JPH02233175A - Coating apparatus - Google Patents

Abstract

PURPOSE:To reduce the irregularity of a film thickness at the time of rotary coating by a method wherein monochromatic light is allowed to be incident to the surface of an object to be coated and the intensity of the reflected light from said surface is monitored during rotary coating and the rotational speed of the object to be coated is controlled on the basis of the intensity of the reflected light. CONSTITUTION:An object 1 to be coated is irradiated with laser beam from a laser 10 and the intensity of the reflected light from said object 1 is detected by a light detector 11 and the output voltage of said detector 11 is inputted to a motor control part 6. In this case, since the output voltage V of the light detector cyclically varies corresponding to the reduction of a film thickness, the output voltage V and the film thickness (l) does not correspond in a ratio of 1 : 1 but said output voltage V corresponds to the film thickness (l) as a combination of V and the time differentiation value of V. Therefore, by observing V and the time differentiation value thereof in place of the measurement of the film thickness (l) itself, the rotation of a motor 5 is controlled. The time differentiation value of V is calculated by the timer built in the controller 6. That is, said value is calculated using the values of standard voltage V, measured voltage Vm, a standard voltage gradient and a measured voltage gradient at time (t).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid coating device, for example, a coating device for spin-coating a photoresist onto the surface of a semiconductor wafer.

[Prior Art] This type of coating device is used in various fields because it is relatively easy to uniformly coat a liquid onto a flat plate. In the semiconductor manufacturing process as well, published by Kogyo Kenkyukai Co., Ltd. [Electronic Materials J (1988, December issue special issue)
As shown on pages 8-83, it is used to coat photoresist onto silicon wafers.

Figure 6 shows a conventional coating device (hereinafter referred to as conventional example 1).
, (1) is an object to be coated such as a silicon wafer, (2) is a coating liquid such as photoresist, (3) is a nozzle for dropping the coating liquid onto the object to be coated, (4) is a chuck, and (5) is (6) is a motor, and (6) is a motor control section.

Next, the operation will be explained using a case where a photoresist is applied to a silicon wafer as an example. First, the motor (5)
The wafer (1) is placed on a chuck (4) connected to the chuck (4), and the wafer (1) is further fixed by, for example, a vacuum suction force. Next, an appropriate amount of photoresist liquid (2) is dropped onto the wafer (1) from the nozzle (3). The resist liquid (2) may be dropped after the rotation of the wafer (1), which will be described below, has started.

Next, the wafer (1) is rotated via the chuck (4) in conjunction with the rotation of the motor (5), which rotates according to a predetermined rotation pattern. During this time, the resist (2) spreads over the wafer (1) by centrifugal force while the solvent evaporates, forming a thin film.

The rotation pattern such as the rotation speed and rotation time of the motor (5) is determined based on the viscosity of the resist (2) used and the desired film thickness.
This is determined by setting conditions in advance.

In Conventional Example 1, as described above, the operation is uniformly performed under predetermined conditions, so when a large number of wafers are processed in succession, it is usually difficult to deal with subtle changes in atmospheric conditions, supply liquid temperature, etc. On the other hand, it is difficult to make the thickness of the resist formed on the Ueno surface constant, resulting in variations in the film thickness.

As a means to eliminate the above-mentioned drawbacks, there is
There is an invention disclosed in Japanese Patent No. -51976 (hereinafter, this invention will be referred to as Conventional Example 2). This is shown in FIG. In the figure, (104) is a film thickness measurement section, (105) is a film thickness control section, (106) is a motor control section, and (100) is a laser beam. In this conventional example 2, the object to be coated (1
) for measuring the film thickness of solution (2) in
04) and a film thickness control part (105) for controlling the rotational speed of the object to be coated (1) being rotated based on the measured value in the measuring part (104) to obtain a predetermined film thickness. It is characterized by having

The method for measuring the film thickness is to make the laser beam (100) almost perpendicular to the object to be coated (1) and observe the interference fringes of the laser beam (100) due to the coating film. .

The rotational speed of the motor is dynamically controlled during coating by comparing the time-film thickness relationship stored in advance with the film thickness measurement value during rotation.

In this way, Conventional Example 2 attempts to solve the problem of film thickness variations by incorporating the idea of feed vanock control into the rotary coating device, which was conventionally operated uniformly under predetermined conditions as in Conventional Example 1. This is consistent with the present invention regarding the point X that feedback control is performed.

