U.S. patent application number 11/499546 was filed with the patent office on 2007-07-26 for cleaning apparatus and high pressure cleaner for use therein.
This patent application is currently assigned to INDUSTRY-UNIVERSITY COOPERATION FOUNDATION SOGANG UNIVERSITY. Invention is credited to Gap Su Han, Young Hoon Kwon, Jong Sung Lim, Ki Pung Yoo.
Application Number | 20070169794 11/499546 |
Document ID | / |
Family ID | 38284340 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070169794 |
Kind Code |
A1 |
Han; Gap Su ; et
al. |
July 26, 2007 |
Cleaning apparatus and high pressure cleaner for use therein
Abstract
A cleaning apparatus in which a cleaning process is simplified,
a time required for the cleaning process is reduced and which has
an excellent cleaning effect, and a high pressure cleaner for use
therein are provided. The cleaning apparatus comprises a liquid
carbon dioxide (CO.sub.2) supply source and a gaseous CO.sub.2
supply source, a high pressure pump changing CO.sub.2 supplied from
the liquid CO.sub.2 supply source to CO.sub.2 having high pressure,
a cleaning additive supply source and a rinsing additive supply
source, a homogeneous transparent phase mixer forming a
supercritical homogeneous transparent phase mixture by mixing a
cleaning additive supplied from the cleaning additive supply source
and supercritical CO.sub.2 supplied from the liquid CO.sub.2 supply
source, or forming a supercritical rinsing mixture by mixing a
rinsing additive supplied from the rinsing additive supply source
and supercritical CO.sub.2 supplied from the liquid CO.sub.2 supply
source, a high pressure cleaner cleaning using the supercritical
homogeneous transparent phase mixture supplied from the homogeneous
transparent phase mixer and performing rinsing using the
supercritical rinsing mixture supplied from the homogeneous
transparent phase mixer, a separator separating gaseous CO.sub.2
from a mixture discharged from the high pressure cleaner, and a
CO.sub.2 condenser condensing the separated CO.sub.2.
Inventors: |
Han; Gap Su; (Yongin-city,
KR) ; Yoo; Ki Pung; (Seoul, KR) ; Lim; Jong
Sung; (Seoul, KR) ; Kwon; Young Hoon; (Seoul,
KR) |
Correspondence
Address: |
FROMMER LAWRENCE & HAUG
745 FIFTH AVENUE- 10TH FL.
NEW YORK
NY
10151
US
|
Assignee: |
INDUSTRY-UNIVERSITY COOPERATION
FOUNDATION SOGANG UNIVERSITY
|
Family ID: |
38284340 |
Appl. No.: |
11/499546 |
Filed: |
August 4, 2006 |
Current U.S.
Class: |
134/94.1 ;
134/105 |
Current CPC
Class: |
H01L 21/67023 20130101;
H01L 21/02101 20130101; G03F 7/422 20130101; H01L 21/31133
20130101; H01L 21/02071 20130101 |
Class at
Publication: |
134/94.1 ;
134/105 |
International
Class: |
B08B 3/00 20060101
B08B003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2006 |
KR |
10-2006-0006590 |
Claims
1. A cleaning apparatus comprising: a liquid carbon dioxide
(CO.sub.2) supply source and a gaseous CO.sub.2 supply source; a
high pressure pump changing CO.sub.2 supplied from the liquid
CO.sub.2 supply source to CO.sub.2 having high pressure; a cleaning
additive supply source and a rinsing additive supply source; a
homogeneous transparent phase mixer forming a supercritical
homogeneous transparent phase mixture by mixing a cleaning additive
supplied from the cleaning additive supply source and supercritical
CO.sub.2 supplied from the liquid CO.sub.2 supply source, or
forming a supercritical rinsing mixture by mixing a rinsing
additive supplied from the rinsing additive supply source and
supercritical CO.sub.2 supplied from the liquid CO.sub.2 supply
source; a high pressure cleaner cleaning using the supercritical
homogeneous transparent phase mixture supplied from the homogeneous
transparent phase mixer and performing rinsing using the
supercritical rinsing mixture supplied from the homogeneous
transparent phase mixer; a separator separating gaseous CO.sub.2
from a mixture discharged from the high pressure cleaner; and a
CO.sub.2 condenser condensing the separated CO.sub.2.
2. The cleaning apparatus of claim 1, further comprising at least
one of a cleaning column and an adsorption column for purifying
CO.sub.2 separated by the separator.
3. The cleaning apparatus of claim 1, wherein CO.sub.2 condensed in
the CO.sub.2 condenser is provided to the liquid CO.sub.2 supply
source and is re-used.
4. The cleaning apparatus of claim 1, further comprising a heater
heating CO.sub.2 supplied from the liquid CO.sub.2 supply source,
the cleaning additive supplied from the cleaning additive supply
source, and the rinsing additive supplied from the rinsing additive
supply source.
5. The cleaning apparatus of claim 1, wherein the homogeneous
transparent phase mixer forms the supercritical homogeneous
transparent phase mixture by mixing the cleaning additive supplied
having atmospheric pressure or a low pressure less than 10 bar with
the supercritical CO.sub.2 having high pressure of 120 to 300 bar,
using a large pressure difference therebetween.
6. The cleaning apparatus of claim 1, further comprising a pressure
regulating valve connected to the high pressure cleaner and
regulating pressure inside the high pressure cleaner.
7. The cleaning apparatus of claim 1, further comprising: a
circulation line connecting an outlet of the high pressure cleaner
to a middle point between the high pressure cleaner and the
homogeneous transparent phase mixer; and a circulation pump
connected to the circulation line.
8. The cleaning apparatus of claim 1, wherein an internal or
external circulation unit is provided to the homogeneous
transparent phase mixer.
9. A high pressure cleaner comprising: a wafer loading device on
which a wafer to be cleaned is loaded and which includes a
protrusion; an upper element including an inlet through which a
mixture is injected in a downward direction, a wafer loading device
fixing unit in which the protrusion of the wafer loading device is
inserted and which enables the wafer loading device to be fixed
therein, and a pneumatic cylinder insertion unit in which a
pneumatic cylinder sliding from a side is inserted; an ascending
and descending pneumatic cylinder moving the upper element in
upward and downward directions; a lower element including a
pneumatic cylinder insertion unit in which a pneumatic cylinder
sliding from a side is inserted and an outlet through which a
mixture is discharged and forming a space between the lower element
and the upper element in which the wafer loading device can be
disposed; and an adherent type pneumatic cylinder sliding into the
pneumatic cylinder insertion unit of the upper element and the
pneumatic cylinder insertion unit of the lower element and
combining the upper element and the lower element when the upper
element descends and is engaged with the lower element.
10. The high pressure cleaner of claim 9, further comprising a
sealant disposed between an edge of a surface of the upper element
in a direction of the lower element and an edge of a surface of the
lower element in a direction of the upper element and sealing a
space between the upper element and the lower element from the
outside.
11. The high pressure cleaner of claim 10, further comprising a
first bended portion disposed at an edge of a surface of the upper
element in a direction of the lower element, and a second bended
portion disposed at an edge of a surface of the lower element in a
direction of the upper element, and a first sealant and a second
sealant disposed in the first bended portion and the second bended
portion, respectively.
12. The high pressure cleaner of claim 9, wherein a groove is
formed in a circumferential direction of the wafer loading device
on a surface of the wafer loading device in a direction of the
upper element, and a plurality of spray outlets are provided along
the groove.
13. The high pressure cleaner of claim 12, wherein the inlet of the
upper element is provided so that a material injected through the
inlet of the upper element is injected in a direction of the groove
of the wafer loading device.
14. The high pressure cleaner of claim 9, wherein the upper element
further comprises an upper element guide pin and the lower element
further comprises a guide pin insertion portion in which the upper
element guide pin is inserted.
15. The high pressure cleaner of claim 9, wherein the inlet and the
outlet are provided in opposite directions.
16. The high pressure cleaner of claim 9, further comprising a
heating source and a cooling source controlling temperature of the
high pressure cleaner.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application claims the benefit of Korean Patent
Application No. 10-2006-0006590, filed on Jan. 21, 2006, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a cleaning apparatus and a
high pressure cleaner for use therein, and more particularly, to a
cleaning apparatus in which a cleaning process is simplified and a
time required for the cleaning process is reduced. The apparatus
has an excellent cleaning effect and a high pressure cleaner for
use therein.
