Drainage structure in polishing plant and method of polishing using structure

A polishing plant includes a polishing apparatus having a top ring for holding a workpiece and a turn table for polishing a surface of the workpiece held by the top ring. A cleaning apparatus has cleaning machines for cleaning the workpiece polished by the polishing apparatus. At least one drainage pipe connected to the polishing apparatus discharges a waste liquid from the polishing apparatus, and at least one drainage pipe connected to the cleaning apparatus to discharges a waste liquid from the cleaning apparatus are provided as separate plural of drainage pipe lines, depending on the type of waste liquid. By use of the polishing plant of the present invention, treatment waste liquids can be efficiently conducted.

BACKGROUND OF THE INVENTION 
The present invention relates to a drainage structure in a polishing plant. 
In the manufacture of semiconductor wafers, a polishing apparatus has been 
used for polishing a semiconductor wafer so as to enable a surface of the 
semiconductor wafer to be made flat with a mirror-surface finish. 
Generally, a polishing apparatus is used in combination with a cleaning 
apparatus for cleaning and drying semiconductor wafers after polishing. In 
a conventional polishing plant comprising a polishing apparatus and a 
cleaning apparatus, a number of drainage pipes are employed to discharge 
various liquids which have been used in various devices in the polishing 
and cleaning apparatuses, and these drainage pipes are connected to a 
single pipe. Therefore, in the above-mentioned conventional polishing 
plant, the liquids which have been used in various devices in the 
polishing and cleaning apparatuses are individually discharged as waste 
liquids through the drainage pipes from those devices, collected into the 
single pipe, and finally discharged from the polishing plant through a 
single drainage pipe line. 
In the above-mentioned conventional polishing plant in which various waste 
liquids are finally discharged from the polishing plant through a single 
drainage pipe line, it is impossible to perform different treatments of 
waste liquids depending on the type of waste liquid to be treated (e.g., 
the concentration of impurities and the type of chemicals). The waste 
liquids finally discharged from the polishing plant are supplied to a 
solid matter-treating apparatus, in which solid matter in the waste 
liquids is removed, and are transferred to a factory drainage line as an 
industrial waste liquid. 
Therefore, in a conventional polishing plant, even a waste liquid which is 
not seriously contaminated or does not contain solid matter is subjected 
to the same treatment as performed with respect to a waste liquid which is 
seriously contaminated or contains solid matter, so that not only does a 
waste liquid-treating plant inevitably become large, but costs of 
operation for treating waste liquids also become high. Further, in a 
conventional polishing plant, it is impossible to reuse a reusable waste 
liquid which is not seriously contaminated, because various types of waste 
liquids are mixed with the reusable waste liquid. In addition, there is a 
danger such that a chemical reaction may occur when various chemicals used 
in the polishing and cleaning apparatuses are mixed. 
SUMMARY OF THE INVENTION 
In view of the above-mentioned situations, the present invention has been 
made. It is a primary object of the present invention to provide a 
drainage structure in a polishing plant, by use of which a waste liquid 
treatment can be efficiently conducted. 
According to the present invention, there is provided a polishing plant 
comprising: 
a polishing apparatus having a top ring for holding a workpiece and a turn 
table for polishing a surface of the workpiece held by the top ring; and 
a cleaning apparatus having cleaning machines for cleaning the workpiece 
polished by the polishing apparatus, 
wherein at least one drainage pipe connected to the polishing apparatus to 
discharge a waste liquid (or water) from the polishing apparatus and at 
least one drainage pipe connected to the cleaning apparatus to discharge a 
waste liquid (or water) from the cleaning apparatus are provided 
separately or divided into a plurality of drainage pipe lines, depending 
on the type of waste liquid. 
