U.S. patent application number 10/998278 was filed with the patent office on 2005-04-07 for process and apparatus for treating a workpiece.
Invention is credited to Bergman, Eric J..
Application Number | 20050072446 10/998278 |
Document ID | / |
Family ID | 26740940 |
Filed Date | 2005-04-07 |
United States Patent
Application |
20050072446 |
Kind Code |
A1 |
Bergman, Eric J. |
April 7, 2005 |
Process and apparatus for treating a workpiece
Abstract
A novel chemistry, system and application technique reduces
contamination of semiconductor wafers and similar substrates and
enhances and expedites processing. A stream of liquid chemical is
applied to the workpiece surface. Ozone is delivered either into
the liquid process stream or into the process environment. The
ozone is preferably generated by a high capacity ozone generator.
The chemical stream is provided in the form of a liquid or vapor. A
boundary layer of liquid or vapor forms on the workpiece surface.
The thickness of the boundary layer is controlled. The chemical
stream may include ammonium hydroxide for simultaneous particle and
organic removal, another chemical to raise the pH of the solution,
or other chemical additives designed to accomplish one or more
specific cleaning steps.
Inventors: |
Bergman, Eric J.;
(Kalispell, MT) |
Correspondence
Address: |
PERKINS COIE LLP/SEMITOOL
PO BOX 1208
SEATTLE
WA
98111-1208
US
|
Family ID: |
26740940 |
Appl. No.: |
10/998278 |
Filed: |
November 23, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10998278 |
Nov 23, 2004 |
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09621028 |
Jul 21, 2000 |
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09621028 |
Jul 21, 2000 |
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PCT/US99/08516 |
Apr 16, 1999 |
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PCT/US99/08516 |
Apr 16, 1999 |
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09061318 |
Apr 16, 1998 |
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09061318 |
Apr 16, 1998 |
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08853649 |
May 9, 1997 |
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6240933 |
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Current U.S.
Class: |
134/2 ; 134/105;
134/19; 134/94.1; 257/E21.228 |
Current CPC
Class: |
B08B 3/02 20130101; B08B
3/08 20130101; B08B 2203/005 20130101; H01L 21/02052 20130101; H01L
21/02054 20130101; B08B 7/00 20130101; H01L 21/6704 20130101; B08B
2230/01 20130101; Y10S 134/902 20130101 |
Class at
Publication: |
134/002 ;
134/019; 134/105; 134/094.1 |
International
Class: |
C23G 001/00; B08B
003/00 |
Claims
1. A method for processing a workpiece, comprising: placing the
workpiece into a chamber; pressurizing the chamber to an above
ambient pressure; directly or indirectly heating the workpiece,
providing water vapor into the chamber, with the water vapor
exceeding about 100 C; and providing ozone gas into the
chamber.
2. The method of claim 1 wherein the workpiece is coated with
photoresist, and with the steam and ozone chemically reacting with
and removing the photoresist.
3. The method of claim 1 wherein the water vapor forms a layer on
the wafer surface, with the layer having a thickness of from about
1-100 microns.
4. The method of claim 1 wherein the water vapor forms a layer a
few molecular layers thick.
5. The method of claim 2 wherein the photoresist is hydrolyzed.
6. The method of claim 1 wherein the water vapor is at about
120-130 C.
7. The method of claim 1 wherein the chamber is flat and
disk-shaped.
8. The method of claim 1 wherein the ozone is provided at a
concentration of at least 12% by weight.
9. The method of claim 1 wherein the ozone and water vapor are
provided into the chamber for about 1-5 minutes.
10. The method of claim 1 further including heating the workpiece
via contact heaters in the chamber.
11. The method of claim 1 with the ozone provided at a flow rate of
at least 10 liters/minute, and at a concentration of at least 12%
by weight.
12. A method for removing photoresist from a wafer, comprising:
placing the wafer into a chamber; directly or indirectly heating
the wafer with one or more heaters in or on the chamber, providing
steam in the chamber; providing ozone gas into the chamber;
pressurizing the chamber; contacting the wafer with steam and
ozone, with the steam and ozone chemically reacting with the
photoresist; and rinsing the wafer.
