JP2006351876A - Evaluation method and evaluation equipment for dechuck characteristic of electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method and evaluation equipment for dechuck characteristics of an electrostatic chuck which can determine dechuck characteristics of a wafer easily, mechanically and quantitatively. <P>SOLUTION: This method evaluates dechuck characteristics when a wafer 3 is removed from an electrostatic chuck. In the method, the lift-up of the wafer 3 from the electrostatic chuck 2 is started after the shutoff of a voltage applied to the electrostatic chuck 2 for the irradiation of a laser beam to the wafer, its reflective light is received for the measurement of the displacement of the wafer 3, and the swinging of the wafer 3 is determined from the relevant measurement data. The displacement of the wafer 3 is measured on the basis of a wafer move-up command signal for starting the lift-up of the wafer 3, then measured data are stored. The displacement of the wafer 3 during lifting-up is measured on a time-axis, and the swinging of the wafer 3 is determined on the basis of the displacement data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an evaluation method and an evaluation apparatus for evaluating dechuck characteristics of an electrostatic chuck when manufacturing an electrostatic chuck used in a film forming apparatus for semiconductor manufacturing.

  In the manufacturing process of semiconductor devices, wafers are processed by plasma etching, CVD, ion plating, etc. in a reduced-pressure atmosphere. When the wafer is heated, it is adsorbed by electrostatic force to fix the wafer on the heater. A fixed electrostatic chuck is used. In the electrostatic chuck, an electrode is disposed on a lower surface of a wafer as an object to be attracted via a thin insulating film, and a voltage is applied to the electrode to fix the wafer with an electrostatic force.

  The adsorption force of the electrostatic chuck depends on the voltage applied to the chuck, the thickness of the insulating film, the dielectric constant thereof, and the electrode area, but an electrostatic force is further added thereto. This electrostatic force is generated by the movement of electric charges in the insulating film, so that the time constant is very large, and also varies greatly depending on the resistance value of the insulating film and the state of the electrostatic chuck surface. Therefore, the time constant of the electrostatic chuck varies depending on the shape / dimension, material, surface finish, etc., and reaches several seconds to several minutes.

  After processing, the wafer fixed on the electrostatic chuck is removed from the electrostatic chuck by lifting the lift pins from below, but if the residual charge remains unevenly on the wafer, the wafer is tilted and tilted. Deviation from a predetermined position may occur.

If the wafer is displaced from a predetermined position, the automated wafer conveyance mechanism cannot correctly hold the wafer, which may cause problems such as damage to the wafer or the conveyance mechanism. Therefore, in order to remove the wafer from the electrostatic chuck (dechuck), it is necessary to wait until the electric charge remaining on the wafer is removed. This waiting time becomes longer as the time constant of the electrostatic chuck becomes larger. Reduce sex.
Therefore, it is necessary to confirm whether the wafer can be dechucked without any trouble in a predetermined time.

  Therefore, it is very important to confirm the dechucking performance of the electrostatic chuck within a predetermined time in order to improve the reliability of the semiconductor manufacturing apparatus. For this reason, conventionally, when performing a dechucking operation by providing a glass viewing window next to the chamber of the electrostatic chuck evaluation device, a measurement person has visually confirmed the state of the wafer. In visual confirmation, it was necessary for the measurer to always be present according to the measurement time, and the measurer's behavior was constrained. In addition, there are individual differences in visual judgments such as slight fluctuations and shaking, and the judgments vary, and there are problems in the stability and reliability of evaluation.

In Patent Document 1, an insulating film is arranged between the surface of the insulating film of the electrostatic chuck and the wafer, the wafer is sucked and fixed, and a change in electrostatic capacitance formed by the wafer and the electrostatic chuck electrode is measured. That is, the time constant of the electrostatic chuck is obtained by continuing the measurement until the reading C (capacitance value) of the capacitance meter reaches a steady value. However, this method for obtaining the time constant does not directly measure the fluctuation that causes the wafer position shift, and therefore has a reliability problem as compared with the method that is tested under actual use conditions.
Also, when examining the time constant, if factors related to the structure of the electrostatic chuck, such as the dielectric constant and thickness of the insulating film, which is the uppermost layer of the electrostatic chuck, change, it is related to the electrical components, such as capacity and frequency. Since it is necessary to replace the parts, there are problems such as complexity.
JP 5-36806

  In order to solve the above-described problems, an object of the present invention is to provide an evaluation method and an evaluation apparatus for dechucking characteristics of an electrostatic chuck that can easily, mechanically and quantitatively determine the dechucking characteristics of a wafer. It is said.

