U.S. patent application number 11/299729 was filed with the patent office on 2006-05-11 for semiconductor wafer washing system and method of supplying chemicals to the washing tanks of the system.
Invention is credited to Jong-Woon Oh, Dong-Jun You.
Application Number | 20060096613 11/299729 |
Document ID | / |
Family ID | 36085537 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060096613 |
Kind Code |
A1 |
You; Dong-Jun ; et
al. |
May 11, 2006 |
Semiconductor wafer washing system and method of supplying
chemicals to the washing tanks of the system
Abstract
A semiconductor wafer washing system can execute a method in
which the washing solution is quickly changed over and over again
without the need to alter the structure of the system. The wafer
washing system includes a washing solution supply section in which
a plurality of chemicals are stored separately, and from which
selected ones of the chemicals can be supplied in a predetermined
ratio into a washing tank. A circulation section includes
circulation piping connected to the washing tank for circulating
the washing solution to and from the tank. A discharge section
selectively discharges residual chemicals or washing solution from
the washing solution supply section, the washing tank and the
circulation section. A controller controls the flow of chemicals
and washing solution in the washing solution supply section, the
circulation section and the discharge section, respectively.
Inventors: |
You; Dong-Jun; (Yongin-city,
KR) ; Oh; Jong-Woon; (Suwon-city, KR) |
Correspondence
Address: |
VOLENTINE FRANCOS, & WHITT PLLC
ONE FREEDOM SQUARE
11951 FREEDOM DRIVE SUITE 1260
RESTON
VA
20190
US
|
Family ID: |
36085537 |
Appl. No.: |
11/299729 |
Filed: |
December 13, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11037129 |
Jan 19, 2005 |
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11299729 |
Dec 13, 2005 |
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09956459 |
Sep 20, 2001 |
6863079 |
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11037129 |
Jan 19, 2005 |
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Current U.S.
Class: |
134/2 ; 134/10;
134/18; 257/E21.228 |
Current CPC
Class: |
H01L 21/67086 20130101;
B08B 3/04 20130101; B08B 3/048 20130101; B08B 3/00 20130101; H01L
21/02052 20130101; Y10S 134/902 20130101; H01L 21/67057 20130101;
B08B 3/14 20130101 |
Class at
Publication: |
134/002 ;
134/010; 134/018 |
International
Class: |
C23G 1/00 20060101
C23G001/00; B08B 7/04 20060101 B08B007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 12, 2001 |
KR |
2001-1732 |
Claims
1. A method of producing semiconductor wafer washing solution
during the manufacturing of semiconductor devices, said method
comprising: storing chemicals, capable of constituting different
forms of washing solution, separately in respective chemical
storage tanks; providing a washing tank having a main part, and a
supplementary part extending around and partitioned from said main
part; supplying chemicals from respective ones of the chemical
storage tanks into the main part of the washing tank in a
predetermined ratio to produce an original washing solution in the
washing tank and until a portion of the washing solution overflows
the main part of the washing tank into the supplementary part;
circulating the washing solution that has flown into the
supplementary part of the washing tank back into the main part of
the washing tank to facilitate the mixing of the chemicals
constituting the washing solution; subsequently submerging
semiconductor wafers into the washing solution in the main part of
the washing tank to thereby wash the wafers; and draining washing
solution circulating from the supplementary part of the washing
tank back to the main part of the washing tank.
2. The method as defined in claim 1, wherein said supplying of the
chemicals into the main part of the washing tank comprises
measuring the flow rates of the chemicals, respectively, as the
chemicals flow from the chemical storage tanks towards the main
part of the washing tank, and regulating the flow of the chemicals
based on the measured flow rates.
3. The method as defined in claim 1, wherein said supplying of the
chemicals into the main part comprises supplying the chemicals into
a mixing tank whereby the chemicals are mixed together, measuring
the level of the mixture of chemicals in the mixing tank, and
supplying the mixture of chemicals from the mixing tank into the
main part of the washing tank once the chemicals supplied into the
mixing tank rise to a predetermined level in the washing tank.
4. The method as defined in claim 3, wherein said supplying of the
mixture of chemicals from the mixing tank into the main part of the
washing tank comprises introducing purge gas into the mixing tank
to pressurize the interior thereof.
5. The method as defined in claim 4, and further comprising cutting
off the flow of the mixture of chemicals from the mixing tank to
the washing tank, and positioning the end of a discharge guide pipe
at a predetermined position in the top portion of the mixing tank,
and while the flow of the mixture of chemicals from the mixing tank
to the washing tank is cut off, opening the discharge guide pipe to
a drain when the level of the chemicals in the tank exceeds said
predetermined level, whereby pressure in the mixing tank created by
the purge gas discharges an excess of the mixture of chemicals from
the mixing tank through the discharge guide pipe and to the
drain.