13. The method of claim 12 with the steam forming a molecular layer
on a surface of the workpiece.
14. The method of claim 13 with the workpiece surface having a
temperature exceeding 100 C.
15. The method of claim 12 with the photoresist having
carbon-carbon bonds hydrolyzed in the presence of the steam and
ozone.
16. A method for cleaning a workpiece, comprising: placing the
workpiece into a chamber; directly or indirectly heating the
workpiece with one or more heaters, providing heated water vapor in
the chamber; providing ozone gas into the chamber; pressurizing the
chamber to an above ambient pressure; contacting the workpiece with
heated and ozone, with the steam and ozone chemically reacting, in
the presence of hydroxyl radicals, to clean the workpiece; and
rinsing the workpiece.
17. The method of claim 16 with the heated water vapor forming a
layer on the workpiece, and with the ozone gas diffusing through
the layer.
18. The method of claim 16 including providing the ozone gas at a
concentration of at least 12% and a flow rate of at least 10
liters/minute.
19. A system for cleaning a workpiece, comprising: a pressurizable
chamber; a heated water vapor supply associated with the chamber;
an ozone gas supply connecting into the chamber; a workpiece
support in the chamber for supporting the workpiece; and a
workpiece heater in the chamber on or in the wafer support for
directly heating the wafer.
20. The system of claim 19 with the chamber is disk-shaped.
21. The system of claim 19 with the ozone gas supply providing at
least 90 grams/hour of ozone.
Description
[0001] This Application is a Continuation of U.S. patent
application Ser. No. 09/621,028, filed Jul. 21, 2000 and now
pending and incorporated herein by reference, which is a
Continuation-in-Part of U.S. patent application Ser. No.
PCT/US99/08516, which is a Continuation-in-Part of U.S. patent
application Ser. No. 09/061,318, filed Apr. 16, 1998 and now
abandoned, which is a Continuation-in-Part of U.S. patent
application Ser. No. 08/853,649, filed May 9, 1997, now U.S. Pat.
No. 6,240,933. This Application also is a Continuation-in-Part of
U.S. patent application Ser. No. 60/145,350, filed Jul.
23,1999.
FIELD OF THE INVENTION
[0002] The cleaning of semiconductor wafers is often a critical
step in the fabrication processes used to manufacture integrated
circuits or the like. The geometries on wafers are often on the
order of fractions of a micron, while the film thicknesses may be
on the order of 20 Angstroms. This renders the devices highly
susceptible to performance degradation due to organic, particulates
or metallic/ionic contamination.
[0003] Although wafer cleaning has a long history, the era of
modern cleaning techniques is generally considered to have begun in
the early 1970s when RCA developed a cleaning sequence to address
the various types of contamination. Although others developed the
same or similar processes in the same time frame, the general
cleaning sequence in its final form is basically the same.
[0004] While this process has been effective for a number of years,
it nevertheless has certain deficiencies. Such deficiencies include
the high cost of chemicals, the lengthy process time required to
get wafers through the various cleaning steps, high consumption of
water due to the need for extensive rinsing between chemical steps,
and high disposal costs. The result has been an effort to devise
alternative cleaning processes that yield results as good as or
better than the existing four-chemistry clean process, but which
are more economically attractive.
[0005] Various chemical processes have been developed in an attempt
to replace the existing cleaning process. However, such cleaning
processes have failed to fully address all of the major cleaning
concerns of the semiconductor processing industry. More
particularly, they have failed to fully address the problem of
minimizing contamination from one or more of the following
contaminants: organics, particles, metals/ions, and silicon
dioxide.
STATEMENT OF THE INVENTION
[0006] A novel chemistry, application technique, and system is used
to reduce the contamination and speed up processing in the
manufacturing of semiconductor wafers, memory disks, photomasks,
optical media, and other substrates (collectively referred to here
as "wafers") requiring a high level of clean. Contamination may
occur from organics, particles, metal/ions, and silicon dioxide.