However, in Conventional Example 2, in order to perform feedback control, the film thickness value itself is measured, and one example of the measurement method is observation of interference fringes by a laser, and other specific film thickness measurement methods are used. has not been stated. Normally, in order to dynamically control spin coating, which completes in a few tens of seconds at most, control strategies must be determined quickly.
For this reason, it is considered inappropriate to measure the film thickness itself. Therefore, in order to provide a faster control method, it is preferable to monitor at least one other amount of information related to the film thickness rather than measuring the film thickness value itself. Of course, if this amount of information is
ff This does not apply to cases where it can be easily converted to film thickness, such as the measured weight of resist on a wafer, but it is possible to calculate the thickness of the liquid film from observation of interference fringes, as in the conventional/conventional example 2 above. Requiring high speeds is usually difficult and requires expensive equipment.

[Problems to be Solved by the Invention] The coating device of Conventional Example 2 as described above monitors the film thickness value itself for feedback control, and in addition, the method involves the complicated observation of interference fringes. A method is used. Furthermore, there were other problems such as the equipment being expensive.

This invention was made in order to solve the above problems, and in order to prevent variations in film thickness due to supply liquid temperature and ambient temperature, the idea of feedback control is adopted. The purpose of the present invention is to detect the amount of information and determine control measures at high speed, thereby making the control more reliable, and to obtain a coating device with a simple structure and low cost.

[Means for Solving the Problems] The coating device according to the present invention makes monochromatic light incident on the surface of the object to be coated, monitors the intensity of the reflected light during spin coating, and determines the direction of the object to be coated based on the intensity of the reflected light. It is designed to control the rotation speed of the body.

[Function] In this invention, feed/sj ivy control of film thickness can be performed at high speed, and as a result, variations in film thickness due to fluctuations in supply liquid temperature and atmospheric conditions are minimized.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 5. In Figure 1, the object to be coated (1), the coating liquid (2)
, the stopper (4), the motor (5), etc. are the same as those in the conventional example 1 shown in FIG. The nozzle for dropping the coating liquid was omitted.

Here, a laser (10) which is a monochromatic light source and a light intensity detector (11) such as a photodiode are provided. (6) is a motor control section.

Next, the operation will be explained. The coating liquid (2) dropped onto the object to be coated (1) is subjected to centrifugal force due to the rotation of the object to be coated (1) due to the rotation of the motor (5), and spreads over the object to be coated (1). Teyu《. When the coating iffl(2) contains an evaporable solvent, such as a photoresist in a semiconductor process, in addition to the reduction of the liquid film due to the centrifugal force, the reduction of the liquid film also occurs due to solvent evaporation. Now, in this conventional example, a laser beam (lO) is irradiated onto the object to be coated (1) at the start of motor rotation or continuously before that, and the intensity of the reflected light is measured by a detector (11). Detected. In this example, the laser (IO) is several meters long.
A lie-Me laser (wavelength: 6328 angstroms) of about W is used. A photodiode is used as the photodetector (l1), and current output is converted into voltage output across a constant resistor for detection.

At this time, a voltage of several IQmV or more can be easily obtained as a voltage output, and the photodiode has excellent linearity of light amount and voltage output, and furthermore, the response speed is sufficiently fast for feedback control of spin coating.

Although there is no particular restriction on the incident angle of the laser, here the condition is set to be almost perpendicular.

The voltage signal output by the photodetector (11) is taken into the motor control section (6), where a control policy is determined. Below, before explaining the control method of this embodiment, its basic principle will be described. The energy intensity of the reflected light changes periodically as the thickness Q of the liquid film (2) changes. This situation is shown in FIG. Three graphs are shown in FIG. 2, and the horizontal axis in all graphs indicates rotation time. The vertical axis is the graph (2-1)
Graph (2-2) shows the film thickness e, graph (2-2) shows the reflected light intensity (■), and graph (2-3) shows the output voltage of the light intensity detector (■). Graph (2-1) shows how the thickness of the liquid film decreases with rotation. Graph (2-2) shows how the reflected light intensity changes periodically as the liquid film thickness decreases. This oscillation of reflected light intensity is caused by a constant amount Δ of the liquid film thickness.
It occurs every time g decreases, and λ? e =■ ・ ・ ・ ・(1) Given by 2nt. λ is the wavelength of the laser beam, n is the coating liquid (2
) is the refractive index. In this example, since a He-Ne laser is used, the wavelength λ is 6328.

If n is a typical value for liquids, for example 1.5, then
△e is approximately 2100 people = 0. It becomes 21 μm. However, equation (1) is an equation in the case of vertical incidence, and for the sake of simplicity, the following description will be made assuming that the laser beam is perpendicular to the object to be coated.

Graph (2-3) shows the time change of the voltage signal output by the photodetector (11).

