Apparatus and method for drying wafers by a solvent

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

Reexamination Certificate

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C034S524000, C034S548000, C034S558000, C034S570000

Reexamination Certificate

active

06401361

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for drying semiconductor wafers and more particularly, relates to an apparatus and a method for drying semiconductor wafers by a solvent that has high volatility in a wafer drying apparatus that is equipped with an interlock system for stopping the drying operation when solvent vapor is not detected in the apparatus.
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 Marangoni dryer, the drying principal is based on the different surface tension of IPA and DI water. The different surface tension causes the ejection of water molecules from the wafer surface which are then collected by a reservoir in the drying apparatus. The Marangoni 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.
In the conventional solvent dryer
10
shown in
FIG. 1
, the IPA vapor is fed from the solvent reservoir tank
26
by conduit
30
through a three-way flow control valve
32
which is pneumatically operated. When the pneumatically controlled three-way flow valve
32
malfunctions such that the flow of IPA vapor through conduit
30
into the tank cavity
22
is stopped, there is no alarm or interlocking function to safeguard such malfunction which can cause serious processing problems since the wafers are no longer dried. It would be highly desirable to provide an alarm or interlocking system to safeguard the three-way flow control valve that feeds IPA vapor into the dryer such that any malfunction of the valve can be detected in time in order to shut-down the drying operation and to stop loading wafers into the drying chamber.
It is therefore an object of the present invention to provide an apparatus for drying wafers that do not have the drawbacks or shortcomings of the conventional wafer drying apparatus.
It is another object of the present invention to provide an apparatus for drying wafers by a high volatility solvent equipped with an alarm and interlocking system for stopping the operation of the drying apparatus when solvent vapor does not flow into the apparatus.
It is a further object of the present invention to provide an apparatus for drying wafers wherein the apparatus is equipped with a three-way flow control valve and an interlocking device for detecting any malfunction of the flow control valve.
It is another further object of the present invention to provide an apparatus for drying wafers utilizing isopropyl alcohol vapor that is equipped with an interlocking device for shutting-down the operation of the drying apparatus when IPA vapor does not flow into the apparatus.
It is still another object of the present invention to provide a method for drying a semiconductor wafer by a solvent wherein a valve opening of a three-way flow control valve for the solvent vapor flow is connected to a vapor pressure sensor and an alarm.
It is yet another object of the present invention to provide a method for drying a semiconductor wafer by a solvent which is capable of detecting a malfunction of a flow control valve which stops the flow of a solvent vapor into the drying chamber.
It is still another further object of the present invention to provide a method for drying a semiconductor wafer by flowing IPA vapor in a N
2
carrier gas into the drying chamber and detecting any stoppage of the IPA vapor flow by an alarm and an interlock system.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus and a method for drying semiconductor wafers by a high volatility solvent is provided.
In a preferred embodiment, an apparatus for dying wafers is provided which includes a tank body for storing a quantity of a solvent in a bottom portion and for suspending a wafer in a top portion that is unfilled, the solvent has a volatility not less than the volatility of isopropyl alcohol; a three-way flow control valve; a solvent reservoir for storing a quantity of the solvent; a first conduit providing fluid communication between the top portion of the tank body and a first valve opening in the three-way valve for flowing a solvent vapor into the tank body; a second conduit for transporting a carrier gas to the solvent reservoir tank and for

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