JP2002222850A - Method for detaching attracted object in electrostatic chuck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for detaching an attracted object, which is capable of reliably detaching it from an electrostatic chuck. SOLUTION: A wafer 14 is held by attraction on an electrostatic chuck 11 by applying a voltage between the wafer 14 and the electrostatic chuck 11. After the wafer 14 is processed, the wafer 14 is detached from the electrostatic chuck 11 by applying a reverse bias voltage, whose polarity is opposite to the voltage applied before between the wafer 14 and the electrostatic chuck 11. The voltage or the applied time of the reverse bias voltage is varied as the time elapses depending on the number of wafers 14 that are processed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing a wafer from the electrostatic chuck in a semiconductor manufacturing apparatus that uses an electrostatic chuck to suction-hold the wafer when processing the wafer, for example. It is.

[0002]

2. Description of the Related Art A conventional method for releasing an object to be attracted such as a wafer in an electrostatic chuck is disclosed in, for example,
No. 544 discloses one. FIG. 8 is a diagram showing a configuration of an electrostatic chuck to which a conventional method of detaching an object to be adsorbed is applied. In the figure, 1 is a disk-shaped conductor, 2 is a dielectric provided on the outer surface of the conductor 1, 3 is an adsorbed object such as a wafer, 4 is an electrostatic cylinder, 4a is a pressing member, 5 is A first DC power supply, 6 is a second DC power supply, 7 is a power switch, 8 is a ground switch, and 9 is a control unit.

Next, the operation will be described. When the object to be sucked 3 is sucked and held by the electrostatic chuck having the above configuration, the object to be sucked 3 is first placed in close contact with the surface of the dielectric 2. The conductor 1 is connected to a first DC power supply and is in a positively charged state. When a part of the object 3 is connected to the ground via the grounding switch 8 in such a state, an electrostatic force is generated between the conductor 1 and the object 3, and the object 3
Is held by suction. In order to remove the object 3 from the electrostatic chuck after the object 3 held by suction is subjected to a processing such as a film forming process or an etching process, a signal is first sent from the control unit 9 to the power switch 7. The conductor 1 is connected to the second DC power supply 6 and changes from a positively charged state to a negatively charged state. A DC voltage (reverse bias) is applied. After reducing the electrostatic force in this way, a signal is issued from the control unit 9 to the solenoid S. When the solenoid S is energized, the electromagnetic cylinder 4 operates to move the pressing member 4a in a direction protruding from the surface of the dielectric 2, and the object 3 is pressed in a direction to separate from the dielectric surface. In this way, a reverse bias is applied between the conductor 1 and the object 3 in the direction opposite to the direction of the adsorption, the electrostatic force between the two is reduced, the adsorption force is reduced, and the object 3 is separated from the object 3. When a force is applied, the substance to be adsorbed can be quickly separated with a slight separation force.

[0004]

The method of detaching an object to be adsorbed such as a wafer in a conventional electrostatic chuck has been performed as described above. However, in some semiconductor manufacturing apparatuses, the state of adsorption of the object to be adsorbed is determined. It changes over time, and the preset values for the reverse bias (voltage value, application time, etc.) become unsuitable, and the wafer is displaced, dropped, or cracked in an attempt to release the wafer while the residual suction force is large. There is a problem that the abnormal detachment occurs. In addition, the apparatus is stopped to cope with such abnormalities, which is a major factor in reducing the productivity of the apparatus.

For example, in a dry etching apparatus, reaction products adhere to a processing chamber as the number of processed wafers increases. When a reaction product adheres to the chamber, the plasma impedance changes. In that case, the chucking voltage applied for chucking the wafer changes, and the required reverse bias also changes. When the voltage changes, the suction characteristics of the electrostatic chuck change.

