U.S. patent application number 09/724999 was filed with the patent office on 2001-05-31 for polishing liquid supply apparatus.
Invention is credited to Chono, Keiko, Kawashima, Kiyotaka, Shimomoto, Hiroshi, Tanikawa, Mutsumi.
Application Number | 20010002361 09/724999 |
Document ID | / |
Family ID | 18307518 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010002361 |
Kind Code |
A1 |
Kawashima, Kiyotaka ; et
al. |
May 31, 2001 |
Polishing liquid supply apparatus
Abstract
A polishing liquid supply apparatus supplies a polishing liquid
to a polishing unit. The polishing liquid supply apparatus includes
a supply tank for storing a polishing liquid having a predetermined
concentration, and a polishing liquid pipe for delivering the
polishing liquid from the supply tank to a polishing liquid supply
nozzle in the polishing unit. The polishing liquid supply apparatus
further includes an additive tank for storing an additive having a
predetermined concentration, and an additive supply pipe for adding
the additive supplied from the additive tank to the polishing
liquid stored in the supply tank or to the polishing liquid in a
polishing liquid passage including the polishing liquid pipe.
Inventors: |
Kawashima, Kiyotaka;
(Yokohama-shi, JP) ; Tanikawa, Mutsumi;
(Yokohama-shi, JP) ; Shimomoto, Hiroshi;
(Yokohama-shi, JP) ; Chono, Keiko; (Fujisawa-shi,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
Suite 800
2033 K Street, N.W.
Washington
DC
20006
US
|
Family ID: |
18307518 |
Appl. No.: |
09/724999 |
Filed: |
November 29, 2000 |
Current U.S.
Class: |
451/443 |
Current CPC
Class: |
B24B 37/04 20130101;
B24B 57/02 20130101; B01F 23/49 20220101 |
Class at
Publication: |
451/443 |
International
Class: |
B24B 001/00; B24B
007/30; B24B 021/18; B24B 055/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 29, 1999 |
JP |
11-337319 |
Claims
What is claimed is:
1. An apparatus for supplying a polishing liquid to a polishing
unit for polishing a workpiece, comprising: a supply tank for
storing a polishing liquid having a predetermined concentration; a
polishing liquid pipe for delivering the polishing liquid from said
supply tank to a polishing liquid supply nozzle in said polishing
unit; an additive tank for storing an additive having a
predetermined concentration; and an additive supply pipe for adding
the additive supplied from said additive tank to the polishing
liquid stored in said supply tank or to the polishing liquid in a
polishing liquid passage including said polishing liquid pipe.
2. An apparatus according to claim 1, further comprising: an
additive concentration adjusting device for adjusting said additive
to said predetermined concentration.
3. An apparatus according to claim 2, wherein said additive
concentration adjusting device has an additive preparing device for
mixing a raw material powder and a solvent to form said additive
having said predetermined concentration.
4. An apparatus according to claim 1, further comprising: an
additive quantity adjusting device provided in at least one of said
additive tank and said additive supply pipe for adjusting the
quantity of said additive which is added to said polishing
liquid.
5. An apparatus according to claim 2, further comprising: a sensor
for detecting the concentration of said additive; and a controller
for controlling said additive concentration adjusting device based
on an output signal from said sensor.
6. An apparatus according to claim 4, further comprising: a sensor
for detecting the concentration of said additive; and a controller
for controlling said additive quantity adjusting device based on an
output signal from said sensor.
7. A polishing apparatus for polishing a workpiece, comprising: a
polishing unit for polishing a workpiece by holding the workpiece
by a workpiece holder and pressing the workpiece against a
polishing surface on a polishing table; and a polishing liquid
supply apparatus for supplying a polishing liquid to said polishing
unit, said polishing liquid supply apparatus comprising: a supply
tank for storing a polishing liquid having a predetermined
concentration; a polishing liquid pipe for delivering the polishing
liquid from said supply tank to a polishing liquid supply nozzle in
said polishing unit; an additive tank for storing an additive
having a predetermined concentration; and an additive supply pipe
for adding the additive supplied from said additive tank to the
polishing liquid stored in said supply tank or to the polishing
liquid in a polishing liquid passage including said polishing
liquid pipe.
