Cleaning and liquid contact with solids – Processes – With treating fluid motion
Reexamination Certificate
2001-01-16
2002-12-31
Coe, Philip (Department: 1746)
Cleaning and liquid contact with solids
Processes
With treating fluid motion
C134S182000, C134S186000, C134S902000
Reexamination Certificate
active
06500274
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for wet cleaning wafers without ammonia vapor damage and more particularly, relates to an apparatus and a method for cleaning wafers with an ammonia-containing solution by trapping ammonia vapor in a cup-shaped container immersed in the cleaning solution such that ammonia vapor does not escape into the cleaning tank to attack wafers that are being cleaned in the tank.
BACKGROUND OF THE INVENTION
Deionized water is frequently used in a wet bench process after a chemical process has been conducted on a semiconductor wafer. When residual chemical must be removed, deionized water rinse is used in a wet bench process for semiconductor wafer processing to perform two major functions of a quick dump rinse (QDR) and a cascade overflow rinse. Conventionally, the two functions are carried out in separate tanks in order to produce the desirable result. One of the major processing issues presented by the conventional dual-tank process is the particle re-deposition problem during a withdrawal step when cassettes are transported from a quick dump rinse tank to a cascade overflow tank. A second major issue is the large floor space required for accommodating the two tanks.
A conventional wet bench wafer cleaning process is shown in FIG.
1
. The wet bench wafer cleaning process
10
for cleaning wafer
12
is carried out in six separate cleaning and rinsing tanks sequentially of a HF cleaning tank
14
, a first quick dump rinse (QDR) tank
16
, a SC-
1
cleaning tank
18
, a second quick dump rinse tank
20
, a SC-
2
cleaning tank
22
and a third quick dump rinse tank
24
. The first HF cleaning tank is used to hold a diluted HF solution, for instance, at a concentration of 0.5% HF in H
2
O for removing a thin native oxide layer from the wafer surface. After the diluted HF cleaning process, the wafer
12
is rinsed in a first quick dump rinse tank
16
with deionized water. Wafer
12
is then cleaned in a second cleaning tank filled with SC-
1
cleaning solution, i.e. a mixture of NH
4
OH, H
2
O
2
and DI water at a ratio of 1:1:5. The SC-
1
cleaning solution is used at a temperature between 70~80° C. for a suitable time period. The wafer
12
is then rinsed again in a second quick dump rinse tank
20
that is filled with DI water. In the final stage of cleaning, the wafer
12
is cleaned in tank
22
filled with a cleaning solution of SC-
2
which is a mixture of HCl, H
2
O
2
and DI water at a ratio of 1:1:6. The wafer
12
is then rinsed in a third quick dump rinse tank
24
with DI water.
The wet bench wafer cleaning process
10
shown in
FIG. 1
is conventionally used for pre-diffusion clean, pre-gate oxidation clean, pre-CVD clean, etc. For instance, in the ULSI fabrication of integrated devices, the conventional wet bench wafer cleaning process
10
can be advantageously used for wafer surface cleaning before a coating process in a CVD chamber or an oxidation process in a furnace.
Despite the fact that the conventional wet bench wafer cleaning process
10
is widely used, numerous processing difficulties of the process have been observed. For instance, during the SC-
1
cleaning process carried out in tank
18
, since SC-
1
contains about 28% NH
4
OH which forms ammonia vapor in the tank cavity over the surface of the solution. When wafer
12
(or a whole wafer boat) is removed from the SC-
1
cleaning solution and taken out of tank
18
, ammonia vapor attacks the cleaned, bare wafer surface, i.e. the fresh silicon surface of the wafer. As a consequence, a defect known as “silicon hole” occurs wherein craters in the silicon surface are formed due to the ammonia vapor attack.
Another processing difficulty encountered in the conventional wet bench cleaning process
10
is that, in order to perform the wafer cleaning process in a reliable and repeatable manner, the concentration and temperature of the cleaning solutions in the cleaning tanks must be maintained at constant values. For instance, during a typical wafer cleaning process, the SC-
1
solution in tank
18
must be constantly replenished since the components in the SC-
1
solution evaporates rapidly at a temperature higher than 50° C. As a consequence, during a wafer cleaning process, fresh NH
4
OH must be constantly added into the SC-
1
tank
18
in order to maintain a suitable concentration. A suitable method for monitoring the concentration of the SC-
1
cleaning solution is by using an infrared analysis technique.
In a conventional method of adding NH
4
OH to the SC-
1
tank
18
, as shown in
FIG. 2
, wherein the tank
18
is further equipped with an outer tank (or an overflow tank)
26
, the addition of the NH
4
OH liquid or any other ammonia-containing liquid further complicates the wafer cleaning process. The flow of NH
4
OH into the tank
18
causes agitation at the surface of the SC-
1
liquid
28
and thus producing ammonia vapor
30
at or near the top surface of the SC-
1
liquid
28
. The ammonia vapor further presents a problem for attacking the bare, or freshly cleaned silicon wafer surface. This has been observed when NH
4
OH liquid was used to replenish either the SC-
1
solution
28
in the SC-
1
tank
18
, or when the NH
4
OH liquid was used to replenish the SC-
1
solution
32
in the outer tank
26
.
It is therefore an object of the present invention to provide an apparatus for cleaning semiconductor wafers by wet bench that does not have the drawbacks or shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for cleaning semiconductor wafers by wet bench without causing damages to the wafer surface by ammonia vapor.
It is a further object of the present invention to provide an apparatus for cleaning semiconductor wafers by wet bench without causing ammonia vapor damages to the wafer surface by minimizing the generation of ammonia vapor.
It is another further object of the present invention to provide an apparatus for cleaning semiconductor wafers by wet bench without causing ammonia vapor damages to the wafer surface by positioning a feed conduit for an ammonia-containing liquid through a bottom wall of a holding tank with outlet end of the conduit immersed in the cleaning solution.
It is another further object of the present invention to provide an apparatus for cleaning semiconductor wafers by wet bench without causing ammonia vapor damages to the wafer surface by positioning a feed conduit for an ammonia-containing liquid through a bottom wall of the holding tank with an outlet end of the conduit immersed in the cleaning solution and covered by a cup-shaped container such that any ammonia vapor generated is trapped in the container.
It is yet another object of the present invention to provide an apparatus for cleaning semiconductor wafers by wet bench without causing ammonia vapor damages to the wafer surface by positioning a feed conduit for an ammonia-containing liquid through a bottom wall of an outer tank with the liquid outlet end of the conduit immersed in a cleaning solution.
It is still another further object of the present invention to provide a method for cleaning semiconductor wafers by wet bench without causing ammonia vapor damages to the wafer surface by mounting a feed conduit for an ammonia-containing liquid through a bottom wall of a holding tank such that an outlet end of the feed conduit is immersed in the cleaning solution.
It is yet another further object of the present invention to provide a method for cleaning semiconductor wafers by wet bench without causing ammonia vapor damages to the wafer surface by mounting a cup-shaped container on top of a feed conduit for an ammonia-containing liquid such that any ammonia vapor generated is trapped by the cover that is immersed inside a cleaning solution.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus and a method for cleaning wafers by wet bench without causing ammonia vapor damages occurring to the wafer surface are provided.
In a preferred embodime
Cheng Chia-Chun
Guo Ming-Dar
Twu Jih-Churng
Coe Philip
Taiwan Semiconductor Manufacturing Company Ltd
Tung & Associates
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