U.S. patent application number 11/823159 was filed with the patent office on 2008-01-10 for cleaning method and cleaning apparatus.
This patent application is currently assigned to SONY CORPORATION. Invention is credited to Hideo Watanabe.
Application Number | 20080006291 11/823159 |
Document ID | / |
Family ID | 38918084 |
Filed Date | 2008-01-10 |
United States Patent
Application |
20080006291 |
Kind Code |
A1 |
Watanabe; Hideo |
January 10, 2008 |
Cleaning method and cleaning apparatus
Abstract
A method of cleaning an object in a processing chamber by
supplying a supercritical fluid with an additive and rinsing the
object with the supercritical fluid alone includes the steps of:
opening a back-pressure valve of a branch pipe branched from an
additive pipe on the rinse processing; and purging a residual
additive from the additive pipe by circulating the supercritical
fluid alone into the additive pipe and the branch pipe.
Inventors: |
Watanabe; Hideo; (Kanagawa,
JP) |
Correspondence
Address: |
ROBERT J. DEPKE;LEWIS T. STEADMAN
ROCKEY, DEPKE & LYONS, LLC, SUITE 5450 SEARS TOWER
CHICAGO
IL
60606-6306
US
|
Assignee: |
SONY CORPORATION
|
Family ID: |
38918084 |
Appl. No.: |
11/823159 |
Filed: |
June 27, 2007 |
Current U.S.
Class: |
134/1.3 ;
134/22.12 |
Current CPC
Class: |
H01L 21/02101 20130101;
H01L 21/67057 20130101; B08B 7/0021 20130101; G03F 7/427
20130101 |
Class at
Publication: |
134/1.3 ;
134/22.12 |
International
Class: |
C25F 3/00 20060101
C25F003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2006 |
JP |
P2006-189553 |
Claims
1. A method of cleaning an object in a processing chamber by
supplying a supercritical fluid with an additive and rinsing the
object with the supercritical fluid alone, comprising the steps of:
opening a back-pressure valve of a branch pipe branched from an
additive pipe on the rinse processing; and purging a residual
additive from the additive pipe by circulating the supercritical
fluid alone into the additive pipe and the branch pipe.
2. A method of cleaning an object according to claim 1, further
comprising the steps of: providing the additive pipe joined to a
main pipe for supplying the supercritical fluid with a first
open/close valve at a side of the main pipe and a second open/close
valve for supplying the additive, deriving the branch pipe
including the back-pressure valve from an intermediate portion
between the first open/close valve and the second open/close valve,
and opening the first open/close valve and the back-pressure valve
on the rinse processing and closing the second open/close valve to
purge the residual additive.
3. A method of cleaning an object in a processing chamber by
supplying a supercritical fluid with an additive and rinsing the
object with the supercritical fluid alone, comprising the steps of:
opening a back-pressure valve of a branch pipe branched from an
additive pipe on the rinse processing; and purging a residual
additive from the additive pipe through the branch pipe using a
differential pressure between a high pressure within the processing
chamber and a low pressure caused by opening the back-pressure
valve.
4. A method of cleaning an object according to claim 3, further
comprising the steps of: providing the additive pipe joined to a
main pipe for supplying the supercritical fluid with a first
open/close valve at a side of the main pipe and a second open/close
valve used for supplying the additive, deriving the branch pipe
including the back-pressure valve from an intermediate portion
between the first open/close valve and the second open/close valve,
and opening the first open/close valve and the back-pressure valve
on completion of the rinse processing and closing a back-pressure
valve of a discharge pipe of the processing chamber and the second
open/close valve to purge the residual additive.
5. An apparatus for cleaning an object in a processing chamber by
supplying a supercritical fluid with an additive and rinsing the
object with the supercritical fluid alone, comprising: a main pipe
for supplying the supercritical fluid to the processing chamber
through an open/close valve; a discharge pipe for discharging the
supercritical fluid from the processing chamber through a first
back-pressure valve; an additive pipe for supplying an additive to
the main pipe through a first open/close valve and a second
open/close valve used for supplying the additive; and a branch pipe
derived from an intermediate portion between the first open/close
valve and the second open/close valve, the branch pipe including a
second back-pressure valve.
6. A cleaning apparatus according to claim 5, wherein the second
back-pressure valve is opened on the rinse processing, and the
supercritical fluid alone is circulated into the additive pipe and
the branch pipe to purge a residual additive from the additive
pipe.
7. A cleaning apparatus according to claim 5, wherein the second
back-pressure valve is opened on completion of the rinse
processing, and a residual additive is purged from the additive
pipe through the branch pipe using a differential pressure between
a high pressure within the processing chamber and a low pressure
caused by opening the second back-pressure valve.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present invention contains subject matter related to
Japanese Patent Application JP 2006-189553 filed in the Japanese
Patent Office on Jul. 10, 2006, the entire contents of which being
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a cleaning method and a
cleaning apparatus using a supercritical fluid, applicable to
cleaning of semiconductor substrates in a semiconductor
manufacturing process or cleaning of substrates in a process of
manufacturing a photo-mask or a liquid-crystal display substrate,
for example.