The evaluation method of the dechuck characteristic of the electrostatic chuck of the present invention is a method for evaluating the dechuck characteristic when a wafer is removed from the electrostatic chuck, and after the voltage applied to the electrostatic chuck is cut off, The wafer is started to be lifted up, laser light is irradiated onto the wafer, the reflected light is received to measure the displacement of the wafer, and the shaking of the wafer is determined from the measured data.
The laser beam irradiation is performed after evacuation of the chamber containing the wafer is started, and the displacement of the wafer is measured and the measurement data is stored based on a wafer lift instruction signal for starting the lift-up of the wafer. Here, the wafer rise instruction signal and the wafer rise may be set at an appropriate rest time so that the rise starts after data collection is started, not at the same timing.
The wafer displacement at the time of lift-up is measured on the time axis, and the shaking of the wafer is determined based on this displacement data. Further, it is possible to determine the shaking of the wafer based on the change in the velocity of the wafer obtained by time differentiation of the displacement data.

The apparatus for evaluating dechuck characteristics of an electrostatic chuck according to the present invention is an apparatus for evaluating dechuck characteristics when a wafer is removed from the electrostatic chuck. The wafer is irradiated with laser light and lifted up from the electrostatic chuck. A laser displacement meter for measuring the displacement of the wafer to be measured, a window through which the laser beam is transmitted, and a recording device for storing the displacement data obtained by the measurement.
The measurement time of the laser displacement meter is 500 μsec or less, and the time interval for measuring the displacement of the wafer is 20 msec or less.

  According to the evaluation method and the evaluation apparatus for the dechuck characteristic of the electrostatic chuck of the present invention, the dechuck characteristic of the wafer of the electrostatic chuck is optically non-contacted, and the wafer shake and position displacement are directly measured with high accuracy. Can do. Moreover, since it is possible to perform unattended with a simple apparatus, the reliability of the electrostatic chuck used in the semiconductor manufacturing apparatus can be evaluated in advance, which contributes to the improvement of the reliability of the wafer manufacturing apparatus.

  The electrostatic chuck evaluation method of the present invention irradiates the wafer with laser light through a glass window on the upper surface of the chamber containing the electrostatic chuck, and the distance from the laser displacement meter to the wafer is increased from the start of the lift-up operation to the end of the operation. By measuring until time, the displacement of the surface position of the wafer lifted from the electrostatic chuck by lift pins or the like is recorded on the time axis, and the shaking of the wafer is determined based on these data.

Hereinafter, the evaluation method and the evaluation apparatus of the present invention will be described in more detail with reference to the drawings.
FIG. 1 shows an example of an evaluation apparatus according to the present invention. An electrostatic chuck 2 is placed in a chamber 1 and a wafer 3 is lifted by wafer lift pins 4. From the laser displacement meter 5, laser light is irradiated onto the wafer 3 through a glass window 6 provided on the upper surface of the chamber, and the reflected light is received to measure the displacement of the wafer 3. Further, the laser displacement meter 5 is connected to a data recording device 7 which is also a determination unit, and is configured to start data recording with the rising timing of the wafer as a trigger signal.

  When measuring the dechuck characteristic, the inside of the chamber 1 is evacuated by the vacuum pump 8 and depressurized, the high voltage DC power supply 9 is turned on and applied to the electrostatic chuck 2, and the wafer 3 is attracted and fixed on the electrostatic chuck 2. . After a predetermined time has elapsed, the voltage applied to the electrostatic chuck is cut off. The electric charge charged in the electrostatic chuck electrode 10 is guided to the ground from the switched wiring and removed. The electric charge is erased from the wafer 3 and the electrostatic chuck 2, and the measurement of the distance between the laser displacement meter 5 and the wafer 3 is started based on the lift-up start signal, and continuously until the rising of the wafer 3 is finished. The distance is measured, and the measurement data is recorded by the data recording device 7.

The shaking of the wafer 3 is determined from the obtained measurement data, that is, the displacement data of the wafer 3. At the same time, the presence or absence of shaking of the wafer 3 was also observed from the viewing window 11 with the naked eye. The measurement was controlled by a control device (sequencer) 12 based on a predetermined program. The measurement time of the laser displacement meter 5 is preferably 500 μsec or less, and if it exceeds this time, the collected data tends to be moving average on the time axis, and it becomes difficult to catch the strength of the signal. Also, the time interval is preferably 20 msec or less. The smaller the frequency used for measurement, the shorter the time interval and the shorter the measurement time for a single measurement.
The displacement data of the wafer during lift-up obtained in this way reflects the temporal change in the capacitance removed from the wafer and the electrostatic chuck.

