Measuring and testing – Testing of apparatus
Reexamination Certificate
1996-05-29
2001-10-09
Kwok, Helen (Department: 2856)
Measuring and testing
Testing of apparatus
Reexamination Certificate
active
06298737
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the testing and maintenance of semiconductor processing equipment. The present invention especially relates to the testing and maintenance of etching devices.
Etchers such as LAM Research 9600 available from the LAM Research Corporation of Fremont, Calif., use a wafer clamp to hold a wafer in position during processing.
FIG. 1
is a partial cross-sectional view of prior etcher
10
, including a wafer clamp
12
, wafer
14
, and bottom electrode
16
. This diagram exaggerates the curvature of the bottom electrode
16
and is not to scale. The wafer
14
is positioned in the etcher by a robotic handler (not shown). The wafer clamp
12
comes down and holds the wafer
14
against the bottom electrode
16
. An overlap
18
between the wafer clamp
12
and the wafer
14
is usually kept relatively small so that the largest possible area of the wafer
14
is available to be processed. In etchers such as the LAM Research 9600 series, helium gas flows around the back side of the wafer
14
to cool the wafer
14
during the etching.
One problem that has occurred during processing is that the photoresist on the wafer
14
can melt when excess heat accumulates on the wafer
14
. Melted photoresist will prevent the circuit pattern from being accurately etched onto the wafer
14
. This will cause the failure of the wafer
14
. Failure caused by melted photoresist is not immediately noticeable; the wafer
14
will go through additional processing steps and other wafers will be improperly processed in the etcher. The damaged wafers and wasted processing time can produce a considerable expense.
There is thus a need for a better approach for evaluating the extent of wear of a wafer clamp that is more reliable and less cumbersome.
SUMMARY OF THE INVENTION
It has been found that the wearing of the wafer clamp can cause the overlap between the clamp and the wafer to decrease. In most etchers, including LAM Research etchers, helium backside wafer cooling is done by supplying a fixed helium pressure to the backside of the wafer. Heat is transferred from the backside of the wafer to the helium. When the wafer clamp has worn so that the overlap distance between the clamp and the wafer is decreased, a greater amount of the helium gas will leak out at an undesirable rate, thereby adversely affecting the backside cooling of the wafer. The wafer processing machine will in turn increase the level of helium supplied to the backside in order to maintain a fixed pressure. However, the helium will flow past the backside of the wafer too quickly for effective heat transfer. The wafer can heat up to a temperature that causes the resist material to melt, resulting in the failure of the process discussed above.
Worn wafer clamps also contribute to the misalignment of the wafer on the electrode. The misalignment can result in a non-uniform cooling of the wafers affecting the product yield.
The wear on a wafer clamp is generally not noticeable merely with visual inspection. One way to measure the size of the opening on the wafer clamps to detect wear is with calipers. It is difficult for the user to position the calipers so that they correctly measure the inner diameter of the wafer clamp. The use of calipers also relies heavily upon the judgment and skill of the person making the measurement. Therefore, the caliper method does not provide consistent results among different measurements.
The present invention concerns a testing object with a shape that can be used to distinguish between a worn wafer clamp and a wafer clamp that is suitable for use. If the opening of the wafer clamp slips past an upper portion of the testing object, the wafer clamp is considered to be unsuitable for use and is replaced. If the opening of the wafer clamp cannot slip past an upper portion of the testing object, the wafer clamp is considered to be suitable for use in the semiconductor processing machine.
A wafer clamp is determined to be worn when the overlap distance between the wafer and the wafer clamp is reduced from the initial overlap distance. In a preferred embodiment, if the overlap distance of a wafer clamp is reduced to 1 millimeter or less from an initial overlap distance of 1.5 millimeters, the wafer clamp is determined to be worn. The wafer clamp should be removed from the semiconductor processing machine before the overlap distance is reduced to 0.5 millimeters. Wafer clamps with an overlap distance of 0.5 millimeters have been found to cause some of the problems discussed above.
In a preferred embodiment, the testing object is circular except for a chord cut portion. The chord cut portion maintains a gap between the wafer clamp and the testing object at the chord cut portion. This gap ensures that the chord cut portion of the testing object will not affect the wear test.
The testing object preferably has an angled portion which helps position the wafer clamp with the center of the wafer clamp at the center of the testing object. The testing object can also be mounted on a base. The base can include guiding pins which help position the wafer clamp about the testing object.
The testing object can be used to test the wear of wafer clamps as part of the regular maintenance of the semiconductor processing machine. The wafer clamp is removed from the semiconductor processing machine, and placed on the testing object. If the testing object passes through the center of the wafer clamp, the wafer clamp is replaced. If the testing object does not pass through the center of the wafer clamp, the wafer clamp is not replaced, but put back onto the semiconductor processing machine.
REFERENCES:
patent: 4429464 (1984-02-01), Burrus
patent: 4628991 (1986-12-01), Hsiao et al.
patent: 4744713 (1988-05-01), Hrovath
patent: 4772846 (1988-09-01), Reeds
patent: 5436790 (1995-07-01), Blake et al.
patent: 5460703 (1995-10-01), Nulman et al.
patent: 5468302 (1995-11-01), Thietje
Fayyaz Nashmiya
Integrated Device Technology Inc.
Kwok Helen
McAndrews Isabelle R.
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