6. The method as defined in claim 3, and further comprising cutting
off the flow of the mixture of chemicals from the mixing tank to
the washing tank, and positioning the end of a discharge guide pipe
at a predetermined position in the bottom portion of the mixing
tank, and while the flow of the mixture of chemicals from the
mixing tank to the washing tank is cut off, opening the discharge
pipe to a drain.
7. The method as defined in claim 1, and further comprising
filtering the washing solution circulating from the supplementary
part of the washing tank towards the main part of the washing tank
to remove impurities from the washing solution, and effecting a
heat exchange with the washing solution circulating from the
supplementary part of the washing tank towards the main part of the
washing tank to maintain the washing solution at a constant
temperature while the wafers are being washed.
8. The method as defined in claim 7, wherein said circulating of
the washing solution from the supplementary part of the washing
tank back to the main part of the washing tank comprises measuring
the pressure of the washing solution flowing from the supplementary
part of the washing tank, and based on the measured pressure,
regulating the pressure of the washing solution that is flowing
from the supplementary part of the washing tank back to the main
part of the washing tank, and wherein said draining of the washing
solution circulating from the supplementary part of the washing
tank back to the main part of the washing tank is carried out when
the pressure of the washing solution flowing from the supplementary
part of the washing tank exceeds a predetermined pressure.
9. The method as defined in claim 1, and further comprising drawing
the original washing solution from the washing tank into a washing
solution storage tank after the wafers have been washed, and
subsequently supplying chemicals from respective ones of the
chemical storage tanks into the main part of the washing tank in a
ratio different from said predetermined ratio to produce a new form
of washing solution in the washing tank.
10. The method as defined in claim 9, and further comprising, after
the original washing solution has been drawn into the washing
solution storage tank and before the chemicals constituting the new
form of washing solution have been supplied into the washing tank,
supplying a cleaning washing solution into the washing tank,
circulating the cleaning washing solution between the main and
supplementary parts of the washing tank to thereby clean the
washing tank, and then draining the cleaning washing solution.
11. The method as defined in claim 9, and further comprising
drawing said new form of the washing solution from said washing
tank into another washing solution storage tank, supplying
chemicals from respective ones of the chemical storage tanks into
the main part of the washing tank in said predetermined ratio to
produce a cleaning washing solution in the washing tank having the
same characteristics as the original washing solution that is
stored in the washing solution storage tank, circulating the
cleaning washing solution between the main and supplementary parts
of the washing tank to thereby clean the washing tank, subsequently
draining the cleaning washing solution, and, after the washing tank
is cleaned, drawing the original washing solution from the washing
solution storage tank back into the washing tank.
12. The method as defined in claim 9, and further comprising
drawing said new form of the washing solution from said washing
tank into another washing solution storage tank, subsequently
supplying the original washing solution from the washing solution
storage tank back into the washing tank to produce a cleaning
washing solution in the washing tank, circulating the cleaning
washing solution between the main and supplementary parts of the
washing tank to thereby clean the washing tank, subsequently
draining the cleaning washing solution, and after the washing tank
is cleaned supplying chemicals from respective ones of the chemical
storage tanks into the main part of the washing tank in said
predetermined ratio to produce a second batch of washing solution
in the washing tank having the same characteristics as the original
washing solution.
13. The method as defined in claim 1, and further comprising
temporarily storing the washing solution drained in the course of
its circulating from the supplementary part of the washing tank
back to the main part of the washing tank, diluting the temporarily
stored washing solution, and then discharging the diluted washing
solution.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of application Ser. No. 11/038,127,
filed Jan. 19, 2005, which is a divisional of application Ser. No.
09/956,459, filed Sep. 20, 2001, now U.S. Pat. No. 6,863,079,
issued Mar. 8, 2005, which is incorporated herein by reference in
its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the washing of
semiconductor wafers to remove impurities or particles from the
wafers during the manufacturing of semiconductor devices. More
particularly, the present invention relates to a semiconductor
wafer washing system and to a method of supplying chemicals to the
washing tanks thereof to produce a washing solution.
[0004] 2. Description of the Related Art
[0005] Semiconductor devices are generally made by forming at least
one circuit pattern on a wafer through repeated and selected
processes such as photoresist patterning, etching, washing,
diffusion, and metal deposition processes. The washing process is
performed to remove various types of particles and impurities that
have been produced during the previous processes so that such
particles and impurities do not affect the subsequent processes.
For instance, the etching away of a patterned photoresist can
produce particles of polymer. The wafer is washed after the etching
process to remove the particles.
