Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
1999-04-14
2001-04-17
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S471000, C034S476000, C034S510000, C034S517000, C034S069000, C034S072000, C034S256000, C034S258000
Reexamination Certificate
active
06216364
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and an apparatus for drying washed objects, and more particularly to a method and an apparatus for rinsing and drying objects such as semiconductor wafers, glass substrates or the like which have been washed.
Drying of a precision substrate such as a finely-formed or fined wafer, glass substrate or the like following washing thereof is importantly affected by a degree at which a moisture entering trenches thereof is removed therefrom. In view of such a situation, a drying apparatus in which vapor of an organic solvent is used has been conventionally put to practice for this purpose. The drying apparatus using organic solvent vapor is constructed in such a manner as shown in
FIG. 10
by way of example. More specifically, the drying apparatus includes a drying tank
40
and a heater
41
mounted on an outer surface of a bottom of the drying tank
40
. The drying tank
40
is charged therein with an organic solvent
42
, which is heated to a boiling point thereof by means of the heater
41
, so that vapor of the organic solvent
42
may be formed in an upper region or portion of the tank
40
. Then, objects
43
such as wafers or the like which have been subjected to washing and rinsing using water or the like are placed in the vapor. This results in the organic solvent which is evaporated more readily than water being condensed on a surface of the object
43
while being substituted for water adhered to the surface of the object
43
.
The objects
43
in the vapor are gradually increased in temperature to a vapor temperature or boiling point of the organic solvent
42
and then taken out of the vapor atmosphere, resulting in the solvent adhered to the objects
43
being rapidly evaporated due to reduced latent heat thereof, leading to completion of drying of the objects
43
. The drying tank
40
has a cooling coil
44
arranged in the upper portion thereof, which functions to condense the organic solvent evaporated by heating. The organic solvent thus condensed is dropped onto a liquid receiver
45
and then recovered for reuse. Likewise, the organic solvent in the form of liquid containing water which is dropped from the objects
43
is recovered by another liquid receiver
46
.
Unfortunately, in the conventional drying apparatus thus constructed, it is required that an operator is highly careful with fire because the organic solvent is heated. Also, it causes energy consumption to be substantially increased due to both heating and cooling of the organic solvent. Further, it requires much time for the drying because of heating the organic solvent to form a layer of the vapor and is increased in consumption of the organic solvent due to loss by evaporation. In addition, when the objects are brought into contact with the layer of the vapor, heat of the vapor (gaseous phase) is removed by the objects to cause a rapid phase change of the organic solvent from gas to liquid. This reduces the vapor layer, to thereby cause the objects to be exposed to an ambient atmosphere, leading to problems such as contamination of the objects, a failure in drying thereof and the like. Also, there is likelihood that the organic solvent is contaminated by dust contained in the ambient atmosphere, leading to contamination of the objects.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing disadvantages of the prior art.
Accordingly, it is an object of the present invention to provide a method and an apparatus for drying washed objects which are capable of satisfactorily drying the objects in a reduced period of time.
It is another object of the present invention to provide a method and an apparatus for drying washed objects which are capable of effectively preventing contamination of the objects during drying thereof.
It is a further object of the present invention to provide a method and an apparatus for drying washed objects which are capable of attaining energy saving and a reduction in consumption of chemicals used.
It is a still further object of the present invention to provide a method and an apparatus for drying washed objects which are capable of efficiently generating mist of an organic solvent acting as a drying agent at a low temperature.
In accordance with one aspect of the present invention, a drying method for washed objects is provided. The drying method comprises the steps of: rinsing the objects which are immersed in pure water in a pure water tank; generating mist of an organic solvent at a normal temperature in an organic solvent mist generating tank by exciting the organic solvent by means of an ultrasonic wave; supplying the organic solvent mist to the pure water tank from the organic solvent mist generating tank while discharging the pure water from the pure water tank at a predetermined rate to thereby place the objects in an atmosphere of the organic solvent mist; and feeding nitrogen gas to the pure water tank to purge the organic solvent mist with the nitrogen gas.
In a preferred embodiment of the present invention, the drying method further comprises the step of maintaining the temperature of the organic solvent at a normal temperature.
In a preferred embodiment of the present invention, the organic solvent is excited by an ultrasonic wave having a frequency in the Megahertz range and the organic solvent mist is adsorbed on surfaces of the objects.
In a preferred embodiment of the present invention, the organic solvent is excited by an ultrasonic wave having a frequency in the range of 0.5 MHz to 10 MHz, the temperature of the organic solvent mist is selected to be 20° C. to 50° C., and droplets of the organic solvent mist have a diameter not greater than 100 &mgr;m.
In a preferred embodiment of the present invention, the predetermined rate at which the pure water is discharged from the pure water tank is selected so that droplets of the pure water and organic solvent or a liquid film of the pure water and organic solvent having a thickness of 10 nm to 1 &mgr;m is formed on the surfaces of the objects without forming a mixed layer of the pure water and the organic solvent on a surface of the pure water.
In accordance with another aspect of the present invention, a drying apparatus for washed objects is provided. The drying apparatus includes a pure water tank constructed so as to permit pure water to be introduced thereinto and discharged therefrom, to thereby rinse the objects which are immersed in the pure water; an organic solvent mist generating tank arranged so as to selectively communicate at an upper portion thereof with the pure water tank and constructed so as to permit an organic solvent charged therein to be excited by means of an ultrasonic wave, to thereby generate mist of the organic solvent at a normal temperature in the organic solvent mist generating tank; an organic solvent mist supplying means for supplying the organic solvent mist to the pure water tank from the organic solvent mist generating tank; a pure water discharge means for discharging the pure water from the pure water tank at a predetermined rate while the pure water tank and organic solvent mist generating tank are operated to communicate with each other to thereby place the objects in an atmosphere of the organic solvent mist; and a nitrogen gas feeding means for feeding nitrogen gas to the pure water tank to purge the organic solvent mist with the nitrogen gas.
In a preferred embodiment of the present invention, the organic solvent mist generating tank has a double-tank structure including an inner tank member and an outer tank member, the outer tank member being mounted on an outer surface of a bottom thereof with a vibration plate having an ultrasonic transducer attached thereto, the inner tank member having a bottom formed with a thickness which permits ultrasonic energy to penetrate therethrough, the inner tank member and outer tank member being arranged so as to permit circulating water for temperature adjusting to flow within a space defined between the inner tank member and outer tank m
Maki Isao
Okano Shoichi
Tanaka Akinori
Kaijo Corporation
Lerner David Littenberg Krumholz & Mentlik LLP
Wilson Pamela
LandOfFree
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