Further, a part of the reaction product adheres to the surface of the electrostatic chuck. The reaction product forms the electrical characteristics between the electrostatic chuck and the object (dielectric constant, resistivity, etc.)
And, consequently, the electrical characteristics of the electrostatic chuck. As the reaction product gradually increases depending on the number of processed wafers, the electric characteristics of the electrostatic chuck also change with time, and the suction state of the wafer changes with time. Therefore, even if a predetermined reverse bias is applied, the residual attraction force cannot be reduced, and the wafer cannot be stably released.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a detaching method capable of stably detaching an object such as a wafer from an electrostatic chuck. An object of the present invention is to prevent the apparatus from being stopped due to a problem such as a wafer shift, a wafer drop, or a wafer crack due to an unstable wafer detachment, and to increase the productivity of the apparatus.

[0008]

According to the method of the present invention, a voltage is applied between an object to be attracted and the electrostatic chuck, and the object is attracted to and held by the electrostatic chuck. Then, after the object to be processed is processed, a reverse bias having a polarity opposite to the applied voltage is applied between the object to be attracted and the electrostatic chuck to cause the object to be detached from the electrostatic chuck. At this time, the voltage value of the reverse bias or the application time of the reverse bias is changed with time according to the number of processed workpieces.

Further, in the method for detaching an object to be adsorbed in the electrostatic chuck according to the present invention, in the above-mentioned detaching method, a reverse bias voltage value or a reverse bias application time necessary for detaching the object to be adsorbed is previously set to the number of processed sheets. Based on the relationship between the number of processed sheets obtained and the obtained reverse bias voltage value or reverse bias application time, the reverse bias voltage value or reverse bias application time applied at the time of detachment is changed over time. It is a thing which changes it.

The method of releasing an object to be adsorbed in the electrostatic chuck according to the present invention is the method of the above-mentioned method, wherein the pressure of the heat transfer promoting gas introduced between the object to be adsorbed and the electrostatic chuck or the pressure of the adsorbed object is increased. Current value between the object and the electrostatic chuck,
Alternatively, by detecting the capacitance value between the object to be attracted and the electrostatic chuck and measuring the adsorption state of the object to be attracted, the reverse bias voltage or reverse bias required for detachment of the object to be attracted is detected. The application time is measured.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of an electrostatic chuck used in a dry etching apparatus according to Embodiment 1 of the present invention. In the figure,
11 is an electrostatic chuck, 12 is an electrode, 13 is a dielectric film provided on the electrode surface, 14 is a wafer as an object to be adsorbed, 15
Is a power supply, 17 is a plasma, 18 is He gas, 19 is a pressure sensor, 20 is a conductance valve, and 21 is a computer. In the drawings, the wafer transfer system, the entire chamber, the plasma generator, and the like are not shown.

The electrostatic chuck 11 is formed by forming a dielectric film 13 on an aluminum electrode 12 serving as a base material by a ceramic plasma spraying method. A wafer 14 is placed on this, and a voltage is supplied from a power supply 15. Wafer 1
4 is connected to the ground via the plasma 17,
A voltage is applied between the wafer 14 and the electrode 12, and the dielectric film 13 is dielectrically polarized, so that the wafer 14 is suction-held by the electrostatic chuck 11. On the back surface of the wafer 14, the wafer 1 is used for processing such as dry etching.
A heat transfer gas (He gas 18) is introduced to improve heat transfer to the heat transfer member 4. He gas 18 is maintained at a constant pressure by a pressure sensor 19 and a conductance valve 20. These controls are collectively performed by the computer 21.

