JP4580283B2 - Evaluation method of electrostatic chuck - Google Patents

Description

  The present invention relates to an evaluation method for an electrostatic chuck used in a film forming apparatus for semiconductor manufacturing.

When a semiconductor wafer is subjected to predetermined processing or inspected under a microscope, it must be held by a fixing means so that the semiconductor wafer does not move or fall on the sample stage during processing or inspection. There is. Conventionally, mechanical chucks have been used as holding means, but vacuum chucks have been frequently used because of the advantage of not shielding the surface of the sample. However, when it is necessary to hold the semiconductor wafer under reduced pressure or in a vacuum, the vacuum chuck cannot be used, and an electrostatic chuck has been developed and used instead.
In the electrostatic chuck, an electrostatic chuck electrode is provided under an insulating film, and the electrostatic chuck electrode and the sample are separated by this insulating film.

When manufacturing a semiconductor device, a polysilicon film, an oxide film, a conductor film, a dielectric film, or the like is formed on a silicon wafer (hereinafter simply referred to as a wafer) by a CVD apparatus or a sputtering apparatus. It is manufactured by etching these thin films with an etching apparatus.
There are two types of wafer processing: batch type and single wafer type. The single wafer type is inferior in terms of throughput compared to the batch type, but single wafer type sputtering is used to make the substrate temperature uniform, stabilize the film formation rate, and film composition. Yes.

The wafer processed by the transfer device is advanced to the next process. However, in the single wafer type, when the wafer is removed from the electrostatic chuck (dechuck) and lifted up, it is affected by residual charges remaining on the wafer. In some cases, the wafer shakes, causes a positional shift, and the process must be stopped without successfully riding on the transfer device. Even when the deviation is small and the sheet can be transported successfully, a slight positional deviation may occur in the next process, and desired characteristics may not be obtained.
Therefore, among the characteristics required for the electrostatic chuck, it is an essential condition that the wafer is not displaced when the wafer is dechucked. For this reason, it is necessary to accurately evaluate the dechuck characteristic of the electrostatic chuck.

In the case of an electrostatic chuck having a heater function, in addition to the dechuck characteristic, the temperature distribution of the wafer during chucking and the rate of temperature increase are important.
The inspection method of the electrostatic chuck is to observe the behavior of the wafer when it is dechucked and lifted up after chucking the wafer on the electrostatic chuck using the same wafer as that used in the actual machine Is. When evaluating the temperature characteristics, the electrostatic chuck is heated to evaluate the temperature distribution and the heating rate of the wafer.

The wafer used for evaluation is repeatedly used for evaluating the electrostatic chuck. However, when repeatedly used, even when an electrostatic chuck having similar characteristics is evaluated, the behavior of the wafer may be different.
An object of the present invention is to provide an electrostatic chuck evaluation method capable of performing an accurate evaluation without different behavior depending on wafers that are repeatedly used.

Evaluation method of the electrostatic chuck of the present invention uses a silicon wafer Ha Te method odor of evaluating dechucking characteristics of the electrostatic chuck, the silicon wafer contact angle of water to the electrostatic chuck is 45 ° or less Chat after King, it is the features that you observe the behavior of the wafer at the time of lift-up and de-chucking. The silicon wafer having a water contact angle of 45 ° or less is preferably preheated in vacuum at a temperature of 300 to 700 °.
In the method for evaluating the heating characteristics of the electrostatic chuck using a silicon wafer, after chucking a silicon wafer having a water contact angle of 45 ° or less to the electrostatic chuck, the electrostatic chuck is heated, The temperature distribution and the heating rate of the wafer are observed. The silicon wafer having a water contact angle of 45 ° or less is preferably preheated in vacuum at a temperature of 300 to 700 °.

  By controlling the cleanliness of a wafer that is repeatedly used and defining the cleanliness that can be accurately evaluated, the electrostatic chuck can be evaluated stably and accurately at all times.

  As a result of diligent research by the present inventors, there is a close relationship between the contamination of the wafer surface and the dechucking characteristics of the electrostatic chuck, and as the contamination progresses, the dechucking characteristic deteriorates. It was found that even if an electric chuck was evaluated, a valid evaluation could not be performed. Therefore, by controlling the cleanliness of the inspection wafer used when evaluating the characteristics of the electrostatic chuck and using wafers with a contact angle with water of 45 ° or less, the characteristics of the electrostatic chuck can always be evaluated stably. As a result, the present invention has been made.