8. A polishing apparatus according to claim 7, further comprising:
an additive concentration adjusting device for adjusting said
additive to said predetermined concentration.
9. A polishing apparatus according to claim 8, wherein said
additive concentration adjusting device has an additive preparing
device for mixing a raw material powder and a solvent to form said
additive having said predetermined concentration.
10. A polishing apparatus according to claim 7, further comprising:
an additive quantity adjusting device provided in at least one of
said additive tank and said additive supply pipe for adjusting the
quantity of said additive which is added to said polishing
liquid.
11. A polishing apparatus according to claim 8, further comprising:
a sensor for detecting the concentration of said additive; and a
controller for controlling said additive concentration adjusting
device based on an output signal from said sensor.
12. A polishing apparatus according to claim 10, further
comprising: a sensor for detecting the concentration of said
additive; and a controller for controlling said additive quantity
adjusting device based on an output signal from said sensor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing liquid supply
apparatus for use in a polishing unit for polishing a surface of a
workpiece such as a semiconductor wafer, and more particularly to a
polishing liquid supply apparatus which is capable of supplying a
polishing liquid that stably contains an additive.
[0003] 2. Description of the Related Art
[0004] Recent rapid progress in semiconductor device integration
demands smaller and smaller wiring patterns or interconnections and
also narrower spaces between interconnections which connect active
areas. One of the processes available for forming such
interconnection is photolithography. Though the photolithographic
process can form interconnections that are at most 0.5 .mu.m wide,
it requires that surfaces on which pattern images are to be focused
by a stepper be as flat as possible because the depth of focus of
the optical system is relatively small.
[0005] It is therefore necessary to make the surfaces of
semiconductor wafers flat for photolithography. One customary way
of flattening the surfaces of semiconductor wafers is to polish
them with a polishing apparatus.
[0006] FIG. 5 of the accompanying drawings shows a conventional
polishing unit. As shown in FIG. 5, the conventional polishing unit
comprises a turntable 142 with a polishing cloth 140 attached to an
upper surface thereof, a top ring 144 for holding a semiconductor
wafer W which is a workpiece to be polished while rotating the
semiconductor wafer W and pressing the semiconductor wafer W
against the polishing cloth 140, and a polishing liquid supply
nozzle 146 for supplying a polishing liquid Q to the polishing
cloth 140. The top ring 144 is connected to a top ring drive shaft
148, and vertically movably supported by an air cylinder (not
shown).
[0007] The top ring 144 supports on its lower surface an elastic
pad 150 made of polyurethane or the like. The semiconductor wafer W
is held on the top ring 144 in intimate contact with the elastic
pad 150. The top ring 144 also has a cylindrical guide ring 152
mounted on a lower outer circumferential surface thereof for
preventing the semiconductor wafer W from being dislodged from the
lower surface of the top ring 144 while the semiconductor wafer W
is being polished. The guide ring 152 is fixed to the top ring 144,
and has a lower end projecting downwardly beyond the lower holding
surface of the top ring 144 to define a recess between the lower
holding surface of the top ring 144 and the projecting lower end of
the guide ring 152 for holding the semiconductor wafer W
therein.
[0008] With the above structure, the semiconductor wafer W is held
against the lower surface of the elastic pad 150 on the lower
surface of the top ring 144, and pressed against the polishing
cloth 140 by the top ring 144. The turntable 142 and the top ring
144 are rotated about their own axes to move the polishing cloth
140 and the semiconductor wafer W relatively to each other for
thereby polishing the semiconductor wafer W. At this time, the
polishing liquid Q is supplied from the polishing liquid supply
nozzle 146 to the polishing cloth 140. The polishing liquid Q
comprises fine abrasive particles suspended in, for example, an
alkaline solution. Therefore, the semiconductor wafer W is polished
by a composite action of a chemical action of the alkaline solution
and a mechanical action of the fine abrasive particles. Such a
polishing process is referred to as chemical mechanical polishing
(CMP).
