of one embodiment of the present invention, and the sound wave generator is not limited to a speaker, but any device that generates sound waves can be used, and the present invention is applicable not only to resist coating. , it can also be applied to coating equipment that coats other rotary disks.

[0016]

[Effects of the Invention] As is clear from the above description, according to the resist coating method for semiconductor wafers of the present invention, by applying sound waves to the resist solution, the turbulent region can be moved outside the semiconductor wafer area. Therefore, it is possible to apply a resist with a uniform thickness on the semiconductor wafer without causing striations, and therefore, it is possible to manufacture high-quality semiconductor wafers by forming a uniform pattern with high precision.

[Brief explanation of drawings]

[Fig. 1] A configuration diagram of an embodiment to which the resist coating method of the present invention is applied.

[Fig. 2] A perspective view showing a resist coating film formed by a conventional example.

[Explanation of symbols]

1... Semiconductor wafer 4...Resist coating device

Claims (1)

[Claims] 1. When rotating a semiconductor wafer on which a resist has been dropped and applying the resist to the surface of the semiconductor wafer, a sound wave is irradiated to the resist that has been dropped on the semiconductor wafer to uniformly coat the resist. A resist coating method characterized by coating in a thick film.