JPH04271286A - Electrostatic chuck - Google Patents

Abstract

PURPOSE:To provide an electrostatic chuck which can attracts and release a wafer with a force weaker than the attraction force of residual electric charges and to prevent the wafer from cracking or positional shift during conveyance. CONSTITUTION:Through-holes for lift pins or pressurized gas ejection ports 6 are made at a plurality of points in the periphery of a surface for attraction holding an object 3 which is attracted or released by lifting/lowering the lift pins or by ejecting pressurized gas. The object 3 to be attracted is a wafer and the through-holes for the lift pins or the pressurized gas ejection ports 6 are made at corresponding positions on the outside of device forming area on the wafer.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck for suctioning and fixing objects such as wafers. In recent years, as semiconductor manufacturing processes have become drier and wafers have become larger in diameter, highly uniform processing is required, and to achieve this, it is necessary to securely hold the wafer.

[0002] In addition to mechanical and vacuum type holding means, an electrostatic chuck is used as such holding means. Electrostatic chucks have the advantage of improving wafer flatness and can be used in a vacuum.

However, in conventional electrostatic chucks, simply by stopping the application of voltage to the electrodes, the wafer cannot be easily removed due to residual charges, etc. Therefore, countermeasures are required, and various measures have been taken.

The present invention can be used as an electrostatic chuck that can be effectively detached.

[0005]

2. Description of the Related Art Examples of conventional wafer detachment methods include the following. ■Special Publication No. 62-277234 Pressurized gas is ejected between the wafer and the suction surface. ■ Japanese Patent Publication No. 62-120931 A lift pin located in the center of the suction surface lifts up the wafer and removes it.

[0006] However, in the above method (2), since the adsorption force due to residual electric charge etc. is not constant, it is necessary to set a considerably large amount of pressure. Therefore, the wafers were sometimes broken when they were transferred to the transfer tray. or,
The flow of pressurized gas tilted the wafer after it was released from the chuck, making the position at which it was transferred to the transfer tray unstable, and the misaligned wafer could break during transfer.

[0007] In addition, in method (2) above, the wafer is pushed up by the lift pins against the adsorption force due to residual charges, etc., so if the adsorption force is strong, the wafer bounces on the lift pins, causing misalignment, and the misaligned wafer Sometimes it broke during transportation. At this time, even if the speed at which the lift pins are used to push up the wafer is slowed down, the wafer still bounces.

[0008]

[Problem to be Solved by the Invention] In the conventional example, in order to prevent the wafer from shifting or cracking, there was a problem in that if the pressure or pushing force was weakened, the wafer could not be removed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrostatic chuck that can detach a wafer with a force smaller than the adhesion force due to residual electric charges, thereby preventing cracking of the wafer and displacement of the wafer during transportation.

0010

[Means for solving the problem] The solution to the above problem is 1)
A lift pin through-hole or a pressurized gas outlet 6 is provided at multiple locations around the suction surface that holds the adsorbed object 3 by suction, and means is provided for removing the adsorbed object by means of the upper and lower parts of the lift pin or by jetting out pressurized gas. an electrostatic chuck; or 2) the object to be attracted 3 is a wafer, and the through hole of the lift pin or the pressurized gas outlet 6 is provided at a position corresponding to the outside of the device forming area of the wafer;
This is achieved by the electrostatic chuck described in ).

[0011]

[Operation] FIGS. 2(A) and 2(B) are diagrams explaining the principle of the present invention. In the figure, 1 is an electrostatic chuck, 2 is an insulator, and 3 is an electrostatic chuck.
is a wafer, 4 is a tape, and 5 is a spring.

The wafer 3 to which the tape 4 was attached was attracted to the electrostatic chuck 1, the voltage application was stopped, and the wafer was released by pulling with a spring balance to examine the attraction force. In the case of Figure 2 (A) where the tape is attached to the center of the wafer, it is 1k.
The wafer did not come off even if it was pulled with g
It was able to detach with a pull of 200 to 500 g.

[0013] This means that if the wafer is regarded as a rigid body, both forces should be the same, but experimental results show that pushing at multiple points around the wafer requires less force than pushing at the center. It shows.

[0014] Furthermore, as an additional effect, if a through hole for a lift pin or a gas jet port is provided in the periphery of the electrostatic chuck,
Since this position corresponds to an area other than the device formation area (effective chip area) of the wafer, the presence of through holes and gas jets improves cooling efficiency (as devices become smaller, low-temperature etching is increasingly used) It is possible to prevent a decrease in the processing speed and improve the uniformity of processing within the wafer.