[0009] In order to polish the semiconductor wafer W satisfactorily
by the polishing apparatus, it is necessary that the polishing
liquid having a constant concentration be supplied stably at a
constant rate to the polishing unit. The polishing liquid is
supplied from a polishing liquid supply system which includes a raw
material tank for storing a raw material that comprises a mixture
of KOH, NH.sub.4OH, or the like, and powder silica, and an
adjustment tank for adjusting the raw material supplied from the
raw material tank to a predetermined concentration by diluting the
raw material with pure water or a chemical solution. The polishing
liquid supply system further includes a supply tank for temporarily
storing a polishing liquid adjusted by the adjustment tank and
supplying the polishing liquid, and a polishing liquid supply
piping system interconnecting the tanks for supplying the polishing
liquid from the supply tank to the polishing liquid supply nozzle
146 in the abrasive unit.
[0010] The polishing liquid contains an additive such as an
oxidizing agent for modifying or reforming the polished surface of
the semiconductor wafer. Specifically, an oxidizing agent such as
H.sub.2O.sub.2 (hydrogen peroxide) is added for the purpose of
oxidizing a metal film of copper or tungsten that has been
deposited on the semiconductor wafer. It has been customary to add
the additive when the polishing liquid is produced. Thus, in the
case where the additive, like oxidizing agent, added to the
polishing liquid is chemically unstable, the properties of the
polishing liquid tend to be changed when the polishing liquid with
the additive is held in stock for a long period of time, with the
result that the polishing capability of the polishing liquid
becomes unstable.
[0011] If the additive is added to the polishing liquid in the
polishing liquid supply system, then it has been the general
practice to supply the additive, which has been diluted to a
desired concentration with a solvent such as pure water in a
polyethylene container or the like, from an additive supply unit to
the polishing liquid supply system. Thus, the additive supply unit
is relatively large in size, and needs a large installation space.
In addition, because the additive is added in a small quantity to
the polishing liquid in the polishing liquid supply system, the
additive is required to be supplied highly accurately.
SUMMARY OF THE INVENTION
[0012] It is therefore an object of the present invention to
provide a polishing liquid supply apparatus which is capable of
supplying a polishing liquid that stably contains an additive to a
polishing unit, and a polishing apparatus having such polishing
liquid supply apparatus.
[0013] According to an aspect of the present invention, there is
provided an apparatus for supplying a polishing liquid to a
polishing unit for polishing a workpiece, comprising: a supply tank
for storing a polishing liquid having a predetermined
concentration; a polishing liquid pipe for delivering the polishing
liquid from the supply tank to a polishing liquid supply nozzle in
the polishing unit; an additive tank for storing an additive having
a predetermined concentration; and an additive supply pipe for
adding the additive supplied from the additive tank to the
polishing liquid stored in the supply tank or to the polishing
liquid in a polishing liquid passage including the polishing liquid
pipe.
[0014] Since the additive is added to the polishing liquid at a
position close to the polishing unit where the polishing liquid is
used, the polishing liquid that contains the additive of stable
quality at a required concentration can be supplied to the
polishing unit even if the additive comprises an oxidizing agent or
the like that tends to be easily degraded or decomposed due to
aging. Therefore, the polishing unit can polish a workpiece stably
in a high quality with the polishing liquid. The additive may
comprise an oxidizing agent such as iron nitrate, an aqueous
solution of hydrogen peroxide or ammonium persulfate, or material
of stabilizing the distribution of particle diameters of abrasive
particles in the polishing liquid.
[0015] The polishing liquid supply apparatus may further comprise
an additive concentration adjusting device for adjusting the
concentration of the additive. The additive concentration adjusting
device may comprise an additive preparing device for mixing a raw
material powder and a solvent to form the additive. Inasmuch as the
additive is prepared from its raw material immediately before it is
used, the additive is prevented from being degraded or decomposed
due to aging.
[0016] The polishing liquid supply apparatus may further comprise
an additive concentration adjusting device associated with the
additive tank or the additive supply pipe, for adjusting the
concentration of the additive, or an additive quantity adjusting
device associated with the additive tank or the additive supply
pipe, for adjusting the quantity of the additive which is added to
the polishing liquid. The additive concentration adjusting device
and/or the additive quantity adjusting device are effective to keep
the concentration of the additive in the polishing liquid at a
desired value so as to meet the required conditions.