[0006] The density, quantity, and temperature of the washing
solution must be established and controlled on the basis of various
parameters, such as the manufacturing processes involved, the type
of wafer, and the like. To meet such requirements, the washing
apparatus has various kinds of sensors, including an optical
sensor, to provide feedback for the control of the chemical
characteristics, the quantity and temperature of the washing
solution, etc. The general structure and operation of a
conventional washing apparatus will now be described with reference
to FIGS. 1 and 2.
[0007] A plurality of wafers W are transferred with a cassette K to
the apparatus (ST10) where they are positioned in a loading zone 10
(ST12). Then, the cassette K and wafers W are transferred to an
aligner 12 in which the wafers are arranged (ST14) with their flat
zones (not shown) aligned at a reference position in the cassette.
Subsequently, the cassette K and the wafers W are transferred to a
first transfer station 16 by a transfer device 14 (ST16).
[0008] The first transfer station 16 confirms the number of the
wafers W (ST18) and, at the same time, transfers the wafers from
the cassette K (ST20) to a robot 18 having a robot chuck (ST22).
The cassette K is then transferred by the transfer device 14 to a
stand-by area 20 and, after a predetermined period of time, is
placed at a second transfer station 26 (ST24)(ST26). The wafers are
then successively transferred by the robot 18 into a plurality of
washing tanks 22 containing washing solution (ST28).
[0009] The wafers W are submerged in the washing solution by the
robot so that impurities on the wafers W are washed away by the
washing solution. The wafers W are then transferred by the robot 18
to a drying station 24 where the wafers W are dried (ST30). The
wafers W are then transferred by the robot 18 to the second
transfer station 26. The second transfer station 26 arranges the
wafers W again and confirms whether the same number of wafers W
that arrived at the first transfer station 16 have undergone the
washing process (ST32).
[0010] The cassette K is transferred from the stand-by area 20 to
the second transfer station 26 prior to the arrival of the wafers
W. The second transfer station 26 loads the wafers W back onto the
cassette K that has been so transferred from the stand-by area 20
to the second transfer station 26 (ST34). In this way, the wafers W
and cassette K are continuously unloaded and transferred to a
position in preparation for the next process (ST36).
[0011] As was mentioned previously, the conditions of the washing
solution in each of the washing tanks 22, i.e., the concentration,
quantity, temperature, etc. must be maintained constant according
to the type of wafer W or process that dictates the need for
cleaning the wafers W. Accordingly, when a new type of wafer is to
be washed, a new type of washing solution must be used. It is
difficult to create new environments that facilitate the cleaning
of new types of wafers with new cleaning solutions. In addition,
the old type of washing solution must be discharged out of the
system regardless of the remaining useful life thereof, and the
washing tanks 22 and washing solution supply 28 must be thoroughly
cleaned before they are to accommodate the new type of washing
solution. This process of changing the washing solution requires a
lot of time.
[0012] In addition, the process also suffers from inefficiency
because effort must be spent in converting the apparatus to provide
for the new washing solution conditions. For instance, the new
washing conditions may require additional washing tanks 22 to be
provided in the washing apparatus. Due to space considerations,
this sometimes requires the removal of existing elements, including
the washing tanks 22, from the apparatus and the addition of
completely new washing elements. Changing the existing tanks also
requires a lot of time.
[0013] As an alternative to modifying the washing apparatus, a
completely new washing system may be provided in the production
line. However, this may require reducing the size of the existing
line or the new washing system might be just too large to
incorporate into the existing line. In addition, fabricating and
installing a completely new washing system is much more expensive
in terms of material and labor than merely modifying the existing
washing system.
[0014] As is also apparent from the description above, the elements
of the washing apparatus are arranged in line so that the wafers
can be cleaned in a continuous operation. As shown in FIG. 3, the
washing solution, which comprises a mixture of chemicals, is
supplied to the washing tanks 22 through a pipeline of a washing
solution supply 28. The efficacy of the washing solution is reduced
as the washing solution undergoes chemical reactions with the
impurities on the wafers W. Therefore, the washing solution is
discharged out of the system after a predetermined period of time
so that pure washing solution can be introduced into the tanks 22.
Nonetheless, it is difficult to maintain the required concentration
of the washing solution even when a plurality of washing tanks is
provided.
[0015] Moreover, the period of refreshing the washing solution is
relatively short. Thus, the conventional method suffers from a
drawback in terms of the costs associated with the amount of
washing solution that must be used.
SUMMARY OF THE INVENTION
[0016] An object of the present invention is to provide a
semiconductor wafer washing system and method by which washing
solution can be changed and/or the washing solution can be
conditioned in a short period of time without altering the basic
structure and arrangement of the existing washing tanks.
[0017] Another object of the present invention is to provide a
semiconductor wafer washing system and method by which the washing
solution can be conserved, whereby the system is environmentally
friendly and economical to use.
