Liquid overflow tank combined with partition isolating two chambers

An overflow tank for rinsing an article such as a wafer with a liquid such as pure water is continuously supplied with the liquid. The tank comprises a partition isolating two adjacent chambers from each other, and is utilized as a passage for transferring an article from one of the chambers to the other chamber. The overflow tank has two opening sections that are opened at the two chambers, respectively, and each of the opening sections is defined by a continuous and level peripheral edge so that an overflow of the liquid can occur over all of the peripheral edge. During the passage of the article through the overflow tank, the article is rinsed with the water.

BACKGROUND OF THE INVENTION 
1) Field of the Invention 
The present invention refers to an overflow tank continuously supplied with 
a liquid such as pure water including a partition isolating two adjacent 
chambers from each other, and is utilized as a passage for transferring an 
article from one of the two chambers to the other chamber. Such an 
overflow tank may be advantageously used to rinse a silicon wafer with 
pure water in a wafer fabrication process in which a plurality of 
integrated circuits is formed over a surface of the silicon wafer. 
2) Description of the Related Art 
As is well known, the wafer fabrication process involves steps of: washing 
the wafers with a solution based upon alkali, a solution based upon acid, 
and an organic solution for removing organic material dust and metal dust 
therefrom; and rinsing the wafers with a liquid such as pure water after 
washing the wafers with each of the solutions. For example, the washing 
and rinsing steps are carried out before an oxide layer formation process 
and after a photoetching process. Of course, the organic material dust and 
metal dust must be removed from the wafers because they cause defects such 
as short circuits, and circuit breakages in the integrated circuits formed 
over the wafer surface. 
The washing and rinsing steps must be carried out in a closed washing space 
so that the wafers can be protected from dust in the atmosphere. Also, 
when the wafer is washed in the closed washing space with at least two 
different solutions, the closed washing space must be divided by a 
partition into two washing chambers that are isolated from each other 
thereby, and in which the respective different solutions are independently 
used. This is because it is necessary to prevent a chemical reaction 
between the vapors of the different solutions. For example, when the 
different solutions comprise an alkali-based solution and an acid-based 
solution, respectively, and when the wafer is washed in a commom closed 
washing space with said solutions, vapors from the alkali-based and 
acid-based solutions easily mix to produce a salt by the chemical reaction 
therebetween, and thus the wafers may be polluted by the salt. Thus, when 
the wafer is washed with different solutions, the closed space must be 
divided into separate washing chambers so that independent washing of the 
wafer with the different solutions can be carried out. 
Note, the solutions are frequently heated to enhance a washing effect 
thereof. For example, the washing temperature of an NH.sub.4 OH solution, 
an HCl solution, or the like is about 80.degree. C., and the washing 
temperature of an H.sub.2 SO.sub.4 solution or the like and the organic 
solution such as a dichlorobenzene solution is about 120.degree. C. The 
heated solutions generate large quantities of vapor thereby emphasizing 
the need for isolated chambers. 
Conventionally, a movable partition is used to divide the closed washing 
space into separate washing chambers because it is necessary to transfer 
the wafers from one of the washing chambers to another washing chamber. 
Namely, the partition is moved between a closed position in which the 
washing chambers are isolated from each other and an opened position so 
that the washing chambers are in communication with each other for 
transferring the wafers. The use of the movable partition results in a 
large and expensive wafer washing installation because a drive mechanism 
is necessary to operate the movable partition. Also, when the partition is 
opened, the vapors inevitably mix with each other. 
Thus, it has been suggested that an overflow tank for rinsing the wafers 
with a liquid such as pure water be utilized as a passage for transferring 
the wafers from one of the washing chambers to another washing chamber. In 
particular, the overflow tank is combined with a fixed partition in such a 
manner that the wafers can be transferred from one of the washing chambers 
to the other washing chamber through the overflow tank. With this 
arrangement, a wafer washing installation can be smaller because no drive 
mechanism is necessary for the partition, and the adjacent washing 
chambers are always isolated from each other. Nevertheless, the 
conventional arrangement, in which the overflow tank is utilized as the 
passage for transferring the wafers, involves drawbacks which should be 
further eliminated for the reasons as discussed hereinafter in detail. 
On the other hand, a production of a liquid crystal display, in which a 
fine electrode pattern is formed over a display substrate by a 
photoetching process, involves the same problem as mentioned above. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide an improved 
overflow tank for rinsing an article such as a wafer with a liquid such as 
pure water that is combined with a partition isolating two adjacent 
chambers from each other, and is utilized as a passage for transferring 
the article from one of the chambers to the other chamber. 