[0004] 2. Description of the Related Art
[0005] In a semiconductor wafer manufacturing process, a
photoresist (PR) layer should be formed on a semiconductor
substrate and removed after a predetermined process. The process of
removing the photoresist (PR) layer is referred to as a cleaning
process. The cleaning process can be performed after a variety of
operations of the semiconductor wafer manufacturing process, such
as a front end of the line (FEOL) operation, a back end of the line
(BEOL) operation or ion implantation. The cleaning process is a
process in which contaminants, such as a photoresist or photoresist
residues, are removed from a surface of a substrate in a ultra-fine
pattern. To this end, a wet cleaning process using water and
various solvents and a dry cleaning process using supercritical
carbon dioxide (CO.sub.2) have been developed.
[0006] In a conventional wet cleaning method including an RCA
method, a cleaning process can be properly performed for purposes.
However, many problems exist in that the conventional wet cleaning
method is not suitable for manufacture of an ultra large scale
integrated circuit (ULSI). For example, in a wet cleaning process,
wettability of cleaning fluid to a fine structure having a high
aspect ratio is lowered, and due to repeated rinsing and drying
processes, unwanted particles are generated. In addition, there are
problems concerning metal inadvertently contaminated by a
liquid-phase chemical solution, water marks and corrosion, costs
for ultra-pure purification and high purity purification of
chemicals. Process equipment clusterization is not easily performed
because of the large size of equipment and complicated process. In
addition, there are problems with environmental contamination
caused by waste water and waste fluid and costs for treating waste
water.
[0007] In addition, since a large quantity of chemical solvent is
used in a conventional RCA cleaning method, problems exist in that
a wafer may be damaged and a photoresist layer may not be
completely removed. To address the problems, new solvent has been
developed. However, in the conventional wet cleaning process, due
to a characteristic of the molecular structure of cleaning fluid,
molecules of the cleaning fluid cannot easily infiltrate an
ultra-fine structure less than 65 nm. In particular, it is not easy
to clean copper for manufacturing a high performance semiconductor
in a next generation fine pattern having a low-K dielectric layer
material.
[0008] To address the problems, the development of plasma, gaseous
or supercritical dry cleaning technology is needed. However, when a
photoresist is removed using an oxygen plasma ashing method used in
a dry cleaning process, a wafer is damaged and contaminated by
oxygen plasma, and due to the existence of contaminants, an
additional wet cleaning process needs to be performed. In addition,
damages due to a wet method or a plasma dry cleaning process do not
occur in a cleaning process using the oxidation action of ozone
that has been recently developed. However, problems such as
environmental contamination caused by ozone exist.
[0009] During semiconductor manufacture, processes such as dry
etching or wet etching, ashing or ion implantation are performed,
and photoresist may remain on a wafer. Accordingly, conventionally,
a partial drying process and a wet process, that is, two processes
such as ashing and organic strip processes, are performed to remove
the photoresist and thus, the number of processes is increased,
resources are consumed and numerous costs for waste water treatment
are needed.
[0010] In addition, when wet cleaning is accompanied as described
above, an additional drying process, such as spin drying, isopropyl
alcohol (IPA) vapor drying, or marangoni drying, is needed. In
these drying methods, water marks are left and strain is generated
and the possibility of recontamination caused by an electrostatic
force is high. In particular, in the case of IPA vapor drying, a
high temperature (greater than 200.degree. C.) for IPA vaporization
should be maintained and a large amount of IPA is required.
[0011] A semiconductor wafer cleaning method using a supercritical
process in which supercritical CO.sub.2 and several common solvent
are mixed has been already introduced. However, because a
homogeneous transparent phase cannot be formed by simply mixing
polar common solvent with supercritical nonpolar CO.sub.2, problems
concerning the conventional wet cleaning process are not solved and
cleaning efficiency is low. Even though a homogeneous transparent
phase supercritical state is formed, a temperature greater than
100.degree. C. and a pressure greater than 300 bar are needed and
thus, costs are increased. To address these problems, even when a
surfactant is introduced, an additional mixer or a ultrasonic
device is needed so as to form a supercritical homogeneous
transparent phase and thus, manufacturing time is increased.
[0012] In addition, high purity (greater than 99.99%) CO.sub.2 is
used to manufacture a semiconductor. In the prior art, an efficient
purification process of purifying and recovering used CO.sub.2 to
reuse CO.sub.2 cannot be performed.
SUMMARY OF THE INVENTION
[0013] The present invention provides a cleaning apparatus in which
a cleaning process is simplified and a time required for the
cleaning process is reduced. The apparatus has an excellent
cleaning effect and a high pressure cleaner for use therein.
[0014] According to an aspect of the present invention, there is
provided a cleaning apparatus comprising: a liquid carbon dioxide
(CO.sub.2) supply source and a gaseous CO.sub.2 supply source; a
high pressure pump changing CO.sub.2 supplied from the liquid
CO.sub.2 supply source to CO.sub.2 having high pressure; a cleaning
additive supply source and a rinsing additive supply source; a
homogeneous transparent phase mixer forming a supercritical
homogeneous transparent phase mixture by mixing a cleaning additive
supplied from the cleaning additive supply source and supercritical
CO.sub.2 supplied from the liquid CO.sub.2 supply source, or
forming a supercritical rinsing mixture by mixing a rinsing
additive supplied from the rinsing additive supply source and
supercritical CO.sub.2 supplied from the liquid CO.sub.2 supply
source; a high pressure cleaner cleaning using the supercritical
homogeneous transparent phase mixture supplied from the homogeneous
transparent phase mixer and performing rinsing using the
supercritical rinsing mixture supplied from the homogeneous
transparent phase mixer; a separator separating gaseous CO.sub.2
from a mixture discharged from the high pressure cleaner; and a
CO.sub.2 condenser condensing the separated CO.sub.2.
[0015] The cleaning apparatus may further comprise at least one of
a cleaning column and an adsorption column for purifying CO.sub.2
separated by the separator.
[0016] CO.sub.2 condensed in the CO.sub.2 condenser may be provided
to the liquid CO.sub.2 supply source and may be re-used.
[0017] The cleaning apparatus may further comprise a heater heating
CO.sub.2 supplied from the liquid CO.sub.2 supply source, the
cleaning additive supplied from the cleaning additive supply
source, and the rinsing additive supplied from the rinsing additive
supply source.
[0018] The homogeneous transparent phase mixer may form the
supercritical homogeneous transparent phase mixture by mixing the
cleaning additive supplied having atmospheric pressure or a low
pressure less than 10 bar with the supercritical CO.sub.2 having
high pressure of 120 to 300 bar, using a large pressure difference
therebetween.
[0019] The cleaning apparatus may further comprise a pressure
regulating valve connected to the high pressure cleaner and
regulating pressure inside the high pressure cleaner.
[0020] The cleaning apparatus may further comprise: a circulation
line connecting an outlet of the high pressure cleaner to a middle
point between the high pressure cleaner and the homogeneous
transparent phase mixer; and a circulation pump connected to the
circulation line.
[0021] An internal or external circulation unit may be provided to
the homogeneous transparent phase mixer.
[0022] According to another aspect of the present invention, there
is provided a high pressure cleaner comprising: a wafer loading
device on which a wafer to be cleaned is loaded and which includes
a protrusion; an upper element including an inlet through which a
mixture is injected in a downward direction, a wafer loading device
fixing unit in which the protrusion of the wafer loading device is
inserted and which enables the wafer loading device to be fixed
therein, and a pneumatic cylinder insertion unit in which a
pneumatic cylinder sliding from a side is inserted; an ascending
and descending pneumatic cylinder moving the upper element in
upward and downward directions; a lower element including a
pneumatic cylinder insertion unit in which a pneumatic cylinder
sliding from a side is inserted and an outlet through which a
mixture is discharged and forming a space between the lower element
and the upper element in which the wafer loading device can be
disposed; and an adherent type pneumatic cylinder sliding into the
pneumatic cylinder insertion unit of the upper element and the
pneumatic cylinder insertion unit of the lower element and
combining the upper element and the lower element when the upper
element descends and is engaged with the lower element.
[0023] The high pressure cleaner may further comprise a sealant
disposed between an edge of a surface of the upper element in a
direction of the lower element and an edge of a surface of the
lower element in a direction of the upper element and sealing a
space between the upper element and the lower element from the
outside.
[0024] The high pressure cleaner may further comprise a first
bended portion disposed at an edge of a surface of the upper
element in a direction of the lower element, and a second bended
portion disposed at an edge of a surface of the lower element in a
direction of the upper element, and a first sealant and a second
sealant disposed in the first bended portion and the second bended
portion, respectively.