[0018] Still another object of the present invention is provide a
semiconductor wafer washing system and method by which the washing
tanks can be flushed in such a way as to quickly facilitate the use
of a new form of washing solution.
[0019] In order to accomplish these objects, the washing system
according to the present invention comprises a washing solution
supply section that includes a plurality of chemical storage tanks
in which a plurality of chemicals are stored, respectively, and
supply piping connected to the chemical storage tanks, a washing
tank that receives the chemicals from the washing solution supply
section via the supply piping, and a discharge section having a
drain and discharge piping that allows residual chemicals and/or
washing solution to be discharged from various parts of the system
to the drain. The washing system may also comprise a circulation
section and a washing solution storage section. The circulation
section includes circulation piping connected to the washing tank
and through which piping washing solution is circulated from and
back to the tank to enhance the mixing of the chemicals
constituting the washing solution. The washing solution storage
section has one or more washing solution storage tanks connected to
the washing tank and circulation piping for storing washing
solution used to replenish and/or flush the washing tank and
circulation piping.
[0020] Furthermore, each of the sections of the semiconductor
washing system includes flow control means for controlling the flow
of chemicals or washing solution. A controller is operatively
connected to the flow control means of each section of the system
so as to issue control signals that regulate the flow of the
chemicals or washing solution to and from the sections of the
system as conditions warrant. The controller may comprise a central
processing unit (CPU) or individual processing units provided in
the sections of the semiconductor washing system, respectively.
[0021] For instance, the flow control means of the washing solution
supply section comprises flow control valves disposed in the supply
piping. The controller controls the flow control means of the
washing solution supply section such that selected ones of the
chemicals are supplied to the washing tank in a predetermined
ratio. Likewise, the flow control means of the discharge section
may comprise flow control valves disposed in the discharge piping.
The controller controls these flow control valves such that washing
solution is discharged from the washing tank in various instances.
On the other hand, the flow control means of the circulation
section comprises a variable output pump and/or a flow control
valve disposed in the circulation piping. Also, a pressure gauge
may be provided for monitoring the pressure of the washing fluid
flowing through the circulation piping so that the pump may be
feed-back controlled by the controller. The flow control means of
the washing solution storage section comprises a purge gas supply
system for introducing purge gas into the at least one washing
solution storage tank and/or a variable output pump to force
washing solution from the washing solution storage tank(s) into the
washing tank and circulation piping. A flow control valve of the
purge gas supply system and/or the pump is/are controlled by the
controller.
[0022] In addition to enhancing the mixing of the chemicals
constituting the washing solution, the circulation section is used
to condition the washing solution. To this end, one or more filters
are provided in the circulation piping for filtering impurities
from the washing solution. In addition, a heat exchanger is
provided in a heat-exchanging relationship with the circulation
piping so that the washing solution can be maintained at a desired
temperature.
[0023] Preferably, the washing solution supply section also
includes a quantitative supply part for mixing precise amounts of
the chemicals together before the chemicals are dispensed to the
washing tank. The quantitative supply part includes at least one
mixing tub connected to the washing tank, a cover covering the
mixing tub so as to form a mixing tank therewith, a level sensor
for sensing the level of chemicals in the tub and issuing a signal
indicative of the level of chemicals in the tub to the controller,
and a purge gas supply system for introducing purge gas into the
covered tub and/or a variable output pump for forcing the mixture
of chemicals from the mixing tub and into the washing tank.
[0024] In this case, the flow control means of the discharge
section includes elements associated with the quantitative supply
part. Specifically, the flow control means of the discharge section
will comprise a discharge guide pipe(s) extending into the mixing
tub, and driving means for raising and lowering the discharge guide
pipe(s) such that an end thereof is positionable at a desired level
within the mixing tub. The driving means may be any known linear
driving mechanism appropriate for moving the guide pipe between two
end limit positions and keeping the guide pipe temporarily fixed in
place at the desired position, in response to a signal issued by
the controller on the basis of information received from the level
sensor.
[0025] In order to accomplish the above-mentioned objects of the
present invention, the semiconductor wafer washing method includes
steps of supplying chemicals from respective ones of the chemical
storage tanks into the washing tank in a predetermined ratio to
produce an original washing solution in the washing tank,
circulating the washing solution from a supplementary part of the
washing tank back into a main part of the washing tank to
facilitate the mixing of the chemicals constituting the washing
solution, subsequently submerging semiconductor wafers into the
washing solution in the washing tank to thereby wash the wafers,
and draining washing solution circulating from the supplementary
part of the washing tank back to the main part of the washing
tank.