Cleaning of wafers is achieved by delivery of a chemical stream to
the workpiece surface. Ozone is delivered into the process
environment. The chemical stream, which may be in the form of a
liquid or vapor, is applied to the wafer in a system which allows
for control of the liquid boundary layer thickness.
[0007] While ozone has a limited solubility in the hot liquid
solution, it is still able to diffuse through the solution and
react with the surface of the wafer (whether it is silicon,
photoresist, etc.) at the liquid/solid interface. Thus diffusion,
rather than dissolution, is the primary mechanism used to deliver
ozone to the surfaces of the wafers. Water apparently helps to
hydrolyze carbon-carbon bonds or accelerate the oxidation of
silicon surfaces by hydrolyzing silicon-hydrogen or
silicon-hydroxyl bonds. The elevated temperature promotes the
reaction kinetics and the high concentration of ozone in the gas
phase promotes diffusion of the ozone through the liquid film, even
though the increased temperature of the liquid film does not result
in a solution having a high concentration of ozone dissolved in
it.
[0008] The flow of ozone can be delivered to the process chamber
through a vapor generator or the like. Such a generator is filled
with water, which is temperature controlled. Thus the ozone gas
stream is enriched with water vapor which maintains the boundary
layer on each wafer surface at a minimal thickness so that the
layer does not inhibit diffusion. At the same time, such delivery
assists in preventing the wafers from drying completely during the
process.
[0009] A high capacity ozone generator is preferably used to
produce a mixed effluent containing a high concentration of ozone
in combination with a high flow rate. A higher concentration of
ozone increases the quantity of ozone provided to the surface of
the wafer. A higher flow rate increases the rate at which fresh
reactants are replenished, and spent or exhausted reactants are
carried away from the wafer.
[0010] Purely maximizing the concentration of ozone is not optimal
for process performance, as the amount of ozone then generated is
then too small to create an adequate concentration within the
process chamber. On the other hand, simply maximizing flow rate or
volume, without sufficient concentration will result in rapid
depletion of ozone in the process chamber (as a the ozone will
react rapidly with organic materials in the process chamber). Thus,
both high concentration and high flow rates are needed.
[0011] To further enhance the process, the temperature of the
liquid supply (water supply) can be heated to generate a supply of
saturated steam under pressure to the process chamber. Under such
circumstances, it is possible to achieve wafer surface temperatures
in excess of 100 degrees Celsius, thereby further accelerating the
reaction kinetics. A steam generator may be used to pressurize the
process chamber to achieve the desired temperatures. For example,
saturated steam at 126 degrees Celsius may be used with a
corresponding increase in the pressure of the process chamber to
240 K Pa (35 psia). The increased pressure within the processing
chamber also provides for use of higher ozone concentrations,
thereby generating a higher diffusion gradient across the boundary
layer at the surface of each wafer. The process is applicable to
various manufacturing steps that require cleaning or selective
removal of contaminants from the surface of a workpiece. For
example, one or more of the steps may be used to remove photoresist
from the surface of a semiconductor wafer.
[0012] Novel aspects include:
[0013] 1) The use of a temperature controlled liquid chemical
source delivered to the wafer surface to stabilize the temperature
of the wafer and, depending on the liquid utilized, provide a
supply of water to support hydrolysis of the carbon-carbon bonds of
contaminants at the surface of each wafer.
[0014] 2) The control of the thickness of the boundary layer of
liquid present on the wafer surface so that it is not of sufficient
thickness to significantly inhibit the diffusion of ozone to the
wafer surface. As such, the ozone is allowed to diffuse through the
controlled boundary layer, where it can oxidize silicon, organics,
or metals at the surface, or otherwise support any desired
reaction. The boundary layer may be controlled through the control
of wafer rotation rate, vapor delivery, controlled liquid spray,
the use of steam, the use of surfactants or a combination of more
than one of these techniques.
