Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
2001-04-18
2002-07-30
Lu, Jiping (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S469000, C034S357000, C034S201000
Reexamination Certificate
active
06425191
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for drying semiconductor wafers in a solvent-type dryer and more particularly, relates to an apparatus and a method for reducing solvent residue in a solvent-type dryer after a drying cycle for semiconductor wafers is completed by incorporating an exhaust system in the dryer.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor devices, a large quantity of deionized (DI) water is frequently used to clean wafers in a wet bench process. For instance, when residual chemical must be removed from the surface of a wafer, DI water rinse is used in the wet bench process to perform major wafer cleaning operations such as quick-dump-rinse and cascade overflow rinse. It is desirable that the surface of the wafer be cleaned by DI water after a chemical or polishing process has been conducted on the wafer, i.e. oxide or nitride deposition, etching or chemical mechanical polishing process. The wet bench wafer cleaning step can be accomplished by equipment that is installed either in-line or in a batch-type process.
A typical automated wafer scrubber combines brush and solution scrubbing by DI water. The scrubber utilizes a hyperbolic high-pressure spray of DI water with a retractable cleaning brush. A typical wafer scrubbing process consists of a DI water spray step followed by a spin dry and nitrogen gas blow dry step. More recently, the solvent drying technology such as the use of isopropyl alcohol (IPA) has been developed to further improve the drying technology.
In a solvent drying technology, such as one that utilizes IPA shown in
FIG. 1
, the drying process is conducted in a static manner or with the wafer positioned statically without movement. The wafer drying
10
is constructed of a drying tank
12
constructed with a wafer receptacle
14
, a chiller
16
, a sidewall heater
18
and a bottom heater
20
. A cleaned and wet wafer is transported into the drying tank
12
, or the vapor chamber. A vapor of IPA is transported into the chamber cavity
22
by a carrier gas such as a high purity nitrogen, or any other high purity inert gas. The vapor enters into cavity
22
is then heated by the bottom heater
20
such that IPA is further vaporized and rises into the cavity
22
. The wafer
24
is surrounded by the IPA vapor and, due to the high volatility of IPA, water on the wafer surface can be evaporated away without leaving any water mark, contaminating particles or metal particles. The vapor pressure of IPA can be suitably adjusted such that there is a steady flow of IPA vapor in the cavity
22
fed from the IPA reservoir tank
26
.
In the conventional IPA drying tank
10
shown in
FIG. 1
, the only moving part for transferring wafers into and out of the chamber cavity is a robot arm. There are no other moving parts which can produce contaminating particles. The IPA drying chamber can thus be kept in an extremely clean condition to avoid any contamination of the wafer surface. To further maintain the cleanliness of the chamber cavity
22
, an air filter
28
is utilized for filtering incoming air into the cavity
22
and for providing a suitable flow rate of the IPA vapor. After the cleaning process is completed, the water-containing IPA vapor is condensed by the chiller
16
into IPA liquid and is collected at the bottom of the drying chamber
12
for recycling and reuse by the process. The IPA vapor drying process is normally controlled by three major elements, i.e. the purity and the water content of IPA; the flow rate and flow speed of the IPA vapor; and the cleanliness of the IPA vapor.
An improved solvent drying technique has been proposed in recent years which is similar in principal to that described above. In a Maragoni dryer, the drying principal is based on the different surface tensions of IPA and DI water. The different surface tensions cause the ejection of water molecules from the wafer surface which are then collected by a reservoir in the drying apparatus. The Maragoni drying process is carried out by slowly withdrawing a wafer from a DI water tank immersed in DI water. At the same time, IPA vapor carried by N
2
carrier gas is flown onto the wet wafer surface such that IPA is saturated on the exposed wafer surface above the water level. Since the concentration of IPA on the surface of the exposed wafer is larger than the concentration of DI water, the surface tension of IPA is smaller than the surface tension of water in the water tank. This causes the water molecules on the surface of the exposed wafer to be retracted into the water tank and thus achieving the drying purpose.
A typical Maragoni dryer
40
is shown in FIG.
2
. The Maragoni dryer
40
is constructed by an upper chamber section
52
, a lower chamber section
44
which is also an outer tank, an inner tank
42
for holding a volume of DI water
62
therein, a drain conduit
50
in fluid communication with the outer chamber
44
, a wafer carrier
46
for carrying a plurality of semiconductor wafers
60
, an elevator means
48
for raising and lowering the wafer carrier
46
into and out of the volume of DI water
62
, and a tank cover, or lid member
54
. The outer tank
44
is formed by a tank wall
68
defining a cavity
56
therein for receiving an overflow of DI water
62
from the inner tank
42
when the wafer cassette
46
is lowered into the volume of DI water
62
. The inner tank
42
is defined by sidewall
72
for holding the volume of DI water
62
therein. A cavity
58
is formed when the wafer carrier
46
is lowered into the volume of DI water
62
and the tank cover
54
is slid over the top of the inner tank
42
forming a hermetically sealed chamber.
A wafer drying process. typically can be carried out in the Maragoni dryer
40
in the following manner. First, the wafer carrier
46
, together with the plurality of wafers
60
, i.e. as many as 50 wafers, are first immersed in the volume of DI water
62
for rinsing the wafers and for removing any residual processing chemicals which may have been left on the wafer surface. After a soaking time of approximately between 1 and 2 min., a drying cycle of approximately 10 min. is carried out. In the first part of the drying cycle, instead of only nitrogen gas being flown into the chamber cavity
58
during the DI water soaking cycle, additional amounts of IPA vapor is flown into the chamber cavity
58
through a multiplicity of apertures
64
provided in a lower compartment wall
66
of a compartment
70
. These are shown in
FIGS. 3A and 3B
of a top view and a side view of tank cover
54
, respectively. At the end of the Part
1
drying cycle, the DI water
62
is drained out of the inner tank
42
. During the Part
1
of the drying cycle, the wafer carrier
46
, together with the plurality of wafers
60
, are slowly raised out of the volume of DI water
62
and thus a Maragoni drying process is conducted by the saturated IPA vapor.
In the second part of the drying cycle, which takes only about 60 sec., the flow of IPA vapor into the tank cavity
58
is stopped such that only nitrogen is flown into the tank cavity
58
. The DI water
62
is completely drained out of the inner tank
42
, such that the wafer carrier
46
and the plurality of wafers
60
in their dried state can be lowered into the empty inner tank
42
. The tank cover
54
is then slid to the side (as shown in
FIG. 2
) to allow access to the wafer carrier
46
after it is moved up by the elevator means. The plurality of wafers
60
is then removed by robot means (not shown) and thus, the Maragoni drying process is completed.
Also shown in
FIGS. 3A and 3B
are a solvent vapor dispersing conduit
74
and a plurality of partition plates
76
to allow a more uniform distribution of the solvent vapor into the tank cavity
58
during the Maragoni drying process.
While the Maragoni drying process has been satisfactorily utilized in drying semiconductor wafers, certain drawbacks of the process do exist. One of the drawbacks is that the flow of solvent vapor into the drying tank
Cheng Chia-Chun
Guo Ming-Dar
Kao Rong-Hui
Tsai Tsung-Chieh
Twu Jih-Churng
Lu Jiping
Taiwan Semiconductor Manufacturing Co. Ltd
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