[0025] A groove may be formed in a circumferential direction of the
wafer loading device on a surface of the wafer loading device in a
direction of the upper element, and a plurality of spray outlets
may be provided along the groove.
[0026] The inlet of the upper element may be provided so that a
material injected through the inlet of the upper element is
injected in a direction of the groove of the wafer loading
device.
[0027] The upper element may further comprise an upper element
guide pin and the lower element may further comprise a guide pin
insertion portion in which the upper element guide pin is
inserted.
[0028] The inlet and the outlet may be provided in opposite
directions.
[0029] The high pressure cleaner may further comprise a heating
source and a cooling source controlling temperature of the high
pressure cleaner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The above and other features and advantages of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
[0031] FIG. 1 is a schematic view of a cleaning apparatus used in a
cleaning process according to an embodiment of the present
invention;
[0032] FIG. 2 is a schematic view of a cleaning apparatus used in a
cleaning process according to another embodiment of the present
invention;
[0033] FIG. 3 is a front view of a high pressure cleaner included
in the cleaning apparatus illustrated in FIG. 2;
[0034] FIG. 4A is a front view of an upper element of the high
pressure cleaner illustrated in FIG. 3;
[0035] FIG. 4B is a bottom view of the upper element of the high
pressure cleaner illustrated in FIG. 3;
[0036] FIG. 5A is a cross-sectional view of a lower element of the
high pressure cleaner illustrated in FIG. 3;
[0037] FIG. 5B is a plan view of the lower element of the high
pressure cleaner illustrated in FIG. 3;
[0038] FIG. 6A is a schematic view of a combined structure of the
upper element illustrated in FIG. 4A, the lower element illustrated
in FIG. 5A and a wafer loading device;
[0039] FIG. 6B is a plan view of a wafer loading device illustrated
in FIG. 6A;
[0040] FIG. 7A is a front view of a modified example of FIG.
6A;
[0041] FIG. 7B is a plan view of the wafer loading device
illustrated in FIG. 7A;
[0042] FIG. 8 is a graph of time versus pressure with respect to
all sections of a cleaning process using the cleaning apparatus
illustrated in FIG. 2;
[0043] FIG. 9 is a photo of a supercritical homogeneous transparent
phase mixture used in a supercritical cleaning process;
[0044] FIG. 10A is a cross-sectional photo showing a wafer that has
gone through a back-end-of-the-line (BEOL) process but is not
cleaned using a cleaning process according to an embodiment of the
present invention;
[0045] FIGS. 10B through 10E are cross-sectional photos showing the
case where the wafer of FIG. 10A has been cleaned using a cleaning
process according to an embodiment of the present invention;
[0046] FIG. 10F is a cross-sectional photo showing the case where a
wafer has been cleaned using a conventional wet cleaning
process;
[0047] FIG. 10G is a cross-sectional photo showing the case where
the wafer of FIG. 10A has been cleaned using a cleaning process
that does not satisfy conditions according to an embodiment of the
present invention;
[0048] FIG. 11A is a cross-sectional photo showing a wafer that has
gone through a front-end-of-the-line (FEOL) process but is not
cleaned using the cleaning process according to an embodiment of
the present invention;
[0049] FIG. 11B is a photo of the surface of the wafer illustrated
in FIG. 11A;
[0050] FIG. 11C is a cross-sectional photo showing the case where
the wafer of FIGS. 11A and 11B has been cleaned using the cleaning
process according to an embodiment of the present invention;
[0051] FIG. 11D is a photo of the surface of the wafer illustrated
in FIG. 11C;
[0052] FIG. 12A is a photo of the surface of a wafer that has gone
through a post ion implantation process but is not cleaned using a
cleaning process according to an embodiment of the present
invention; and
[0053] FIGS. 12B and 12C are photos of the surface of the wafer of
FIG. 12A that has been cleaned using a cleaning process according
to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0054] The present invention will now be described more fully with
reference to the accompanying drawings, in which exemplary
embodiments of the invention are shown.
[0055] FIG. 1 is a schematic view of a cleaning apparatus used in a
cleaning process according to an embodiment of the present
invention. Referring to FIG. 1, the cleaning apparatus includes a
high pressure cleaner 60, a gaseous carbon dioxide (CO.sub.2)
supply source 20 and a liquid CO.sub.2 supply source 21 which are
connected to the high pressure cleaner 60, a high pressure pump 24
for supplying high pressure CO.sub.2, a cleaning additive supply
source 25 for supplying an additive for cleaning and a rinsing
additive supply source 26 for supplying an additive for rinsing,
heaters 31, 32, and 33 installed on supply lines L2, L3, and L4,
respectively, to heat CO.sub.2 and additives, a homogeneous
transparent phase mixer 70 for supplying a predetermined amount of
cleaning additive while forming a supercritical homogeneous
transparent phase mixture, a pressure regulating valve 54 connected
to the high pressure cleaner 60 to maintain a predetermined
pressure, a separator 61 connected to the high pressure cleaner 60
to separate gaseous CO.sub.2 and a liquid-phase additive from a
mixture discharged from the high pressure cleaner 60, a gas
scrubbing column 63 and an adsorption column 64 for purifying the
separated gaseous CO.sub.2, a CO.sub.2 condenser 23 for condensing
and reusing the purified gas, a heating medium, a coolant supplier,
and on-off automatic valves 1 to 12.
[0056] A supercritical state is a state existing at a point greater
than a critical temperature and a critical pressure. Properties of
a supercritical fluid are very different from those of a fluid in a
normal state. That is, properties of the supercritical fluid, such
as density of a fluid, viscosity, solubility, thermal capacity or
dielectric constant, vary rapidly. The supercritical fluid state is
a state existing at a point greater than the critical temperature
and the critical pressure. The critical temperature is temperature
at which gas is not liquefied even though pressure is increased,
and the critical pressure is pressure at which liquid is not
vaporized even though temperature is raised. For example, the
critical temperature of CO.sub.2 is about 31.06.degree. C. and the
critical pressure of CO.sub.2 is about 73.8 bar. The supercritical
fluid is a fluid in which a gaseous state and a liquid state cannot
be discriminated from each other. The supercritical fluid has a
similar characteristic to that of a liquid in that it has large
solubility. In addition, the supercritical fluid has similar
characteristics to that of a gas in that it has low viscosity,
large diffusivity, and low surface tension and can easily
infiltrate a fine structure.
[0057] The gaseous CO.sub.2 supply source 20 and the liquid
CO.sub.2 supply source 21 are connected to the high pressure
cleaner 60 via supply lines L1 and L2. The cleaning additive supply
source 25 and the rinsing additive supply source 26 are connected
to the supply line L3 and supply a cleaning additive and a rinsing
additive to the homogeneous transparent phase mixer 70 via a
cleaning additive supply pump 27 and a rinsing additive supply pump
28. The homogeneous transparent phase mixer 70 connected to the
high pressure cleaner 60 forms a supercritical homogeneous
transparent phase mixture by mixing the cleaning additive having
atmospheric pressure or a low pressure state with the supercritical
CO.sub.2 by using a large pressure difference therebetween. In
addition, the homogeneous transparent phase mixer 70 may form a
supercritical rinsing mixture by mixing the rinsing additive and
the supercritical CO.sub.2, and a process thereof will be described
later.
[0058] The cleaning apparatus of FIG. 1 may further include a
circulation line L8 and a circulation pump 29, as illustrated in
FIG. 2 which is a schematic view of a cleaning apparatus used in a
cleaning process according to another embodiment of the present
invention. The circulation line L8 and the circulation pump 29 are
connected to the homogeneous transparent phase mixer 70. The
circulation line L8 and the circulation pump 29 enable the supplied
supercritical homogeneous transparent phase mixture to be
stabilized by formation of an external circulation flow of the high
pressure cleaner 60 and a mixing effect and a heat exchanging
effect to be improved.
[0059] A cleaning process performed using the cleaning apparatus
will now be described in detail.
[0060] First, a wafer is loaded in the high pressure cleaner 60,
which will be described later below.
[0061] If the wafer is loaded in the high pressure cleaner 60,
high-purity gaseous CO.sub.2 (greater than 99.99%) having low
pressure (less than 20 psig) by the pressure regulators 52 and 53
is injected into the high pressure cleaner 60 via the corresponding
on-off automatic valves 3 and 4 and the supply line L1 from the
gaseous CO.sub.2 supply source 20. This causes fine contaminants
inside the high pressure cleaner 60 to be removed. If the high
pressure cleaner 60 is sealed (a process thereof will be described
later), high-purity gaseous CO.sub.2 having high pressure (about
30-50 bar) is injected into the high pressure cleaner 60. This
causes a mixed fluid to smoothly flow into the high pressure
cleaner 60, which will be described later.