[0004] 2. Description of the Related Art
[0005] In most of semiconductor apparatus manufacturing processes,
for example, patterning processes for forming electrodes of desired
shapes of planes, wiring patterns and contact holes are carried out
by etching patterns on an electrode layer, a wiring layer, an
insulating layer and the like deposited on a semiconductor
substrate.
[0006] In such pattern etching, a resist film is formed on a wiring
layer formed on a substrate, for example. Then, a resist mask
having a resist pattern the shape of which is the same as that of a
desired wiring pattern is formed by patterning the resist film.
Thereafter, the resist mask is used as an etching mask and the
wiring layer is etched to form a wiring pattern. After etching the
wiring layer, the resist mask on the wiring pattern will be removed
in a mask removing process.
[0007] In the mask removing process, the resist mask is typically
removed from a substrate by immersing the substrate with the resist
mask formed thereon into a resist removing solution such as a
sulfate solution, an amine-based resist/polymer remover, a
fluorine-based resist/polymer remover and the like during a
predetermined time period.
[0008] A line width of wiring in the wiring pattern has been
reduced since a semiconductor apparatus has been further integrated
in recent years. In LSI (large-scale integration) circuits, a line
width of wiring becomes substantially not more than 100 nm and also
an aspect ratio (height/width) of wiring pattern is increased.
[0009] As a result, according to a related-art method in which the
resist mask is removed by immersing the substrate into the resist
removing solution, large suction force is generated at a gas-liquid
interface due to large surface tension of the resist removing
solution. Hence, there is a risk that a pattern with a high aspect
ratio will be damaged, that is, a pattern may collapse.
[0010] A damage on a fine structure, such as a pattern collapse may
occur in the process of removing a resist mask when a micromachine
(MEMS: Micro Electro Mechanical Systems) having a hollow structure
that includes a gap between a movable portion and a substrate is
cleaned in the manufacturing process thereof. In addition, such
damage may occur when a porous low-dielectric constant interlayer
insulator is cleaned in the process of forming a wiring structure
based on a damocene method, which is employed in the process of
manufacturing a semiconductor apparatus.
[0011] That is, when an object with a fine structure is cleaned,
according to a related-art cleaning method using a cleaning
solution that has a large surface tension, it is difficult to clean
the object without damaging the fine structure.
[0012] Japanese Unexamined Patent Application Publication No.
1-200828, Japanese Unexamined Patent Application Publication No.
1-286314, Japanese Unexamined Patent Application Publication No.
9-43857, and Japanese Unexamined Patent Application Publication No.
8-181050, for example, disclose respective supercritical
technologies that use a supercritical fluid which may not cause
surface tension as a resist removing solution or a cleaning
solution.
[0013] When a temperature and a pressure of a material increase to
be a critical temperature and a critical pressure specific to the
material or higher than these conditions, the material is given
intermediate properties between liquid and solid and therefore
becomes a supercritical fluid which may not cause surface tension.
The supercritical technologies use such supercritical fluid in a
cleaning processing or the like.
[0014] In particular, carbon dioxide (CO.sub.2) becomes a
supercritical fluid at a temperature of 31.degree. C. under a
pressure of 7.38 MPa, and hence it is not difficult to be used from
an industrial standpoint.
[0015] However, even when an object is cleaned using the
supercritical fluid CO.sub.2 as a cleaning solution, it is
difficult for the supercritical fluid CO.sub.2 to dissociate a
resist or a resist residue from the object, so that the resist or
the resist residue may not be completely removed from the
object.
[0016] Accordingly, dissociation chemicals (hereinafter referred to
as "additives") to remove the resist and the resist residue from
the object or a dissociation solvent thereof has been added to
facilitate the removal of a resist mask from the object. Here, the
dissociation solvent is a dissolution-assisting agent for an
additive and used when the additive may not be highly soluble in
the supercritical fluid CO.sub.2.
[0017] U.S. Patent Unexamined Patent Application Publication No.
US2002/0048731 A1 discloses a method of removing a photoresist film
or a photoresist residue (hereinafter both referred to as a "resist
film") from a semiconductor substrate (hereinafter referred to as a
"wafer") by applying a supercritical fluid technology. The method
is specifically described below.
[0018] First, a wafer with a resist film deposited on its surface
is placed within a processing chamber of a cleaning apparatus.
Then, a pressure in a pressure chamber is adjusted and a
supercritical fluid CO.sub.2 and an additive are placed within the
pressure chamber. Further, the pressure in the pressure chamber is
adjusted and the supercritical fluid CO.sub.2 and the additive are
introduced into the pressure chamber. The wafer is maintained in
the supercritical fluid CO.sub.2 in which the additive is
dissolved, such that the supercritical fluid CO.sub.2 including the
additive may contact with the resist film until the resist film is
removed from the wafer. After the resist film is removed from the
wafer, the pressure is released and the wafer is cleaned.