[0017] The polishing liquid supply apparatus may further comprise a
sensor associated with the polishing liquid pipe for detecting the
concentration of the additive, and a controller for controlling the
additive concentration adjusting device in response to an output
signal from the sensor. Further, the polishing liquid supply
apparatus may further comprise a sensor associated with the
polishing liquid pipe for detecting the concentration of the
additive, and a controller for controlling the additive quantity
adjusting device in response to an output signal from the
sensor.
[0018] According to another aspect of the present invention, there
is provided a polishing apparatus for polishing a workpiece,
comprising: a polishing unit for polishing a workpiece by holding
the workpiece by a workpiece holder and pressing the workpiece
against a polishing surface on a polishing table; and a polishing
liquid supply apparatus for supplying a polishing liquid to the
polishing unit, the polishing liquid supply apparatus comprising: a
supply tank for storing a polishing liquid having a predetermined
concentration; a polishing liquid pipe for delivering the polishing
liquid from the supply tank to a polishing liquid supply nozzle in
the polishing unit; an additive tank for storing an additive having
a predetermined concentration; and an additive supply pipe for
adding the additive supplied from the additive tank to the
polishing liquid stored in the supply tank or to the polishing
liquid in a polishing liquid passage including the polishing liquid
pipe.
[0019] The above and other objects, features, and advantages of the
present invention will become apparent from the following
description when taken in conjunction with the accompanying
drawings which illustrate preferred embodiments of the present
invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic view of a polishing apparatus which
incorporates a polishing liquid supply apparatus according to a
first embodiment of the present invention;
[0021] FIG. 2 is a schematic view of the polishing liquid supply
apparatus shown in FIG. 1;
[0022] FIG. 3 is a schematic view of an additive supply unit of the
polishing apparatus shown in FIG. 1;
[0023] FIG. 4 is a schematic view of a polishing apparatus which
incorporates a polishing liquid supply apparatus according to a
second embodiment of the present invention; and
[0024] FIG. 5 is a vertical cross-sectional view of a conventional
polishing apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Like or corresponding reference numerals denote like or
corresponding parts throughout views.
[0026] A polishing apparatus which incorporates a polishing liquid
supply apparatus according to a first embodiment of the present
invention will be described below with reference to FIG. 1.
[0027] As shown in FIG. 1, the polishing apparatus generally
comprises a polishing unit 12, a polishing liquid supply unit 10
for supplying a polishing liquid to the polishing unit 12, and an
additive supply unit 200 for supplying an additive to the polishing
liquid supply unit 10. The polishing unit 12 has a turntable 142
and a polishing liquid supply nozzle 146, and is of a structure
identical to the conventional polishing unit shown in FIG. 5. The
polishing cloth 140 on the turntable 142 constitutes a polishing
surface on a polishing table.
[0028] The polishing liquid supply unit 10, partly shown in FIG. 1,
will be described in detail below with reference to FIG. 2. As
shown in FIG. 2, the polishing liquid supply unit 10 includes a
plurality of raw liquid tanks 14 for storing a raw polishing
liquid, and an adjustment tank 16 for adjusting the raw polishing
liquid supplied from the raw liquid tanks 14 to a predetermined
concentration by diluting the raw polishing liquid with pure water
or a chemical solution. The polishing liquid supply unit 10 further
includes a supply tank 18 for temporarily storing the polishing
liquid whose concentration has been adjusted by the adjustment tank
16, and supplying the polishing liquid to the polishing unit 12.
Each of the tanks 14, 16 and 18 houses therein an agitator 22 that
is rotated by a motor 20. A pure water line 24 is connected to the
raw liquid tanks 14 and the adjustment tank 16. The raw liquid
tanks 14 and the adjustment tank 16 are interconnected by a raw
liquid pipe 28 having a raw liquid pump 26.
