JP3488334B2 - Electrostatic chuck - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck used to hold a wafer such as a semiconductor wafer or a glass substrate in a process of manufacturing a semiconductor device or a liquid crystal substrate. It is about. 2. Description of the Related Art Conventionally, in a manufacturing process of a semiconductor device,
A jig for holding a semiconductor wafer with high precision is used in a film forming apparatus for forming a film on a semiconductor wafer, an etching apparatus for performing fine processing, and an exposure apparatus for performing an electron beam exposure process. Is used as an electrostatic chuck. As this kind of electrostatic chuck, FIG.
(A), a disk-shaped insulating substrate 22 as shown in (b)
In some cases, an electrostatic electrode 23 is provided above the inside of the substrate, and a resistance heating element 24 is buried below the inside. Then, an electric current is applied between the semiconductor wafer 30 placed on the suction surface 25 and the electrostatic electrode 23 so that the insulating base between the wafer 30 and the electrostatic electrode 23 acts as the dielectric layer 22a. The wafer 30 is sucked and held flat on the suction surface 25 by Coulomb force due to dielectric polarization generated between the suction surface 30 and the suction surface 25 and Johnson-Rahbek force due to minute leakage current, and heat is applied to the resistance heating element 24 to generate heat. As a result, the wafer 30 on the suction surface 25 is uniformly heated. A plurality of holes 26 are formed in the periphery of the insulating base 22 as a mechanism for removing the semiconductor wafer 30 having undergone various processing from the suction surface 25 in the electrostatic chuck 21. In some cases, the lift pins 27 protrude from the holes 26 to lift and remove the semiconductor wafer 30 on the suction surface 25 (see Japanese Utility Model Publication No. 3-4037). [0005] However, FIG.
There is a problem in that when the semiconductor wafer 30 that has been processed is removed using the electrostatic chuck 21 shown in (a) and (b), the wafer 30 is damaged by the lift pins 27. That is, in order to remove the wafer 30 from the suction surface 25, it is first necessary to turn off the power supply to the electrostatic electrode 23 to remove the suction force.
Even if F, the charge charged on the suction surface 25 does not immediately disappear, so that a suction force remains, and the semiconductor wafer 30 is lifted without knowing that the residual suction force remains, and is a hard and brittle material. Lift the wafer 30 with the lift pins 2
7 had been damaged. For this reason, the wafer 30 may be removed by adjusting the lift timing of the lift pins 27 by measuring the time required for the residual attraction force to attenuate. However, there has not yet been obtained a device capable of completely controlling the timing of the lift pins 27 under all process conditions because the timing varies with the type of carrier gas, processing temperature, high-frequency voltage, and the like. For this reason, in the conventional electrostatic chuck, the wafer 3
However, there is still a risk that the wafer 30 may be damaged, and when the wafer 30 is damaged, in an automated semiconductor device manufacturing process, there is a problem in that normal processing cannot be performed on the wafer 30 that has been sent next due to broken fragments. there were. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrostatic chuck capable of removing a wafer after various processings without damaging the wafer and notifying an operator or the like when the wafer is damaged. Is to provide. In view of the above problems, the present invention has been made in consideration of the above problems, and has been developed in consideration of the above problem. Is a suction surface for holding a wafer, a groove portion having a depth of 50 to 200 μm in which a corner portion between a tapered side wall surface and a bottom surface is formed in a curved surface, and a gas is supplied to the groove portion. It has a through hole for supplying, an electrostatic electrode at the upper inside of the insulating substrate, a resistance heating element at the lower inside, and a lift pin which can protrude from the suction surface at the periphery of the insulating substrate. A detection unit for detecting a change in gas pressure supplied to the groove, and a control unit for controlling a lift timing of the lift pin based on a signal from the detection unit, below the insulating substrate. When holding the wafer on the attracting surface, to express electrostatic attraction between the wafer by energizing the above electrostatic electrodes,
