JP2004153262A - Method of spin coating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of spin coating which prevents wastage of excessively supplying a coating liquid in applying a coating liquid such as a photoresist onto a semiconductor wafer or a glass substrate for a liquid-crystal display. <P>SOLUTION: After a coating liquid is supplied onto a substrate, the substrate is rotated at high speed with acceleration up to a rotation speed at which the spreading velocity of the coating liquid becomes the maximum. The substrate surface is effectively coated with a small quantity of the coating liquid by rotating the substrate with a rotational acceleration of 4,000rpm/s until the rotation speed reaches at 20,000rpm. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a spin coating method suitable for applying a coating liquid such as a photoresist on a semiconductor wafer or a glass substrate for a liquid crystal display.

In a semiconductor IC manufacturing process, a spin coating method is generally used in order to uniformly apply a photoresist to a semiconductor wafer.
In this spin coating method, the semiconductor wafer on which the photoresist solution is dropped is rotated at 1000 rpm to 2000 rpm. A coating liquid such as a photoresist liquid supplied onto a substrate such as a semiconductor wafer is spread on the substrate surface by centrifugal force due to the rotation of the substrate, whereby the coating liquid is applied almost uniformly to the surface of the substrate. .

However, in the conventional spin coating method as described above, when the supply amount of the coating liquid containing a volatile organic solvent onto the substrate surface is not sufficient, the coating liquid is spread by evaporation of the organic solvent when the coating liquid spreads on the substrate. The viscosity of the liquid was increased, and there was a possibility that uneven coating might occur.
Therefore, in order to apply the photoresist liquid as the coating liquid to the surface of the semiconductor wafer as the substrate surface without causing uneven coating, the amount of the coating liquid supplied to the substrate surface is rotated by an amount exceeding substantially 95%. An extremely large amount of excess coating solution is supplied onto the substrate so that the coating solution is scattered by the centrifugal force from the outer edge of the substrate.
Therefore, from the viewpoint of resource saving, a technology capable of reducing the supply amount of the useless coating liquid has been desired.
Japanese Patent Application Laid-Open No. 04-098823 JP 07-328517 A JP-A-03-169006

  The problem to be solved is that an excessive amount of the coating liquid must be supplied to the substrate.

  The present invention solves the above problems by rotating the substrate to which the coating liquid is supplied at a high speed which could not be considered by the conventional spin coating method, and discharging a large amount of the excess coating liquid as in the conventional method from the outer periphery of the substrate. The following configuration is adopted based on the basic concept of effectively applying the substrate surface with a small amount of coating liquid without dissipating.

  A method according to the present invention is a spin coating method in which a coating liquid is supplied onto a substrate that has stopped rotating, and then the substrate is accelerated and rotated to spread the coating liquid on the substrate. The coating liquid is accelerated and rotated to a rotational speed at which the spreading speed of the coating liquid is maximized.

  The method according to the present invention is characterized in that, when a rotational acceleration of 4000 rpm / s or more is applied to the substrate, the rotational speed at which the spreading speed of the coating liquid is maximized becomes approximately 20,000 rpm.

  The method according to the present invention is characterized in that the coating liquid is covered with a solvent for the coating liquid in order to suppress volatilization of the coating liquid supplied onto the substrate.

  In the spin coating method according to the present invention, the substrate is accelerated and rotated to a rotation speed at which the spreading speed of the coating liquid on the substrate is maximized, for example, 20,000 rpm, so that the coating liquid spreads on the substrate at the highest speed at this rotation speed. Therefore, the coating liquid can be applied to the substrate while the amount of the solvent in the coating liquid is small, so that it is not necessary to supply the coating liquid in excess.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 is a graph showing the relationship between the number of rotations of the substrate according to the present invention and the minimum necessary supply amount of the coating liquid which does not cause strong unevenness that substantially influences. Prior to the description, the spin coater shown in FIG. 2 will be described.

FIG. 2 is a schematic view schematically showing a semiconductor wafer spin coating apparatus suitable for performing the spin coating method of the present invention.
The spin coater 10 has a rotary shaft 11 driven at a high speed of, for example, 4000 rpm or more, a chuck 13 provided with a circular table 12 which is integrally rotated with the rotary shaft 11, and a chuck 13. 13 and a wafer handling device 15 for removing the semiconductor wafer 14 after spin coating from the table 12 of the chuck 13, and a semiconductor wafer 14 on the surface of the semiconductor wafer 14 on the table 12. It includes a well-known coating liquid supply nozzle 16 as a coating liquid supply means for dropping a resist liquid.