[0029] The adjustment tank 16 and the supply tank 18 are
interconnected by a liquid feed pipe 32 having a liquid feed pump
30 and a shut-off valve 32a. The liquid feed pipe 32 is branched
into a return pipe 33 which is connected to an upper end of the
adjustment tank 16 via a shut-off valve 33a. The supply tank 18 is
connected to a polishing liquid pipe 46 of the polishing unit 12 by
a supply pipe 36 having a supply pump 34. The supply pipe 36 is
branched into a return pipe 37 which is connected to an upper end
of the supply tank 18 via a shut-off valve (circulation valve)
50.
[0030] The liquid feed pipe 32 and the supply pipe 36 are also
branched respectively at positions upstream of the pumps 30, 34 and
connected to a drain line 38 via respective shut-off valves 38a,
38b. The drain line 38 extending from the supply pipe 36 is shunted
by a forced drain line 44 having a drain pump 40 and a drain valve
42. The polishing liquid pipe 46 connected to the downstream
portion of the supply pipe 36 serves to supply the polishing liquid
to the turntable 142 of the polishing unit 12. The turntable 142
constitutes a polishing table having a polishing surface thereon.
The polishing liquid pipe 46 has a polishing liquid supply valve
48, and the return pipe 37 has a circulation valve 50 positioned
downstream of the point where the return pipe 37 is branched from
the supply pipe 36.
[0031] The supply pipe 36 is branched into extraction pipes 62a,
62a and 62b having an abrasive particle diameter distribution
measuring device 52, a coarse particle measuring device 54, and an
oxidation-reduction electrometer 56. The extraction pipes 62a, 62a
and 62b are joined together at a position downstream of the
measuring devices 52, 54 and the electrometer 56, and connected to
the drain line 38. The supply pipe 36 has a solid material
concentration measuring device 58 positioned downstream of the
points where the extraction pipes 62a, 62b are branched from the
supply pipe 36. Measured results from the measuring devices 52, 54,
58 and the electrometer 56 are inputted into a controller 60. The
supply pipe 36 is shunted by a bypass line 98, with a filter 100,
which is connected to the supply pipe 36 via valves 96a, 96b.
[0032] The additive supply unit 200 will be described below with
reference to FIGS. 1 and 3. The additive supply unit 200 comprises
a constant rate feeder 202 for receiving a raw material powder of
the additive from a raw material cartridge 201 and feeding a
constant rate, at a time, of the raw material powder, a
concentration adjustment tank 203 for being supplied with the raw
material powder, and an additive supply pump 219. The raw material
cartridge 201 comprises a closed container having an openable lid
in its bottom, and can be placed on the upper part of the constant
rate feeder 202.
[0033] The constant rate feeder 202 comprises a container placed on
a weighing machine 211, and has a mount base for the raw material
cartridge 201, and a hand-operated valve 204 and a hopper 205 that
are positioned below the mount base. The hand-operated valve 204
serves to open the openable lid in the bottom of the raw material
cartridge 201. The constant rate feeder 202 houses centrally
therein an agitator 206 for agitating and compacting the supplied
raw material powder, and also houses in its lower portion a screw
feeder 208 for discharging the raw material powder through a powder
supply pipe 209 that projects laterally from a lower side wall of
the constant rate feeder 202. The agitator 206 has agitating vanes
mounted on a horizontal drive shaft that is rotated by a motor 207.
When rotated, the agitating vanes compact the raw material powder
to a desired density and supply the compacted raw material powder
to the screw feeder 208. The screw feeder 208 has an end coupled to
a motor 210 by which the screw feeder 208 is rotated about its own
axis for thereby feeding the compacted raw material powder into the
powder supply pipe 209.
[0034] The powder supply pipe 209 has an L-shaped structure
including a horizontal section which receives an outer end portion
of the screw feeder 208 and a vertical section extending downwardly
from an outer end of the horizontal section. The vertial section
has a lower portion inserted into an opening 215 of a lid 217 of
the concentration adjustment tank 203. The powder supply pipe 209
has a lower tip end connected to a moisture blocking damper 216.
The moisture blocking damper 216 is opened when the raw material
powder is supplied, and is closed when the raw material powder is
not supplied, whereby a vapor in the concentration adjustment tank
203 is preventing from entering the powder supply pipe 209.