The wafer is heated by energizing the resistance heating element while supplying the gas to the groove, and the temperature of the wafer is made uniform by detaching the wafer from the suction surface. In some cases, the energization of the electrostatic electrode and the supply of gas are stopped, and when the gas pressure of the detection means reaches a predetermined value, the lift pin is made to protrude from the suction surface based on a signal from the control unit to be separated. Thus, an electrostatic chuck is formed. An embodiment of the present invention will be described below. FIG. 1 is a view showing an electrostatic chuck 1 as an example of an embodiment according to the present invention. FIG. 1A is a perspective view, FIG. An electrostatic electrode 3 is buried above the inside and a resistance heating element 4 is buried below the inside. The suction surface 5 has a groove 8 formed of a concentric groove 8a and a groove 8b extending radially from the center, and a through hole for supplying a gas such as He to the groove 8 is formed in the center. 9 is drilled. The material constituting the insulating substrate 2 includes:
An alumina sintered body, a silicon nitride-based sintered body, and an aluminum nitride-based sintered body can be used, and among these, it is particularly preferable to configure the aluminum nitride-based sintered body having excellent plasma resistance and heat resistance. An introduction pipe 10 for introducing a gas such as He is connected to the through hole 9, and a gas cylinder 14 and a flow control valve 13 for adjusting the flow rate of the gas are provided at the end of the introduction pipe 10. And a detecting means for detecting a change in gas pressure supplied to the groove 8 of the adsorption surface 5 by measuring the pressure in the introduction pipe 10 in the branch pipe 11 branched from the introduction pipe 10. The pressure sensor 12 is provided, and the pressure detected by the pressure sensor 12 is transmitted to the control unit 18 as an electric signal. Further, a plurality of holes 6 are formed in the peripheral edge of the insulating substrate 2, and a driving mechanism (not shown) provided separately in the holes 6.
A lift pin 7 that moves back and forth from the suction surface 5 is arranged, and the lift timing of the lift pin 7 is controlled by a control unit 18. The semiconductor chuck 3 is formed by the electrostatic chuck 1.
0, first, the semiconductor wafer 30
Is placed, and an electric current is applied between the wafer 30 and the electrostatic electrode 3 so that the insulating substrate between the wafer 30 and the electrostatic electrode 3 acts as the dielectric layer 2a. The wafer 30 is sucked and held flat on the suction surface 5 by Coulomb force due to dielectric polarization generated between the wafers and Johnson-Rahbek force due to minute leakage current. In addition, a gas cylinder 14 inserts an inlet pipe 1 into a groove 8 of the suction surface 5.
A gas such as He having good heat transfer characteristics is supplied through the through hole 9 and the through hole 9, and the resistance heating element 4 is energized to generate heat, thereby uniformly heating the wafer 30 on the suction surface 5. I have. The gas pressure supplied to the groove 8 is preferably about 20 Torr, so that high uniformity of the wafer 30 can be obtained. Next, a description will be given of a mechanism for removing the semiconductor wafer 30 that has been subjected to various types of processing using the electrostatic chuck 1 according to the present invention. FIG. 2 is a flowchart showing a process of removing the semiconductor wafer 30 after the processing. First, the energization of the electrostatic electrode 3 and the supply of gas such as He are turned off, and the pressure in the groove 8 (≒ introduction pipe 1
(Pressure within 0) is measured by the pressure sensor 12. That is,
When the power supply to the electrostatic electrode 3 is turned off, the residual suction force gradually decreases, and the gas supplied to the groove 8 flows out of the gap between the semiconductor wafer 30 and the suction surface 5 and the pressure in the groove 8 decreases. This pressure change is measured by the pressure sensor 12. In addition, since the electrostatic chuck 1 according to the present invention has the grooves 8 formed on the suction surface 5, the charge on the suction surface 5 is small, and the responsiveness after the chuck is released can be improved. The controller 18 controls the pressure in the groove 8 to form an infinite loop without applying a lift timing until the pressure in the groove 8 decreases to a predetermined pressure. In this case, the lift pins 7 protrude from the suction surface 5 to push the wafer 30 off the suction surface 5. For example, if the lift timing is set when the pressure in the groove 8 becomes 1/2 or less of the initial pressure of 20 Torr, that is, 10 Torr or less, the suction force hardly remains. Therefore, even if the lift pins 7 protrude from the suction surface 5, the semiconductor wafer 30 can be removed without being damaged. However, regarding the pressure value for applying the lift timing, the wafer 30
The limit value of the pressure in the groove portion 8 at which no breakage occurs may be measured, and the lift timing may be set within this limit value. As described above, by detecting the absolute pressure in the groove 8 by the pressure sensor 12, the lift timing of the lift pin 7 can be easily controlled. If it is necessary to advance the lift timing of the semiconductor wafer 30 for the sake of work, the time until the pressure in the groove 8 becomes zero when the semiconductor wafer 30 is lifted is measured. By comparing with the time when the semiconductor wafer 30 is normally lifted, it is possible to detect whether or not the wafer 30 is damaged.