FIG. 2 shows the transition of the voltage applied to the wafer and the pressure of the He gas 18 on the back surface of the wafer during the processing of the apparatus. During the processing, a suction voltage (suction voltage value V1) is applied to attract the wafer, but when the processing is completed, a reverse bias (voltage value V2) having a polarity opposite to the suction voltage is applied, and the remaining voltage is applied. Attempts to reduce the suction force quickly. Further, after the processing is completed, the conductance valve 20 is closed, and the He gas 18 on the back surface of the wafer is sealed. By doing so, the He gas 18 leaks from the back surface of the wafer due to a decrease in the residual suction force of the electrostatic chuck, and the pressure decreases. By monitoring the pressure with the pressure sensor 19, it is determined whether the residual suction force has decreased. A constant value (Δ
When the pressure decreases by P), it is determined that the residual suction force has decreased, and the time from the end of the processing until the pressure decreases by ΔP is referred to as the charge removal time Td. If the charge elimination time Td is short, it means that the residual adsorptive force has been rapidly reduced. Conversely, if the rate of decrease of the residual attraction force is very slow or does not decrease at all, the neutralization time Td becomes longer.

In order to stably detach the wafer, it is necessary to optimally set the static elimination parameters (reverse bias voltage value V2, reverse bias application time T2). FIG. 3 shows the relationship between the reverse bias application time T2 and the static elimination time Td when the reverse bias voltage value V2 is fixed. The static elimination time (≒ residual adsorption force) approximately draws a quadratic curve with respect to the reverse bias application time T2. The point at which this curve has the minimum value is the optimum value T2 'of the reverse bias application time.

However, the optimum reverse bias application time T2 '
Is not always constant. In some semiconductor manufacturing apparatuses, the wafer suction state changes with time, and the preset static elimination parameters become unsuitable, and the wafer is displaced, dropped, or removed in an attempt to release the wafer while the residual suction force is large. Abnormal detachment such as cracking has occurred, and the device has to be stopped for countermeasures, which has been a major factor in lowering the productivity of the device. For example, in this dry etching apparatus, as the number of processed wafers increases, reaction products adhere to the processing chamber. When a reaction product adheres to the chamber, the plasma impedance changes. As a result, wafer 1
The suction voltage applied between the electrode 4 and the electrode 12 changes, and similarly, the reverse bias voltage also changes. When these voltages change, the chucking characteristics of the electrostatic chuck change. Further, a part of the reaction product adheres to the surface of the electrostatic chuck. The reaction product changes the electrical characteristics (dielectric constant, resistivity, etc.) between the electrostatic chuck and the object to be attracted, and as a result, changes the electrical characteristics of the electrostatic chuck. The reaction product gradually increases depending on the number of processed wafers, so that the adsorption state of the wafer changes over time.

FIG. 4 shows a change in the optimum reverse bias application time T2 'with respect to the number of processed wafers after the periodic maintenance. As shown in the figure, the optimum reverse bias application time T2 '
Varies depending on the number of processed wafers. Therefore, if the reverse bias application time is set at the beginning of the number of processed wafers and is used continuously with the same reverse bias application time, the optimum reverse bias application time T2 'becomes longer as the number of processed wafers increases. In addition, the charge is not sufficiently removed, and the residual adsorption force increases. However, if the static elimination parameter (here, reverse bias application time) is changed according to the number of processed wafers according to the curve shown in FIG. 4, the optimal reverse bias application time T2 'will always be used.

Therefore, the relationship of FIG. 4 is expressed as a mathematical expression as follows. T2 '= a + b · n c where, T2'; optimum reverse bias application time n; regular after maintenance wafer processing sheets a, b, c; constants (a = 8.970, b = 0.122
8, c = 0.438) (However, V2 = 600V fixed)

The reverse bias application time T according to the above equation
2 ′ is controlled by the control computer 21 so as to change over time. The control computer 21 previously stores several sets of constants a, b, and c determined from the relationship between the static elimination parameter measured according to the type of wafer to be processed and the number of processed wafers. For example, it is possible to cope with different types of processed wafers and different degrees of change with time. This makes it possible to always use the optimal reverse bias application time regardless of the number of processed wafers and the type of wafer to be processed, and to stably release the wafer.

Further, in the present embodiment, the relationship between the number of processed wafers and the optimum reverse bias application time is represented by an exponential relationship.
When the relationship between the number of processed wafers and the optimal reverse bias application time is expressed by another equation, the same effect can be obtained by controlling the reverse bias application time using an equation that best represents the relationship. it can.