[0035] The concentration adjustment tank 203 is positioned below
the constant rate feeder 202. A solvent supply pipe 212 is also
inserted into the lid 217 of the concentration adjustment tank 203.
The solvent supply pipe 212 serves to supply a solvent to the
concentration adjustment tank 203. The solvent supply pipe 212 has
an orifice 213 and a flow rate regulating valve 214. The
concentration adjustment tank 203 houses therein an agitator 218
for mixing the raw material powder and the solvent to form an
additive having uniform concentration. The agitator 218 comprises
agitating vanes mounted on a vertical drive shaft extending
downwardly from the lid 217, and a drive motor mounted on the lid
217 and coupled to the drive shaft. The agitator 218 may be
replaced with a magnet stirrer disposed in a lower portion of the
concentration adjustment tank 203.
[0036] An additive supply pipe 220 is connected to the bottom of
the concentration adjustment tank 203. The additive supply pipe 220
serves to deliver the additive to a polishing liquid supply system
with an additive supply pump 219. The additive supply pump 219 may
comprise a diaphragm pump, a plunger pump, a tubing pump, or the
like for supplying the additive at a controlled constant rate. It
is desirable that the additive supply pump 219 comprises a plunger
pump for supplying the additive at a highly stable rate. The
polishing liquid supply system refers to a system downstream of the
loop which comprises the supply tank 18, the supply pump 34, and
the supply pipe 36.
[0037] The additive supply pump 219 has an outlet connected to the
supply tank 18 via, the additive supply pipe 220, an additive
supply pipe 221 and an air-operated valve 300 or to the supply
nozzle 146 via, the additive supply pipe 220, an additive supply
pipe 222 and a valve 301. The additive supply pipe 222 is branched
into a return pipe 223 which returns the additive to the
concentration adjustment tank 203 when the polishing unit is at
rest. There turn pipe 223 is connected to the concentration
adjustment tank 203 via a return valve 302. The supply tank 18, the
supply nozzle 146, or any other desired location, to which the
additive is to be supplied, may be selected depending on the type
and properties of the polishing liquid used. If the polishing
liquid used has a constant nature, then a permanently fixed piping
system may be employed to supply the additive to one location.
[0038] The polishing liquid pipe 46 has a flow rate sensor 303 and
a concentration sensor 305 and the additive supply pipe 222 has a
flow rate sensor 304 for confirming whether the polishing liquid
supply system is supplied with a predetermined quantity of the
additive. Although the additive supply pipe 222 may have an
additive concentration sensor, since it is usually difficult to
measure an additive concentration from the additive alone, the
typical property of the polishing liquid is detected by the
concentration sensor 305 after the additive is added to the
polishing liquid. The concentration sensor 305 comprises an
ultrasonic concentration sensor, for example, and each of the flow
rate sensors 303, 304 comprises an ultrasonic flow rate sensor, for
example.
[0039] Output signals from the sensors 303, 304 and 305 are
inputted into the controller 60. Based on the inputted signals, the
controller 60 outputs control signals to control the concentration
of the additive in the concentration adjustment tank 203 and the
flow rate of the additive discharged from the additive supply pump
219 in a feedback control loop. Therefore, a polishing liquid
having a constant additive concentration can be supplied to the
polishing liquid supply system.
[0040] Operation of the polishing apparatus thus constructed will
be described below.
[0041] The raw polishing liquid in the raw liquid tanks 14 is
delivered to the adjustment tank 16 by the raw liquid pump 26. In
the adjustment tank 16, the raw polishing liquid is diluted to a
predetermined concentration with pure water that is supplied from
the pure water line 24. The polishing liquid whose concentration
has thus been adjusted is then delivered to the supply tank 18 by
the liquid feed pump 30.