In accordance with the present invention, there is provided an overflow 
tank for rinsing an article with a liquid and is continuously supplied 
with the liquid. The overflow tank comprising: a partition isolating two 
adjacent chambers from each other; and a tank body having two opening 
sections and incorporated in the partition member in such a manner that 
the opening sections are opened at the two chambers, respectively, whereby 
the article can be transferred from one of the chambers to the other 
chamber through the tank body as it is rinsed with the liquid. Each of the 
two opening sections being defined by a flush peripheral edge so that an 
overflow of the liquid can occur over all of the peripheral edges. 
According to another aspect of the present invention, there is provided an 
overflow tank for rinsing an article such as a wafer with liquid such as 
pure water in a closed washing space in which the article is washed with 
at least two different solutions. The overflow tank comprising: a tank 
body having an upper peripheral edge positioned at the same horizontal 
plane to define an upper opening thereof; a groove formation member 
bridging across the upper opening of the tank body to divide it into first 
and second opening sections and having a bottom wall portion disposed at a 
level lower than that of the upper peripheral edge of the tank body, and 
opposed side wall portions extended upward from and along the side edges 
of the bottom wall portion, the bottom wall portion and opposed side wall 
portions of the groove formation member defining a groove opened at ends 
thereof, each of the opposed side wall portions of the groove formation 
member having an upper edge positioned flush with the upper peripheral 
edge of the tank body and partially defining the corresponding first or 
second opening sections; and a partition member combined with the tank 
body and the groove formation member and dividing the closed washing space 
into first and second washing chambers in which the article is washed with 
the respective different solutions, the tank body being utilized as a 
passage for transferring the article from the first washing chamber to the 
second washing chamber, at least a portion of the partition member being 
extended along the groove of the groove formation member and in contact 
with an upper surface of the bottom wall portion thereof, the tank body 
being continuously supplied with the liquid, whereby an overflow of the 
liquid can occur over the peripheral edges defining the first and second 
opening sections without stagnating the liquid at any locations thereof, 
while the article is rinsed with the liquid during the transferring of the 
article from the first washing chamber to the second washing chamber 
through the overflow tank.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First, for a better understanding of the present invention, prior arts are 
explained with reference to FIGS. 1 to 7. 
FIG. 1 schematically shows a conventional wafer washing installation by way 
of example. This wafer washing installation comprises a housing 10 for 
defining a closed space therein. The closed space or interior space of the 
housing 10 is divided by a movable partition 12 into two washing chambers 
14 and 16. In the first washing chamber 14, a washing tank 14a and two 
water tanks 14b and 14c are disposed, and in the second washing chamber 
16, a washing tank 16a and two water tanks 16b and 16c are disposed. The 
washing tanks 14a and 16a are filled with, for example, an alkali solution 
such as NH.sub.4 OH+H.sub.2 O.sub.2 +H.sub.2 O and an acid solution such 
as HCl+H.sub.2 O.sub.2 +H.sub.2 O, respectively, solutions of which are 
heated up to a temperature of about 80.degree. C., so that the washing 
chambers 14 and 16 are permeated with alkali and acid vapors generated 
from the alkali and acid solutions, respectively. The water tanks 14b, 14c 
and 16 b, 16c are filled with pure water. The movable partition 12 is 
moved by a suitable drive mechanism (not shown) between a closed position 
(FIG. 1) in which the washing chambers are isolated from each other and an 
opened position (not shown) so that the washing chambers 14 and 16 are in 
communication with each other. 
In FIG. 1, reference numeral 18 indicates a carrier for receiving some 
silicon wafers W, supported and moved by a well-known transfer machine 
(not shown), as indicated by arrows A.sub.1, A.sub.2, A.sub.3, A.sub.4, 
A.sub.5, and A.sub.6. In particular, the carrier 18 is first immersed in 
the alkali solution held by the washing tank 14a, so that the wafers W are 
washed with the alkali solution, and is then moved from the washing tank 
14a to the water tank 14b, as indicated by the arrow A.sub.1, so that the 
wafers W are rinsed with the pure water. Successively, the carrier 18 is 
moved from the water tank 14b to the water tank 14c, as indicated by the 
arrow A.sub.2, so that the wafers W are further rinsed with the pure 
water. When the rinsing of the wafers W with the pure water held by the 
water tank 14c is completed, the partition 12 is moved from the closed 
position to the opened position. Thus, the carrier 18 with the wafers W 
can be transferred from the first washing chamber 14 to the second washing 
chamber, and can then be immersed in the acid solution held by the washing 
tank 16a, as indicated by the arrow A.sub.4. After the washing of the 
wafers W with the acid solution is completed, the carrier 18 is 
successively moved as indicated by the arrows A.sub.4 and A.sub.5, so that 
the wafers W are rinsed with the pure water held by the water tanks 16b 
and 16c. Thereafter, the carrier 18 with the wafers W is transferred from 
the second washing chamber 16 to another processing station (not shown), 
as indicated by the arrow A.sub.6. 