Embodiment 2 In the first embodiment, the reverse bias application time to be applied at the time of detachment is changed according to the relational expression between the previously measured optimal reverse bias application time and the number of processed workpieces. It is also possible to stably release the wafer by changing the reverse bias application time applied during the release stepwise based on the relationship between the application time and the number of processed wafers.

In the case of processing a wafer in the same dry etching apparatus as in the first embodiment, if the allowable static elimination time Td is set to 20 seconds or less, the range of the reverse bias application time T2 is optimal according to FIG. Reverse bias application time T
3 seconds around 2 '. Therefore, when the wafer is detached, the optimal reverse bias application time T2 'is not applied strictly in accordance with the number of processed wafers, but is applied for detachment as shown in Table 1 and FIG. 5 (shaded area). When the reverse bias application time T2 is divided stepwise according to the number of processed wafers, control becomes easy. That is, in the state shown in FIG. 3, the optimal reverse bias application time T2 'is 10.5 seconds, but since the static elimination time is 20 seconds or less for 3 seconds centering on 10.5 seconds, the optimal reverse bias application time T2' is 10.5 seconds. The number of processed wafers in which the time T2 ′ is 12 seconds from 9 seconds (0 to 0 in FIGS. 4 and 5)
In the case of (1500 sheets), the reverse bias application time T2 applied for detachment may be 10.5 seconds. Similarly, assuming that the reverse bias application time T2 is 12.5 seconds, the optimal reverse bias application time T2 'is 14 seconds from 11 seconds when the number of processed wafers (700 to 4800 in FIGS. 4 and 5). The reverse bias application time T2 applied for separation is set to 1
It may be 2.5 seconds. Thus, based on the range of the number of processed wafers allowed by each reverse bias application time T2,
The reverse bias application time T2 applied for detachment is changed according to the number of processed wafers at intervals (here, two-second intervals) within a range in which one reverse bias application time can be detached. In Table 1 and the shaded portion in FIG. 5, there is shown an example in which the reverse bias application time is divided stepwise according to the number of processed wafers.

[0022]

[Table 1]

As in the first embodiment, the control computer 21 can store several types of stepwise reverse bias application time change setting patterns as shown in Table 1 depending on the type of wafer to be processed. For example, even if the degree of change with time differs depending on the processing wafer, the wafer can be stably detached.

Embodiment 3 FIG. In the first and second embodiments, the reverse bias application time T2 is used as the static elimination parameter, the reverse bias voltage value V2 is fixed, and the reverse bias application time T2 applied at the time of separation is changed with time according to the number of processed workpieces. Even if the reverse bias voltage value V2 is used as the static elimination parameter, the reverse bias application time T2 is fixed, and the reverse bias voltage value V2 is changed with time according to the number of processed workpieces, the wafer can be stably released. Can be.

FIG. 6 shows a change in the optimum reverse bias voltage value V2 'with respect to the number of processed wafers after the periodic maintenance when the reverse bias application time is fixed. The relationship between the optimum reverse bias application time and the number of processed wafers shown in FIG. 6 is measured in advance, and a relational expression thereof is obtained, and the wafer processing is performed according to the above relational expression from which the static elimination parameter (here, the reverse bias voltage value) is obtained. If it is changed according to the number of wafers, the optimum reverse bias voltage value V2 'can always be used, and the wafer can be stably detached.

The relationship shown in FIG. 6 is expressed by the following equation. 'Here ^{= d + e · n f,} V2'V2; optimum reverse-bias voltage value n; regular after maintenance number of processed wafers d, e, f; constant (d = 472, e = 10.10 , f =
0.387) (However, T2 = 11 seconds fixed)

The reverse bias voltage value V2 'according to the above equation
Is controlled by the control computer 21 to change over time. The control computer 21 includes:
By storing in advance several sets of constants d, e, and f determined from the relationship between the static elimination parameters measured according to the type of wafer to be processed and the number of processed wafers, the type of wafer to be processed is stored. However, even if the degree of change with time is different, it is possible to respond. By doing so, the optimum reverse bias voltage value can always be used regardless of the number of processed wafers and the type of wafer to be processed, and the wafer can be stably detached.