[0015]

Embodiment FIGS. 1A and 1B are a plan view and a sectional view illustrating an embodiment of the present invention. In the figure, 1 is an electrostatic chuck, 2 is an insulator, 3 is a wafer, 3A is an effective chip area of the wafer, 6 is a through hole or gas jet port of a lift pin, and 7 is a lift pin.

In this example, lift pin through holes or gas jet ports 6 are provided at four locations around the electrostatic chuck 1, and these are located outside the effective chip area 3A of the wafer.

FIG. 3 is a cross-sectional view of the sample used in the example. In the figure, a thermal oxide film 32 is formed on a wafer 3, and a polysilicon film 3 is formed by chemical vapor deposition (CVD).
2 is grown and a resist film 3 is patterned thereon.
3 was formed.

FIG. 4 shows a conventional reactive ion etching (RIE) apparatus used in the example. Next, we will discuss examples in which the number and position of the through-holes of the lift pins or the gas jet ports 6 are varied in the case where polysilicon is etched using the apparatus shown in Fig. 4 and the sample shown in Fig. 3. I will explain about it.

FIGS. 5A to 5D are plan views illustrating another embodiment of the present invention. In Figure 5(A),
1) After lift pin etching, the lift pin was pushed up to remove the wafers, and when 10,000 wafers were transferred, the wafers were removed reliably and no wafer cracks occurred.

The uniformity of the polysilicon etch rate within the effective chip area was ±7%. 2) When 10,000 wafers were transferred using pressurized gas instead of pressurized gas lift pins, the wafers were removed reliably and no wafer cracking occurred.

[0021] The pressure of the pressurized gas at this time was 3 kg
/cm2 was 0.7 kg/cm2
Met. In Figure 5 (B), 1) After lift pin etching, the lift pins were pushed up to release the wafers, and when 10,000 wafers were transferred, the removal of the wafers was performed reliably and no cracking of the wafers occurred.

In this case, the wafer could be removed more quickly and stably than in FIG. 5(A). The uniformity of the polysilicon etch rate within the effective chip area was ±3%. 2) When 10,000 wafers were transferred using pressurized gas instead of pressurized gas lift pins, the wafers were removed reliably and no wafer cracking occurred. The pressurized gas at this time is also 0.7 kg as in Figure 5(A).
/cm2.

In FIG. 5(C), after etching, the lift pins are pushed up to remove the wafer and the wafer is removed for 10,000 steps.
When the wafers were transported, the wafers could be removed reliably.
No cracking of the wafer occurred.

In this case as well, the wafer could be removed more quickly and stably than in FIG. 5(A). The uniformity of the polysilicon etch rate within the effective chip area was ±6%.

In FIG. 5(D), after etching, the lift pins are pushed up to remove the wafer, and the wafer is removed for 10,000
When the wafers were transported, the wafers could be removed reliably.
No cracking of the wafer occurred.

Furthermore, the uniformity of the polysilicon etch rate within the effective chip area was improved to ±3%.

[0027]

Effects of the Invention: An electrostatic chuck capable of detaching a wafer with a force smaller than the attraction force due to residual electric charge, etc., was obtained, and cracking of the wafer and misalignment during transportation could be prevented.

As a result, the wafer could be removed and transferred reliably in a short time, contributing to improved device productivity.

[Brief explanation of the drawing]

[Fig. 1] A plan view and a cross-sectional view illustrating an embodiment of the present invention.

[Figure 2] Diagram explaining the principle of the present invention

[Figure 3] Cross-sectional view of the sample used in the example

[Figure 4]
Ordinary RIE apparatus used in the examples

FIG. 5 A plan view illustrating another embodiment of the present invention.

[Explanation of symbols]

1 Electrostatic chuck 2 Insulator 3 Wafer 3A Device formation area of wafer (effective chip area)
4 Tape 5 Spring balance 6 Lift pin through hole or gas outlet 7 Lift pin

Claims (2)

[Claims] [Claim 1] Lift pin through-holes or pressurized gas jet ports (6) are provided at multiple locations around the suction surface that holds the adsorbed object (3) by suction, and the lift pin is provided with through holes or pressurized gas jet ports (6) at multiple locations around the suction surface that holds the target (3) by suction. An electrostatic chuck characterized by having a means for releasing an object to be attracted. [Claim 2] The object to be attracted (3) is a wafer,
The lift pin through hole or pressurized gas outlet (6)
2. The electrostatic chuck according to claim 1, wherein the chuck is provided at a position corresponding to the outside of a device forming area of the wafer.