[0015] 3) The process takes place in an enclosed processing
chamber, which may or may not be used to produce a pressurized
processing environment.
[0016] 4) The process utilizes a mixed effluent having a higher
concentration of ozone in combination with a higher flow rate for
increasing the rate at which fresh reactants are supplied to the
surface of the wafer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic block diagram of one embodiment of an
apparatus for treating a semiconductor workpiece in which ozone is
injected into a line containing a pressurized treatment liquid.
[0018] FIG. 2 is a schematic block diagram of one embodiment of an
apparatus for treating a semiconductor workpiece in which the
semiconductor workpiece is indirectly heated by heating a treatment
liquid that is sprayed on the surface of the workpiece.
[0019] FIG. 3 is a flow diagram illustrating one embodiment of a
process flow for treating a semiconductor workpiece with a
treatment fluid and ozone.
[0020] FIG. 4 is a schematic block diagram of an alternative
embodiment of the system set forth in FIG. 2 wherein the ozone and
treatment fluid are provided to the semiconductor workpiece along
different flow paths.
[0021] FIG. 5 is a schematic block diagram of an embodiment of an
apparatus for treating a semiconductor workpiece in which
pressurized steam and ozone are provided in a pressurized chamber
containing a semiconductor workpiece.
[0022] FIG. 6 is a schematic block diagram of an embodiment of an
apparatus for treating a semiconductor workpiece in which an
ultra-violet lamp is used to enhance the kinetic reactions at the
surface of the workpiece.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Referring to FIG. 1, the treatment system, shown generally
at 10, includes a treatment chamber 15 that contains one or more
workpieces 20, such as semiconductor wafer workpieces. Although the
illustrated system is directed to a batch workpiece apparatus, it
is readily adaptable for use in single workpiece processing as
well.
[0024] The semiconductor workpieces 20 are preferably supported
within the chamber 15 by one or more supports 25 extending from,
for example, a rotor assembly 30. Rotor assembly 30 may seal with
the housing of the treatment chamber 15 to form a sealed, closed
processing environment. Further, rotor assembly 30 is provided so
that the semiconductor workpieces 20 may be spun about axis 35
during or after treatment with the ozone and treatment liquid.
[0025] The chamber 15 has a volume which is minimized, and is as
small as permitted by design considerations for any given capacity
(i.e., the number and size of the substrates to be treated). The
chamber 15 is preferably cylindrical for processing multiple wafers
in a batch, or a flatter disk-shaped chamber may be used for single
wafer processing. Typically, the chamber volume will range from
about 5 liters, (for a single wafer) to about 50 liters (for a 50
wafer system).
[0026] One or more nozzles 40 are disposed within the treatment
chamber 15 to direct a spray mixture of ozone and treatment liquid
onto the surfaces of the semiconductor workpieces 20 that are to be
treated. In the illustrated embodiment, the nozzles 40 direct a
spray of treatment fluid to the underside of the semiconductor
workpieces 20. However, the fluid spray may be directed
alternatively, or in addition, to the upper surface of the
semiconductor workpieces 20. The fluid may also be applied in other
ways besides spraying, such as flowing, bulk deposition, immersion,
etc.
[0027] Treatment liquid and ozone are preferably supplied to the
nozzles 40 by system components uniquely arranged to provide a
single fluid line comprising ozone mixed with the treating liquid.
A reservoir 45 defines a chamber 50 in which the liquid that is to
be mixed with the ozone is stored. The chamber 50 is in fluid
communication with, or connected to, the input of a pump mechanism
55. The pump mechanism 55 provides the liquid under pressure along
a fluid flow path, shown generally at 60, for ultimate supply to
the input of the nozzles 40. The preferred treatment fluid is
deionized water. Other treatment fluids, such as other aqueous or
non-aqueous solutions, may also be used.