  The chuck 13 is provided with, for example, a conventionally well-known vacuum suction means (not shown) for holding the semiconductor wafer 14 on the table 12. The center of gravity of the chuck 13 is determined by the rotation of the rotating shaft 11. It is set on the axis 11a.

FIG. 3 is a plan view of the semiconductor wafer 14.
The semiconductor wafer 14 has a circular outer shape as a whole, but a circular arc portion at an outer edge is cut out along a straight chord as a mark portion 17 for specifying a crystal orientation. Therefore, the center position indicated by reference numeral 18 of the semiconductor wafer 14 is located at the intersection of the two diameter lines of the circular outer shape of the semiconductor wafer 14, but the center of gravity position 19 of the semiconductor wafer 14 does not coincide with the center position 18. The center position 18 is more deviated to the side opposite to the side where the mark portion 17 is provided.

Therefore, when the semiconductor wafer 14 is placed on the table 12 with the center position 18 thereof coincident with the rotation axis 11a by the wafer handling device 15, the overall center of gravity of the chuck 13 holding the semiconductor wafer 14 is shifted from the rotation axis 11a. It will come off.
This shift may adversely affect high-speed rotation of 4000 rpm or more as in the present invention.

Therefore, as shown in FIG. 2, there is provided an adjusting means 20 for correcting the shift of the overall center of gravity in relation to the wafer handling device 15 and making the overall center of gravity coincide with the rotation axis 11a. .
In the example shown in FIG. 2, the adjusting means 20 is fixed to one side of the table 12, and adjusts the position of the counterweight 21 for compensating for the weight of the defect of the semiconductor wafer 14 due to the mark 17 and the position of the counterweight 21. And a detector 22 such as an infrared sensor or a reflection sensor for detection.

  The wafer handling device 15 detects the position of the counterweight 21 based on information from the detector 22 when placing the semiconductor wafer 14 on the table 12, and as shown in FIG. The semiconductor wafer 14 is placed on the chuck 13 such that the center position 18 coincides with the rotation axis 11 a and the mark 17 is located on the counterweight 21 side.

Due to the compensation effect of the counterweight 21, even if the center of gravity 19 of the semiconductor wafer 14 is shifted from the rotation axis 11a, the total center of gravity of the semiconductor wafer 14 and the chuck 13 is adjusted on the rotation axis 11a.
Therefore, even if the table 12 is rotated at a high speed exceeding 4000 rpm, and the semiconductor wafer 14 is rotated at a high speed integrally with the rotation of the table 12, the semiconductor wafer 14 is rotated in a stable posture without causing blurring. Is done.

In the dynamic dispense method, a resist liquid is dropped from a coating liquid supply nozzle 16 onto a surface of a semiconductor wafer 14 which rotates integrally with the table 12 in a state of high-speed rotation without stopping the rotation.
The resist liquid dropped from the coating liquid supply nozzle 16 onto the surface of the semiconductor wafer 14 instantaneously extends outward in the radial direction of the semiconductor wafer 14 due to the strong centrifugal force caused by the high-speed rotation of the semiconductor wafer 14.

FIG. 5 is a graph showing the results of an experiment for determining the relationship between the rotation speed of the semiconductor wafer 14 under the resist droplet and the spreading diameter of the dropped resist solution.
The X-axis shows the rotation speed (rpm) when the resist solution is supplied, and the Y-axis shows the spreading diameter (mm) of the resist solution at that time. A 6-inch (about 15 cm) semiconductor wafer was used as a sample substrate, and three types of resist solutions having viscosities of 10 cp, 100 cp, and 180 cp were used as resist solutions.

There is a slight difference in the supply amount of the resist solution dropped according to the respective viscosities. The resist solution having the lowest viscosity of 10 cp is 0.34 g, the resist solution of 100 cp is 0.3 g, and the viscosity is highest. For the 180 cp resist solution, 0.35 g of the resist solution was supplied. Characteristic lines for resist solutions of respective viscosities are indicated by symbols A, B, and C, respectively.
As is clear from the comparison of the characteristic lines A, B, and C having different viscosities, the spreading diameter of the resist liquid increases in accordance with the increase in rotation during the dropping of the resist liquid. At the same rotational speed, the spreading diameter increases as the viscosity of the resist liquid decreases.

