Brushing – scrubbing – and general cleaning – Machines – Brushing
Reexamination Certificate
2001-06-21
2003-03-11
Till, Terrence R. (Department: 1744)
Brushing, scrubbing, and general cleaning
Machines
Brushing
C015S102000, C279S003000
Reexamination Certificate
active
06530103
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and an apparatus for transferring wafers in a process machine by using a vacuum pad and more particularly, relates to a method and apparatus for eliminating wafer breakage problem during wafer transfer by a vacuum pad in a process machine by cleaning the pad with a rotating brush or by applying vacuum pressure to the pad at a slow rate.
BACKGROUND OF THE INVENTION
In semiconductor processing, the process of backside grinding, or backlapping process, is frequently used in reducing the thickness of a wafer and in correcting any curvature in the wafer to achieve planarity and parallelism of the top and bottom surfaces of a wafer. Since a wafer polishing process can only remove a maximum thickness of about 5 &mgr;m, the polishing process cannot be used effectively to thin down a wafer or to correct the curvature of a wafer and achieve parallelism of the surfaces. Furthermore, the backside grinding or the backlapping process is frequently used before a wafer polishing process to achieve major thickness reductions. The wafer backside grinding process can be carried out in a lapping apparatus which may be a single-side lapping or a double-side lapping.
In a commercial backside grinding apparatus, such as one made by the Disco Company of Japan, a wafer transfer arm or a robotic arm is used for transferring wafers from one polishing station to another polishing station. For instance, in a backside grinding apparatus, there are usually at least three separate stations of a course grinding station, a fine grinding station and a cleaning/spin dry station.
As shown in
FIG. 1
, a T-shaped arm
12
is used in a backside grinding apparatus chamber
10
for transferring wafers from station to station. The T-shaped transfer arm
12
is constructed by a robotic arm
14
equipped with three vacuum conduits
16
,
18
and
20
. At the end of each of the vacuum conduits
16
~
20
, is provided with a wafer transfer pad
22
. The wafer transfer pad is fabricated of a sintered ceramic material that has a multiplicity of vacuum passageways therethrough. The wafer transfer pads
22
are shaped in the shape of a flat disk that has a diameter of approximately 4″ when used to transfer 6″ wafers. As shown in
FIG. 1
, wafers
24
are positioned at the center of chuck tables
26
for processing at various polishing stations. The sintered ceramic material may be formed of glass powders that are fused together at a high sintering temperature forming a sponge-like structure and thereby providing a multiplicity of vacuum passageways therethrough.
The wafer transfer pad
22
functions when the T-shaped arm
12
turns at an angle, as shown in
FIG. 2
, such that the wafer transfer pads
22
are positioned directly on top of the wafers
24
. After a vacuum is withdrawn from the conduits
18
,
20
, the wafer
24
is picked-up by the wafer transfer pads
22
. After the wafers
24
are picked-up by the wafer transfer pads
22
, the T-shaped arm
12
turns to a predetermined angle such that wafers
24
can be either unloaded from the backside grinding apparatus
10
or transferred to the next process station by positioning the wafer
24
onto a chuck table
26
.
During the operation of the backside grinding apparatus, various grinding debris and by-products in the form of particles are generated. In order to avoid contamination by the debris or particles to the wafer surface, the wafer transfer pads
22
must be frequently cleaned in order to remove any particle that is left on the surface of the pad
22
.
A typical wafer transfer pad cleaning process and apparatus are shown in FIG.
3
. The cleaning apparatus
30
consists of a solenoid valve
32
for the vacuum source, a vacuum sensor
34
, a solenoid valve
36
for the water and air mixed flow, flow meters
38
,
40
for air and water, respectively, and a wafer transfer pad
22
. A water/air mixture is fed through the backside of the wafer transfer pad
22
by conduit
42
. The water/air mixture purges through a thickness of the wafer transfer pad
22
to flush out all contaminating particles and backside grinding debris.
During a normal wafer transfer process, vacuum pressure is applied through the wafer transfer pad
22
for picking-up a wafer. A profile of the vacuum pressure vs. time is shown in
FIG. 4
for a conventional vacuum system. It is seen that within a period of time of 1 sec., the vacuum pressure applied increases from about 15 psi to about 75 psi. The rate of pressure increase is therefore about 60 psi/sec.
Problems are frequently caused by either the conventional pad cleaning process shown in
FIG. 3
, or by the conventional vacuum pressure system shown in FIG.
4
. For instance, the conventional pad cleaning method of
FIG. 3
is not always effective in removing all backside grinding debris and contaminating by-product particles. Any residual particles left on the surface of the wafer transfer pad
22
creates a pressure point when the particle is caught in-between the wafer transfer pad and a wafer. Such pressure point, or stress concentration point, can cause wafer breakage. The conventional vacuum pressure system of
FIG. 4
may further cause problems in that the sudden increase in the vacuum pressure, i.e. at a rate of about 60 psi per sec., may impact the wafer and cause the wafer to break or fracture.
It is therefore an object of the present invention to provide a wafer transfer pad cleaning method that does not have the drawbacks or shortcomings of the conventional pad cleaning process.
It is another object of the present invention to provide a wafer transfer pad cleaning method in which all contaminating particles can be removed from the surface of the wafer transfer pad.
It is a further object of the present invention to provide a wafer transfer pad cleaning method by utilizing a rotating brush on the surface of the pad simultaneously with the spray of a cleaning solvent.
It is another further object of the present invention to provide a wafer transfer pad cleaning process that utilizes a rotating brush which rotates at a speed of less than 500 rpm.
It is still another object of the present invention to provide a vacuum pressure system in a wafer transfer pad that does not cause breakage of the wafer when contacting the wafer due to a sudden pressure surge.
It is yet another object of the present invention to provide a vacuum pressure system for a wafer transfer pad which is adapted to apply a vacuum pressure at a rate smaller than 30 psi/sec.
It is yet another further object of the present invention to provide a vacuum pressure system for a wafer transfer pad that does not cause an impact on the wafer and subsequent breakage of the wafer upon contacting the wafer during the pick-up process.
It is still another further object of the present invention to provide an apparatus for eliminating wafer breakage during wafer transfer by a vacuum pad by incorporating a pressure regulating valve situated in a vacuum conduit for regulating a vacuum pressure applied at a rate not higher than 30 psi/sec. to the surface of the wafer transfer pad.
SUMMARY OF THE INVENTION
The method can be carried out by first providing a wafer transfer pad that is fabricated of a sintered ceramic material, i.e. such as a sintered glass, with a multiplicity of vacuum passageways therethrough, then cleaning a surface of the pad that contacts a wafer by contacting a rotating brush and a spray of water, then removing substantially all particles from the surface of the pad, contacting the surface of the pad to a surface of the wafer, applying a vacuum pressure to the surface of the pad by withdrawing air through the multiplicity of vacuum passageways, and picking-up the wafer and transferring to a different process station in the grinding apparatus.
The invention further discloses an apparatus for eliminating wafer breakage during a wafer transfer process in a grinding apparatus by utilizing a wafer transfer pad. The apparatus includes a wafer transfer pad that is fabricated of a sintered
Pan Jeng-Yang
Tang Wen-Fang
Wu Chia-Chun
Yang Huai-Tei
Yeh Su-Yu
Taiwan Semiconductor Manufacturing Company , Ltd.
Till Terrence R.
Tung & Associates
LandOfFree
Method and apparatus for eliminating wafer breakage during... 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 eliminating wafer breakage during..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for eliminating wafer breakage during... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3075373