Brushing – scrubbing – and general cleaning – Machines – Brushing
Reexamination Certificate
2000-03-29
2003-09-23
Spisich, Mark (Department: 1744)
Brushing, scrubbing, and general cleaning
Machines
Brushing
C015S088300, C134S902000, C239S550000, C239S589000, C239S596000, C239S601000, C239SDIG001
Reexamination Certificate
active
06622335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor wafer cleaning and, more particularly, to techniques for applying fluids over a cleaning brush and improving wafer cleaning throughput and efficiency.
2. Description of the Related Art
In the semiconductor chip fabrication process, it is well-known that there is a need to clean a wafer where a fabrication operation has been performed that leaves unwanted residuals on the surface of the wafer. Examples of such a fabrication operation include plasma etching (e.g., tungsten etch back (WEB)) and chemical mechanical polishing (CMP). If left on the surface of the wafer for subsequent fabrication operations, the unwanted residual material and particles may cause, among other things, defects such as scratches on the wafer surface and inappropriate interactions between metallization features. In some cases, such defects may cause devices on the wafer to become inoperable. In order to avoid the undue costs of discarding wafers having inoperable devices, it is therefore necessary to clean the wafer adequately yet efficiently after fabrication operations that leave unwanted residue on the surface of the wafer.
FIG. 1A
shows a high level schematic diagram of a wafer cleaning system
50
. The cleaning system
50
typically includes a load station
10
where a plurality of wafers in a cassette
14
may be inserted for cleaning through the system. Once the wafers are inserted into the load station
10
, a wafer
12
may be taken from the cassette
14
and moved into a brush station one
16
a
, where the wafer
12
is scrubbed with selected chemicals and water (e.g., de-ionized (DI) water). The wafer
12
is then moved to a brush station two
16
b
. After the wafer has been scrubbed in brush station
16
, the wafer is moved into a spin, rinse, and dry (SRD) station
20
where DI water is sprayed onto the surface of the wafer and spun to dry. During the rinsing operation in the SRD station, the wafer rotates at about 100 rotations per minute or more. After the wafer has been placed through the SRD station
20
, the wafer is moved to an unload station
22
.
FIG. 1B
shows a simplified view of a cleaning process performed in a brush station
16
. In brush station
16
, the wafer
12
is inserted between a top brush
30
a
and a bottom brush
30
b
with top surface
12
a
facing up. The wafer
12
is capable of being rotated with rollers (not shown) to enable the rotating brushes
30
a
and
30
b
to adequately clean the entire top and bottom surfaces of the wafer
12
. In certain circumstances, the bottom surface of the wafer is required to be cleaned as well because contaminants from the bottom may migrate to the top surface
12
a
. Although both the top surface
12
a
and the bottom surface of the wafer
12
are scrubbed with the brushes
30
, the top surface
12
a
that is scrubbed with the top brush
30
a
is the primary surface targeted for cleaning, since the top surface
12
a
is where the integrated circuit devices are being fabricated. To more effectively clean the wafer
12
, a cleaning solution can be applied onto the top brush
30
a
by the use of a drip manifold
13
a
. In this example, the drip manifold
13
a
is attached to a drip control
13
which is in turn connected to a fluid source
24
. The fluid source
24
pumps fluid (e.g., any cleaning chemical or DI water) through the fluid control
13
which controls the amount of fluid entering the drip manifold
13
a
. After receiving the fluid from the fluid control
13
, the drip manifold
13
a
then expels a non-uniform drip
32
onto the top brush
30
a
. As will be discussed below, this non-uniform drip
32
has been observed to cause problems in cleaning operations.
FIG. 1C
shows a cross sectional view of the elements depicted in FIG.
1
B. When the wafer
12
has been placed on the bottom brush
30
b
, the top brush
30
a
is lowered onto the wafer
12
. As the top brush
30
a
is lowered onto the wafer
12
, drip control
13
starts the flow of fluid to the drip manifold
13
a
which releases the non-uniform drip onto the top brush
30
a
. During this time, both the bottom brush
30
a
and
30
b
turn to create the mechanical scrubbing action.
FIG. 1D
shows a more detailed side view of the wafer cleaning structure depicted in FIG.
1
B. In general, it is a goal to have the fluid provided to the drip manifold
13
a
expel “droplets” of fluid evenly over the entire length of the brush
32
a
. To do this, it is common practice to introduce the fluid into the drip manifold
13
a
at reduced flow rates and pressures. To accomplish this, the fluid source
24
supplies the cleaning fluid through the drip control
13
which regulates the amount of fluid injected into a near end
3
la of the drip manifold
13
a
. Unfortunately, as the fluid enters into the near end
31
a
, the fluid tends to flow out of the drip manifold faster at that end than at a far end
31
b
. This differential fluid expulsion occurs because most of the fluid is released through the drip holes at the near end
31
a
before the fluid can reach the drip holes at the far end
31
b
. Therefore, if the drip manifold
13
a
were totally horizontal, more near end drops
32
a
will be expelled than far end drops
32
b
. In the prior art, the drip manifold
13
a
was sometimes tilted downward slightly at a manifold angle Ø
42
to allow more fluid to reach the far end
31
b
. The manifold angle
42
is determined by finding the optimal angle of the drip manifold
13
a
which produces the equivalent amount of drip from both the near end
31
a
and the far end
31
b
. This manifold angle
42
is measured relative to a y-axis
40
a
and an x-axis
40
b
. As the drip manifold
13
a
expels the far end drops
32
a
and near end drops
32
b
onto the top brush
30
a
, the brushes
30
turn to scrub the wafer
12
.
Unfortunately, calibrating the drip manifold
13
a
to produce the right amount of fluid flow can be a very time consuming and a difficult process. By guesswork and trial and error, numerous manifold angles Ø
42
must be tried to find the optimal flow rate of the cleaning fluid. Even after the optimal flow rate has been found, the drip manifold may need re-calibrating every time the cleaning apparatus is moved to another location. This problem occurs because each different location (even a different section of the same room) can have a floor angle that is different from the previous location. Therefore, as is often the case, if the cleaning apparatus must be moved frequently, the need for constant re-calibration can create large wastes of time and reduce wafer cleaning throughput. In addition, further problems in the maintenance of manifold angle Ø
42
may occur if the drip manifold is moved by a bump or nudging of the cleaning apparatus because even a slight movement of the drip manifold can have the effect of altering the manifold angle Ø
42
. Therefore, the prior art drip manifold
13
a
must often be re-calibrated far more often than is desirable or practical.
FIG. 1E
depicts a more detailed cross-sectional view of the drip manifold
13
a
which is expelling the non-uniform drip
32
through a drip hole
13
b
. As is common practice, the drip hole
13
b
is formed by drilling a hole into the drip manifold
13
a
. Unfortunately, the drilling process is known to leave hole shavings
13
c
in and around the drip holes
13
b
. These shavings can potentially be introduced over wafers as particulates causing damage to circuits or retard the flow of fluid, thus causing un-even fluid sprays along the drip manifold
13
a
. To compensate for potential hole shavings
13
c
and un-even fluid delivery, it is common practice to deliver fluids to the drip manifold
13
a
at high pressures and flow rates. This is believed to improve the distribution of fluid out of all of the drip holes
13
b
along the drip manifold
13
a
. As consequence, however, this high pressure delivery and flows tend to produce high pressure jets
32
′.
Although the distribution of fluids out
Anderson Don E.
de Larios John M.
Mikhaylich Katrina A.
Ravkin Mike
Lam Research Corporation
Martine & Penilla LLP
Spisich Mark
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