  Examples of the present invention will be described below by taking measurement of dechuck characteristics of a bipolar electrostatic chuck as an example. However, the present invention is not limited to these, and various modes are possible.

Example 1
Si wafer with a thickness of 100μm and an electrostatic chuck with a bipolar heater on which a surface dielectric layer with a volume resistivity of 5 × 10 ^-12 [Ωcm] is formed, and an SiO ₂ film (film thickness 100 nm) on both sides (With a thickness of 0.8 mm), ± 300 VDC was applied between the electrodes at a surface temperature of about 200 ° C. for about 3 minutes, and then the applied voltage was turned off. 29.5 seconds after the voltage was turned off, a trigger signal was output from the control sequencer, and the displacement data recording device started recording with the signal from the sequencer. After 30 seconds, the lift pin started to rise. Displacement data collection was stopped when the lift-up was completed.
At this time, the sampling rate of the laser displacement meter was 140 μsec, and four moving average values were recorded at intervals of 2 msec. The displacement data is shown in FIG. Furthermore, the speed data obtained by differentiating the displacement data with respect to time is shown in FIG. No abnormalities were found in any of the figures. Also, no abnormality was observed by visual observation through a window provided beside the chamber.

(Example 2)
An electrostatic chuck with a bipolar heater on which a surface dielectric layer with a volume resistivity of 9 × 10 ^-11 [Ωcm] is formed, and Si with a SiO ₂ film (film thickness of 100 nm) on both sides Using a wafer (thickness 0.8 mm), ± 300 VDC was applied between the electrodes at a surface temperature of about 200 ° C. for about 3 minutes, and then the applied voltage was turned off. A trigger signal was output from the control sequencer 29.3 seconds after the voltage was turned off, and the displacement data recording device started recording with the signal from the sequencer. After 30 seconds, the lift pin started to rise. Displacement data collection was stopped when the lift-up was completed.
At this time, the sampling rate of the laser displacement meter was 140 μsec, and four moving average values were recorded at intervals of 2 msec. The displacement data is shown in FIG. Furthermore, the speed data obtained by differentiating the displacement data with respect to time is shown in FIG.
From FIG. 4, the abnormal displacement immediately after the start of lift-up can be read, and the abnormal speed can also be read from FIG. In addition, a slight shaking of the wafer was also observed by visual observation through a window provided beside the chamber.

(Example 3)
An electrostatic chuck with a bipolar heater on which a surface dielectric layer with a volume resistivity of 9 × 10 ^-11 [Ωcm] is formed, and Si with a SiO ₂ film (film thickness of 100 nm) on both sides Using a wafer (thickness 0.8 mm), measurement was performed in the same manner as in Example 2 to obtain displacement data and velocity data. The displacement data is shown in FIG. 6 and the velocity data is shown in FIG.
From FIG. 6, the abnormal displacement immediately after the start of lift-up can be read, and the abnormal speed can also be read from FIG. In addition, slight wafer shaking was also observed by visual observation from a window provided beside the chamber.

Example 4
Furthermore, an electrostatic chuck with a bipolar heater in which a surface dielectric layer having a volume resistivity of 9 × 10 ⁻¹¹ [Ωcm] is formed to a thickness of 100 μm and polysilicon of 300 nm are deposited on the back surface (chuck contact side). Using a quartz substrate (thickness 1.2 mm), ± 300 VDC was applied between the electrodes for about 3 minutes at a chuck surface temperature of about 200 ° C., and then the applied voltage was turned off. About 30 seconds after the voltage was turned off, a trigger signal was output from the control sequencer. The displacement data recording apparatus starts recording with a trigger signal from the control sequencer. After 30 seconds, the lift pin begins to rise.
When the lift-up is completed, the collection of the displacement data recording device is stopped. At this time, the sampling rate of the laser displacement meter was 140 μs, and four moving average values were recorded at intervals of 2 msec. In this case as well, although not shown, displacement data was measured in the same manner, but no shaking was confirmed. In addition, no shaking was confirmed in the visual inspection as well.