[0062] The cleaning additive and the supercritical CO.sub.2 having
higher pressure than a supercritical cleaning pressure (pressure in
a cleaning process in the high pressure cleaner 60 is, preferably,
about 120-300 bar) is injected into the homogeneous transparent
phase mixer 70, which will be described later. The supercritical
CO.sub.2 is supplied from the CO.sub.2 condenser 23. That is, the
supercritical CO.sub.2 is automatically supplied from the CO.sub.2,
condenser 23 by opening and closing the on-off automatic valves 1,
2, 5, and 8 installed on the supply line L2 and via the high
pressure pump 24 for supplying CO.sub.2. The supercritical CO.sub.2
may be heated by the heater 31 to become the supercritical
CO.sub.2, before it reaches the homogeneous transparent phase mixer
70.
[0063] The gaseous CO.sub.2 supplied from the gas scrubbing column
63 and the adsorption column 64 is condensed using a refrigerant in
the CO.sub.2 condenser 23 and thus, the supercritical CO.sub.2 is
formed. At this time, initial liquid CO.sub.2 and CO.sub.2
corresponding to wasted CO.sub.2 in a cleaning process are supplied
from the liquid CO.sub.2 supply source 21 via the liquid CO.sub.2
supplementing valve 51.
[0064] The supercritical CO.sub.2 is mixed with the cleaning
additive and becomes a supercritical homogeneous transparent phase
mixture for use in a cleaning process in the sealed high pressure
cleaner 60. In addition, the supercritical CO.sub.2 is mixed with
the rinsing additive and becomes a supercritical rinsing mixture
for use in the cleaning process in the sealed high pressure cleaner
60.
[0065] The additives are automatically supplied from the cleaning
additive supply source 25 and the rinsing additive supply source 26
via the on-off automatic valves 6 and 7 installed on the supply
lines L3 and L4 and the quantity regulating supply lines. In this
case, the supplied CO.sub.2 and the additives are heated by the
heaters 31, 32, and 33 installed on the supply lines L2, L3, and
L4, respectively, or by a line heater at a predetermined
temperature or temperature in a predetermined range (for example,
about 35-100.degree. C.).
[0066] The cleaning additive is instantaneously mixed by the
homogeneous transparent phase mixer 70 with the supercritical
CO.sub.2 at a large pressure difference and becomes a supercritical
homogeneous transparent phase mixture flowing into the high
pressure cleaner 60 and used in the cleaning process. More
specifically, the cleaning additive having atmospheric pressure or
a low pressure less than 10 bar is supplied to the homogeneous
transparent phase mixer 70 and then, the CO.sub.2 having a higher
pressure than the supercritical cleaning pressure is supplied to
the homogeneous transparent phase mixer 70 so that the
supercritical homogeneous transparent phase mixture can be formed
using a mixing effect caused by a large pressure difference.
[0067] In general, since the supercritical CO.sub.2 is nonpolar and
the cleaning additive is polar, a higher super-high temperature and
pressure than that used in the above-described conditions are
needed to mix the supercritical CO.sub.2 and the cleaning additive.
As such, cleaning costs are greatly increased. Accordingly, to
address these problems, in the cleaning process according to the
present embodiment, the cleaning additive further includes a
surfactant so that the supercritical homogeneous transparent phase
mixture can be easily formed under the above-described cleaning
conditions such as super-high pressure and super-high temperature.
In addition, the cleaning additive and the supercritical CO.sub.2
are mixed with each other using a large pressure difference in the
homogeneous transparent phase mixer 70 so that the supercritical
homogeneous transparent phase mixture can be easily formed within a
short time without using an additional mixer or an ultrasonic
device.
[0068] To this end, the cleaning additive may include a fluoride
group surfactant. The fluoride group surfactant may use fluoride
group carboxylic acid having a carbon number 2 to 20, perfluoro
ether polymer having an average molecular weight of 300 to 5000 or
a mixture thereof.
[0069] The composition of the cleaning additive will now be
described in greater detail. The cleaning additive may include
fluorosurfactant 0.01 to 90 wt %, aliphatic amine 0.01 to 15 wt %,
polar organic solvent 0.01 to 15 wt %, alcohol-based solvent 0.1 to
20 wt %, ether-based solvent 0.1 to 30 wt %, anticorrosive agent 0
to 5 wt %, and water 0 to 15 wt %. In the present embodiment, the
fluorosurfactant is fluoride group carboxylic acid having a carbon
number of 2 to 20, perfluoro ether system polymer having an average
molecular weight of 300 to 5000 or a mixture thereof. The aliphatic
amine is monoethanolamine, 2-(2-aminoethoxy) ethanol,
diethanolamine, amino bis propylamine, 2-methylaminoethanol,
triethylaminoethanol or a mixture thereof. The polar organic
solvent is N,N'-dimethylacetamide, dimethylsulfuroxide,
1-methyl-2-pyrrolidinone, N,N'-dimethylformamide, ammonium fluoride
or a mixture thereof. The alcohol-based solvent is methanol,
ethanol, isopropanol or a mixture thereof. The ether-based solvent
is ethyleneglycol methylether, ethyleneglycol ethylether,
ethyleneglycol butylether, diethyleneglycol methylether,
diethylenglycol ethylether, triethyleneglycol methylether,
triethyleneglycol ethylether or a mixture thereof. The
anticorrosive agent is catechol, gallic acid or a mixture
thereof.
[0070] Of course, a cleaning additive having a different
composition from the composition described above may be used. For
example, the cleaning additive may include fluorosurfactant 0 to 90
wt %, semiconductor cleaning stripper 0.1 to 15 wt %, alcohol-based
solvent 0.1 to 20 wt %, and water 0 to 15 wt %. In this case, the
fluorosurfactant is fluoride group carboxylic acid having a carbon
number of 2 to 20, perfluoro ether system polymer having an average
molecular weight of 300 to 5000 or a mixture thereof. The
alcohol-based solvent is methanol, ethanol, isopropanol or a
mixture thereof.
[0071] The volume of the cleaning additive in the supercritical
homogeneous transparent phase mixture in which the cleaning
additive and the supercritical CO.sub.2 are mixed may be 2 to 30
percent by volume.
[0072] The homogeneous transparent phase mixer 70 for forming the
supercritical homogeneous transparent phase mixture by mixing the
cleaning additive and the supercritical CO.sub.2 is a high pressure
vessel like a high pressure cylinder, and so on. In this case, a
heating source may be attached to the homogeneous transparent phase
mixer 70 and the homogeneous transparent phase mixer 70 may be
adjusted to a predetermined temperature or to a temperature in a
predetermined range. A minimum space is provided in which the fixed
quantity of the cleaning additive needed for cleaning can be
supplied, the cleaning additive can be mixed with the supercritical
CO.sub.2 and the supercritical homogeneous transparent phase
mixture can be formed. In addition, if necessary, an internal or
external circulation unit may be further provided in the
homogeneous transparent phase mixer 70 so as to maximize a mixing
effect and a heat exchanging effect.
[0073] If the supercritical homogeneous transparent phase mixture
is directly injected into the high pressure cleaner 60, due to a
large pressure difference, the supercritical homogeneous
transparent phase mixture is not maintained and is deformed. In
order to prevent this problem, before the supercritical homogeneous
transparent phase mixture is injected into the high pressure
cleaner 60, CO.sub.2 having a lower pressure than a supercritical
cleaning pressure is injected into the high pressure cleaner 60 via
an auxiliary line L6 using 3-way on-off automatic valves 5 and 8 on
the supply line L2. At this time, the pressure in the high pressure
cleaner 60 is regulated to a predetermined pressure or to a
pressure in a predetermined range (for example, pressure less than
10 to 40 bar of the supercritical cleaning pressure) using the
pressure regulating valve 54.
[0074] Before the supercritical homogeneous transparent phase
mixture is injected into the high pressure cleaner 60, CO.sub.2
having a lower pressure than the supercritical cleaning pressure is
injected into the high pressure cleaner 60 such that the
supercritical homogeneous transparent phase mixture is not deformed
and is maintained and cleaning can be effectively performed. In
this case, CO.sub.2 is injected into the high pressure cleaner 60
at pressure lower than the supercritical cleaning pressure so that
due to a pressure difference, the supercritical homogeneous
transparent phase mixture can be naturally injected into the high
pressure cleaner 60.