[0042] The polishing liquid stored in the supply tank 18 is caused
to flow through the supply pipe 36 by the supply pump 34. When the
polishing unit 12 is operated to polish a semiconductor wafer, the
polishing liquid supply valve 48 is opened to supply the polishing
liquid via the polishing liquid pipe 46 and the polishing liquid
nozzle 146 onto the polishing surface of the turntable 142 in the
polishing unit 12. When polishing of the semiconductor wafer is
completed, the polishing liquid supply valve 48 is closed, and the
circulation valve 50 is opened to circulate the polishing liquid
through a circulation passage comprising the supply tank 18, the
supply pipe 36, and the return pipe 37. Therefore, even when the
polishing liquid is not supplied to the polishing unit 12, the
polishing liquid is prevented from remaining stagnant in the pipes
36, 37 and 46, and hence abrasive particles in the polishing liquid
are prevented from being deposited in these pipes 36, 37 and 46.
The adjustment tank 16 is also associated with a similar
circulation passage for returning the polishing liquid back to the
adjustment tank 16 when the polishing liquid is not supplied to the
supply tank 18.
[0043] The additive supply unit 200 is operated as follows: The raw
material cartridge 201 is set to the upper portion of the constant
rate feeder 202, and the hand-operated valve 204 is operated to
open the bottom of the raw material cartridge 201 for thereby
supplying the raw material powder of the additive into the hopper
205. The raw material powder is supplied through the hopper 205
into the constant rate feeder 202 where it is agitated and
compacted to a constant density by the agitator 206 actuated by the
motor 207. The motor 210 is energized to rotate the screw feeder
208 for thereby supplying the raw material powder via the powder
supply pipe 209 into the concentration adjustment tank 203 at a
given rate that is controlled by adjusting the rotational speed of
the motor 210. The supplied quantity of the raw material powder can
be confirmed by the weighing machine 211 disposed beneath the
constant rate feeder 202.
[0044] The raw material powder is supplied into the concentration
adjustment tank 203 through the opening 215 of the lid 217, and is
uniformly mixed with the solvent supplied from the solvent supply
pipe 212 by the agitator 218 in the concentration adjustment tank
203, thus preparing an additive having a predetermined
concentration. The prepared additive is then supplied from the
concentration adjustment tank 203 via the additive supply pipe 220
to the supply tank 18, for example, by the supply pump 219. The
supplied quantity of the additive is adjusted based on the flow
rate detected by the flow rate sensor 303 and the concentration
detected by the concentration sensor 305 so that the concentration
of the additive in the polishing liquid in the supply tank 18 is
kept constant. If the additive used is susceptible to deterioration
with age, then the additive should preferably be supplied directly
to the polishing liquid nozzle 146 via the additive supply pipe
222. That is, the concentration adjustment tank 203 constitutes an
additive tank for storing an additive having a predetermined
concentration. The flow rate sensor 303, the concentration sensor
305, the controller 60 and the supply pump 219 constitute an
additive quantity adjusting device for adjusting the quantity of
the additive which is added to the polishing liquid.
[0045] The abrasive particle diameter distribution, the number of
coarse particles, the oxidation-reduction potential, and the solid
material concentration of the polishing liquid flowing through the
supply pipe 36 are measured respectively by the abrasive particle
diameter distribution measuring device 52, the coarse particle
measuring device 54, the oxidation-reduction electrometer 56, and
the solid material concentration measuring device 58. Measured data
from these measuring devices 52, 54, 58 and the electrometer 56 are
inputted into the controller 60 and monitored thereby. Based on the
inputted measured data, the controller 60 determines whether the
abrasive particle diameter distribution has changed or not and
whether coarse particles have been produced or not. If the abrasive
particle diameter distribution has changed, then the controller 60
outputs a control signal to actuate ultrasonic oscillators 94a, 94b
attached to the respective tanks 16, 18.
[0046] The polishing liquid supply unit 10 combined with the
additive supply unit 200 is capable of adding the additive such as
an oxidizing agent to the polishing liquid while adjusting the
quantity of the additive, in a downstream region close to the
polishing unit 12. Therefore, the polishing liquid supply unit 10
can supply the polishing liquid that contains the additive of
stable quality and concentration without deterioration or
decomposition with age to the polishing unit 12. Thus, the
semiconductor wafers can be polished stably in a desired
quality.