[0019] According to US2002/0048731 A1, the method can remove not
only the photoresist film and the photoresist residue but also
other particles and a metal contaminated material on the wafer.
[0020] Further, if the additive is difficult to be dissolved into
the supercritical fluid CO.sub.2, in addition to the additive, a
dissociation solvent may be added to the supercritical fluid
CO.sub.2 as a solvent for combining the additive and the
supercritical fluid CO.sub.2. Through those processes, a wafer and
others may be cleaned using a supercritical fluid.
[0021] Japanese Unexamined Patent Application Publication No.
11-216437 discloses a technology in which, in a supercritical fluid
cleaning method, a pressure is rapidly reduced by discharging a
supercritical fluid from a cleaning bath to a separating bath in
the cleaning process so that a flow rate of the supercritical fluid
can be increased to improve cleaning effects.
[0022] FIG. 1 is a schematic diagram showing a supercritical fluid
cleaning apparatus according to related art. As shown in FIG. 1, a
supercritical cleaning apparatus 40 includes a substrate cleaning
bath (i.e., processing chamber) 41, a main pipe (supercritical
fluid pipe) 42 for supplying supercritical fluid, in which a
supercritical fluid CO.sub.2 and an additive are mixed, to the
substrate cleaning bath 41, a discharge pipe 43 for discharging the
supercritical fluid used for cleaning from the substrate cleaning
bath 41 and additive pipes 44 and 45 for supplying the additive to
the supercritical CO.sub.2 pipe (main pipe) 42. In this example,
the supercritical fluid cleaning apparatus 40 includes two systems
of the additive pipes 44 and 45. Also, the pipes 42, 43, 44 and 45
are respectively provided with a supercritical CO.sub.2 supplying
valve (open/close valve) 46, a back-pressure valve 47 and additive
supplying valves (open/close valves) 48 and 49.
[0023] In the cleaning apparatus 40, when an object is cleaned,
such object as a semiconductor wafer is placed within the substrate
cleaning bath 41. Then, the supercritical CO.sub.2 supply valve 46,
the back-pressure valve 47 and the two additive supply valves 48
and 49 are opened and the supercritical fluid in which additives 52
and 53 are added to the supercritical CO.sub.2 51 is supplied
through the main pipe 42 to the substrate cleaning bath 41 to clean
the wafer. After the wafer is cleaned, the additive supply valves
48 and 49 are closed and the supercritical CO.sub.2 51 alone will
be supplied to rinse the wafer. After the wafer is rinsed, the
supercritical CO.sub.2 supply valve 46 is closed, a pressure in the
substrate cleaning bath 41 is reduced to return to the atmospheric
pressure. Subsequently, the semiconductor wafer thus cleaned is
taken out from the substrate cleaning bath 41.
SUMMARY OF THE INVENTION
[0024] The above-mentioned supercritical fluid cleaning is used in
order to prevent a fine structure from being damaged, that is, a
pattern from collapsing, which occurs in a process of removing a
resist mask. However, there still remains a problem that an
additive dissolved into a supercritical fluid remaining in an end
pipe is liquidized in the reduced-pressure state after the wafer is
cleaned, entered into the substrate cleaning bath to wet the wafer
and as a result the fine structure may be damaged. Further, since
the semiconductor wafer is cleaned and rinsed with the
supercritical fluid under an extremely high pressure, it is
difficult to purge the remaining additives from the end pipe in the
rinsing process. If the pressure in the apparatus is returned to an
ordinary pressure in the condition in which the additive is
insufficiently purged from the end pipe, the liquidized additive
enters rapidly into the substrate cleaning apparatus to wet the
semiconductor wafer.
[0025] Further, the above-described problems will be described in
detail with reference to FIG. 1 and FIGS. 2A to 2D. It should be
noted that broken lines in FIGS. 2A to 2D represent flows of
supercritical CO.sub.2 and that solid lines represent flows of
additives and residual additives. In addition, in FIGS. 2A to 2D,
open valves represent valves in the open state and solid valves
represent valves in the closed state.
[0026] When a substrate is cleaned (FIG. 2A), four valves 46, 47,
48 and 49 are all open under a pressure of pipes. At that time,
although the additives 52 and 53 added are pressurized in the
additive pipes 44 and 45, they are generally retained in a liquid
phase. The additives 52 and 53 are added to the supercritical fluid
CO.sub.2 51 to be the supercritical state. Subsequently, the
supercritical fluid to which the additives are added is used to
clean the semiconductor wafer in the substrate cleaning bath
41.