[0026] The supplying of the chemicals from the chemical tanks into
the washing tank can be carried out with an enhanced degree of
precision by using the quantitative supply part as follows. The
chemicals are first supplied at rates regulated by the controller
into the mixing tank. During this time, the level of the chemicals
in the mixing tank is measured and the flow of chemicals from the
mixing tank to the washing tank is cut off. The end(s) of the
discharge guide pipe(s) are positioned in the mixing tank, and once
the level of the chemicals in the mixing tank exceeds a
predetermined level, the discharge guide pipe(s) is/are opened to
the drain. Accordingly, pressure in the mixing tank created by
purge gas discharges an excess of the mixture of chemicals from the
mixing tank through the discharge guide pipe and to the drain.
Then, the mixture of chemicals is allowed to flow from the mixing
tank to the washing tank.
[0027] As was mentioned above, as the washing solution is being
circulated from the supplementary part of the washing tank back to
the main part of the washing tank, the washing solution is
conditioned. The washing solution is filtered and the temperature
of the washing solution is adjusted, if necessary.
[0028] Manufacturing requirements may dictate that a new form of
the washing solution be used to wash a batch of wafers. In this
case, the original washing solution is drawn from the washing tank
into a washing solution storage tank after the first batch of
wafers have been washed. Subsequently, chemicals from respective
ones of the chemical storage tanks are supplied into the main part
of the washing tank in a new ratio to produce a new form of washing
solution in the washing tank. Alternatively, the new form of
washing solution can be taken from another one of the washing
solution storage tanks, if such washing solution has, for example,
already been produced by the washing solution supply section and
has been (used and then) stored.
[0029] In addition, the washing tank and the circulation piping
should be flushed prior to introducing a new form of the washing
solution into the washing tank, to thereby eliminate remnants of
the original washing solution that would otherwise alter the
composition of or otherwise contaminate the new washing solution.
Basically, this process entails supplying a cleaning washing
solution into the washing tank after the original washing solution
has been drawn into the washing solution storage tank and before
the chemicals constituting the new form of washing solution have
been supplied into the washing tank. Then, the cleaning washing
solution is circulated between the main and supplementary parts of
the washing tank to thereby clean the washing tank. Finally, the
cleaning washing solution is drained.
[0030] The cleaning washing solution can come from one of the
washing storage solution tanks. Alternatively, the cleaning washing
solution can come directly from the chemical storage tanks. In
either of these cases it is most effective if the cleaning washing
solution has the same composition as the new washing solution that
is to be used next. In any case, the washing solution that is
drained in the course of its circulating from the supplementary
part of the washing tank back to the main part of the washing tank
is temporarily stored. The temporarily stored washing solution is
then diluted and discharged from the system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a schematic diagram of a conventional washing
apparatus;
[0032] FIG. 2 is a flow chart of the operation of the washing
apparatus shown in FIG. 1;
[0033] FIG. 3 is a schematic diagram of a washing system of the
conventional apparatus;
[0034] FIG. 4 is a schematic diagram of one embodiment of a washing
system of semiconductor wafer washing apparatus according to the
present invention;
[0035] FIG. 5 is a schematic diagram of another embodiment of a
washing system of semiconductor wafer washing apparatus according
to the present invention; and
[0036] FIG. 6 is a schematic diagram of part of the washing
solution supply section of the system of FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] The present invention will now be described with reference
to FIGS. 4 through 6.
[0038] Basically, the semiconductor wafer washing system includes a
washing solution supply section 30 that stores each of the various
chemicals making up the washing solution and controls the flow rate
of the chemicals, a washing tank 32 that receives the chemicals
from the washing solution supply section 30 and mixes the chemicals
to make a washing solution used to wash the wafers W, a circulation
section 34 for circulating the washing solution through the tank
32, and a discharge section 36 that discharges the residual
chemicals and washing solution from the system.
[0039] The washing tank 32 consists of a main part A, and a
supplementary part B partitioned from one another. The washing
solution is stored in the main part A as the solution is being
mixed with chemicals supplied from the washing solution supply part
30, and the wafers W are cleaned in the main part A in the
solution. The supplementary part B contains excess washing solution
overflowing from the main part A.
[0040] The circulation section 34 is connected to the washing tank
32 to circulate the washing solution through the main part A and
supplementary part B of the washing tank 32. The circulation
section 34 thus serves to maintain the desired characteristics of
the washing solution.
[0041] The discharge section 36 is directly connected to the supply
section 30, the washing tank 32 and the circulation section 34 to
selectively discharge from the system the washing solution or
residual chemicals from the supply section 30, washing tank 32, and
circulation section 34.
[0042] The operation of the washing solution supply section 30,
circulation section 34, and discharge section 36 are is controlled
by a controller 100.
[0043] The structure of the semiconductor wafer washing system will
be explained in more detail below.
