Apparatus and method for preventing droplets on wafers...

Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material

Reexamination Certificate

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C034S469000, C034S073000

Reexamination Certificate

active

06658764

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for drying semiconductor wafers in a solvent dryer and more particularly, relates to an apparatus and a method for preventing solvent droplets from falling on wafers during a solvent drying process in the solvent 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, i.e., with the wafer positioned statically without movement. The wafer dryer
10
is constructed of a drying tank
12
equipped 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. 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 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 dryer
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 that 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 parameters, 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.
Another solvent drying technique has been developed in recent years which is similar in principal to that described. 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 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.
In either the solvent dryer or the maragoni dryer, a chiller arrangement may be utilized to condensed, collect and recycle the solvent vapor. This is shown in
FIG. 1
as chiller
16
which condenses the water-containing IPA vapor into IPA liquid such that it may be collected at the bottom of the drying chamber
12
for recycling and reuse. The chiller
16
is constructed of a plurality of condenser coils which are kept at a temperature below the vaporization temperature of the solvent. The plurality of condenser coils
70
are shown in FIG.
3
. The solvent dryer
74
shown in
FIG. 3
is similar to that shown in
FIG. 1
with the chamber cavity shown in an enlarged view. A processing problem occurred when condensed solvent droplets
76
fall from the condenser coils
70
onto the surface of wafer
24
during the vapor drying process. The solvent droplets, when fall on the wafer surface, can cause severe contamination of the wafer.
It is therefore an object of the present invention to provide a solvent dryer for drying semiconductor wafers that does not have the drawbacks or shortcomings of the conventional solvent dryers.
It is another object of the present invention to provide a solvent dryer that is equipped with condenser coils and drip-proof guards for preventing solvent condensation from falling on the wafer.
It is a further object of the present invention to provide a solvent dryer for semiconductor wafers that is equipped with a plurality of condensing plates attached to a plurality of condenser coils.
It is another further object of the present invention to provide a solvent dryer for semiconductor wafers that is equipped with a plurality of condensing plates which are kept at a temperature below the vaporization temperature of the solvent.
It is still another object of the present invention to provide a method for preventing solvent droplets from falling on wafers during a solvent drying process for semiconductor wafers.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus and a method for preventing solvent droplets from falling on semiconductor wafers during a solvent drying process are provided.
In a preferred embodiment, a solvent dryer equipped with condenser coils and drip-proof guards is provided which includes a cavity for holding a wafer therein; means for introducing a solvent vapor in the cavity; a plurality of condenser coils positions on an inside wall of the cavity

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