  FIG. 1 shows a case where a resist solution having a viscosity of 10 cp shown in FIG. 5 is used, the number of rotations of the 6-inch semiconductor wafer 14 at the time of dropping of the resist solution, 6 is a graph showing an experimental result in which a relationship between a minimum supply amount of a liquid, that is, a necessary minimum drop amount is obtained.

  As can be seen from the graph of FIG. 1, at a relatively low rotation speed of less than 2000 rpm as in the conventional case, it is necessary to drop a resist solution exceeding 2 cc. Moreover, of the supplied 2 cc resist solution, a large amount of approximately 1.9 cc of the resist solution of about 95% does not adhere to the surface of the semiconductor wafer 14 and goes outward from the outer edge of the rotating semiconductor wafer 14 as an excess. It is useless because it splatters.

On the other hand, in the high-speed rotation of, for example, 4000 rpm according to the method of the present invention, the surface of the semiconductor wafer 14 can be entirely covered with the resist liquid by dropping 1 cc of the resist liquid which is the conventional half value.
As a result, the resist liquid can be applied without causing strong unevenness, and the amount of the resist liquid radiated from the edge of the semiconductor wafer 14 becomes a small amount of less than 1 cc.

At a rotation speed of 6000 rpm, a resist supply amount of about 0.5 cc is sufficient, and the excess amount radiated from the edge of the semiconductor wafer 14 is only 0.4 cc of 80% of the supply amount.
Further, when the rotation speed at the time of dropping the resist droplets reaches 7000 rpm, the supply amount of the resist of about 0.3 cc is sufficient, and the amount of the resist dissipated as an excess is 0.2 cc, which is about 66% of the supply amount. Trace amount.

  Regarding the increase in the rotation speed, in the high-speed region exceeding 7000 rpm indicated by the broken line of the characteristic line in FIG. 1, the rotation speed is increased, and the required minimum amount of resist dripping is further reduced. It can be estimated that the excess can be further reduced.

Although the example in which the present invention is applied to the dynamic dispense method has been described above, the present invention can be applied to the static dispense method.
FIG. 6 shows the relationship between the rotational acceleration of the semiconductor wafer and the spreading diameter of the resist liquid at that time in a so-called static dispense method in which the resist liquid is dropped while the rotation of the semiconductor wafer is stopped, and then the semiconductor wafer is rapidly rotated. 6 is a graph showing an experimental result of obtaining.

  In the experiment of FIG. 6, when the 6-inch semiconductor wafer 14 was stopped, 0.35 g of a resist solution having a viscosity of 180 cp was supplied to the semiconductor wafer 14. The X-axis and Y-axis of the graph of FIG. 6 indicate the rotational acceleration (rpm / s) and the spreading diameter (mm) of the resist solution applied to the semiconductor wafer 14 after the resist solution is supplied, respectively.

The characteristic lines D, E, F, G, and H represent the characteristics in each example where the rotational acceleration after the supply of the resist liquid is 2000 rpm / s, 4000 rpm / s, 5000 rpm / s, 7000 rpm / s, and 8000 rpm / s.
As is clear from the characteristic lines D to H, as the rotational acceleration increases, the spreading diameter of the resist liquid also increases. Also, the rotation speed that gives the maximum value to the diameter spreading speed of the resist solution exists at approximately 20,000 rpm.
Therefore, in the case of a resist solution having a high viscosity such as 180 cp, by selecting the duration of this speed as appropriate at the rotation speed indicating the maximum resist solution spreading speed, the resist can be cleaned up without waste as in the dynamic dispensing system speed. Can be applied.

  In the spin coating method by high-speed rotation of the present invention, a clearer and more remarkable resource saving effect was confirmed in the latter method, comparing the dynamic dispensing method and the static dispensing method.

  The spreading speed of the resist solution by the spin coating method can be controlled by adjusting the viscosity of the resist solution. However, when the viscosity is relatively high, the vaporization of the organic solvent in the resist solution is accelerated during high-speed rotation. May not spread sufficiently. When such a high-viscosity resist solution is used, the organic solvent of the resist solution is continuously supplied so as to cover the high-viscosity resist solution supplied on the semiconductor wafer 14 in order to suppress volatilization of the organic solvent. In this state, the semiconductor wafer 14 can be rotated at a high speed.