[0027] Next, after the semiconductor wafer is cleaned, the additive
supply valves 48 and 49 provided to the additive pipes 44 and 45
for supplying the additives are closed (FIG. 2B). At that time,
part of the additives 52A and 53A flowed at the instant that the
additive supply valves 48 and 49 are closed remains in the portion
near the additive supply valves 48 and 49. Subsequently, the
semiconductor wafer is rinsed with the supercritical CO.sub.2 51
alone. At that time, since the pressure of the pipe to the
substrate cleaning bath 41 is high, the additives 52A and 53A left
at the portions near the additive supply valves 48 and 49 remain in
these portions. That is, the additives remaining in the pipes 44
and 45 to the substrate cleaning bath 41 may not be purged
sufficiently.
[0028] After the semiconductor wafer is rinsed using the
supercritical CO.sub.2 51 (FIG. 2C), the supercritical CO.sub.2
supply valve 46 is closed, the supercritical fluid discharging
valve 47 is opened to the atmospheric pressure and the
supercritical fluid is discharged from the pipe 42 and the
substrate cleaning bath 41 (FIG. 2D).
[0029] At that time, since the pressures in the pipe 42 and the
substrate cleaning bath 41 are reduced, the additives 52A and 53A
left, in the portions near the additive supply valves 48 and 49 are
moved with a differential pressure in the liquidized state and
entered the substrate cleaning bath 41 (see a magnified view in
FIG. 2D) . As a result, the semiconductor wafer becomes wet with
the liquidized additives 52A and 53A and the fine structure thereof
may be damaged. Therefore, the supercritical technology may not be
utilized sufficiently.
[0030] Further, if the additives are not purged sufficiently as
described above, additives are mixed when another additive is added
using the same pipe in the next wafer processing, causing a problem
that processing intended to perform may not be carried out.
[0031] As another method of purging additives, there may be a
method of causing a large amount of supercritical CO.sub.2 51 to
flow and replace the additives 52A and 53A left in the portions
near the additive supply valves 48 and 49, when the semiconductor
wafer is rinsed. In this case, however, there may be problems
regarding costs and a period of processing time.
[0032] It is desirable to provide a cleaning method and a cleaning
apparatus in which additives remaining within pipes can be purged
sufficiently after a wafer is cleaned.
[0033] According to an embodiment of the present invention, there
is provided a cleaning method in which on rinse processing, a
back-pressure valve of a branch pipe branched from an additive pipe
is opened and a supercritical fluid is circulated into the additive
pipe and the branch pipe to purge a residual additive from the
additive pipe.
[0034] According to an embodiment of the present invention, there
is provided a cleaning method in which on rinse processing, the
back-pressure valve of the branch pipe is opened to reduce and
release pressures in the additive pipes, so that the supercritical
fluid is discharged through the additive pipe and the branch pipe
together with the residual additive to purge the residual
additive.
[0035] According to an embodiment of the present invention, there
is provided a cleaning method in which on completion of the rinse
processing, the back-pressure valve of the branch pipe branched
from the additive pipe is opened, and residual additive is purged
from the additive pipe through the branch pipe using a differential
pressure between a high pressure within the processing chamber and
a low pressure caused by opening the back-pressure valve.
[0036] In the cleaning method according to an embodiment of the
present invention, after the rinse processing, pressure in the
additive pipe is reduced and released by opening the back-pressure
valves of the branch pipe, so that the supercritical fluid is
discharged through the additive pipe and the branch pipe together
with the residual additive to purge the residual additive.
[0037] According to another embodiment of the present invention,
there is provided a cleaning apparatus in which an object in a
processing chamber is cleaned by supplying a supercritical fluid
with an additive and in which the object is rinsed with the
supercritical fluid alone. The cleaning apparatus includes a main
pipe, a discharge pipe, an additive pipe, and a branch pipe. The
main pipe supplies the supercritical fluid to a cleaning bath
through an open/close valve. The discharge pipe discharges the
supercritical fluid from the processing chamber through a first
back-pressure valve. The additive pipe supplies an additive to the
main pipe through a first open/close valve and a second open/close
valve used for an additive. The branch pipe is branched from an
intermediate portion between the first open/close valve and the
second open/close valve, including a back-pressure valve.
[0038] In the cleaning apparatus according to an embodiment of the
present invention, the additive pipe is provided with the first
open/close valve and the second open/close valve and the branch
pipe including the back-pressure valve is derived from the
intermediate portion of the two open/close valves. Accordingly, if
a pressure in the additive pipe is reduced by opening the
back-pressure valve of the branch pipe on the rinse processing on
completion of the cleaning processing, that is, immediately before
the rinse processing is ended, the residual additive is discharged
from the additive pipe from the branch pipe together with the
supercritical fluid to purge the residual additive.
[0039] Further, after the rinse processing is ended, if a pressure
in the additive pipe is reduced by opening the back-pressure valve
of the branch pipe, then the residual additive is discharged from
the additive pipe through the branch pipe together with the
supercritical fluid to purge the residual additive.