That is, when the semiconductor wafer 30 is normally lifted, it takes some time until the pressure in the groove 8 becomes zero, whereas when the semiconductor wafer 30 is damaged during the lift, the pressure in the groove 8 is reduced for a short time. Therefore, the presence or absence of breakage of the wafer can be easily detected by comparing these times. In the above embodiment, the lift timing of the lift pin 7 is controlled by the absolute pressure in the groove 8. However, the pressure in the chamber and the pressure in the groove 8 are detected, and the differential pressure between the two is detected. May be measured to control the lift timing of the lift pins 7.
That is, if the lift timing is applied when the pressure difference between the pressure in the chamber and the pressure in the groove 8 becomes substantially zero, the residual suction force generated between the wafer 30 and the suction surface 5 is substantially reduced. Since it is zero, the wafer 30 can be removed without damaging it. However, the depth T of the groove 8 of the suction surface 5 is an important requirement for detecting the gas pressure in the groove 8 by the pressure sensor 12 and confirming whether or not the wafer 30 is damaged. That is, the depth T of the groove 8 of the suction surface 5 is 50 μm.
m, the gas pressure in the groove 8 decreases slowly even if the wafer 30 is damaged.
This is because it is not possible to detect the presence or absence of damage. However, if the depth T of the groove 8 is greater than 200 μm, when the electrostatic chuck 1 is heated, heat stress may be concentrated at the bottom corner of the groove 8 to cause cracks and the like. The heat uniformity decreases. Therefore, the depth T of the groove 8 is 50 to 20.
Preferably, it is provided in a range of 0 μm. The cross-sectional shape of the groove 8 formed on the suction surface 5 is such that the side wall 15 constituting the groove 8 as shown in FIG. Preferably, the corner portion 17 is formed in a curved shape. With such a structure, it is possible to prevent the corner portion 17 from cracking due to thermal stress concentration. Preferably, the groove 8 has a sectional shape having the following relationship, where L is the width, and Z is the angle of the side wall surface 15. [Relational Expression] L> T, Z <60 ° By forming the corner portion 17 and the bottom surface 16 integrally in a curved shape, the thermal stress concentration can be further suppressed. In the embodiment of the present invention, the electrostatic chuck 1 used in the manufacturing process of the semiconductor device has been described. However, the electrostatic chuck 1 may be used for holding a glass substrate constituting a liquid crystal substrate or other articles by suction. Needless to say, it can also be used as the electrostatic chuck 1 that performs the operation. Here, FIG. 1 shows a case where grooves 8 having different depths T are provided.
Was prepared, the semiconductor wafer 30 held by suction was forcibly lifted by the lift pins 7, and the pressure change in the groove 8 when the semiconductor wafer 30 was damaged was measured. The electrostatic chuck 1 used in this experiment had an outer diameter of 2
It has a disk shape of 00 mm and a substrate thickness of 15 mm, and the width of the groove 8 formed on the suction surface 5 is 80 μm. The pressure of the He gas supplied to the groove 8 of the suction surface 5 is set to 20 torr, and the lift pin 7
The time required for the gas pressure in the introduction pipe 10 to become zero when the semiconductor wafer 30 was normally lifted was about 1.5 to 2.0 sec. The results are as shown in Table 1. [Table 1] As a result, in the samples A and B, since the depth T of the groove 8 is less than 50 μm, the time until the gas pressure in the introduction pipe 10 becomes zero when the wafer 30 is forcibly damaged is reduced. It is understood that the presence or absence of breakage of the wafer 30 cannot be determined, which is almost the same as the time when the semiconductor wafer 30 is normally lifted, which is about 1.2 to 1.8 seconds. On the other hand, in the samples C and D, since the depth T of the groove 8 is set to 50 μm or more, the wafer 30
When the gas pressure in the introduction pipe 10 becomes zero when the semiconductor wafer 30 is forcibly broken, the gas pressure immediately drops to 0.4 sec or less, which is apparently the time when the semiconductor wafer 30 is normally lifted. , And the presence or absence of breakage of the wafer 30 can be detected. Therefore, the groove 5 formed on the suction surface 5