Preferably, the at least one drainage pipe connected to the polishing 
apparatus and the at least one drainage pipe connected to the cleaning 
apparatus are divided into a plurality of drainage pipe lines, depending 
on the degree of contamination of the waste liquid, and with respect to 
waste liquids discharged through the plurality of drainage pipe lines, the 
waste liquid exhibiting a low degree of contamination is reused as a 
liquid supplied to a device from which a waste liquid exhibiting a high 
degree of contamination is discharged. 
The foregoing and other objects, features and advantages of the present 
invention will be apparent from the following detailed description and 
appended claims taken in connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinbelow, embodiments of the present invention are described in detail, 
with reference to the accompanying drawings. 
First, description is made on a general construction of a polishing plant 
comprising a polishing apparatus and a cleaning apparatus. FIG. 2 is a 
schematic plan view showing an internal structure of a polishing plant 3 
comprising a polishing apparatus 30 and a cleaning apparatus 50 according 
to the present invention. 
As shown in FIG. 2, the polishing apparatus 30 comprises: a turn table 33 
provided in the center of the polishing apparatus 30; a polishing unit 37 
having a top ring 35 provided at one side of the turn table 33; a dressing 
unit 41 having a dressing tool 39 provided at the other side of the turn 
table 33; and a work-transferring device 43. The cleaning apparatus 50 
comprises: two central conveying robots 51 and 53 shiftable in directions 
shown by a double-headed arrow C; a first cleaning machine 55, a second 
cleaning machine 57 and a spin drier 59 having a cleaning ability (the 
spin drier 59 may not have a cleaning ability in the present invention), 
all of which are disposed side by side at one side of the conveying robots 
51 and 53; and two work turning-over machines 61 and 63 which are disposed 
side by side at the other side of the conveying robots 51 and 53. 
In the polishing plant 3 arranged as mentioned above, for example, when a 
cassette 65 in which semiconductor wafers before polishing are contained 
is set at a position shown in FIG. 2, the conveying robot 53 takes out one 
semiconductor wafer from the cassette 65 and conveys the wafer to the work 
turning-over machine 63, where the wafer is turned over. Then, the wafer 
is transferred from the work turning-over machine 63 to the conveying 
robot 51, and the conveying robot 51 conveys the wafer to the 
work-transferring device 43. 
The wafer is transferred from the work-transferring device 43 onto the turn 
table 33 as indicated by an arrow A while being held by a lower surface of 
the top ring 35 of the polishing unit 37, and is polished by a polishing 
surface 34 of the turn table 33 which is rotating. In this instance, an 
abrasive liquid is supplied from a supply pipe 24 (shown in FIG. 1) to the 
polishing surface 34. 
After polishing, the wafer is returned to the work-transferring device 43 
and conveyed to the work turning-over machine 61 by the conveying robot 
51. In the work turning-over machine 61, the wafer is turned over while 
being rinsed with purified water. Subsequently, the wafer is washed with 
chemicals and purified water in the first cleaning machine 55 and the 
second cleaning machine 57. The resultant wafer is cleaned and then 
spin-dried in the spin drier 59 having a cleaning ability. Then, the wafer 
is returned to the cassette 65 by the conveying robot 53. 
With respect to the dressing unit 41, it is appropriately moved onto the 
turn table 33 as indicated by an arrow B. The dressing tool 39 which is 
rotating is pressed against the polishing surface 34 of the turn table 33 
which is also rotating, so that the polishing surface 34 is refreshed and 
conditioned. In this instance, purified water is supplied from a supply 
pipe 25 (shown in FIG. 1) to the polishing surface 34. 
FIG. 1 is a plan view showing a base 20 on which various devices in the 
polishing apparatus 30 and the cleaning apparatus 50 are provided and also 
showing drainage pipes, etc. which are provided in parts of the base 20. 
As shown in FIG. 1, the base 20 as a whole is arranged in planar form by 
assembling a number of steel materials, each having a cross-section in the 
form of an inverted C (or in an I form or a generally square form). 