[0040] In the cleaning method and the cleaning apparatus according
to the embodiments the present invention, the residual additive can
be sufficiently purged from the additive pipe. Therefore, when a
pressure in the substrate cleaning bath is reduced (when the
pressure in the substrate cleaning bath is returned to an
atmospheric pressure) after the cleaning processing and the rinse
processing, it is possible to prevent liquidized additives from
flowing into the processing chamber. As a result, such problems as
a fine structure of an object being damaged by the liquidized
additive and the object being wet can be prevented. Further, even
in the case where another additive is added to the object using the
same pipe in the subsequent processing, additives can be prevented
from being mixed and hence an intended processing can be carried
out.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 is a schematic diagram showing a part of a
supercritical substrate cleaning apparatus near a substrate
cleaning bath according to related art;
[0042] FIGS. 2A to 2D are schematic process diagrams showing a
cleaning method using a supercritical substrate cleaning apparatus
according to the related art;
[0043] FIG. 3 is a schematic diagram showing a part of a
supercritical fluid substrate cleaning apparatus near a substrate
cleaning bath according to an embodiment of the present
invention;
[0044] FIGS. 4A to 4E are schematic process diagrams showing a
supercritical substrate cleaning method according to a first
embodiment of the present invention; and
[0045] FIGS. 5A to 5E are schematic process diagrams showing a
supercritical substrate cleaning method according to a second
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] According to embodiments of the present invention, a
separate line branched from an additive pipe for supplying an
additive and connected to a back-pressure valve, that is, a branch
pipe is provided. In addition, an open/close valve is provided to
the additive pipe at a position between a connecting main pipe for
supplying a supercritical fluid and the branch pipe.
[0047] A cleaning method according to the embodiments of the
present invention, that is, a method of purging a residual additive
from the additive pipe is performed using a supercritical fluid
with a high pressure which is a feature thereof. According to a
first method, while an object is being rinsed with the
supercritical fluid, the open/close valve is opened to purge the
residual additive from the additive pipe with the supercritical
fluid while the pressure is being controlled using the
back-pressure valve of the branch pipe branched from the additive
pipe. Specifically, the back-pressure valve of the discharge pipe
of the processing chamber is closed and the back-pressure valve of
the branch pipe is opened to cause the supercritical fluid to flow
into the additive pipe and the branch pipe to purge the residual
additive together with the supercritical fluid. Further, on
completion of the rinse processing including the purging of the
residual from the additive pipe, the above-described open/close
valve provided to the additive pipe at a position between a
connecting main pipe and the branch pipe is closed. Accordingly,
pressure of the pipe from the open/close valve to the back-pressure
valve is returned to an ordinary pressure to further facilitate
discharge of the residual additive. After the rinse processing, the
back-pressure valve of the discharge pipe of the processing chamber
is opened to return the pressure in the processing chamber to an
ordinary pressure. Through such operations, the residual additive
within the additive pipe can be prevented from flowing into the
processing chamber.
[0048] According to a second method, on completion of the object
being rinsed with the supercritical fluid, the back-pressure valve
branched from the additive pipe is opened in the supercritical
state so as to retain a sufficiently high pressure. The additive is
discharged from the back-pressure valve together with the
supercritical fluid using a differential pressure between a high
pressure in the processing chamber and a low pressure caused by
opening the back-pressure valve in the branch pipes. Further, the
pipe from the open/close valve to the back-pressure valve is
returned to the ordinary pressure by closing the open/close valves
immediately after opening the back-pressure valve to further
facilitate discharge of the additive. After the open/close valve is
closed, the back-pressure valve directly connected to the
processing chamber is opened to return the pressure in the
processing chamber to the ordinary pressure. According to the
above-mentioned operations and pressure control, the additive
remaining in the additive pipe can be prevented from flowing into
the processing chamber.
[0049] In the embodiments of the present invention, any material
can be used as long as the material is capable of phase transition
to the supercritical fluid. Preferably, carbon dioxide gas which
can be phase-changed to the supercritical fluid at a substantially
ordinary temperature under relatively low pressure is used as a
supercritical fluid generating material. Other materials capable of
phase transition to supercritical fluid have their own
supercritical conditions.
[0050] In addition, in the embodiments of the present invention, at
least any material selected from HF, hydroxyamine-based additive,
alkanolamine-based additive, alkysil-amine-based additive, ammonium
fluoride, water, IPA, methanol, ethanol, isopropanol, ethylene
glycol, acetone, metyl ethyl ketone, dimethyl sulfoxide and
N-methyl pyrrolidine can be used as the additive. According to the
embodiments of the present invention, one kind of additive, or two
or more kinds of additives mixed may be used.
[0051] Embodiments of the present invention will be described below
in detail with reference to the drawings.
[0052] FIG. 3 is a schematic diagram showing an arrangement of a
cleaning apparatus using a supercritical fluid according to an
embodiment of the present invention.