  Each time an inspection wafer is used, its cleanliness decreases, and the dechucking characteristics and temperature characteristics of the electrostatic chuck cannot be accurately evaluated. The cause is contamination of the wafer's electrostatic chuck and the applied voltage may not be applied effectively due to the degree of contamination, or the charge will remain even if the application is stopped and the charge will not be immediately removed. is there.

  Therefore, in order to correctly evaluate the electrostatic chuck, it is necessary to perform evaluation using a wafer having a high surface cleanliness. In order to evaluate the cleanliness of the inspection wafer, it is simple and accurate to examine the contact angle with water. If the surface is clean, it is usually about 20 °. However, the degree of cleanliness decreases as the measurement is repeated and the number of treatments increases. For correct evaluation, the contact angle is set to 45 ° or less, more preferably 40 ° or less. If a wafer with a cleanliness exceeding 45 ° is used, the electrostatic chuck cannot be accurately evaluated. That is, when the wafer is released after dechucking, an electrostatic attraction force may remain in part, causing a wafer position shift, and giving an erroneous evaluation to the electrostatic chuck.

  In the case of an electrostatic chuck with a heater, if the cleanliness of the wafer is low, the chucking force becomes weak, and the temperature distribution becomes non-uniform or the temperature rise rate slows down. Can not. Therefore, even in the case of an electrostatic chuck with a heater, it is necessary to make an evaluation by using a wafer with a contact angle with respect to water of the inspection wafer of 45 ° or less and always using a highly clean wafer. The evaluation of the wafer temperature distribution characteristic and the temperature increase rate characteristic of the electrostatic chuck can be performed by embedding a thermocouple at a desired point on the wafer.

  Possible causes of the decrease in the cleanliness of the wafer due to repeated use of the wafer include contamination from an electrostatic chuck, which is an object to be inspected, and contamination during handling by a person. The wafer is handled using a glove for a clean room, and it is considered that contamination due to contact with the glove or human sweat is the largest. For this reason, wafers that are repeatedly used for inspection are handled with great care, but the cleanliness gradually decreases.

Conventionally, wafers used for electrostatic chuck evaluation were each wiped with a clean wiper impregnated with an organic solvent such as isopropyl alcohol, methyl alcohol, or ethyl alcohol. It is difficult to return, and surface contamination accumulates.
It is necessary to recover this to an initial state with a high degree of cleanness. For this, a method of decomposing organic substances adhering to the wafer surface by UV irradiation, ozone water cleaning or the like is effective. In addition, a method of decomposing organic substances by heat treatment in a high temperature vacuum at a temperature of 300 to 700 ° C. is also effective.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to these, Various aspects are possible.

Example 1
Heater function in which a PBN insulator layer is formed on a graphite substrate with a diameter of 300mm and a thickness of 20mm, a conductor layer of pyrolytic graphite (PG) is formed on it, and a PBN dielectric layer with a thickness of about 100μm is formed on it. The dechucking characteristics and temperature characteristics of the attached electrostatic chuck were evaluated by the following procedure.
An inspection wafer having a diameter of 300 mm, a thickness of 0.7 mm, and a contact angle of 19 ° with respect to water was prepared, and thermocouples for temperature distribution measurement were embedded at five locations on the wafer.

  First, the chucking characteristics of the electrostatic chuck were measured at a temperature of 300 ° C. and an applied voltage of 0.3 kV. As a result, the temperature rise rate of the inspection wafer and the temperature distribution between the five points embedded with the thermocouple were good, and the movement of the wafer when releasing after dechucking was smooth. After the measurement was completed, the surfaces of the wafer and the electrostatic chuck were once wiped with isopropyl alcohol, and the same measurement was repeated. After the 15th measurement, when the contact angle of water with the wafer was measured, it was 35 °, and when the contact angle was measured by UV irradiation, it was restored to 22 °. Furthermore, when measured after the 30th measurement, the contact angle was 36 ° and 24 ° after UV irradiation.