It can be understood that if the depth T is 50 μm or more, the breakage of the wafer 30 can be easily detected. As described above, according to the present invention, the upper surface of the insulating substrate made of any one of the alumina sintered body, the silicon nitride based sintered body, and the aluminum nitride based sintered body can be used as a wafer. A groove having a depth of 50 to 200 μm in which a corner portion between a tapered side wall surface and a bottom surface is formed into a curved surface, and a gas supplied to the groove portion. The insulating substrate is provided with an electrostatic electrode above the inside thereof, a resistance heating element below the inside thereof, and a lift pin protruding from the suction surface at the periphery of the insulating substrate. Below the substrate, there is provided a detecting means for detecting a change in the pressure of the gas supplied to the groove, and a control unit for controlling the lift timing of the lift pins based on a signal from the detecting means. On the surface When holding the wafer, the electrostatic electrode is energized to develop an electrostatic attraction force between the wafer and the wafer, and is attracted to the suction surface, and the resistive heating element is energized to heat the wafer. Gas is supplied to the groove to make the temperature of the wafer uniform, and when the wafer is separated from the suction surface, the supply of electricity and gas to the electrostatic electrode is stopped, and the gas pressure of the detection means is reduced. When the predetermined value is reached, the lift pin is made to protrude from the suction surface based on a signal from the control unit and is released to form an electrostatic chuck, so that the wafer having undergone various types of process processing can be removed from the suction surface. The wafer can be removed without being damaged by the lift pins, and even if the wafer is forcibly removed when it is forcibly removed, the presence or absence of damage can be easily detected. In addition, even if the resistance heating element generates heat, the insulating substrate is not damaged.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing an electrostatic chuck according to the present invention;
(A) is a perspective view, (b) is the XX line sectional view. FIG. 2 is a flowchart illustrating a wafer removing step in the electrostatic chuck according to the present invention. FIG. 3 is an enlarged view showing a cross-sectional shape of a groove of the electrostatic chuck according to the present invention. 4A and 4B are views showing a conventional electrostatic chuck, in which FIG. 4A is a perspective view, and FIG. 4B is a sectional view taken along line YY. [Description of Signs] 1 ... Electrostatic chuck 2 ... Insulating substrate 3 ...
・ Electrostatic electrode, 4 ・ ・ ・ resistance heating element, 5 ・ ・ ・ adsorption surface,
6 ... Hole, 7 ... Pin, 8 ... Groove, 9.
..Through holes, 10 ・ ・ ・ Introduction pipe, 11 ・ ・ ・ Branch pipe, 12 ・
..Pressure sensors, 13 ... Flow control valves, 14 ... Gas cylinders

Claims (1)

(57) [Claim 1] The upper surface of an insulating substrate made of any one of an alumina sintered body, a silicon nitride based sintered body, and an aluminum nitride based sintered body is used as a suction surface for holding a wafer. , On the adsorption surface,
A groove having a depth of 50 to 200 μm in which a corner between a tapered side wall surface and a bottom surface is formed in a curved surface, and a through hole for supplying gas to the groove, In addition to the above, an electrostatic electrode is provided, a resistance heating element is provided below the inside, a lift pin protruding from the suction surface is provided on the periphery of the insulating substrate, and a gas pressure supplied to the groove is provided below the insulating substrate. Detecting means for detecting a change in the pressure, and a control unit for controlling the lift timing of the lift pins based on a signal from the detecting means. When the wafer is held on the suction surface, the electrostatic electrode To generate an electrostatic attraction force between the wafer and the wafer, to cause the wafer to be attracted to the suction surface, and to heat the wafer by energizing the resistance heating element , and supply gas to the groove. Wafer temperature The result so as to equalize, when disengaging the wafer from the suction surface, deenergized and the supply of gas to the electrostatic denden pole, from the control unit when the gas pressure of the detection means becomes a predetermined value An electrostatic chuck characterized in that the lift pin is made to protrude from the suction surface and is released based on the signal of (1).