Various devices shown in FIG. 2 are provided on the base 20. The turn 
table 33, the work turning-over machine 61, the work turning-over machine 
63, the first cleaning machine 55, the second cleaning machine 57 and the 
spin drier 59 having a cleaning ability (a third cleaning machine) are 
provided in a part D, a part E, a part F, a part G, a part H and a part I 
of the base 20, respectively. Abrasive liquid and purified water are 
supplied to the part D through the supply pipe 24 and the supply pipe 25, 
respectively, and a first cleaning liquid, a second cleaning liquid and a 
third cleaning liquid are supplied to the part G, the part H and the part 
I through a supply pipe 26, a supply pipe 27 and a supply pipe 28, 
respectively. Further, a cleaning liquid, such as purified water, is 
supplied to the part E through a supply pipe 29. Each of the liquids 
supplied to the supply pipes 24 to 29 may be a liquid which has not yet 
been used. 
A waste liquid W1 containing the abrasive liquid and the purified water for 
dressing which have been used on the turn table 33 is discharged to the 
outside from a drainage pipe 10 connected to a pipe connector 101 in a 
lower surface of the turn table 33. 
A liquid which has been used in the work turning-over machine 61 is 
discharged as a waste liquid W2' from a drainage pipe 12 connected to a 
pipe connector 120 in a lower surface of the work turning-over machine 61. 
A liquid which has been used in the first cleaning machine 55 is 
discharged as a waste liquid W2" from a drainage pipe 13 connected to a 
pipe connector 130 in a lower surface of the first cleaning machine 55. 
The drainage pipe 13 is connected to the drainage pipe 12. Thus, a mixture 
of the waste liquid W2' and the waste liquid W2" is discharged as a waste 
liquid W2 from the drainage pipe 12 to the outside. 
A liquid which has been used in the second cleaning machine 57 is 
discharged as a waste liquid W3' from a drainage pipe 14 connected to a 
pipe connector 140 in a lower surface of the second cleaning machine 57. A 
liquid which has been used in the spin drier 59 having a cleaning ability 
is discharged as a waste liquid W3" from a drainage pipe 15 connected to a 
pipe connector 150 in a lower surface of the spin drier 59 having a 
cleaning ability. The drainage pipe 15 is connected to the drainage pipe 
14. Thus, a mixture of the waste liquid W3' and the waste liquid W3" is 
discharged as a waste liquid W3 from the drainage pipe 14 to the outside. 
That is, in the above-mentioned embodiment of the present invention, a 
drainage pipe line for discharging a liquid which has been used in the 
polishing apparatus 30, a drainage pipe line for discharging both a liquid 
which has been used in the work turning-over machine 61 and a liquid which 
has been used in the first cleaning machine 55 in the cleaning apparatus 
50, and a drainage pipe line for discharging both a liquid which has been 
used in the second cleaning machine 57 and a liquid which has been used in 
the spin drier 59 having a cleaning ability in the cleaning apparatus 50 
are provided as separate drainage pipe lines. 
Further, in this embodiment, the drainage pipe 10 is connected to a solid 
matter-treating apparatus 21 for separating solid matter from the waste 
liquid W1, which apparatus is connected to a factory drainage line 11. The 
factory drainage line 11 is connected to a waste liquid-treating plant 23 
in the factory. Thus, the waste liquid W1 is treated, together with 
industrial waste liquids discharged from various sites in the factory. 
The drainage pipe 12 is connected to the waste liquid-treating plant 23 
directly or through the factory drainage pipe line 11. 
Further, the drainage pipe 14 is connected to a waste liquid-reusing 
apparatus 22, for example, the supply pipe 29 for the work turning-over 
machine 61, through a waste liquid tank T, a pump P, a flow control valve 
V and a filter S for removal of particles. In case that it is desired to 
reuse the waste liquid as a highly pure liquid, an ion-exchange separation 
device is arranged between the pump P and the filter S so that ionic 
impurities in the waste liquid are removed. 