  As described above, the cleanliness of the inspection wafer was recovered after the 15th and 30th measurements, and a total of 40 measurements were performed, but a stable measurement value could always be obtained. FIG. 1 shows (1) the first measurement (initial state), (2) the 16th (immediately after cleaning), and (3) the temperature rise curve immediately after the 40th application. It can be seen that the temperature rise rate is stable even after repeated measurement.

(Example 2)
The dechucking characteristics and temperature characteristics of the electrostatic chuck with a heater function were measured. Except that the cleanliness of the inspection wafer was recovered by heat treatment at a temperature of 500 ° C. for about 30 minutes, the measurement was performed according to Example 1, and the wafer was heat-treated after the 15th and 30th measurement, for a total of 40 times. Was measured. As in Example 1, stable measurement results were always obtained.

(Example 3)
The dechucking characteristics and temperature characteristics of the electrostatic chuck with a heater function were measured. The measurement was performed according to Example 1 except that the cleanliness of the inspection wafer was recovered by immersing in ozone water (ozone concentration 0.3 ppm) for 60 minutes. After the 15th and 30th measurement, the wafer was washed with ozone water. Cleaning was performed and a total of 40 measurements were taken. As in Example 1, stable measurement results were always obtained.

(Comparative Example 1)
The measurement was repeated according to Example 1 except that the inspection wafer was not cleaned after the 15th and 30th measurements, and the movement of the wafer during dechucking and release was observed.
When the 33rd measurement was reached, the adsorption force remained when the wafer was released, and it did not peel off smoothly. When the contact angle of this wafer was measured, it was as high as 47 ° and the cleanliness was low.

(Comparative Example 2)
The measurement was repeated according to Example 1 except that the inspection wafer was not cleaned after the 15th and 30th measurements, and the temperature characteristics were evaluated.
FIG. 2 shows temperature rise curves immediately after the application in (1) first measurement, (2) 16th time, and (3) 30th time. It is recognized that the temperature rise rate decreases every time the number of measurements is repeated, and if it is not cleaned, the temperature rise rate drops at the 16th time, and the measured value at the 30th time is not a sufficient temperature rise rate. The value was such that it was judged that there was a problem with the characteristics of. When the contact angle of the wafer at the end of the 30th measurement was measured, it was as high as 47 ° and the cleanliness was low.

Example 4
When the wafer for inspection measured 30 times in Comparative Example 2 was irradiated with UV, the contact angle with water decreased to 25 °. Further, when the temperature characteristics of the cleaned wafer were measured, the temperature rise curve was as shown in FIG. 3, and the initial state could be recovered.

  Even if the inspection wafer is used repeatedly, the electrostatic chuck can always be correctly evaluated.

3 is a graph for evaluating the temperature characteristics of the electrostatic chuck in Example 1. (1) is the first measurement, (2) is the 16th measurement, and (3) is the 40th measurement. It is a graph which evaluates the temperature characteristic of the electrostatic chuck in the comparative example 2, (1) is the first measurement, (2) is the 16th measurement, and (3) is the 30th measurement. 6 is a graph for evaluating temperature characteristics of an electrostatic chuck in Example 3.

Claims (4)

The silicon wafer Te commentary worth method odor dechucking characteristics of the electrostatic chuck using, after a contact angle of water was chucking the silicon wafer is 45 ° or less to the electrostatic chuck, when lifted up by dechucking evaluation method of the electrostatic chuck characterized that you of observing the behavior of the wafer.   The method for evaluating an electrostatic chuck according to claim 1, wherein the silicon wafer having a water contact angle of 45 ° or less is preheated in vacuum at a temperature of 300 to 700 °.   In the method for evaluating the heating characteristics of an electrostatic chuck using a silicon wafer, after chucking a silicon wafer having a water contact angle of 45 ° or less to the electrostatic chuck, the electrostatic chuck is heated to An electrostatic chuck evaluation method characterized by observing the temperature distribution and the heating rate of the electrostatic chuck.   The method for evaluating an electrostatic chuck according to claim 3, wherein the silicon wafer having a water contact angle of 45 ° or less is preheated in a vacuum at a temperature of 300 to 700 °.

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