[0044] The washing solution supply section 30 comprises a plurality
of chemical storage tanks 38 containing the chemicals,
respectively, that are to make up the washing solution. At least
one of the chemicals is pure water or a diluent for diluting the
other chemicals or for preventing hardening. Each of the chemical
storage tanks 38 is connected to the washing tank 32 through supply
piping provided therein with at least one flow control valve V. The
piping may consist of main supply pipes S, or main and branch
supply pipes S, S=. A filter 40 for filtering the chemicals may be
provided in any of the pipes. The filter 40 is connected to a
discharge pipe D through which a portion of the chemicals or
impurities filtered by the filter 40 is discharged from the
system.
[0045] A flowmeter 42 is also provided in each of the supply pipes.
Each flow meter 42 measures the flow rate of the chemical flowing
through the pipe and outputs a signal indicative of the flow rate
to the controller. The controller, in turn, controls the flow
control valves V to maintain a desired flow rate of the chemicals.
The flow rate of most of the chemicals can be controlled to some
extent by the flow control valves V. However, the controlling of
the flow rate of some exceptional chemicals or an accurate mixing
of some chemicals might require the use of discrete quantitative
supply apparatus 44 connected to the supply piping S, S=, as shown
in FIG. 5.
[0046] The quantitative supply apparatus 44 includes a quantitative
mixing tank 46 connected to a chemical storage tank 38 via piping.
A level sensor 48 is provided in the quantitative mixing tank 46
for measuring the amount of chemicals within the tank. The level
sensor 48 also outputs a signal, indicative of the amount of
chemicals within the tank 46, to the controller. The controller
controls the flow control valves V in the piping connected to the
quantitative mixing tank 46, thereby controlling the rate at which
the chemicals flow into the tank 46.
[0047] The chemicals are typically volatile and so would evaporate
if exposed to air. Hence, a cover 50 is detachably mounted to the
quantitative mixing tank 46 so as to cover the tank 46 and thereby
prevent a reduction in the quality of chemicals in the tank 46 that
would otherwise be caused by evaporation. In addition, a source of
purge gas that does not react with air, e.g. a nitride gas, is
connected to the quantitative mixing tank 46 through the cover 50
by purge gas supply piping 52.
[0048] The quantitative supply apparatus 44 may also include a pump
54 provided in-line with the supply piping S, S' to pump the
chemicals from the quantitative mixing tank 46 to the washing tank
32. The pump 54 is preferably a variable speed pump connected to
the controller so as to generate a selected pressure in response to
signals from the controller. Alternatively, the chemicals can be
forced from the quantitative mixing tank 46 to the washing tank 32
by pressure generated by the purge gas supplied into the tank 46
through the purge gas supply piping 52.
[0049] In addition, the quantitative supply apparatus 44 should be
connected to the discharge section 36 so that any excessive amount
of chemicals can be drained from the tank 46. To this end, the
discharge section 36 may comprise a first (discharge guide) drain
pipe 56 extending through the cover 50 of the quantitative tank 46.
The drain pipe 56 is movable up and down (FIG. 6) by a driving
mechanism so that the end thereof that is located in the tank 46
may be repositioned. The end of the drain pipe 56 is set by the
driving mechanism at a level corresponding to the desired level of
chemicals in the tank 46, i.e., to regulate the amount of chemicals
in the tank. When an excessive amount of chemicals are present in
the tank 46, the flow of chemicals from the chemical tanks 38 to
the washing tank 32 via the quantitative mixing tank 46 is cut off.
In this state, the excess chemicals in the tank 46 are forced
through the drain pipe 56 and to the drain of the discharge section
36 by pressure in the tank 46 generated by purge gas supplied to
the tank 46 through the purge gas supply piping 52.
[0050] The discharge section 36 may also include a second
(discharge guide) drain pipe 58 that extends through the bottom of
the quantitative tank 46 and is connected to the drain of the
discharge section 36. The second drain pipe 58 is also movable up
and down by a driving mechanism. In the operational state that
prevents the chemicals from flowing from the chemical tanks 38 to
the washing tank 32 via the quantitative tank 46, excess chemicals
in the quantitative tank 46 can be drained through the second drain
pipe 58 by the purge gas.
[0051] The first and second drain pipes 56, 58 may be selectively
used or may be used at the same time to drain chemicals from the
tank 46. In addition, a pump may be provided in the first and
second drain pipes 56, 58 to force the chemicals therethrough.
[0052] The circulation section 34, as shown in FIG. 4 or 5,
includes circulation piping R through which the mixture of washing
solution is circulated between the main part A and supplementary
part B of the washing tank 32. At least one flow control valve V is
provided in the circulation piping R for controlling the flow of
the washing solution therethrough in response to a signal issued by
the controller. Also, at least one filter 40 is provided in the
circulation piping R for filtering impurities from the washing
solution.