[0053] As shown in FIG. 3, a cleaning apparatus according to the
embodiment of the present invention, that is, a supercritical
cleaning apparatus 1 includes a processing chamber 2, a main pipe
3, additive pipes 4 and 5, and a discharge pipe 6. An object is
placed in the processing chamber (hereinafter referred to as
"substrate cleaning bath" where wafers are cleaned according to the
embodiment) 2. The main pipe 3 supplies supercritical CO.sub.2 21
to the substrate cleaning bath 2 as a supercritical fluid. The
additive pipes 4 and 5 are connected to the main pipe 3 and supply
two kinds of additives 22 and 23 respectively, according to this
embodiment. The discharge pipe 6 discharges a supercritical fluid
used in the substrate cleaning bath 2. The main pipe 3 is provided
with an open/close valve 7 used for supplying the supercritical
CO.sub.2, the discharge pipe 6 is provided with a back-pressure
valve 10 and the additive pipes 4 and 5 are provided with first
open/close valves 8 and 9 used for supplying additives.
[0054] In addition, according to the embodiment of the present
invention, second open/close valves 15 and 16 are provided to the
additive pipes 4 and 5 at a position between a connecting main pipe
3 and the first open/close valves 8 and 9. A branch pipe 11 is
derived from an intermediate portion between the first open/close
valve 8 and the second open/close valve 15 of one additive pipe 4.
Also, a branch pipe 12 is derived from an intermediate portion
between the first open/close valve 9 and the second open/close
valve 16 of the other additive pipe 5. The two branch pipes 11 and
12 are provided with back-pressure valves 13 and 14,
respectively.
[0055] The back-pressure valve 10 of the discharge pipe 6 and the
back-pressure valves 13 and 14 of the branch pipes 11 and 12 are
valves with which pressure can be controlled.
[0056] Next, a first embodiment of a cleaning method for cleaning
an object, for example, a semiconductor wafer (hereinafter referred
to as a "wafer") using the supercritical cleaning apparatus 1
according to the embodiment will be described with operation
processes.
[0057] FIGS. 4A to 4E are respective diagrams showing those
operation processes. It should be noted that open valves represent
valves in the open state and that solid valves represent valves in
the closed state in FIGS. 4A to 4E. Also, thick broken lines
represent flows of supercritical CO.sub.2 and thick solid lines
represent flows of additives and residuals thereof.
[0058] First, a wafer is accommodated and placed within the
substrate cleaning bath 2. Next, as shown in FIG. 4A, cleaning
processing is carried out. Specifically, the open/close valve 7 and
the back-pressure valve 10 are opened so as to retain a
supercritical state and a supercritical CO.sub.2 21 heated and
pressurized is supplied to the substrate cleaning bath 2 through
the main pipe 3. Further, in the state in which the back-pressure
valves 13 and 14 of the branch pipes 11 and 12 are closed, the
first open/close valves 8 and 9 and the second open/close valves 15
and 16 of the additive pipes 4 and 5 are opened. Accordingly, first
and second additives 22 and 23 are supplied through the additive
pipes 4 and 5 to be added to the supercritical CO.sub.2 21 in the
main pipe 3. A supercritical fluid containing the first and second
additives 22 and 23 dissolved into the supercritical CO.sub.2 21 is
supplied to the substrate cleaning bath 2 to clean the wafer.
[0059] Next, on completion of the cleaning process using the
supercritical fluid containing the dissolved additives, as shown in
FIG. 4B, rinse processing is carried out while the supercritical
fluid containing the dissolved additives is being substituted with
a pure supercritical fluid. Specifically, the closed states of the
back-pressure valves 13 and 14 of the branch pipes 11 and 12 are
maintained and the first open/close valves 8 and 9 of the additive
pipes 4 and 5 are closed to stop the supply of the first and second
additives 22 and 23. In that state, the supercritical CO.sub.2 21
alone is supplied and the wafer placed in the substrate cleaning
bath 2 is rinsed with the supercritical CO.sub.2 21. During the
rinse processing, the wafer is rinsed while the supercritical fluid
is discharged with the pressure thereof adjusted using the
back-pressure valve 10. For example, since CO.sub.2 becomes
supercritical at a temperature of 31.degree. C. under a pressure of
7.38 MPa, the back-pressure valve 10 is opened in conditions higher
than the above-described temperature and pressure. In the rinse
processing, while the additive pipes 4 and 5 at the downstream side
of the first open/close valves 8 and 9 are also rinsed, additives
22A and 23A are partly left at portions near the first open/close
valves 8 and 9.
[0060] Next, during the rinse processing, as shown in FIG. 4C,
residual additives 22A and 23A are purged from the additive pipes 4
and 5 immediately before the end of the rinse processing according
to this embodiment. Specifically, the back-pressure valves 13 and
14 of the branch pipes 4 and 5 are opened during the rinse
processing. When the back-pressure valves 13 and 14 are opened, the
back-pressure valve 10 of the discharge pipe 6 is closed
simultaneously. At that time, the back-pressure valves 13 and 14
are opened, while maintaining the rinsing supercritical fluid
within the substrate cleaning bath 2 at a temperature and a
pressure to retain the supercritical state. As a result, the
supercritical CO.sub.2 21 is discharged through the additive pipes
4 and 5 and the branch pipes 11 and 12. At the same time, the
residual additives 22A and 23A are also discharged with the
supercritical CO.sub.2 21 and the inside of the additive pipes 4
and 5 are purged.
