JPH02233177A - Coating apparatus - Google Patents

Abstract

PURPOSE:To effectively control a film thickness even with respect to an object to be coated having no uniform surface state by mounting a phase detection means constituted so that monochromatic light is allowed to be incident to the surface of the object to be coated and the intensity of the reflected light from said object is detected to be applied to a control part performing the control of a coating condition on the basis of the detected intensity of the reflected light to detect a rotary phase. CONSTITUTION:When the part A having no pattern 12 on a wafer 1 becomes the irradiation spot of a laser 10, the light from a light source 20 passes through the part of the slit 23 of a disc 22 to be detected by a photodetector 21. A control part 6 triggers the pulse signal emitted from the photodetector 21 at a cycle once per one rotation to read the voltage signal from a reflected light intensity detector 11. By this method, since the control part 6 obtains smooth output voltage, the control of a coating condition is performed on the basis of said voltage.

Description

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

[Prior art] Rotary coating equipment is relatively easy to uniformly apply a liquid to a flat plate, so it has been used in semiconductor manufacturing processes in various fields. Published "Electronic Materials" (1988, December issue special edition)
It has been used to apply photoresist onto silicon wafers, as shown on pages 78-83.

FIG. 4 shows a conventional coating device of this type, and in the figure (1
) is the object to be coated such as silicon wafer, (2) is the coating liquid such as photoresist, (3) is the nozzle for dropping the coating liquid (2) onto the object to be coated, (4) is the chuck, and (5) is the The motor (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 silicon wafer (1) is placed on top of the chuck (4) connected to the
) is installed, and the wafer (1) is fixed by, for example, 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.

The wafer (1) is then rotated by the rotation of the motor (5) via the chuck (4) 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 in advance by determining conditions based on the viscosity of the resist liquid (2) used and the desired film thickness.

Conventional coating equipment as described above is operated uniformly under predetermined conditions, so when a large number of wafers are processed in succession, subtle changes in atmospheric conditions, supply liquid temperature, etc. However, it is difficult to make the thickness of the resist formed on the wafer surface constant, resulting in variations in the thickness.

The present inventors previously made an invention to eliminate the above-mentioned drawbacks (hereinafter referred to as the prior invention).

One embodiment is shown in FIG. In the figure, (10) is a laser, (l1) is a light intensity detector such as a photodiode, and (6) is a motor control section. In addition, the same reference numerals as in FIG. 4 indicate the same parts.

Next, the operation will be explained. The coating liquid (2) dropped onto the limb coating body (1) is subjected to centrifugal force due to the rotation of the limb coating body (1) due to the rotation of the motor (5), and the coating liquid (2) drops onto the limb coating body (1).
It tingles above me and expands.

When the coating liquid (2) contains an evaporable solvent such as a photoresist used in a semiconductor process, in addition to the reduction in the liquid film caused by the centrifugal force, the reduction in the liquid film also occurs due to solvent evaporation. Now, here, at the start of motor rotation or continuously before that, laser light is irradiated from the laser (■0) onto the limb application body (1), and the intensity of the reflected light is measured by the detector (1).
1) is detected. Now, if we use an IleNe laser (wavelength 6328 angstroms) of several mW as a laser and a photodiode as a detector to convert the current output into a voltage output across a constant resistor and detect it,
A voltage of several tens of mV or more can be easily obtained as a voltage output. Furthermore, since a photodiode is used, the linearity of light intensity and voltage output is excellent, and the response speed is sufficiently fast for feedback control of spin coating.

FIG. 6 shows changes in the reflected light intensity and the output voltage of the photodetector (11) as the film thickness decreases during spin coating. As shown in this figure, the reflected light intensity and the corresponding output voltage fluctuate periodically, and the oscillation period becomes larger with the passage of time. Therefore, for example, the output voltage value and its time derivative when a desired film thickness is achieved are determined in advance through experiments, and the data is stored in the motor control section (6), and the motor control section continues to control it during coating. From the output voltage value taken in (6), the time derivative is calculated in the motor control section (6),
When these two values reach the predetermined values, the motor (5
), a coating film of desired thickness can be obtained.