[0053] The circulation section 34 also includes a variable speed
pump 54 that operates in response to a signal issued by the
controller, and a pressure gauge 62 for measuring the pressure of
the washing solution and outputting a signal indicative of the
pressure to the controller. A check valve 64 in the circulation
piping R discharges the washing solution to the discharge part 36
through discharge piping D as long as the pressure of the washing
solution does not exceed a certain predetermined pressure.
[0054] In addition, the circulation section 34 may include a heat
exchanger 60 operatively associated with the circulation piping R
such that the temperature of the washing solution flowing through
the piping R is maintained constant.
[0055] The circulation section 34 serves to condition the washing
solution, e.g., to provide the correct composition and temperature.
To this end, the chemicals supplied from the washing solution
supply section 30 are mixed in the course of being introduced into
the main part A of the washing tank 32 to form the washing
solution. Excess washing solution overflows into the supplementary
part B from the main part A. The controller opens the flow control
valve V in the circulation piping R, and at the same time signals
the pump 54 to operate, whereby the washing solution in the
supplementary part B is re-circulated to the main part A.
[0056] During this time, impurities or chemicals that harden the
washing solution are filtered from the washing solution by the
filter 40. The pressure of the washing solution produced by the
pump 54 is monitored by the pressure gage 62. The signals output by
the pressure gage 62 to the controller are used to control the
operation of the pump 54, whereby the pressure of the washing
solution is kept within a predetermined range.
[0057] Note, the washing solution is discharged through the
discharge piping D of the discharge section 36 until the pump 54
starts operating and produces a sufficient pressure.
[0058] The aforementioned operation is carried out until the
chemicals are sufficiently mixed and the washing solution attains a
certain temperature, whereupon the wafers W are submerged in the
washing solution in the washing tank 32.
[0059] The discharge section 36 also includes at least one drain
tub 66, and discharge piping D'. The residual washing solution is
stored in the at least one drain tub 66 and is discharged therefrom
through a pipe of the discharge piping D. A supply pipe S extends
into the tub 66 from the chemical storage tank 38 in which pure
water or diluent is stored. When the washing solution stored in the
drain tub 66 starts to harden, the controller opens the valve V in
the supply pipe extending into the tub 66 from the chemical storage
tank 38 in which pure water or diluent is stored, thereby
preventing the discharge piping D from being clogged with chemical
precipitate of the hardened washing solution. Another pipe of the
discharge piping D branches from the circulation piping R such that
washing solution can be discharged from the circulation section 34.
The discharge piping D is provided with valves V that are
controlled by the controller to selectively discharge the washing
solution from the circulation section 34.
[0060] As shown in FIG. 5, the semiconductor wafer washing system
may also include a washing solution storage section 70, connected
to the washing tank 32 and circulation section 34, for selectively
storing washing solution having a predetermined composition. The
storage section 70 includes at least one storage tank 72,
connection piping C that allows the washing solution stored in the
tank 72 to be reintroduced into the circulation piping R, and a
valve(s) V provided in the connection piping C for controlling the
flow of washing solution in response to a signal from the
controller.
[0061] The storage section 70 may also comprise means for creating
pressure by which the washing solution is forced from the tank 72.
The means may be a source of purge gas, such as N.sub.2, and a
purge gas supply pipe 52 connected to the storage tank 72 and/or a
variable speed pump 54 provided in the connecting pipe C. The
controller controls the flow of the purge gas into the storage tank
72 to produce a certain amount of pressure therein, and controls
the pump 54 as well, to thereby regulate the flow of the stored
washing solution from the tank 72 and through the connection pipe
C. The purge gas supply and the pump 54 may be operated together or
individually by the controller.
[0062] The washing solution storage section 70 stores washing
solution that can be used when new or other wafers W require new
conditions to be cleaned under.
[0063] As described above, in the semiconductor wafer washing
system according to the present invention, a plurality of chemicals
are separately stored in each of the chemical storage tanks 38. The
chemicals are supplied to the main part A of the washing tank 32
via elements such as the flow control valves V and/or quantitative
mixing tank 46.
[0064] When the chemicals are supplied via the quantitative mixing
tank 46, the first and second discharge guide pipes 56, 58 are
placed at predetermined positions in response to signal issued by
the controller. In addition, pressure is created in the
quantitative mixing tank 46 by the purge gas supply and which
pressure is regulated by the controller. Still further, at least
some of the chemicals are filtered by the filter 40 provided in the
supply piping before the chemicals are supplied to the washing tank
32.
[0065] Thus, the chemicals are mixed together in a predetermined
ratio to form the washing solution. An excess amount of the washing
solution in the main part A overflows into the supplementary part
B, and the excess or residual solution is re-circulated back to the
main part A via the recirculation section 34 to further enhance the
mixing of the chemicals constituting the washing solution and so
that the solution can be conditioned, e.g. temperature-conditioned,
if necessary.