[0075] The supercritical homogeneous transparent phase mixture as
described above is injected into the high pressure cleaner 60 in
which the supercritical CO.sub.2 is charged and can be used in a
non-circulating state in a cleaning process without an additional
device. Unlike FIG. 1, an external circulation flow is formed using
the circulation line L8 and the circulation pump 29 and a cleaning
operation is performed so that the homogeneous transparent phase
mixture supplied to the high pressure cleaner 60 can be stably
maintained and a mixing effect and a heat exchanging effect can be
improved.
[0076] If a photoresist or etch residues on the wafer are removed
using the cleaning operation, the cleaning additive and cleaning
contaminants such as a solvated photoresist residues need not to
remain in the surface of the wafer. To this end, the homogeneous
transparent phase mixer 60 mixes the rinsing additive supplied from
the rinsing additive supply source 26 and the supercritical
CO.sub.2 so that a supercritical rinsing mixture can be formed and
injected into the high pressure cleaner 60 and a cleaning mixture
is removed. The supercritical rinsing mixture containing the
supercritical CO.sub.2 and the mainly alcohol-based rinsing
additive can be formed by simple mixture of the rinsing additive
and the supercritical CO.sub.2. The rinsing process may be
performed using the supercritical rinsing mixture having pressure
of about 80 to 250 bar.
[0077] Then, the cleaning additive mixture that may exist on the
surface of the wafer can be removed using only the supercritical
CO.sub.2.
[0078] Gaseous CO.sub.2 and a liquid-phase additive are separated
by the separator 61 from the mixture discharged from the high
pressure cleaner 60 after the cleaning and rinsing operations. At
this time, pressure inside the high pressure cleaner 60 is reduced
at a temperature of about 35.degree. C. so that CO.sub.2 is removed
from the high pressure cleaner 60 in a gaseous state without phase
transition to a liquid state. Unlike a conventional cleaning
process, an additional drying device or operation is not required
and problems such as formation of water marks that may occur after
wet etching can be mostly prevented.
[0079] The separator 61 is used to separate a mixture in a high
pressure state. A high pressure cleaning mixture (finally becoming
high pressure CO.sub.2) used in cleaning, rinsing, and dry
operations is discharged into the separator 61 from the high
pressure cleaner 60 using an automatic operation of the 3-way
on-off automatic valve 11 and is purified and re-used.
High-pressure gaseous CO.sub.2 is finally discharged by changing a
direction of the 3-way on-off automatic valve 11 and is separately
treated.
[0080] The high pressure CO.sub.2 separated from the separator 61
in an upward direction is transferred into the gas scrubbing column
63 via a back pressure regulator 55 attached to a connection line
of an upper discharging portion of the separator 61 and the back
pressure regulator 55 adjusting pressure. The liquid-phase additive
separated from a lower portion of the separator 60 using an
automatic operation of the on-off automatic valve 12 is purified
and re-used via an additional treatment process or is discharged
during general post-processing performed in an existing
semiconductor manufacturing factory. In this case, a heating source
is attached to the discharge line L7 and the separator 61 and
latent heat loss caused by insulation expansion of the
supercritical CO.sub.2 or the liquid CO.sub.2 is compensated for
and discharge in a gaseous state is smoothly induced.
[0081] The gaseous CO.sub.2 separated from the separator 61 goes
through a purifying process. That is, the gaseous CO.sub.2 moves
toward the gas scrubbing column 63 via the back pressure regulator
55 and impurities of the gaseous CO.sub.2 are primarily removed.
The gaseous CO.sub.2 moves toward the adsorption column 64 and
impurities of the gaseous CO.sub.2 are secondarily removed and it
becomes high purity gaseous CO.sub.2 (greater than 99.99%). Of
course, only one of the gas scrubbing column 63 and the adsorption
column 64 can be used. That is, purification can be performed
simply using the adsorption column 64. Whether or not purification
is performed simply using only the adsorption column 64 is
determined depending on the components of an additive that can be
changed according to the wafer to be cleaned or formation of a
volatile gas caused by a cleaning reaction.
[0082] After the cleaning process is performed, the high purity
gaseous CO.sub.2 is condensed by the CO.sub.2 condenser 23 into a
liquid state using a circulation coolant system and re-circulated
for another cleaning process.
[0083] According to the cleaning process according to an embodiment
of the present invention, a conventional two-step process including
a plasma ashing process (a drying process) and a wet process used
in removing a photoresist or residues can be substituted for a
one-step drying process using a supercritical homogeneous
transparent phase mixture. In addition, the cleaning, rinsing, and
drying processes are continuously performed in a single high
pressure cleaner. Thus, an additional drying apparatus and process
are not required. CO.sub.2 that goes through pressurization and
depression processes does not leave any residue because of phase
change.
[0084] When only the supercritical CO.sub.2 is used in the cleaning
process, a cleaning effect is restricted. However, in the cleaning
process according to the present embodiment, the cleaning process
is performed by mixing the supercritical CO.sub.2 and the cleaning
additive so that the cleaning effect can be maximized. In this
case, the supercritical CO.sub.2 is nonpolar and the cleaning
additive is generally polar. Thus, a higher super-high pressure and
super-high temperature than those of the above-described conditions
are required so that the supercritical CO.sub.2 and the cleaning
additive can be mixed and a supercritical state can be maintained.
As such, cleaning costs are greatly increased. To address these
problems, in the cleaning process according to the present
embodiment, the cleaning additive includes the surfactant so that
the supercritical homogeneous transparent phase mixture can be
easily formed and maintained even under the above-described
cleaning conditions. In this case, the cleaning additive and the
supercritical CO.sub.2 are mixed in the homogeneous transparent
phase mixer 70 using a large pressure difference such that the
supercritical homogeneous transparent phase mixture can be easily
formed within a short time without using an additional mixer or an
ultrasonic device.
[0085] The cleaning process according to the present embodiment is
used so that the homogeneous transparent phase of the supercritical
homogeneous transparent phase mixture can be easily formed and
maintained within a short time and an automatic cleaning apparatus
and an automatic valve are designed and configured and the cleaning
process can be easily performed using process automation together
with a control system.
[0086] In addition, a high diffusivity of the supercritical
CO.sub.2 is used so that the limit that semiconductor chemicals can
infiltrate a fine structure is overcome, wettability of the fine
structure is maximized using low surface tension and super fine
cleaning required in forming and manufacturing patterns of a super
fine structure can be performed accordingly.
[0087] In order to remove photoresist and residues using only pure
supercritical CO.sub.2 or the supercritical fluid mixture in which
a homogeneous transparent phase is not easily formed, a combination
of the cleaning additive including the surfactant presented in
Table 1, which will be described later, can be used.
[0088] The structure of the high pressure cleaner 60 and cleaning
inside the high pressure cleaner 60 will now be described.
[0089] FIG. 3 is a front view of the high pressure cleaner 60
illustrated in FIGS. 1 and 2, FIG. 4A is a front view of an upper
element of the high pressure cleaner 60 illustrated in FIG. 3, FIG.
4B is a bottom view of the upper element of the high pressure
cleaner 60 illustrated in FIG. 3, FIG. 5A is a cross-sectional view
of a lower element of the high pressure cleaner 60 illustrated in
FIG. 3, and FIG. 5B is a plan view of the lower element of the high
pressure cleaner 60 illustrated in FIG. 3. FIG. 6A is a schematic
view of a combined structure of the upper element illustrated in
FIG. 4A, wherein the lower element illustrated in FIG. 5A and a
wafer loading device, FIG. 6B is a plan view of the wafer loading
device illustrated in FIG. 6A, FIG. 7A is a view of a modified
example of FIG. 6A, and FIG. 7B is a schematic plan view of the
wafer loading device illustrated in FIG. 7A.
[0090] The high pressure cleaner 60 includes an upper element 101
and a lower element 102. The upper element 101 makes a vertical
motion using an upper element-ascending and descending pneumatic
cylinder 105. If the upper element 101 descends, an adherent type
pneumatic cylinder 106 is slid into an adherent type pneumatic
cylinder insertion portion 107 for each of the upper element 101
and the lower element 102 so that the upper element 101 and the
lower element 102 are combined with each other and fixed. If
necessary, an upper element guide pin 230 is provided in the upper
element 101 of the high pressure cleaner 60 and a guide pin
insertion portion 231 is provided in the lower element 102 so that
the upper element guide pin 230 can be inserted into the guide pin
insertion portion 231 and the upper element 101 and the lower
element 102 can be combined with each other in a correct position.