As mentioned above, this conventional installation is relatively large and 
expensive because of the movable partition 18. Also, when the movable 
partition 18 is opened, the alkali and acid vapors inevitably mix with 
each other, and a salt is produced by the chemical reaction therebetween. 
To overcome the problems involved in the above-mentioned installation, it 
has been suggested that an overflow tank for rinsing the wafers with the 
pure water is utilized as a passage for transferring the wafers from one 
of the washing chambers to another washing chamber. With reference to FIG. 
2, such an overflow tank is indicated by reference numeral 20. This 
overflow tank 20 is combined with a fixed partition 22 disposed at a 
boundary between the adjacent washing chambers in such a manner that the 
overflow tank 20 is fitted in an opening formed in the partition 22, and 
is continuously supplied with pure water so that the pure water overflows 
from an upper opening edge of the overflow tank 20, as indicated by arrows 
B. With this arrangement, the adjacent washing chambers are always 
isolated from each other because of the overflow of the pure water. 
With reference to FIGS. 3 and 4, a wafer carrier is indicated by reference 
numeral 24, and a transfer member for supporting and moving the wafer 
carrier 24 is indicated by reference numeral 26. As is apparent from these 
drawings, the transfer member 26 with the wafer carrier 24 is immersed in 
the pure water at one side of the partition 22 (FIG. 3), and is then moved 
to the other side thereof (FIG. 4). Thereafter, the wafer carrier 24 is 
caught and lifted by another transfer member (not shown). Thus, the 
transferring of the wafers from one of the washing chambers to the other 
washing chamber should be carried out in such a manner that these washing 
chambers are isolated from each other. Nevertheless, the isolation between 
the adjacent washing chambers may be broken because a water surface level 
of the pure water held by the overflow tank 20 is lowered when the wafer 
carrier 24 is lifted from the overflow tank 20, and thus the adjacent 
washing chambers are in vapor communication with each other, as indicated 
by arrows C shown in FIG. 5. 
To prevent the vapor communication between the adjacent washing chambers, 
it has been suggested that a portion of the partition 22, which lies 
across the opening of the overflow tank 20, be extended downward, as shown 
in FIG. 6. With this arrangement, although the water surface level of the 
overflow tank 20 is lowered when the wafer carrier 24 is lifted from the 
overflow tank 20, vapor communication between the adjacent washing 
chambers cannot occur. However, the extended portion of the partition 22 
causes another problem which should be overcome. In particular, the water 
held by the overflow tank 20 can stagnate at central zones that are in the 
vicinity of both sides of the partition 22, and thus the pollutant 
substances P removed from the wafers during the rinsing thereof can gather 
at the stagnant zones, as symbolically shown in FIGS. 6 and 7. Of course, 
the pollutant substances P should be discharged with the overflow of the 
water from the overflow tank 20. 
FIGS. 8 and 9 show an embodiment of an overflow tank according to the 
present invention. This overflow tank comprises a box-like tank body 28 
including a rectangular bottom wall 28a, and two pairs of opposed side 
walls 28b; 28c and 28d; 28e extended upward from the two opposed side 
edges of the bottom wall 28a, as shown in FIG. 8. Upper edges of the side 
walls 28b, 28c, 28d, and 28e are positioned on the same horizontal plane 
and cooperate with each other to form a single rectangular peripheral edge 
by which an upper opening of the tank body 28 is defined. Preferably, the 
tank body 28 is integrally formed of a suitable material exhibiting 
corrosion-resistance, such as stainless steel, FRP (fiber reinforced 
plastic), or the like. The overflow tank further comprises a groove 
formation member 30 provided between the opposed side walls 28d and 28e at 
a middle location thereof and preferably formed of the same material as 
the tank body 28. The groove formation member 30 includes a bottom wall 
30a bridging the opposed side walls 28d and 28e and disposed at a level 
lower than that of the upper edges of the side walls 28b, 28c, 28d, and 
28e, and opposed side walls 30b and 30c extending upward from the side 
edges of the bottom wall 30a between the opposed side walls 28d and 28e 
and having upper edges that are flush with the upper edges of the side 
walls 28b, 28c, 28d, and 28e. Thus, the upper opening of the tank body 28 
is divided into two opening sections 32a and 32b by the groove formation 
member 30. As shown in FIG. 8, a groove of the groove formation member 30, 
which is defined by the bottom wall 30a and the side wall 30b and 30c, is 
opened at the ends thereof by forming U-shaped notches 28d.sub.1 and 
28e.sub.1 at the opposed side walls 28d and 28e, respectively. 