In the spin coater 10 shown in FIG. 7, the same organic solvent 24 used for the resist solution 23 is continuously supplied from the solvent supply nozzle 25 so as to cover the high-viscosity resist solution 23 supplied on the semiconductor wafer 14. Supplied. The supply of the solvent 24 is continued until the resist liquid 23 is almost completely spread over the surface of the semiconductor wafer 14 by the high-speed rotation of the semiconductor wafer 14. This solvent 24 suppresses the volatilizing action of the resist solution 23 thereunder.
Therefore, it is possible to apply the resist liquid having a high viscosity almost uniformly by the high-speed rotation of the semiconductor wafer 14.

  When the high-viscosity resist solution 23 is supplied to the semiconductor wafer 14, the resist solution 23 may be temporarily covered with the solvent 24 instead of continuously supplying the solvent 24. The effect of suppressing volatilization can be expected.

Although not shown, as means for suppressing volatilization of the resist liquid supplied to the semiconductor wafer 14, the resist liquid supplied on the semiconductor wafer 14 is rotated at a high speed under a predetermined pressurized atmosphere. it can. In order to realize this pressurized atmosphere, the entire spin coater 10 can be arranged in a pressurized chamber.
For forming the pressurized chamber, a well-known external cup member and a top cup member (not shown) arranged over the outer periphery of the table 12 can be used.
Further, it is preferable to keep the inside of the pressurized chamber under an atmosphere of an organic solvent of the resist solution, and it is possible to suppress volatilization of the resist solution, whereby the resist solution is more uniformly applied to the semiconductor wafer 14. be able to.

  In the example shown in FIGS. 2 and 4, the adjusting means 20 including the counterweight 21 and the detector 22 has been described. However, without providing the counterweight 21 and the detector 22, the wafer handling apparatus 15 itself is not shown in FIG. The semiconductor wafer 14 can be arranged on the table 12 such that the center of gravity position 19 of the semiconductor wafer 14 shown coincides with the rotation axis 11 a of the chuck 13.

  By arranging the position of the center of gravity 19 of the semiconductor wafer 14 so as to coincide with the rotation axis 11a by the wafer handling device 15, the semiconductor wafer 14 can be stably extremely high-speed without using the counterweight 21 and the detector 22 described above. Rotation can be realized.

  The spin coating method according to the present invention is not limited to the application of the photoresist liquid to the semiconductor wafer described above, but is applied to the application of a coating liquid to various substrates, for example, the application of a photoresist liquid to a glass substrate for a liquid crystal display. can do.

4 is a graph showing the relationship between the minimum required amount of resist droplets and the rotation speed of a semiconductor wafer in the spin coating method according to the present invention. FIG. 1 is a schematic view schematically showing a spin coater according to the present invention. It is a top view of the semiconductor wafer concerning the present invention. FIG. 4 is a perspective view showing a mounting posture of the semiconductor wafer to the chuck according to the present invention. 4 is a graph showing the relationship between the rotation speed and the spreading diameter of a resist solution in the spin coating method according to the present invention. 4 is a graph showing a relationship between a rotational acceleration and a spreading diameter of a resist solution in a spin coating method according to the present invention. FIG. 4 is a schematic view schematically showing another example of the spin coater according to the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 10 Spin coater 11 Rotation axis 11a Rotation axis 12 Table 13 Chuck 14 (Substrate) Semiconductor wafer 15 Wafer handling device 16 Coating liquid supply nozzle 17 Marking part 18 Center position 19 Center of gravity position 20 Adjusting means 21 Counter weight 22 Detector 23 (Coating Solution) resist solution 24 solvent 25 solvent supply nozzle

Claims (3)

A spin coating method in which the coating liquid is supplied onto the substrate whose rotation has been stopped, and then the substrate is accelerated and rotated to spread the coating liquid on the substrate,
A spin coating method, wherein the substrate is accelerated and rotated to a rotation speed at which the spreading speed of the coating liquid is maximized. 2. The spin coating method according to claim 1, wherein when a rotation acceleration of 4000 rpm / s or more is applied to the substrate, a rotation speed at which the coating liquid spreads at a maximum becomes approximately 20,000 rpm. The spin coating method according to claim 1, wherein the coating liquid is covered with a solvent of the coating liquid in order to suppress volatilization of the coating liquid supplied on the substrate.

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