Cleaning and liquid contact with solids – Processes – Using solid work treating agents
Reexamination Certificate
2001-12-21
2004-04-27
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Using solid work treating agents
C134S006000, C134S025400, C134S034000, C134S036000, C134S037000, C134S042000, C134S902000, C134S198000, C134S199000, C134S200000, C451S075000, C451S099000, C451S102000
Reexamination Certificate
active
06726777
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for cleaning by spraying a cleaning fluid such as an aerosol containing argon particles toward a surface to be cleaned of an object to be cleaned such as a semiconductor wafer.
BACKGROUND ART
Particles or other contaminants on a surface of a semiconductor wafer in the LSI manufacturing process, and on a surface of a liquid crystal display (LCD), a solar cell, or the like, have a direct bearing on product yields, and therefore surface cleaning of wafers or the like is a crucial step.
Various surface cleaning methods have thus been devised. In the semiconductor manufacturing process, for example, wet bath cleaning methods have been most commonly used, in which objects to be cleaned are cleaned with pure water with the application of ultrasonic wave, or immersed in solutions containing cleaning agents (for example, hydrogen peroxide and ammonium hydroxide, or hydrogen peroxide and sulfuric acid) in pure water.
However, these wet bath-cleaning processes require an extensive site occupied by various pieces of equipment, and proper processing of disposed solutions. Consequently, there has been a desire to move toward a more environmentally friendly cleaning method without disposing any solutions or the like because of the recent increasing need of protecting the environment.
One of the dry cleaning methods, which don't utilize liquids, utilizes chemical reactions by applying a gas, but contaminants in the form of particles can hardly be removed by this method.
Another dry cleaning method may involve colliding particles of dry ice, ice, or solid argon with a surface to be cleaned to remove contaminating particles. However, cleaning with ice particles has the risk of damaging the surface which is being cleaned, and dry ice poses the problem of secondary contamination, because most dry ice products available on the market are made from exhaust gas produced through steel processing or oil refining and the dry ice itself is often contaminated.
On the other hand, the surface cleaning methods disclosed in Japanese Patent Laid-Open Publication Nos. Hei. 6-252114 and Hei. 6-295895, in which an aerosol containing solid argon particles (referred to as “argon aerosol”) is collided with an object in a depressurized atmosphere, do not pose the above-described problems.
FIG. 1
is a piping diagram of the entire construction of one example of a wafer cleaning apparatus using the argon aerosol.
FIG. 2
is a plan view of the same, and
FIG. 3
is a longitudinal cross-section of a cleaning chamber.
Mass flow controllers
30
,
32
are provided for respectively adjusting the flow rates of argon gas and nitrogen gas. The argon gas and nitrogen gas are passed through a filter
34
and cooled within a heat exchanger
38
using, for example, a helium (He) cryocooler
36
, after which they are ejected into a cleaning chamber
42
for cleaning a wafer, as an aerosol
24
from a large number of fine orifices
22
formed in a cleaning nozzle
20
. Inside the cleaning chamber
42
is created a vacuum by a vacuum pump
40
.
The wafer
10
rests on a process hand
46
, which is moved in directions along the X- and Y-axes by a wafer scan mechanism
44
(therefore is referred to also as an “X-Y scan stage”), so that the entire surface of the wafer can be cleaned.
It has been devised to provide an acceleration nozzle
56
for supplying a gas to increase the speed of the aerosol so as to enhance the cleaning effect. Thus, nitrogen gas (referred to accelerating gas
58
) is supplied to the acceleration nozzle
56
through a mass flow controller
52
and a filter
54
, and is blown out from nozzle orifices, accelerating the aerosol
24
ejected from the cleaning nozzle
20
, as illustrated in FIG.
4
.
It has also been suggested that nitrogen gas be introduced as a purge gas
66
into the cleaning chamber
42
through a mass flow controller
62
and a filter
64
from one end (left hand side of
FIG. 2
) of the cleaning chamber
42
, so as to prevent particles that have been removed from being deposited again onto the wafer surface.