[0028] Fluid flow path 60 may include a filter 65 to filter out
microscopic contaminants from the treatment fluid. The treatment
fluid, still under pressure, is provided at the output of the
filter 65 (if used) along fluid flow line 70. Ozone is injected
along fluid flow line 70. The ozone is generated by ozone generator
75 and is supplied along fluid flow line 80 under pressure to fluid
flow line 70. Optionally, the treatment liquid, now injected with
ozone, is supplied to the input of a mixer 90 that mixes the ozone
and the treatment liquid. The mixer 90 may be static or active.
From the mixer 90, the treatment liquid and ozone are provided to
be input of nozzles 40 which, in turn, spray the liquid on the
surface of the semiconductor workpieces 20 that are to be treated
and, further, introduce the ozone into the environment of the
treatment chamber 15.
[0029] To further concentrate the ozone in the treatment liquid, an
output of the ozone generator 75 may be supplied to a dispersion
unit 95 disposed in the liquid chamber 50 of the reservoir 45. The
dispersion unit 95 provides a dispersed flow of ozone through the
treatment liquid to thereby add ozone to the fluid stream prior to
injection of a further amount of ozone along the fluid path 60.
[0030] In the embodiment of the system of FIG. 1, spent liquid in
chamber 15 is provided along fluid line 105 to, for example, a
valve mechanism 110. The valve mechanism 110 may be operated to
provide the spent liquid to either a drain output 115 or back to
the liquid chamber 50 of the reservoir 45. Repeated cycling of the
treatment liquid through the system and back to the reservoir 45
assists in elevating the ozone concentration in the liquid through
repeated ozone injection and/or ozone dispersion.
[0031] The ozone generator 75 is preferably a high capacity ozone
generator. One example of a high capacity ozone generator is the
ASTeX 8403 Ozone Generator, manufactured by Applied Science and
Technology, Inc., Woburn, Mass., U.S.A. The ASTeX 8403 has an ozone
production rating of 160 grams per hour. At this rate a flow of
approximately 12 liters/minute and having a concentration of 19%
ozone, by weight, can be supported. Another example of a suitable
high capacity ozone generator is the Sumitomo GR-RL Ozone
Generator, manufactured by Sumitomo Precision Products Co., Ltd.,
Hyogo, Japan which has an ozone production rating of 180 g/hr. The
ozone generator 75 preferably has a capacity of at least 90 or 100
grams per hour, or 110 or 120 grams per hour, with the capacity
more preferably of at least 135 grams per hour. In terms of flow
rate and concentration, the capacity should be at least 10 liters
per minute at 12%, 13%, 14%, 15% ( or higher) concentration by
weight. Lower flow rate applications, such as with single wafer
processing, may have higher concentrations of e.g., 16-19 or
greater.
[0032] Use of a high capacity ozone generator is especially useful
in connection with the methods and apparatus of the present
application, because the present methods and apparatus provide for
the delivery of ozone independent of the processing fluid.
[0033] In previous methods the ozone was dissolved into the aqueous
solution in order to make it available for the oxidation process on
the surface of the semiconductor wafer. This limited the amount of
ozone, which could be delivered to the surface of the semiconductor
wafer, to the amount of ozone which could be dissolved into the
processing fluid. Correspondingly, there was no incentive to use
higher capacity ozone generators, because any excess ozone produced
would not be absorbed by the process fluid, and would eventually
dissipate and be lost.
[0034] FIG. 1, (as well as the other Figures) illustrates various
components and connections. While showing preferred designs, the
drawings include elements which may or may not be essential to the
invention. The elements essential to the invention are set forth in
the claims. The drawings show both essential and non-essential
elements.
[0035] A further embodiment of a system for delivering a fluid
mixture for treating the surface of a semiconductor workpiece is
illustrated in FIG. 2. Although the system 120 of FIG. 2 appears to
be substantially similar to the system 10 of FIG. 1, there are
significant differences. The system 120 of FIG. 2 is based in part
on the concept that the heating of the surfaces of the
semiconductor workpieces 20 with a heated liquid that is supplied
along with a flow of ozone that creates an ozonated atmosphere is
highly effective in photoresist stripping, ash removal, and/or
cleaning processes. The system 120 therefore preferably includes
one or more heaters 125 that are used to heat the treatment liquid
so that it is supplied to the surfaces of the semiconductor
workpieces at an elevated temperature that accelerates the surface
reactions. It is also possible to directly heat the workpieces to
stimulate the reactions. Such heating may take place in addition to
or instead of the indirect heating of the workpieces through
contact with the heated treatment liquid. For example, supports 25
may include heating elements that may be used to heat the
workpieces 20. The chamber 15 may include a heater for elevating
the temperature of the chamber environment and workpieces.