[0066] The controller also serves to control the flow control means
of the circulation section so that the washing solution contained
in the supplementary part B of the washing tank 32 is re-supplied
to the main part A of the tank. At the same time, the washing
solution is purified by filter 40, and is heated/cooled by heat
exchanger 60. The program of the controller is designed so that the
chemicals constituting the washing solution will be mixed and
conditioned, e.g maintained at a given constant temperature, in
accordance with the washing needs of the wafers W that are to be
cleaned in the main part A of the washing tank 32.
[0067] Also, the controller serves to control the pressure of the
washing solution flowing through the circulation piping R of the
circulation section 34 so that the flow of the washing solution is
stabilized and the pressure is appropriate for the operation of the
filters 40. The pressure gauge 62 serves to measure the pressure in
the section of the circulation piping R extending between the
filters 40. If the pressure becomes excessive such as occurs when
the filter(s) 40 become clogged, the check valve 64 opens allowing
the washing solution to be discharged. That is, the check valve 64
allows the need to exchange the elements of the filters 40 to be
determined.
[0068] The above-described discharge section 36 serves to
temporally store (in the drain tub 66) the residual chemicals,
washing solution, or impurities that are discharged from the
washing solution supply section 30 and the circulation section 34.
The residual chemicals, washing solution, or impurities are mixed
(diluted) in the discharge section with a predetermined amount of
pure water or other diluent whereupon they are discharged from the
system through the discharge piping D and drain.
[0069] Now, after semiconductor wafers have been washed in the main
part A of the washing tank under the operation outlined above, it
may be necessary to wash other wafers using a different form of the
washing solution. In this case, the washing solution is drawn from
the washing tank 32 and circulation piping R through the connection
piping C and into a washing solution storage tank 72. Subsequently,
the controller controls the flow control means, e.g. valves V, of
the washing solution supply section 30 such that the chemical(s)
appropriate for washing the new wafers W are withdrawn form the
respective chemical storage tank(s) 38 and are supplied to the
washing tank 32. An operation similar to that described above is
carried out to produce a new washing solution, i.e., to create the
new environment for washing the next wafers.
[0070] However, before these next wafers are actually washed, and
after the old washing solution has been stored in the washing
solution storage tank 72, some of the new washing solution is
supplied to and circulated through the washing tank 32 and
circulation section 34 for a predetermined period of time. Then,
this portion of the new washing solution is discharged. That is,
the new washing solution contaminated by the remnants of the old
washing solution existing in the system is discharged so that the
system is clean before the new washing solution used to wash the
new wafers is produced in the washing tank 32.
[0071] It may also be necessary to re-establish the original
environment in which the first set of wafers were washed. In this
case, the washing solution stored in the washing solution storage
tank 72 is used. The other (new) washing solution is drawn from the
washing tank 32 and circulation section 34 through a respective
portion of the connection piping C and into another washing
solution storage tank 72. Again, however, first chemicals are
supplied form the washing solution supply section 30 to the washing
tank 32 in a predetermined ratio conforming to that used to produce
the original washing solution. This washing solution is circulated
through the washing tank 32 by the circulation section for a
predetermined period of time to clean the tank 32 and circulation
piping R. Then, the cleaning washing solution is discharged so that
the washing tank 32 and circulation section 34 remain free of the
remnants of the new washing solution that was just used to wash
wafers.
[0072] Conversely, the cleaning washing solution may be the
original washing solution that was stored in the chemical storage
tank 72. In this case, the original environment in which the first
set of wafers were washed is re-established by supplying chemicals
into the washing tank 32 from the washing solution supply section
30 to thereby produce the second batch of original washing solution
in the washing tank 32.
[0073] As an alternative to using the washing solution for
cleaning, i.e., flushing the system, as described above using
either the chemicals from the washing solution supply section 30 or
the washing solution from the storage tank 70, the washing solution
supply section 30 may include a separate chemical storage tank 38
containing pure water or a separate washing device dedicated to the
cleaning of the washing tank 32 and circulation section 34.
[0074] According to the present invention, as described above, the
environment in which wafers are washed, i.e., the characteristics
of the washing solution, can be easily changed in a short period of
time. On the other hand, the characteristic of a particular washing
solution can be maintained over a particularly long washing cycle.
Still further, little washing solution is wasted when having to
switch back and forth between various kinds of washing solutions.
The present invention can provide each and all of these working
advantages without the need to alter the set-up of the washing
tanks. Accordingly, the present invention enhances the efficiency
and reduces the costs currently associated with the washing of
semiconductor wafers during the process of manufacturing
semiconductor devices.
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