Reference numeral
50
in
FIG. 3
represents a shield for controlling the gas flow within the cleaning chamber
42
.
Cassettes
72
accommodating wafers
10
are loaded from the outside of the apparatus into cassette chambers
70
, in which a vacuum is drawn. The cassette chambers
70
are provided in a pair as shown in
FIG. 2
for the exchange of cassettes
72
. Within a robot chamber
80
(or a transfer chamber) is installed a vacuum transfer robot (referred to also as a vacuum robot)
82
, having a robot arm
84
and a robot hand
86
mounted at the distal thereof. The wafers
10
are transferred by the robot hand
86
through gate valves
74
,
76
onto the above-mentioned process hand
46
within a buffer chamber
90
, which is used for transferring the wafer
10
into the cleaning chamber
42
.
The process hand
46
is driven by the wafer scan mechanism
44
to move the wafer
10
thereon from the buffer chamber
90
into the cleaning chamber
42
, and in directions along the Y-axis and the X-axis under the cleaning nozzle
20
.
The front surface of the wafer
10
is thus cleaned entirely by the aerosol
24
ejected from the cleaning nozzle
20
. Thereafter, the cleaned wafer
10
is returned to the cassette chamber
70
through the buffer chamber
90
in reverse motions.
Meanwhile, the increasing demand for higher performance of semiconductor wafers in recent years has highlighted various problems. For example, there is the problem, which the conventional wet bath cleaning method cannot resolve, that the front side of the wafer may be re-contaminated by the contaminants or particles on the backside of the wafer transferring onto the front side of the wafer. Even the cleaning method using aerosol has the problem of particles that have been sputtered away from the front side of the wafer depositing onto the backside of the wafer.
The conventional aerosol cleaning method involves only the cleaning of the upper surface (or front surface) of the wafer
10
by spraying an aerosol
24
containing solid fine particles ejected from the cleaning nozzle
20
from above the wafer
10
downwards, as shown in FIG.
1
. This is because the cleaning fluid is an aerosol, which contains microscopic particles of a solid or a liquid that are strongly affected by gravity. Thus it has not been proposed to clean the lower surface (or backside) of the wafer
10
using an aerosol.
When cleaning a semiconductor wafer with the above-described wafer cleaning apparatus using an aerosol, it is preferable that the aerosol
24
be delivered obliquely toward the downstream of the flow of purge gas as shown in
FIG. 4
, in the case in which no apertures such as via holes are formed in the wafer
10
. However, when the wafer has via holes
12
as shown in
FIG. 5
or other surface irregularities to be cleaned, the aerosol
24
, if delivered obliquely, can hardly reach inside of etched concavities as shown in FIG.
5
. In this case, therefore, it would be more preferable to direct the aerosol vertically as shown in FIG.
6
.
On the other hand, when the number of residual particles on the wafer after cleaning matters most, the aerosol should be delivered toward the wafer at an inclined angle as shown in
FIG. 4
, so as not to disturb the flow of purge gas.
To solve the above-described problems, the ejection angle of the aerosol
24
could be varied by making the mounting angle of the cleaning nozzle
20
adjustable. This will, however, bring about the following problems:
(1) There will be limitations on the angle of ejection because of the liquid argon within the cleaning nozzle
20
;
(2) The adjusting mechanism will be considerably complex because of the necessity to cool the cleaning nozzle
20
to a temperature as low as near that of liquid nitrogen; and
(3) Varying of the angle of the cleaning nozzle
20
during cooling will cause a change in the condition within the nozzle, resulting in unstable discharge of the aerosol
24
.
DISCLOSUR
Sonoda Yuzuru
Yamanishi Toshiyuki
Arent Fox Kintner & Plotkin & Kahn, PLLC
Gulakowski Randy
Sumitomo Heavy Industrie's, Ltd.
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