Further, as in the first embodiment, in this embodiment, the relationship between the number of processed wafers and the optimum reverse bias voltage value is represented by an exponential relationship. When the relationship between the number of processed wafers and the optimum reverse bias voltage value is expressed by another formula, the same effect can be obtained by controlling the reverse bias voltage value using the formula that best represents the relationship. Can be obtained.

Further, in the present embodiment, the reverse bias voltage value to be applied at the time of detachment is changed in accordance with the relational expression between the optimum reverse bias voltage value and the number of processed sheets measured in advance. Based on the relationship between the optimum reverse bias voltage value and the number of processed wafers, the wafer can be stably released by changing the reverse bias voltage value applied at the time of release stepwise similarly to the second embodiment. be able to.

Embodiment 4 In each of the above embodiments, the pressure of the heat transfer gas introduced between the wafer and the electrostatic chuck is detected by the pressure sensor 19 to measure the suction state of the wafer. The reverse bias voltage value or the reverse bias application time required for detachment of the wafer was measured by determining whether the residual attraction force was reduced. A method of measuring a capacitance value may be used.

When the determination is made based on the current value, a device capable of measuring a current is attached to a power supply circuit for applying a voltage to the electrostatic chuck, and when the current during the processing is measured, the current value I shows a behavior as shown in FIG. . FIG. 7 shows the variation of the current value in comparison with the variation of the He gas pressure value shown in the first embodiment. In this embodiment, when the reverse bias voltage value V2 is applied and the current value immediately after cutting the V2 falls below a certain value (ΔI), it is determined that the residual suction force has decreased, and after the V2 is cut. The time from the end point of the processing when ΔI is reached is defined as the charge elimination time Td.

When the determination is made based on the capacitance, a device capable of measuring the capacitance is attached separately from the power supply circuit for applying the voltage to the electrostatic chuck. The device for measuring the capacitance applies a constant frequency (1 kHz or the like) to the electrostatic chuck to determine the capacitance, and does not affect the attraction force and the residual attraction force. When the wafer is attracted to the electrostatic chuck, the electrostatic chuck and the wafer come into close contact with each other, and the capacity increases. Conversely, if the residual attraction force is reduced and the wafer is not attracted, the wafer will not adhere to the electrostatic chuck and the capacitance will be reduced. Therefore, by observing the capacitance, it can be determined whether or not the wafer has been detached. When the capacitance value during the processing is measured, the capacitance value C behaves as shown in FIG. In this case, when the capacitance value after applying the reverse bias voltage value V2 and cutting off the V2 falls below a certain value (ΔC), it is determined that the residual suction force has decreased, and the capacitance value is reduced by ΔC. The time from the end point of the processing at the time of the decrease is defined as the static elimination time Td.

[0033]

As described above, according to the method for detaching an object to be attracted from the electrostatic chuck according to the present invention, a voltage is applied between the object to be attracted and the electrostatic chuck, and the object to be attracted is moved to the electrostatic chuck. After processing the object to be attracted by suction and holding it, a reverse bias having a polarity opposite to the applied voltage is applied between the object to be attracted and the electrostatic chuck, and the object to be attracted is electrostatically chucked. At the time of further detachment, the voltage value of the reverse bias or the application time of the reverse bias is changed with time according to the number of processed workpieces of the adsorption object, so that abnormal detachment of the adsorption object can be prevented. This has the effect of improving the productivity of the processing apparatus.