[0061] Next, as shown in FIG. 4D, after the inside of the additive
pipes 4 and 5 are sufficiently substituted with the supercritical
CO.sub.2 21, the second open/close valves 15 and 16 of the additive
pipes 4 and 5 are closed. As a result, the rinse processing is
ended. At that time, it is preferable that the back-pressure valves
13 and 14 of the branch pipes 11 and 12 should be in the open
state. When the back-pressure valves 13 and 14 of the branch pipes
11 and 12 are opened, the pipes from the second open/close valves
15 and 16 to the back-pressure valves 13 and 14 are returned to an
ordinary pressure. Therefore, it is possible to facilitate the
discharge of a small amount of the additives remaining in the
additive pipes 4 and 5.
[0062] Next, as shown in FIG. 4E, the inside of the substrate
cleaning bath 2 is returned to the ordinary pressure (atmospheric
pressure). Specifically, the open/close valve 7 of the main pipe 3,
the first open/close valves 8 and 9 and the second open/close
valves 15 and 16 of the additive pipes 4 and 5 are closed, and then
the back-pressure valve 10 of the discharge pipe 6 is opened. At
that time, since the second open/close valves 15 and 16 are closed,
even when a small amount of additives is left in the additive pipes
4 and 5, the remaining additives can be prevented from being
liquidized and entering the substrate cleaning bath 2.
Subsequently, the supply of the supercritical CO.sub.2 21 is
stopped, the pressure in the substrate cleaning bath 2 is returned
to be the ordinary pressure, and the substrate cleaning processing
is ended.
[0063] According to the first embodiment of the cleaning method,
the residual additives can be purged from the additive pipes 4 and
5 during the rinse processing. Therefore, when the pressure in the
substrate cleaning bath 2 is returned to be an ordinary pressure
after the rinse processing is ended, the residual additives can be
prevented from flowing into the substrate cleaning bath 2.
[0064] Next, a second embodiment of a cleaning method for cleaning
an object using the supercritical cleaning apparatus 1 shown in
FIG. 3 will be described with the operation processes.
[0065] FIGS. 5A to 5E are diagrams showing those operation
processes. It should be noted that open valves represent valves in
the open state and that solid valves represent valves in the closed
state in FIGS. 5A to 5E. Also, thick broken lines represent flows
of supercritical CO.sub.2 and thick solid lines represent flows of
additives and residual additives.
[0066] First, a wafer is accommodated and placed within the
substrate cleaning bath 2. Next, as shown in FIG. 5A, cleaning
processing is carried out. Specifically, the open/close valve 7 and
the back-pressure valve 10 are opened so as to retain a
supercritical state and a supercritical CO.sub.2 21 heated and
pressurized is supplied to the substrate cleaning bath 2 through
the main pipe 3. Further, in the state in which the back-pressure
valves 13 and 14 of the branch pipes 11 and 12 are closed, the
first open/close valves 8 and 9 and the second open/close valves 15
and 16 of the additive pipes 4 and 5 are opened. Accordingly, first
and second additives 22 and 23 are supplied through the additive
pipes 4 and 5 to be added to the supercritical CO.sub.2 21 in the
main pipe 3. A supercritical fluid containing the first and second
additives 22 and 23 dissolved into the supercritical CO.sub.2 21 is
supplied to the substrate cleaning bath 2 to clean the wafer.
[0067] Next, on completion of the cleaning process using the
supercritical fluid containing the dissolved additives, as shown in
FIG. 5B, rinse processing is carried out while the supercritical
fluid containing the dissolved additives is being substituted with
a pure supercritical fluid. Specifically, the closed states of the
back-pressure valves 13 and 14 of the branch pipes 11 and 12 are
maintained and the first open/close valves 8 and 9 of the additive
pipes 4 and 5 are closed to stop the supply of the first and second
additives 22 and 23. In that state, the supercritical CO.sub.2 21
alone is supplied and the wafer placed in the substrate cleaning
bath 2 is rinsed with the supercritical CO.sub.2 21. During the
rinse processing, the wafer is rinsed while the supercritical fluid
is discharged with the pressure thereof adjusted using the
back-pressure valve 10. For example, since CO.sub.2 becomes
supercritical at a temperature of 31.degree. C. under a pressure of
7.38 MPa, the back-pressure valve 10 is opened in conditions higher
than the above-described temperature and pressure. In the rinse
processing, while the additive pipes 4 and 5 at the downstream side
of the first open/close valves 8 and 9 are also rinsed, additives
22A and 23A are partly left at portions near the first open/close
valves 8 and 9.
[0068] Next, as shown in FIG. 5C, the open/close valve 7 of the
main pipe 3 is closed. Simultaneously, the back-pressure valve 10
of the discharge pipe 6 is closed and the rinse processing is
ended.