(Comparative Example 1)
An electrostatic chuck with a bipolar heater on which a surface dielectric layer with a volume resistivity of 9 × 10 ^-11 [Ωcm] is formed, and Si with a SiO ₂ film (film thickness of 100 nm) on both sides Using the surface of the wafer (0.8 mm thick) with human sebum (hand oil) thinly wiped with IPA (isopropyl alcohol), the laser displacement meter has a sampling rate of 140 μsec and moves 128 times Except that the average value was recorded at intervals of 2 msec, measurement was performed in the same manner as in Example 2 to obtain displacement data and velocity data. The displacement data is shown in FIG. 8, and the velocity data is shown in FIG.
From FIG. 8, the abnormality immediately after the start of lift-up could hardly be read, and from FIG. 9, the abnormal speed could not be read. However, in the observation with the naked eye from the window provided beside the chamber, slight wafer shaking due to sebum dirt was observed.

In the first to third embodiments, if there is an abnormal displacement in the wafer displacement data, an abnormality is recognized in the time corresponding to the speed data, and the shaking of the wafer is also observed by visual observation. Therefore, according to the present invention, it is possible to determine from the recorded data whether or not the wafer is shaken at the time of lift-up with extremely high accuracy even if the measurer is not observing clearly.
In Comparative Example 1, if the number of moving average values when recording displacement data is too large, the displacement data of the wafer surface position is averaged, and it becomes difficult to capture a slight change in position. Show. When this number is 1, the displacement signal affected by the seismic intensity of the measurement system or device may hunt greatly, which may hinder the determination. Therefore, the number of moving average values is preferably 2 to 8 times.

  Since the reliability of the electrostatic chuck can be evaluated in advance, it contributes to the improvement of the reliability of the wafer manufacturing apparatus.

It is a block diagram which evaluates the dechuck characteristic of the electrostatic chuck of this invention. It is a figure which shows the displacement data obtained in Example 1 of this invention. It is a figure which shows the speed data obtained in Example 1 of this invention. It is a figure which shows the displacement data obtained in Example 2 of this invention. It is a figure which shows the speed data obtained in Example 2 of this invention. It is a figure which shows the displacement data obtained in Example 3 of this invention. It is a figure which shows the speed data obtained in Example 3 of this invention. It is a figure which shows the displacement data obtained by the comparative example 1. It is a figure which shows the speed data obtained by the comparative example 1.

Explanation of symbols

1 ... chamber,
2 ... electrostatic chuck,
3 ... wafer,
4 ... Wafer lift pins,
5 ... Laser displacement meter,
6 ... Glass window,
7: Data recording device,
8 ... Vacuum pump,
9 ... DC high voltage power supply,
10 ... Electrostatic chuck (electrode part),
11 ... Peeping window,
12 ... Control device (control sequencer).

Claims (8)

A method for evaluating dechucking characteristics when a wafer is removed from the electrostatic chuck. After the voltage applied to the electrostatic chuck is cut off, the wafer is lifted up from the electrostatic chuck and the laser is applied to the wafer. A method for evaluating dechucking characteristics of an electrostatic chuck, comprising: irradiating light, receiving reflected light thereof, measuring a displacement of the wafer, and determining a shake of the wafer from the measurement data. The evaluation method of the dechuck characteristic of the electrostatic chuck according to claim 1, wherein the laser light irradiation is performed after evacuation of the chamber containing the wafer is started. 3. The method for evaluating dechucking characteristics of an electrostatic chuck according to claim 1, wherein the displacement of the wafer is measured and the measurement data is stored based on a wafer lift instruction signal for starting the lift-up of the wafer. 4. The method for evaluating dechucking characteristics of an electrostatic chuck according to claim 1, wherein the displacement of the wafer at the time of lift-up is measured on a time axis, and the shaking of the wafer is determined based on the displacement data. 5. The method for evaluating dechucking characteristics of an electrostatic chuck according to claim 1, wherein a swing of the wafer is determined based on a change in wafer speed during lift-up. An apparatus for evaluating dechucking characteristics when a wafer is removed from an electrostatic chuck, a laser displacement meter for irradiating a laser beam on the wafer and measuring the displacement of the wafer lifted up from the electrostatic chuck, and a laser An apparatus for evaluating dechucking characteristics of an electrostatic chuck, comprising: a window through which light passes; and a recording device for storing displacement data obtained by measurement. The apparatus for evaluating dechucking characteristics of an electrostatic chuck according to claim 6, wherein the measurement time of the laser displacement meter is 500 μsec or less. The apparatus for evaluating dechucking characteristics of an electrostatic chuck according to claim 6 or 7, wherein a time interval for measuring the displacement of the wafer is 20 msec or less.

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