Method and apparatus for measuring a gap

Details Method and apparatus for measuring a gap Method and apparatus for measuring a gap

1998-06-04

2001-01-09

Roskoski, Bernard (Department: 2859)

Geometrical instruments

Distance measuring

Single contact with a work engaging support

C033S833000

Reexamination Certificate

active

06170165

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to a method and apparatus for measuring a gap between two opposing surfaces and more particularly, relates to a method and apparatus for measuring a gap between two opposing surfaces in a semiconductor process machine of a wafer backside and a knife edge ring by using a dial gauge instead of conventional feeler gauges.
BACKGROUND OF THE INVENTION
In the fabrication process for semiconductor devices, numerous processing steps, i.e., as many as several hundred, must be performed on a semiconducting wafer in order to form the devices. Among the numerous processes, a wafer is frequently positioned on a rotating wafer platform, or a vacuum chuck, for carrying out the specific process. For instance, some of processes are the photoresist coating process, the photoresist developing process and an edge bead rinsing process for removing excess coating.
In a typical photoresist process, a photoresist liquid is first coated onto a wafer by dispensing a small amount of the photoresist liquid at the center of a wafer that rotates at a high speed. Since only a thin coating of the photoresist material is normally required, the amount of the liquid photoresist material dispensed is relatively small. After the photoresist coating process is completed, a wafer can be imaged in a stepper to reproduce the circuits desired on the wafer.
The exposed wafer is then positioned in a second coating chamber wherein a liquid developer material is dispensed on the surface of the wafer by a technique similar to that used in dispensing the photoresist material. A perfectly centered dispensing nozzle for the developing liquid is important to the successful coating of a developing liquid on the wafer surface.
Another important criterion in carrying out a developing process for a photoresist layer is that during the developing process, the backside of the wafer must be protected from being contaminated by the developing liquid. A conventional developing liquid coating apparatus is shown in FIG.
1
.
A conventional developing liquid coating apparatus
10
consists of several main components, first, a center vacuum chuck
12
which can be rotated at a high rotational speed by a shaft
14
. Onto a top surface
16
of the vacuum chuck
12
, a wafer
20
is positioned. The wafer
20
therefore rotates around a center axis
22
of shaft
14
. During a developing liquid coating process, a dispensing nozzle (not shown) is centered with axis
22
and positioned very close to the top surface
24
of the wafer
20
, i.e., at a distance of only a few millimeters apart. During the spin coating process, the backside
26
of the wafer
20
must be protected from contamination by the developing liquid. A drain cup
30
is provided for catching the excess, or spun-off developing liquid which includes a shield portion
32
and a base portion
34
that are usually formed integrally. The shield portion
32
collects droplets of the spun-off developing liquid such that it drains into cup
30
and is then taken away. The base portion
34
of the drain cup
30
is normally provided with backside rinse nozzles
38
which injects a rinse solution
42
toward the back surface
26
of the wafer
20
to further minimize the probability of contamination by the developing liquid sticking to the backside
26
. Additionally, a knife edge ring
40
is utilized for providing a sharp edge
46
forming a seal with the backside
26
of the wafer to stop splattered developing liquid droplets from entering the compartment that houses the vacuum chuck. The knife edge ring
40
is attached to a top surface
36
of the base member
34
with mechanical means such that the gap “X” between the backside
26
of the wafer and the sharp edge, or seal
46
on the knife edge ring
40
can be suitably adjusted.
During a normal developing liquid coating process conducted on an eight inch wafer, a suitable distance of X is maintained at between about 0.5 mm and about 1 mm, and preferably between about 0.6 mm and about 0.8 mm. It should be noted that the drain cup
30
is stationary in relation to a spinning vacuum chuck
14
and wafer
20
carried thereon. Conventionally, the gap X must be adjusted after a preventive maintenance procedure is conducted, or when problem is observed in backside contamination by the developing liquid.
FIG. 2
shows a conventional method for adjusting the gap between the backside
26
of the wafer
20
and the seal
46
on the knife edge ring
40
. The adjustment is carried out by using a set of feeler gauges including the feeler gauge
50
shown in FIG.
2
. After a suitable gap is first determined, e.g., 0.7 mm gap between the backside
26
and the seal
46
, a 0.7 mm feeler gauge can be used for adjusting the position of the knife edge ring in relation to the backside of the wafer. Mechanical means such as adjusting screws are used for such purpose. For instance, for a eight inch wafer, a total of 6 adjusting screws are provided for mounting and adjusting the knife edge ring on the base member
34
of the drain cup
30
. The screws are normally positioned in equal distance radially to the center axis
22
of the drain cup, or the vacuum chuck and circumferentially from each other.
The gap adjustment between the backside of the wafer and the knife edge ring is important such that the contamination of vacuum chuck by the developing liquid can be avoided. Furthermore, a suitable gap distance between the wafer backside and the knife edge ring at approximately 0.7±0.1 mm must also be maintained. When the gap is too large, contamination of the vacuum chuck by the developing liquid can not be prevented. When the gap is too small, the backside rinse process can not be effectively carried out and furthermore, there may be a danger of scratching the backside of the wafer and causing severe damage.
The use of feeler gauges to measure and adjust the gap distance between the wafer backside and the knife edge ring is difficult and inadequate. Not only it is a time consuming process, the feeler gauge method is also very much operator dependent, i.e., skill-level dependent. For instance, feeler gauge adjustments made by different operators may be different and moreover, adjustments made by the same person at different times may also be different.
It is therefore an object of the present invention to provide a method and apparatus for measuring a gap distance between two opposing surfaces that does not have the drawbacks and shortcomings of the conventional methods and apparatus.
It is another object of the present invention to provide a method and apparatus for measuring a gap distance between two opposing surfaces by utilizing a dial gauge instead of feeler gauges.
It is a further object of the present invention to provide a method and apparatus for measuring a gap between two opposing surfaces by utilizing a dial gauge and a calibration block which has a thickness substantially the same as the gap distance to be measured.
It is another further object of the present invention to provide an apparatus for measuring a gap between two opposing surfaces by mounting a dial gauge on a mounting block and through extension arms such that the dial gauge may first be zeroed by using a calibration block and then be used to measure the deviation from zero of one of the opposing surfaces.
It is still another object of the present invention to provide an apparatus for measuring a gap distance between two opposing surfaces wherein a dial gauge is used which is capable of reading to an accuracy of at least 0.01 mm.
It is yet another object of the present invention to provide an apparatus for measuring a gap distance between two opposing surfaces further including the use of a calibration block which has a thickness substantially similar to the gap to be measured such that the dial gauge may first be zeroed on the block.
It is still another further object of the present invention to provide a method for measuring a gap distance between two opposing surfaces by first providing a measuring appara

Affiliated with

Also associated with

Rating

Method and apparatus for measuring a gap does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method and apparatus for measuring a gap, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for measuring a gap will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2508105