[0047] FIG. 4 schematically shows a polishing apparatus which
incorporates a polishing liquid supply apparatus according to a
second embodiment of the present invention.
[0048] The polishing liquid supply unit 10 shown in FIG. 4 supplies
a polishing liquid from a common source to a plurality of polishing
units 12. Although two polishing units 12 are shown as being
connected to the polishing liquid supply unit 10, more polishing
units 12 may be connected to the polishing liquid supply unit 10.
In FIG. 4, the polishing liquid supply unit 10 comprises a buffer
tube 110 in the form of a cylindrical container, a circulation pipe
112 extending from the bottom of the buffer tube 110 through a
region near the polishing units 12 back to the top of the buffer
tube 110, and a plurality of discharge pipes 114 branched from the
circulation pipe 112 to the respective polishing units 12.
[0049] The circulation pipe 112 has a circulation pump 116 for
circulating a predetermined quantity of the polishing liquid at all
times through the circulation pipe 112, a back pressure valve 118
for keeping the pressure in the circulation pipe 112 at a
predetermined level or higher, and a pressure sensor 120 for
detecting the pressure in the circulation pipe 112. Each of the
discharge pipes 114 has a polishing liquid supply valve 122 and a
discharge pump 124 for discharging the polishing liquid from the
circulation pipe 112.
[0050] The buffer tube 110 serves as both the adjustment tank 16
and the supply tank 18 according to the first embodiment. A raw
liquid pipe 28, a pure water line 24, and a chemical liquid supply
line 106 are connected to the top of the buffer tube 110. The
buffer tube 110 is associated with an ultrasonic oscillator 94 as a
first polishing liquid property stabilizing means, a plurality of
level detectors 126a, 126b and 126c for detecting the level of the
polishing liquid in the buffer tube 110, and an air bag 128 made of
an elastically expandable and contractible material. The air bag
128 serves to suppress changes in the pressure in the buffer tube
110 due to changes in the level of the polishing liquid in the
buffer tube 110 while keeping the space in the buffer tube 110
hermetic against the atmosphere around the buffer tube 110.
[0051] In the embodiment shown in FIG. 4, an abrasive particle
diameter distribution measuring device 52, a course particle
measuring device 54, an oxidation-reduction electrometer 56, and a
solid material concentration measuring device 58 are connected to
the circulation pipe 112 at positions downstream of the circulation
pump 116. The circulation pipe 112 is shunted by a bypass line 98,
with a filter 100, which is connected to the circulation pipe 112
through valves 96a, 96b. An additive supply pipe from an additive
supply unit is connected to the buffer tube 110 through a valve 300
or directly to each of the polishing liquid supply nozzles 146
through the additive supply pipe 222 and the valve 301. Various
sensors are positioned in the same manner as with those of the
first embodiment.
[0052] The polishing apparatus shown in FIG. 4 is operated
substantially in the same manner as the polishing apparatus shown
in FIGS. 1 through 3. With the polishing liquid supply unit 10
shown in FIG. 4, since the polishing liquid is circulated at all
times through the circulation pipe 112 from which the polishing
liquid is supplied to the polishing unit 12, the circulation pipe
112 and associated pipes are prevented from being clogged due to
changes in the concentration of the polishing liquid and deposits
of the solid material of the polishing liquid which would otherwise
occur if the polishing liquid remains stagnant. Since the
circulation pipe 112 and associated pipes, which are free of
unwanted clogging, can be increased in length, the polishing liquid
can stably be supplied from the single buffer tube 110 to many
polishing units 12. As a result, the cost of the polishing
apparatus with the polishing liquid supply unit 10 can be
lowered.
[0053] According to the present invention, the raw material powder
of the additive is dissolved in the solvent immediately before the
additive is used, and then the additive is supplied to the
polishing liquid supply system. Therefore, the additive is
prevented from being decomposed or deteriorated while the polishing
liquid is held in storage for a long period of time. The additive
can be supplied at a constant concentration and at a constant rate
to the polishing table for achieving stable polishing capabilities.
Thus, the polishing apparatus can perform good and stable polishing
of semiconductor wafers.
[0054] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
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