The overflow tank is combined with a partition member 34 including an upper 
partition part 34a and a lower partition part 34b. As is apparent from 
FIG. 8, the upper and lower partition parts 34a and 34b have a generally 
U-shaped configuration, and thus are connected by screws 36 to each other 
so as to form a rectangular opening therebetween, in which the overflow 
tank can be fitted and received at the location at which the groove 
formation member 30 is provided. Thus, the upper partition part 34a is 
partially extended along the groove defined by the bottom wall 30a and 
side walls 30b and 30c of the groove formation member 30, and is in 
contact with an upper surface of the bottom wall 30a thereof. Also, the 
upper partition part 30a is partially in contact with outer surfaces of 
the opposed side walls 28d and 28e. Furthermore, the lower portion part 
34b is transversely in contact with a lower surface of the bottom wall 28a 
and is partially in contact with the outer surfaces of the opposed side 
walls 28d and 28e. Although the partition member 34 is shown as being 
small for the convenience of illustration, in actual fact it is wide 
enough so that a closed washing space defined by a housing (not shown) can 
be divided into washing chambers. Note, the upper and lower partition 
parts 34a and 34b may be formed of a stainless steel, a synthetic resin or 
the like. 
In FIG. 8, reference numeral 40 indicates a duct for continuously supplying 
the overflow tank with pure water. The duct 39 is provided with a duct 
section 40a laying on the bottom of the overflow tank and having 
perforations (not shown) formed therein, through which the pure water is 
discharged from the duct section 40a, as indicated by arrows C. Thus, the 
pure water overflows from the opening sections 32a and 32b, as indicated 
by arrows D in FIGS. 8 and 9. Also, reference numeral 38 indicates a 
transfer member for supporting and moving a wafer carrier 39 (FIG. 9) in 
which some silicon wafers are received. The transfer member 38 is moved by 
a drive mechanism (not shown) to transfer the wafer carrier 39 from the 
washing chamber in which the opening section 32b is disposed to the 
washing chamber in which the opening section 32a is disposed. 
In operation, the transfer member 38 with the wafer carrier 39 is immersed 
in the pure water of the overflow tank through the opening section 32b, as 
shown in FIG. 9, and is then moved to a position just below the opening 
sections 32a. Thereafter, the wafer carrier 39 is caught and lifted by 
another transfer member (not shown) through the opening sections 32a. 
Namely, similar to the conventional overflow tank as mentioned above, the 
overflow tank according to the present invention can also be utilized as a 
passage for transferring the wafers from one of the washing chambers to 
the other washing chamber. Of course, during the passage of the wafer 
carrier 39 through the overflow tank, the wafers received therein can be 
sufficiently rinsed with the pure water. 
Although a water surface level of the pure water held by the overflow tank 
is lowered when the wafer carrier 39 is lifted from the overflow tank 
through the opening sections 32a, vapor communication between the adjacent 
washing chambers can be effectively prevented because the groove formation 
member 30 is positioned at a level lower than the water surface level of 
the pure water. Also, although the overflow tank may be received at the 
rectangular opening of the partition member 34 in such a manner that some 
clearance is left therebetween because of a tolerance, these clearances 
can be effectively sealed by water streams which are generated in and 
flowed out of the groove of the groove formation member 30, because of the 
overflow of the pure water from the upper edges of the side walls 30b and 
30c. Furthermore, the clearances that may be formed between the lower 
partition part 34b and the bottom wall 28a of the tank body 28 can be 
effectively sealed by holding the water in the washing chambers at a level 
higher than that of the bottom wall 28a. Note, the level of the water held 
in the washing chambers can be controlled by adjusting the amount of the 
water discharged therefrom. 
On the other hand, according to the present invention, the overflow of the 
pure water can occur all over the peripheral edges defining the opening 
sections 32a and 32b, respectively, because each of the side walls 30b and 
30c of the groove formation member 30 has the upper edge positioned at the 
same level as that of the edges of the side walls 28b, 28c, 28d, and 28e 
of the tank body 28. Thus, the pure water cannot stagnate at any locations 
of the opening sections 32a and 32b. Namely, a gathering of pollutant 
substances as discussed with reference to FIGS. 6 and 7 cannot occur at 
the opening sections 32a and 32b. 
Finally, it will be understood by those skilled in the art that the 
foregoing description is of a preferred embodiment of the disclosed 
overflow tank, and that various changes and modifications may be made to 
the present invention without departing from the spirit and scope thereof.