As described above, according to this prior invention, it is possible to control the film thickness at high speed and with high precision using a simple device, and it is possible to reduce variations in film thickness during spin coating.

[Problems to be Solved by the Invention] The applicator according to the prior invention as described above can be sufficiently effective when the surface of the limb applicator is uniform; When the in-plane surface condition is not uniform, such as on a formed semiconductor wafer,
If the reflected light detection/detection is performed continuously, the output signal will be greatly disturbed, and there is a problem in that it becomes difficult to control the coating conditions based on the signal.

This invention was made in order to solve the above problem, and like a semiconductor wafer, bumps are formed on the surface and the surface condition within the plane is uniform! It is an object of the present invention to provide a coating device that can effectively control the film thickness even for objects other than those to be coated, and can apply a film to a desired thickness.

[Means for Solving the Problems] A coating apparatus according to the present invention comprises means for making monochromatic light incident on the surface of an object to be coated, a light intensity detection means for detecting the intensity of the reflected light, and this detection means. In addition to a control unit that controls the coating conditions based on the light intensity detected by the apparatus, the apparatus includes a phase detection means that detects the rotational phase.

[Function] In the present invention, only the reflected light intensity at a predetermined constant rotation phase is selectively read, and feedback control E of coating conditions is performed based on it. Therefore,
For example, a stable reflected light intensity signal can be obtained even for a silicon wafer with a pattern formed on its surface.

[Example] FIG. 1 shows an example of the present invention, and the figure shows a pattern (l
2) is an example in which a photoresist solution is applied to a semiconductor wafer (1) that has already been formed on the surface, and the broken line (l3)
indicates the position where the laser light hits as Ueno\(1) rotates.

(200) is a rotational phase detection means, a light source (20),
A photodetector (21) and a motor (
The disk (22) attached to the shaft of 5) has a slit (2
3) is cut.

(15) 15 represents the signal flow from the light intensity detector (1l), (25) represents the signal flow from the photodetector (2l), (
35) shows the flow of control signals given to the motor from the control section (6).

In addition, the same reference numerals as in FIG. 5 indicate the same parts.

However, the nozzle for dropping the coating liquid is not shown.

Next, the operation will be explained. In order to finish the liquid film to a predetermined thickness, monochromatic light is incident on the surface of the object to be coated (1) from a laser (10), and the time change in the intensity of the reflected light is used to check whether the film thickness has reached the desired value. The basic idea of determining whether or not the present invention is present and performing feedback control is the same as that of the prior invention described above, and detailed explanation thereof will be omitted.

In this embodiment, monochromatic light is generated by a laser (IO), and the intensity of the reflected light is converted into an electrical signal, specifically a voltage signal, by a light intensity detector (11) using a photodiode and some electrical components. It is converted and taken into the control unit (6).

This voltage signal and the time differential of the voltage signal calculated by processing the voltage signal in the control unit (6) are determined in advance and become a value corresponding to the desired film thickness stored in the control unit (6). At this point, the control unit issues an instruction to stop the rotation of the motor (5). As for the method of this control, in addition to the method using the voltage signal level and its time derivative as described above, methods using the voltage signal and the time from the start of rotation can be considered.

FIG. 2 shows the voltage signal level of the light intensity detector (1l) over time. Figure (a) shows the case where the surface of the object to be coated (1) is uniform and smooth. In the same figure (b), as shown in Fig. 1, there is already a slam (12) on the surface of the wafer (1).
This is the time change of the detected voltage signal when a film is formed, and it is much more disordered than in the case of (a) in the same figure, and it is impossible to control the film thickness as it is. .

Therefore, in this embodiment, a slit (23) is formed on the shaft of the motor (5), and a disc (22) that rotates in the same manner as the wafer (1), a light source (20), and a light receiving element (2l) are used.
We prepared the following. In the figure, when the part A on the wafer (1) without the button (l2) becomes the irradiation spot of the laser (10), the light from the light source (20) passes through the slit l-(23) of the disk (22). The light-receiving element (2
l). In order to obtain the above effect, it is necessary to perform relative alignment between the slit (23) and the wafer (1), but the present invention does not limit this method. With the above configuration, the light receiving element (21)
generates a pulse signal once per rotation, and this pulse signal is taken into the control section (6). The control section (6) may read the voltage signal from the reflected light intensity detector (11) using the pulse signal as a trigger.