In addition, a heating source or a cooling source 108 is attached
to the high pressure cleaner 60 so that the high pressure cleaner
60 can be adjusted at a predetermined temperature or at a
temperature in a predetermined range. In this case, as illustrated
in FIG. 3, the heating source or the cooling source 108 may have a
shape which surrounds the lower element 102 of the high pressure
cleaner 60 and into which a heating medium or coolant flows the
heating source or the cooling source 108. Coils having a large
resistance may be used as the heating source and a variety of
modifications is possible.
[0091] The inner or outer diameter of the high pressure cleaner 60
may be different according to the diameter of a wafer to be
cleaned. The number of adherent type pneumatic cylinders 106 which
combine the upper element 101 and the lower element 102 with each
other may be different according to the size of the wafer to be
cleaned. For example, about 6 to 8 adherent type pneumatic
cylinders 106 may be provided for an 8-inch wafer (see cylinder
insertion portions 107 in FIGS. 4B and 5B).
[0092] As described above, a wafer is loaded in the high pressure
cleaner 60 before cleaning, that is, before the upper element 101
and the lower element 102 are combined with each other. The wafer
to be cleaned is loaded in a wafer loading device 201 illustrated
in FIGS. 6A and 6B. The wafer loading device 201 is fixed when a
pin (a protrusion 210) of the wafer loading device 201 is inserted
into a wafer loading device fixing portion 210a (see FIG. 4A). In
this case, a screw thread is provided in the pin 210 of the wafer
loading device 201 and a screw groove is provided in the wafer
loading device fixing portion 210a of the upper element 101 so that
the wafer loading device 201 can be more securely fixed in the
upper element 101. For your reference, a plurality of wafer loading
device fixing portions 210a are shown in FIG. 4B. However, for
explanatory convenience, only two wafer loading device fixing
portions 210a are shown in FIG. 4A.
[0093] If necessary, an auxiliary pin 211 is provided in the lower
element 102, as illustrated in FIG. 5B, so that a wafer to be
inserted into the wafer loading device 201 can be supported by the
auxiliary pin 211. Of course, only two auxiliary pins 211, as
illustrated in FIG. 5B, need not to be provided and a variety of
modifications is possible.
[0094] The wafer loading device 201 may be a wafer loading device
201 on which a sheet of wafer is loaded, as illustrated in FIG. 6A
or a wafer loading device 201 on which a plurality of wafers are
simultaneously loaded, as illustrated in FIG. 7A.
[0095] After the wafer is loaded in the wafer loading device 201,
high purity (greater than 99.99%) gaseous CO.sub.2 having low
pressure (less than 20 psig) using pressure regulators 52 and 53
(see FIGS. 1 or 2) primarily flows into the high pressure cleaner
60 from the gaseous CO.sub.2 supply source 20 (see FIGS. 1 or 2)
when the upper element 101 descends. As such, fine contaminants
inside the high pressure cleaner 60 are removed. When the upper
element 101 and the lower element 102 of the high pressure cleaner
60 are engaged with each other, the upper element 101 and the lower
element 102 are combined with each other using the adherent type
pneumatic cylinder 106.
[0096] Then, the high purity gaseous CO.sub.2 having high pressure
(about 30 to 50 bar) flows into the high pressure cleaner 60, and
CO.sub.2 having low pressure (for example, pressure lower than
supercritical cleaning pressure of 120 to 300 bar by 10 to 40 bar)
flows into the high pressure cleaner 60 so that the supercritical
homogeneous transparent phase mixture to flow is not deformed. In
this case, pressure of the high pressure cleaner 60 is regulated at
a predetermined pressure or at a pressure in a predetermined range
using the pressure regulating valve 54. Then, the supercritical
homogeneous transparent phase mixture flows into the high pressure
cleaner 60 so that cleaning can be performed.
[0097] At this time, the high pressure cleaner 60 should be
completely sealed so that the CO.sub.2 Of the supercritical
homogeneous transparent phase mixture flowing into the high
pressure cleaner 60 cannot leak. To this end, the high pressure
cleaner 60 may further include a sealant. In FIGS. 6A and 7A, a
first sealant 220 and a second sealant 221 are provided. That is, a
first bended portion is provided at an edge of a surface of the
upper element 101 in a direction of the lower element 102, and a
second bended portion is provided at an edge of a surface of the
lower element 102 in a direction of the upper element 101. The
first sealant 220 and the second sealant 221 are provided in the
first bended portion and the second bended portion, respectively.
The first sealant 220 and the second sealant 221 may have a variety
of shapes. In FIGS. 6A and 7A, the first sealant 220 and the second
sealant 221 have a "E:" shape.
[0098] A pressure-resistant energized Teflon seal or a metal seal
may be used for the first sealant 220 and the second sealant 221.
The energized Teflon seal is formed of pure Teflon or Teflon in
which a charging material is mixed. To ensure elasticity required
as a restoring force of the first sealant 220 and the second
sealant 221, the first sealant 220 and the second sealant 221 may
include a cantilever spring or helicoil spring having the same
material as that of metal seal. When metal seal is used for the
first sealant 220 and the second sealant 221, the first sealant 220
and the second sealant 221 may be formed SUS316-based stainless
steel in which corrosion does not occur, Hastelloy-C or Elgiloy
depending on the composition of an additive.
[0099] Of course, a material for the first sealant 220 and the
second sealant 221 is not limited to this and a variety of
materials of which anticorrosive property and durability are
excellent at a supercritical high pressure and which can be sealed
may be used for the first sealant 220 and the second sealant
221.
[0100] As described above, high purity (greater than 99.99%)
gaseous CO.sub.2 having low pressure (less than 20 psig), high
purity gaseous CO.sub.2 of a high pressure (about 30 to 50 bar),
CO.sub.2 having low pressure than a supercritical cleaning pressure
(for example, pressure lower than the supercritical cleaning
pressure of 120 to 300 bar by 10 to 40 bar), and a supercritical
homogeneous transparent phase mixture flow into the high pressure
cleaner via an inlet 110 provided in the upper element 101 of the
high pressure cleaner 60.
[0101] The inlet 110 is connected to an upper portion of the wafer
loading device 201. A groove 202a is formed in a circumferential
direction of the wafer loading device 201, as illustrated in FIG.
6B, and a plurality of spray outlets 202 are provided inside the
groove 202a in a direction of the top surface of a wafer to be
loaded. The inlet 110 is provided so that a material injected
through the inlet 110 is injected in a direction of the groove 202a
of the wafer loading device 201. Thus, the material passing through
the inlet 110 moves along the groove 202a in the circumferential
direction of the wafer loading device 201 and the wafer that passes
through the spray outlets 202 is cleaned. That is, the wafer
cleaning device 201 divides the supercritical homogeneous
transparent phase mixture in the high pressure cleaner 60 and
maximizes the cleaning effect. Referring to FIGS. 7A and 7B which
illustrates the case where a plurality of wafers are loaded in one
wafer loading device 201, the spray outlets 202 are provided in a
direction of each wafer to be loaded so that, when the wafers are
loaded in the wafer loading device 201, each wafer can be
effectively cleaned.
[0102] The supercritical homogeneous transparent phase mixture
flows into the high pressure cleaner 60 and the homogeneous
transparent phase is maintained at a predetermined pressure or
temperature, whereby each wafer is cleaned. The supercritical
homogeneous transparent phase mixture infiltrates photoresist
polymer and expands so that the photoresist polymer is decomposed
or dissolved together with the cleaning additive. In this
procedure, a photoresist on each wafer or etch residues are
substantially removed.
[0103] If the photoresist or etch residues on each wafer are
removed in this manner, the cleaning mixture is removed using a
supercritical rinsing mixture containing the rinsing additive
supplied from the cleaning additive supply source 26 and the
supercritical CO.sub.2. A rinsing additive mixture that may exist
on the surface of the wafer is removed using only the supercritical
CO.sub.2.
[0104] The material used in the cleaning and rinsing processes is
discharged to the outside via an outlet 111 illustrated in FIGS. 5A
and 5B and post-processed as described above and re-used or
separately processed. The position and shape of the outlet 111 are
not limited to those illustrated in FIGS. 5A and 5B and a variety
of modifications is possible. In this case, as illustrated in FIG.
5B, the outlet 111 may be positioned opposite to the position of
the outlet 110 illustrated in FIG. 4B. To this end, the
supercritical homogeneous transparent mixture or the supercritical
rinsing mixture injected through the inlet 110 passes through the
inside of the high pressure cleaner 60 and is discharged to the
outside so that cleaning and rinsing of the wafer can be
effectively performed.