According to the method for releasing an object to be adsorbed in an electrostatic chuck according to the present invention, in the above-mentioned method for releasing the object, a reverse bias voltage value or an application time of the reverse bias necessary for releasing the object to be adsorbed is previously processed. Based on the relationship between the number of processed sheets obtained and the obtained reverse bias voltage value or reverse bias application time or reverse bias application time, a reverse bias voltage value or reverse bias application time to be applied at the time of separation is obtained. Is changed over time, so that there is an effect that the object to be sucked can be stably released in response to the fluctuation of the residual suction force according to the number of processed wafers.

In the method for releasing an object to be adsorbed in the electrostatic chuck according to the present invention, the pressure of the heat transfer promoting gas introduced between the object to be adsorbed and the electrostatic chuck, Current value between the object and the electrostatic chuck,
Alternatively, by detecting the capacitance value between the object to be attracted and the electrostatic chuck and measuring the adsorption state of the object to be attracted, the reverse bias voltage or reverse bias required for detachment of the object to be attracted is detected. Since the application time is measured, the adsorption state can be easily and accurately measured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an outline of an electrostatic chuck used in a dry etching apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing changes in voltage applied to a wafer and He gas pressure on the back surface of the wafer during processing in the dry etching apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a reverse bias application time and a charge removal time in the dry etching apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a change in an optimum reverse bias application time with respect to the number of processed wafers in the dry etching apparatus according to the first embodiment of the present invention;

FIG. 5 is a diagram for explaining a wafer detaching method according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a change in an optimum reverse bias voltage value with respect to the number of processed wafers in the dry etching apparatus according to the third embodiment of the present invention.

FIG. 7 is a diagram showing changes in a voltage applied to a wafer, a He gas pressure on a back surface of the wafer, a current, and a capacitance value during processing in the dry etching apparatus according to the fourth embodiment of the present invention. FIG. 4 is a diagram illustrating a relationship between a reverse bias application time and a charge removal time.

FIG. 8 is a configuration diagram showing an outline of a conventional electrostatic chuck.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 conductor, 2 dielectric, 3 adsorbed object, 4 electrostatic cylinder, 4 a pressing member, 5 first DC power supply, 6 second
DC power supply, 7 power switch, 8 ground switch, 9 control unit, 11 electrostatic chuck, 12 electrodes, 1
3 Dielectric film, 14 wafer, 15 power supply, 17 plasma, 18 He gas, 19 pressure sensor, 20 conductance valve, 21 computer.

Claims (5)

[Claims] 1. A voltage is applied between an object to be attracted and an electrostatic chuck to attract and hold the object to be attracted to the electrostatic chuck to process the object to be attracted. When applying a reverse bias having a polarity opposite to the applied voltage between the electric chucks to separate the object from the electrostatic chuck, the reverse bias voltage value or the reverse bias application time is set to A method for releasing an object to be attracted from an electrostatic chuck, wherein the method is changed over time according to the number of processed objects to be attracted. 2. A reverse bias voltage value or reverse bias application time required for detachment of an object to be adsorbed is determined in advance in accordance with the number of processed workpieces, and the obtained number of processed workpieces and the reverse bias voltage value or reverse bias voltage are determined. 2. The electrostatic chuck according to claim 1, wherein the voltage value of the reverse bias applied during the detachment or the reverse bias application time is changed with time based on a relationship with the bias application time. How to remove things. 3. A method for detecting the pressure of a heat transfer promoting gas introduced between an object to be adsorbed and an electrostatic chuck and measuring the state of adsorption of the object to be adsorbed, so that the object to be adsorbed is released. 3. The method according to claim 2, wherein a required reverse bias voltage value or reverse bias application time is measured. 4. A reverse bias voltage value required for detachment of the object by detecting a current value flowing between the object and the electrostatic chuck and measuring an adsorption state of the object. 3. The method according to claim 2, wherein the application time of the reverse bias is measured. 5. A reverse bias voltage required for detachment of the object by detecting a capacitance value between the object and the electrostatic chuck and measuring an adsorption state of the object. 3. The method according to claim 2, wherein the value or the application time of the reverse bias is measured.