By the above operation, the control section can detect a smooth output voltage substantially as shown in FIG. 2(a).

Note that the voltage signal corresponding to the intensity of the reflected light obtained is discrete with respect to time, but normally, rotational coating is performed over several tens of seconds.
Since this is done by high-speed rotation of the Orpm and, for example, when the desired film thickness is about 1 μm, the film thickness changes slowly over time in that vicinity, so there is no problem with actual control.

In addition, in the above embodiment, the slit (23) of the disk (22)
Although one slit is used, four slits may be provided every 90 degrees. In that case, A shown in wafer (1) in FIG.
Measurement at four points B, C, and D becomes possible. Furthermore, in the above embodiment, the portion of the wafer (1) without the 7NIL tongue (12) and the slit (23) of the disk (22) were assumed to be relatively aligned by some means; It is also possible to omit the matching means. Next, such other embodiments will be described. The configuration is the same as that in FIG. In the stuttering X, first, the wafer (1) is transferred to a chuck section (not shown in FIG. 1), and is fixed by, for example, vacuum suction. After that, the coating liquid is applied to the wafer (
1) It is dropped onto the wafer (
1) is rotated at a predetermined constant rotation speed. For example, when the pattern is as shown in FIG. 1, the reflected light intensity signal obtained at that time becomes as shown in FIG. 3. In the figure, the part indicated by T corresponds to one revolution of the wafer (1), and there are four parts with smooth signal levels (pit P!
, P a, P 4).

This corresponds to portions A, B, C, and D of the wafer (1) shown in FIG. 1 without the button (12).

In addition to detecting the reflected light as described above, the control unit (6) detects the pulse signal of the light receiving element (21) at the circular part with a slit, and calculates the time between an arbitrary smooth part (for example, P1) and the pulse signal. By looking at the deviation of P. Since the spatial rotational phase shift between the non-patterned portion (for example, A) corresponding to the pattern and the slit (23) is known, this is stored in the control unit (6).

Next, the coating liquid (2) is dropped onto the wafer (1), and rotation for coating is started. At that time, since the phase difference between the slit (23) and the part without the button (I2) is known in the above procedure, the reflected light intensity is determined while taking into account the time difference according to the coating rotation speed from the pulse signal. If detected, a voltage signal corresponding to the reflected light intensity that changes smoothly and periodically over time is obtained, as in the previous embodiment, and coating conditions can be controlled based on this.

In the above embodiments, a laser is used as a monochromatic light source, but a combination of a normal light source and a filter may be used, and the light intensity detector is not limited.

Further, although a method using an optical sensor has been shown as a phase detection means, any method may be used.

[Effects of the Invention] As described above, according to the present invention, in addition to the prior invention, the rotational phase is detected. This has the effect of controlling the film thickness with a simple device and reducing the variation in film thickness during spin coating, especially when the surface is uneven, such as a semiconductor wafer with bumps formed on the surface. It can now be applied to homogeneous objects to be coated, and will greatly contribute to improving the quality and yield of semiconductor products, for example.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of an embodiment of the present invention, FIGS. 2 and 3 are respective time-signal level characteristic curves, FIG. 4 is a schematic side view of a conventional coating device, and FIG. 5 6 is a schematic side view of the coating device according to the prior invention, and FIG. 6 is a characteristic diagram of changes in reflected light intensity and output voltage as the film thickness decreases in the coating device shown in FIG. (1)...limb coating, (2)...coating liquid, (5)...
Motor, (6)...control unit, (IO)...monochromatic light source, (
11)...Light intensity detector, (200)...Rotational phase detection means. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] Dropping the coating liquid onto the object to be coated and rotating the object to be coated;
In a coating device that spreads the coating liquid by centrifugal force to form a coating liquid film on the object to be coated, light intensity detection for making monochromatic light incident on the surface of the object to be coated and detecting the intensity of the reflected light. A coating apparatus comprising: a phase detection means for detecting a rotational phase of the object to be coated; and a control section for controlling coating conditions based on signals from the two detection means.