[0105] By using the above-described high pressure cleaner 60 and
the cleaning process and apparatus described above, the
supercritical CO.sub.2 and the additive form the supercritical
homogeneous transparent phase mixture so that the surface of the
wafer injected into the high pressure cleaner 60 can be cleaned. In
addition, unlike the prior art, the wet process is not performed so
that an excellent cleaning result can be obtained.
[0106] In addition, if the supercritical homogeneous transparent
phase mixture is formed in the homogeneous transparent phase mixer
70, the mixture is supplied as rapid flow onto the wafer via the
spray type wafer loading device 201 such that an excellent cleaning
effect can be achieved even in a non-circulating state (see FIG.
1). In addition, cleaning by contact of the circulation flow (see
FIG. 2) provides fluidity of the mixture so that a contact effect
of the mixture and the wafer is maximized, the dissolved
photoresist and photoresist residues are continuously removed and
the cleaning effect is further enhanced.
[0107] As described above, the cleaning additive and contaminants
that remain on the wafer after the cleaning process can be removed
by supplying the supercritical rinsing mixture which is a mixture
of the supercritical CO.sub.2 and the cleaning additive. The
rinsing additive that remains after the removing process can be
removed by supplying only the supercritical CO.sub.2. The
supercritical rinsing mixture used in this procedure is conducive
to rinsing and auxiliary cleaning so that the cleaning effect is
maximized.
[0108] Even in the rinsing process, the supercritical homogeneous
transparent phase mixture is supplied by a spray type rapid flow
like in the cleaning process so that a wafer to be cleaned can be
cleaned by contact with only a pump flow (see FIG. 1) or by contact
with the pump flow and the circulation flow (see FIG. 2).
[0109] The total process time including the cleaning time and the
rinsing time may be within 10 minutes.
[0110] FIG. 8 is a graph of time versus pressure with respect to
all sections of a cleaning process, as described above, using the
cleaning apparatus illustrated in FIG. 2. In FIG. 8, P.sub.c is a
supercritical pressure and P.sub.0 is a desired supercritical
cleaning pressure. P.sub.1 is greater than P.sub.c and less than
about 10 to 40 bar of cleaning pressure P.sub.0, that is, P.sub.2.
P.sub.1 is pressure in which the supercritical homogeneous
transparent phase mixture formed in the homogeneous transparent
phase mixer can be maintained in a homogeneous transparent
phase.
[0111] As described above, the cleaning process is performed in the
state where only the supercritical CO.sub.2 is primarily filled in
the high pressure cleaner 60 up to pressure P.sub.1 and the
supercritical homogeneous transparent phase mixture is filled in
the high pressure cleaner 60 a short time later. The rinsing
process can be performed even under a lower pressure than cleaning
pressure P.sub.0, as shown by the rinsing section of FIG. 8. Of
course, the process illustrated in FIG. 8 is an example and the
present invention is not limited to this.
Embodiments 1 to 4
[0112] An experiment for dry cleaning a wafer that had gone through
a back-end-of-the-line (BEOL) process using a supercritical
homogeneous transparent phase mixture and removing photoresist
residues having a rabbit ears shape that remained after aluminium
metal etching was carried out.
[0113] The wafer had a layer structure of Si/Si rich oxide 4000
.ANG./Ti 300 .ANG./TiN 900 .ANG./Al 8000 .ANG./Ti 100 .ANG./TiN 400
.ANG., and photoresist residues generated in a metal etching
process remained on the wafer.
[0114] In this case, a cleaning additive mixed with the
supercritical CO.sub.2 was a formulation of a surfactant, a
stripper for semiconductor cleaning or co-solvent mixture, and
ethanol. Only ethanol was used as a primary rinsing additive mixed
with the supercritical CO.sub.2 and only the supercritical CO.sub.2
was used without any additive in a secondary rinsing process which
is a final process.
[0115] The wafer under the above-described conditions was used, and
a cleaning experiment was carried out whereby different surfactant
or rinsing conditions were used. The conditions were shown in Table
1 below.
TABLE-US-00001 TABLE 1 Classification Embodiment 1 Embodiment 2
Embodiment 3 Embodiment 4 Composition of PFOA 83.5
monohydrated-PFOA PFHA 83.5 PFOA 82.7 Cleaning additive Stripper
6.0 87.4 Stripper 6.0 MEA 2.5 (wt %) Ethanol 10.5 Stripper 5.2
Ethanol 10.5 1-M-2-P 1.7 Ethanol 7.4 Ethanol 13.1 Volume of
cleaning 13.6% 16.2% 13.6% 13.6% additive Primary Ethanol Ethanol
Ethanol Ethanol Rinsing additive Volume of primary 16.7% 16.7%
16.7% 16.7% rinsing additive Cleaning conditions 55.degree. C., 148
bar 51.degree. C., 165 bar 54.degree. C., 163 bar 52.degree. C.,
160 bar 3 min 3 min 3 min 3 min (non-circulating) (non-circulating)
(non-circulating) (non-circulating) Primary rinsing 36.degree. C.
45 .+-. 1.degree. C. 42.degree. C. 40 .+-. 1.degree. C. conditions
132 .+-. 6 bar 153 .+-. 12 bar 125 .+-. 3 bar 145 .+-. 5 bar 2
min(flow) 2 min(flow) 2 min(flow) 2 min(flow) Secondary rinsing
39.degree. C. 42.degree. C. 46.degree. C. 40 .+-. 3.degree. C., 136
.+-. 6 bar conditions 122 .+-. 7 bar 148 .+-. 7 bar 121 .+-. 3 bar
2 min 2 min(flow) 2 min(flow) 2 min(flow) (non-circulating)
[0116] Here, the primary rinsing process is a rinsing process using
a supercritical homogeneous transparent phase mixture in which the
cleaning additive and the supercritical CO.sub.2 are mixed, and the
secondary rinsing process is a rinsing process using only the
supercritical CO.sub.2. PFOA is perfluorooctanoic acid, PFHA is
perfluoroheptanoic acid, MEA is monoethanolamine, and 1-M-2-P is
1-methyl-2-pyrrolidinone.
[0117] The premise of supercritical fluid cleaning and rinsing is
to make and maintain a homogeneous transparent phase mixture in
which ingredients of a supercritical fluid mixture are not
separated. A photo of the supercritical homogeneous transparent
phase mixture formed in the cleaning process is shown in FIG.
9.
[0118] After the rinsing process, the result of observing the state
before and after the cleaning process using a scanning electron
microscope (SEM) is shown in FIG. 10A (before cleaning), FIG. 10B
(Embodiment 1), FIG. 10C (Embodiment 2), FIG. 10D (Embodiment 3),
and FIG. 10E (Embodiment 4). Here, FIGS. 10B, 10C, and 10D show the
result in which the cleaning process was carried out in the state
where a cleaning additive was formulated by using a stripper for
semiconductor cleaning and ethanol as a co-solvent and by changing
a surfactant, and FIGS. 10B, 10C, and 10D show different results
according to a cleaning characteristic based on the composition of
the surfactant and the cleaning additive. FIG. 10E shows the case
where a stripper for semiconductor cleaning is not used as a
co-solvent but is selected and formulated by itself, as illustrated
in the above Table 1.
[0119] Referring to FIG. 10A, which shows a wafer before the
cleaning process, photoresist residues formed of polymer generated
in the etching process remain on the surface of the wafer. The
photoresist residues are shown in the form of rabbit ears-shaped
contamination on the wafer.
[0120] FIGS. 10B through 10E are photos showing the case where a
wafer has been cleaned using the supercritical homogeneous
transparent phase mixture under the conditions of Table 1. As
illustrated in FIGS. 10A through 10E, an excellent cleaning effect
in which all rabbit ears-shaped photoresist residues are removed
within 10 minutes of total process time, is obtained.
Comparative Examples 1 and 2
[0121] FIG. 10F is a cross-sectional photo showing the case where a
wafer has been cleaned using a conventional wet cleaning process,
and FIG. 10G is a cross-sectional photo showing the case after the
wafer of FIG. 10A is cleaned using a cleaning process that does not
satisfy conditions according to an embodiment of the present
invention.
[0122] FIG. 10F shows the case where the conventional wet cleaning
process is performed for 120 minutes using the cleaning additive
used in Embodiment 1. Even though the wet cleaning is performed for
120 minutes, unlike the cleaning result of Embodiments 1 and 2,
photoresist residues having a rabbit ears shape remain. As such, a
supercritical dry cleaning process according to the present
invention shows an epoch-making cleaning result compared to the
conventional wet cleaning process.