The waste liquid W1 discharged from the polishing apparatus 30, in which 
semiconductor wafers are polished utilizing an abrasive liquid, has a high 
concentration of impurities due to a large amount of solid matter. By the 
above-mentioned arrangement of the present invention, the waste liquid W1 
having a high concentration of impurities is transferred through the 
drainage pipe 10 to the solid matter-treating apparatus 21 where 
separation of solid matter is effected, and is treated as an industrial 
waste liquid in the waste liquid-treating plant 23 in the factory. 
The waste liquid, from which solid matter contained in the abrasive liquid 
is removed to some extent in the polishing apparatus 30 and of which the 
concentration of impurities is still relatively high although separation 
of solid matter therefrom is not necessary, is transferred to the waste 
liquid-treating plant 23 directly as an industrial waste liquid, and is 
treated. 
The waste liquid W3 obtained by cleaning the wafers in the second cleaning 
machine 57 and the spin drier 59 having a cleaning ability has a low 
concentration of impurities. In this embodiment, the drainage pipe 14 is 
connected to the supply pipe 29 for the work turning-over machine 61, so 
that the waste liquid W3 is mixed with the cleaning liquid, such as 
purified water, supplied from the supply pipe 29 to the work turning-over 
machine 61, and is reused as a rinse liquid for the wafer in the work 
turning-over machine 61. However, although not shown in the drawings, the 
drainage pipe 14 may not be connected to the supply pipe 29, but may be 
connected to the work turning-over machine 61 directly. The waste liquid 
W3, which has a low concentration of impurities, is not necessarily mixed 
with purified water. The waste liquid W3 may be used alone as a rinse 
liquid, and purified water may be used as a supplemental rinse liquid when 
the amount of the waste liquid W3 is insufficient for rinsing. 
In the above-mentioned embodiment of the present invention, waste liquids 
are separately collected, depending on the concentration of impurities, so 
that a treatment of each of the waste liquids can be efficiently 
conducted. Further, a waste liquid having a relatively low concentration 
of impurities which has been collected in one cleaning step can be reused 
in a previous cleaning step, leading to a lowering of costs. Generally, in 
the present invention, a waste liquid supplied from the drainage pipe 14 
is reused alone and when the waste liquid tank T becomes almost empty, 
liquids which have not yet been used may be supplied from the supply pipes 
25, 26, 27 and 29 to the turn table 33, the first cleaning machine 55, the 
second cleaning machine 57 and the work turning-over machine 61. 
In this embodiment, the waste liquid W3 from the drainage pipe 14, which 
has a low concentration of impurities, is reused. However, in the present 
invention, the waste liquid W3 may be discharged directly as an industrial 
waste liquid without being reused. Alternatively, a part of the waste 
liquid W3 from the drainage pipe 14 may be reused and the remaining part 
of the waste liquid W3 may be discharged as an industrial waste liquid. 
Further, in this embodiment, the drainage pipe lines for discharging waste 
liquids are provided separately depending on the concentration of 
impurities in the waste liquid (a degree of contamination of the waste 
liquid). However, in the present invention, the drainage pipe lines may be 
divided or provided separately depending on, for example, the type of 
chemicals in the waste liquid. 
As has been described above, according to the present invention, a 
plurality of drainage pipes connected to the polishing apparatus and the 
cleaning apparatus are divided or provided separately into a plurality of 
drainage pipe lines, depending on the type of waste liquid, so that a 
treatment of each of different types of waste liquids can be efficiently 
conducted. Further, in the present invention, it is possible to reuse the 
waste liquid, so that costs of operation for treating waste liquids can be 
lowered. 
In the embodiment shown in FIG. 3, all the waste liquids W2 and W3 
discharged from cleaning apparatus 20 are treated by a system which 
includes a tank T, a pump P, a flow control valve, a filter S and an 
ion-exchange separation device U so that the entire amount of the pure 
water used in operation of the polishing apparatus 30 is prepared from the 
waste liquid of the cleaning apparatus.