As already mentioned, in this example, the 6
Since the photodiode shown in FIG.

By the way, in spin coating, the change in film thickness gradually becomes smaller with the passage of time. For example, from 3μm to 2μm
The time required to reduce the film thickness by 1μm to 1μm and the time required to further decrease by 1m to form a film thickness of 1μm are more than 5 times different even when the solvent does not evaporate and the viscosity of the liquid does not change. Become.

Since the output voltage (■) of the photodetector (11) changes periodically as the film thickness decreases, there is not a one-to-one correspondence between (■) and the film thickness Q, but from the above, The combination of time/differential (2) corresponds to the film thickness ρ. Therefore, instead of measuring the film thickness Q itself, by looking at ■ and V, it is possible to control the rotational speed of the motor (5). ■ is the output of the photodetector (l1) itself, and ■
can also be easily calculated using a timer built into the motor control section (6).

Below, the output voltage V of the photodetector (l1) and its time differential ■
A method of controlling the motor rotation speed using the following will be explained in detail. The two graphs shown in FIG. 3 both show changes in the output voltage V with respect to time. In the graph, t is the end time of the motor rotation.

The solid curve is a standard time-output voltage relationship determined in advance through experiments, etc., and this relationship is based on the motor control unit (6
) is stored in The broken line in the figure indicates the measured value of the output voltage V of the photodetector (1l). In the graph (a), the broken line lags behind the solid line, and in this case, it is necessary to increase the rotational speed of the motor. In (b), conversely, the broken line is ahead of the solid line, and the rotational speed of the motor must be reduced. Such a control strategy can be determined based on the standard voltage (2), measured voltage Vm, and standard voltage gradient at that time. This flowchart is shown in FIG. In the figure, V1 is an arbitrary voltage approximately between the maximum value and the minimum value of the output voltage, and is used to determine whether the measurement time point is near the maximum value or the minimum value.

FIG. 5 shows the relationship between the standard voltage output and the measured voltage output in eight cases indicated by ■ to ■ in the figure.

The solid line is the standard value, and the broken line is the measured value.

In the above embodiment, the output voltage value ■ from the photodetector (1t) was monitored, but the output voltage value ■ from the photodetector (U) was monitored repeatedly during spin coating while detecting the reflected light intensity during spin coating. Ru. The extremely thick value Vp may be stored in the control section, x-V/Vp may be monitored instead of the output voltage (2), and similar control may be performed using this value and its time differential X. Equipped with a control unit that can make the above judgments, it is possible to control long-term changes in signal level due to fluctuations in the output of the laser (10), dirt on the detection surface of the photodetector (1l), etc. This has the effect that it is not necessary to change the memory regarding the I standard value of the part, and the reliability of the device can be improved.

[Effects of the Invention] As described above, according to the present invention, the monochromatic light reflected by the object to be coated is monitored and the rotational speed of the object to be coated is controlled based on the intensity of the reflected light. It has the effect of being able to provide feedback on film thickness at high speed and reducing variations in film thickness during spin coating.
For example, it greatly contributes to improving the quality and yield of semiconductor products.

[Brief explanation of the drawing]

Figures 1 to 5 show an embodiment of the present invention, with Figure 1 being a schematic side view, Figure 2 being a time-varying characteristic diagram of film thickness, reflected light intensity, and output voltage, and Figure 3 being a graph of reflected light. FIG. 4 is an output voltage characteristic diagram for explaining the basics of the control method, FIG. 4 is a flowchart diagram, and FIG. 5 is a voltage characteristic diagram for supplementary explanation of FIG. 4. FIGS. 6 and 7 Each figure is a schematic side view of a conventional coating device. (1) ... object to be coated, (2) ... coating liquid, 5)
- Motor, (6)... Motor control unit, (10) - Laser (monochromatic light source), (11)... Predetermined detector. In each figure, the same reference numerals indicate the same or equivalent parts. 1: Neyushichi Qdoi 1st place 2nd; 22nd cloth liquid 5: Sofu 10: Laser (monochromatic light point type) 11: Optical technique 7th grade (a) (b) Figure Figure Figure

Claims (1)

[Claims] In a coating device that drops a coating liquid onto an object to be coated, rotates the object to spread the coating liquid by centrifugal force, and forms a film of the coating liquid on the object to be coated, monochromatic light is applied to the object to be coated. a means for making the reflected light incident on the surface of the body; a photodetector for detecting the intensity of the reflected light; and a rotational speed of the rotating object to be coated based on the light intensity detected by the photodetector during coating. A coating device comprising: a motor control section for controlling the coating device.