[0123] FIG. 10G shows the case where a homogeneous transparent
phase is not formed using a surfactant or by changing process
conditions under the conditions of Embodiments 1 to 4, and cleaning
is not satisfactory. Even when a rinsing process according to the
present embodiment is not performed, a similar result to FIG. 10G
is obtained. As such, it is essential for a dry cleaning process
according to the present embodiment to form a homogeneous
transparent phase.
Embodiment 5
[0124] An experiment for removing a photoresist on a wafer during a
wafer manufacturing process that had gone through a
front-end-of-the-line (FEOL) process using a supercritical
homogeneous transparent phase mixture was carried out.
[0125] The wafer had a layer structure of Si/HLD 1000 .ANG./Nitride
4500 .ANG./BPSG 21000 .ANG./PR 10500 .ANG.. The wafer, which was a
p-type wafer on which a positive photoresist was coated, was
heat-treated at 120.degree. C.
[0126] Just ethanol was used for the cleaning additive mixed in the
supercritical CO.sub.2 according to an embodiment of the present
invention, and a rinsing process was performed once only using
supercritical CO.sub.2.
[0127] Cleaning conditions are Table 2 below.
TABLE-US-00002 TABLE 2 Cleaning additive Ethanol Volume of cleaning
additive (%) 13.6% Cleaning conditions 58.degree. C., 150 bar, 2
min(non-circulating) Rinsing conditions 48 .+-. 1.degree. C., 142
.+-. 6 bar, 2 min (flow)
[0128] FIG. 11A is a cross-sectional photo of a wafer that has gone
through an FEOL process but is not cleaned using the cleaning
process according to an embodiment of the present invention, and
FIG. 11B is a photo of the surface of the wafer illustrated in FIG.
11A. Referring to FIG. 11A, a photoresist layer is formed on the
wafer, and a groove is formed in the photoresist layer. When
viewing FIG. 11A, protrusions formed of a photoresist having a
circular cross-section are formed on the wafer as illustrated in
FIG. 11B.
[0129] FIG. 11C is a cross-sectional photo of the case where the
wafer of FIGS. 11A and 11B has been cleaned using the cleaning
process according to an embodiment of the present invention, and
FIG. 11D is a photo of the surface of the wafer illustrated in FIG.
11C. Referring to FIG. 11C, a photoresist layer is completely
removed, unlike FIG. 11A, and this can be seen in FIG. 11D.
Embodiments 6 and 7
[0130] An experiment for cleaning a wafer that has gone through a
post ion implantation process using a supercritical homogeneous
transparent phase mixture and for removing a photoresist or
photoresist residues that remain on an ion-implanted wafer during
an arsenic (As) ion implantation process was carried out. The wafer
has a variety of patterns including, in this case, numbers.
[0131] The wafer had a layer structure of Si/Oxide 5000 .ANG./Poly
2000 .ANG./PR 50000 .ANG.. An As ion implantation energy was 60
KeV, and the wafer doped with ions of 5E13/cm that has gone through
a post ion implantation process was used.
[0132] The cleaning additive mixed with the supercritical CO.sub.2
was formulation of a surfactant, a stripper for semiconductor
cleaning or co-solvent mixture, and ethanol. Only ethanol was used
as a primary rinsing additive mixed with the supercritical CO.sub.2
and only the supercritical CO.sub.2 was used without any additive
in a secondary rinsing process which is a final process.
[0133] The cleaning process was performed so that a supercritical
homogeneous transparent phase mixture (FIG. 9) was formed and
maintained, like in the cleaning process (Embodiments 1 to 4) of
the wafer that went through a BEOL process. The conditions were
shown in Table 3 below.
TABLE-US-00003 TABLE 3 Classification Embodiment 6 Embodiment 7
Composition of cleaning additive PFOA 83.5 PFOA 83.8 (wt %)
Stripper 6.0 Stripper 7.1 Ethanol 10.5 Ethanol 9.1 Volume of
cleaning additive (%) 13.6% 17.5% Primary rinsing additive Ethanol
Ethanol Volume of primary rinsing additive (%) 16.7% 16.7% Cleaning
conditions 59.degree. C. 50.degree. C. 148 bar 150 bar 3 min
(non-circulating) 3 min (non-circulating) Primary rinsing
conditions 43 .+-. 3.degree. C. 42.degree. C. 125 .+-. 5 bar 150
.+-. 3 bar 2 min (flow) 2 min (flow) Secondary rinsing conditions
48 .+-. 3.degree. C. 40.degree. C. 122 .+-. 1 bar 150 .+-. 5 bar 2
min (flow) 2 min (flow)
[0134] FIG. 12A is a photo of the surface of a wafer that has gone
through a post ion implantation process but is not cleaned using a
cleaning process according to an embodiment of the present
invention. Photoresist residues (opaque white dots) remain and
protrude from the wafer having a variety of patterns including
numbers.
[0135] FIGS. 12B and 12C are photos of the surface of the wafer of
FIG. 12A that has been cleaned using a cleaning process according
to an embodiment of the present invention. Photoresist residues can
be safely removed.
[0136] The cleaning additive including a fluoride group surfactant
used in the above-described embodiments may be used as the cleaning
additive in the above-described cleaning process. The fluoride
group surfactant may use fluoride group carboxylic acid having a
carbon number 2 to 20, perfluoro ether system polymer having an
average molecular weight of 300 to 5000 or a mixture thereof.
[0137] In addition, like in the above-described embodiments, the
cleaning additive may include fluorosurfactant 0.01 to 90 wt %,
aliphatic amine 0.01 to 15 wt %, polar organic solvent 0.01 to 15
wt %, alcohol-based solvent 0.1 to 20 wt %, ether-based solvent 0.1
to 30 wt %, anticorrosive agent 0 to 5 wt %, and water 0 to 15 wt
%. Here, 0 wt % means that a corresponding element is not included
in the cleaning additive, which is also applied to a later
description.
[0138] In this case, fluorosurfactant may be fluoride group
carboxylic acid having a carbon number of 2 to 20, perfluoro ether
system polymer having an average molecular weight of 300 to 5000 or
a mixture thereof. The aliphatic amine is monoethanolamine,
2-(2-aminoethoxy) ethanol, diethanolamine, amino bis propylamine,
2-methylaminoethanol, triethylaminoethanol or a mixture thereof.
The polar organic solvent is N,N'-dimethylacetamide,
dimethylsulfuroxide, 1-methyl-2-pyrrolidinone,
N,N'-dimethylformamide, ammonium fluoride or a mixture thereof. The
alcohol-based solvent is methanol, ethanol, isopropanol or a
mixture thereof. The ether-based solvent is ethyleneglycol
methylether, ethyleneglycol ethylether, ethyleneglycol butylether,
diethyleneglycol methylether, diethylenglycol ethylether,
triethyleneglycol methylether, triethyleneglycol ethylether or a
mixture thereof. The anticorrosive agent is catechol, gallic acid
or a mixture thereof.
[0139] Like in the above-described embodiments, the cleaning
additive may include fluorosurfactant 0 to 90 wt %, semiconductor
cleaning stripper 0.1 to 15 wt %, alcohol-based solvent 0.1 to 20
wt %, and water 0 to 15 wt %. In this case, the fluorosurfactant is
fluoride group carboxylic acid having a carbon number of 2 to 20,
perfluoro ether system polymer having an average molecular weight
of 300 to 5000 or a mixture thereof. The alcohol-based solvent is
methanol, ethanol, isopropanol or a mixture thereof.
[0140] Only the alcohol-based solvent may be used as the cleaning
additive, and like in the above-described embodiments, only the
supercritical CO.sub.2 may be used in the process of rinsing the
wafer, and the alcohol-based solvent may be methanol, ethanol,
isopropanol or a mixture thereof.
[0141] In the supercritical homogeneous transparent phase mixture
in which the supercritical CO.sub.2 and the cleaning additive used
in the above embodiments are mixed, the cleaning additive was less
than 30 percent by volume. In addition, in the supercritical
homogeneous transparent phase mixture in which the supercritical
CO.sub.2 and the cleaning additive used in the above embodiments
are mixed, the rinsing additive was less than 30 percent by volume.
In this case, the rinsing additive included methanol, ethanol,
isopropanol or a mixture thereof.
[0142] As described above, in the cleaning apparatus and the high
pressure cleaner thereof according to the present invention, the
cleaning process can be simplified, a time required for the
cleaning process can be reduced and an excellent cleaning effect
can be obtained.
[0143] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims.
* * * * *