[0069] Next, as shown in FIG. 5D, after the rinse processing is
ended, the back-pressure valves 13 and 14 of the branch pipes 11
and 12 are opened to purge the residual additives 22A and 23A from
the additive pipes 4 and 5. Specifically, on completion of the
rinse processing using the supercritical CO.sub.2 21, the
back-pressure valves 13 and 14 of the branch pipes 4 and 5 are
opened simultaneously, while the substrate cleaning bath 2 is
retained at sufficiently high pressure with the supercritical
CO.sub.2. Since CO.sub.2 becomes the supercritical state at a
temperature of 31.degree. C. under a pressure of 7.38 MPa, the
back-pressure valves 13 and 14 are opened in conditions higher than
the above-described temperature and pressure. As a result, using a
differential pressure between the high pressure within the
substrate cleaning bath 2 and the atmospheric pressure caused by
opening the back-pressure valves 13 and 14, the residual additives
22A and 23A within the additive pipes 4 and 5 and the supercritical
CO.sub.2 21 are discharged from the back-pressure valves 13 and 14,
and the pipes are purged.
[0070] Next, as shown in FIG. 5E, the second open/close valves 15
and 16 of the additive pipes 4 and 5 are closed immediately after
the back-pressure valves 13 and 14 are opened. Accordingly, even if
a small amount of additives is left in the additive pipes 4 and 5,
the remaining additives can be prevented from being liquidized and
entering the substrate cleaning bath 2. Subsequently, pressures in
the pipes from the first open/close valves 8 and 9 to the
back-pressure valves 13 and 14 are returned to be an ordinary
pressure and discharge of the additives is further facilitated.
[0071] After the second open/close valves 15 and 16 are closed, the
back-pressure valve 10 of the discharge pipe 6 for the substrate
cleaning bath 2 is opened and the pressure in the substrate
cleaning bath 2 is returned to be an ordinary pressure to end the
cleaning processing.
[0072] According to the second embodiment of the cleaning method,
the residual additives 22A and 23A can be purged using the
differential pressure between the high pressure maintained within
the substrate cleaning bath 2 and the atmospheric pressure caused
by opening the back-pressure valves 13 and 14 after the rinse
processing is ended. Accordingly, when the pressure in the
substrate cleaning bath 2 is returned to an ordinary pressure on
completion of the rinse processing, the residual additives can be
prevented from entering the substrate cleaning bath 2.
[0073] According to the first embodiment, the number of the
cleaning processes is reduced because the additive pipes 4 and 5
can be purged during rinse processing. According to the second
embodiment, the cost is reduced because the additive pipes 4 and 5
can be purged after the supply of the supercritical fluid CO.sub.2
21 is stopped, which prevents a large amount of supercritical fluid
CO.sub.2 from being wasted. Further, the pressure in the substrate
cleaning bath 2 is retained at a high pressure in order to maintain
the supercritical state and the second embodiment uses the fact
that the inside of the substrate cleaning bath 2 is retained at the
high pressure. Hence, characteristics of the supercritical cleaning
can sufficiently be used in the second embodiment.
[0074] As described above, according to the supercritical cleaning
method and the supercritical cleaning apparatus of the embodiments,
the additives in the supercritical fluid remaining in the end pipes
are prevented from being liquidized at the reduced pressure stage
after the wafer is cleaned and rushing into the substrate cleaning
bath to wet the wafer and damage the fine structure. Accordingly,
the supercritical fluid substrate cleaning can be performed
sufficiently, in which the supercritical fluid is used in order to
prevent the fine structure from being damaged by the contact of
liquid such as pattern collapse occurred in the resist mask removal
process.
[0075] Further, according to the supercritical substrate cleaning
apparatus of the embodiment, even if another additive is added from
the same pipe in the next wafer processing, the additives can be
prevented from being mixed and the processing can be carried out in
accordance with the purposes.
[0076] According to the above-mentioned embodiments, back-pressure
valves capable of controlling a pressure are used to adjust the
pressure, however, the additives can be purged while the pressure
in the apparatus can be controlled using the open/close valves.
[0077] In addition, according to the above-mentioned embodiments,
two additive pipe systems are provided, however, it is possible to
increase the number of systems in accordance with the number of
additives used by similarly setting up the back-pressure valves and
the open/close valves.
[0078] It should be noted that alternatively in the above-mentioned
embodiments a wafer may be cleaned using a supercritical fluid
including an additive (chemical) dissolved into an organic solvent
(for example, methanol). Subsequently, rinse processing using the
organic solvent (for example, methanol) and rinse processing using
the supercritical fluid alone may be performed at the subsequent
rinse processing.
[0079] The cleaning method according to the embodiments of the
present invention is applied to cleaning of a semiconductor
substrate. It should be appreciated that the present invention is
not limited to those embodiments and that the cleaning method
according to an embodiment of the present invention can be applied
to cleaning of other objects, such as cleaning of a photo-mask and
a liquid-crystal display substrate.
[0080] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alterations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
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