[0036] The preferred treatment liquid is deionized water, since it
appears to be required to initiate the cleaning/removal reactions
at the workpiece surface, apparently through hydrolysis of the
carbon-carbon bonds of organic molecules. However, significant
amounts of water can form a continuous film on the semiconductor
workpiece surface. This film acts as a diffusion barrier to the
ozone, thereby inhibiting reaction rates. The boundary layer
thickness is controlled by controlling the rpm of the semiconductor
workpiece, vapor delivery, and controlled spraying of the treatment
liquid, or a combination of one or more of these techniques. By
reducing the boundary layer thickness, the ozone is allowed to
diffuse to the surface of the workpieces and react with the organic
materials that are to be removed.
[0037] FIG. 3 illustrates one embodiment of a process that may be
implemented in the system of FIG. 2 when the system 120 is used,
for example, to strip photoresist from the surfaces of
semiconductor workpieces. At step 200, the workpieces 20 that are
to be stripped are placed in, for example, a Teflon wafer cassette.
This cassette is placed in a closed environment, such as in chamber
15. Chamber 15 and its corresponding components may be constructed
based on a well known spray solvent system or spray acid such as
those available from Semitool, Inc., of Kalispell, Mont., U.S.A..
Alternatively, the semiconductor workpieces 20 may be disposed in
chamber 15 in a carrierless manner, with an automated processing
system, such as described in U.S. Pat. No. 5,784,797.
[0038] At step 205, heated deionized water is sprayed onto the
surfaces of the semiconductor workpieces 20. The heated deionized
water heats the surfaces of the semiconductor workpieces 20 as well
as the enclosed environment of the chamber 15. When the spray is
discontinued, a thin liquid film remains on the workpiece surfaces.
If the surface is hydrophobic, a surfactant may be added to the
deionized water to assist in creating a thin liquid boundary layer
on the workpiece surfaces. The surfactant may be used in connection
with hydrophilic surfaces as well. Corrosion inhibitors may also be
used with the aqueous ozone, thin boundary layer process.
[0039] The surface boundary layer of deionized water is controlled
at step 210 using one or more techniques. For example, the
semiconductor workpieces 20 may be rotated about axis 35 by rotor
30 to thereby generate centripetal accelerations that thin the
boundary layer. The flow rate of the deionized water may also be
used to control the thickness of the surface boundary layer.
Lowering of the flow rate results in decreased boundary layer
thickness. Still further, the manner in which the deionized water
is injected into the chamber 15 may be used to control the boundary
layer thickness. Nozzles 40 may be designed to provide the
deionized water as micro-droplets thereby resulting in a thin
boundary layer.
[0040] At step 215, ozone is injected into the fluid flow path 60
during the water spray, or otherwise provided to the internal
chamber environment of chamber 15. If the apparatus of FIG. 2 is
utilized, the injection of the ozone continues after the spray has
shut off. If the workpiece surface begins to dry, a brief spray is
preferably activated to replenish the liquid film on the workpiece
surface. This ensures that the exposed workpiece surfaces remain
wetted at all times and, further, ensures that the workpiece
temperature is and remains elevated at the desired reaction
temperature. It has been found that a continuous spray of deionized
water having a flow rate that is sufficient to maintain the
workpiece surfaces at an elevated temperature, and high rotational
speeds (i.e., >300 rpm, between 300 and 800 rpm, or even as high
as or greater than 1500 rpm) generates a very thin boundary layer
which minimizes the ozone diffusion barrier and thereby leads to an
enhanced photoresist stripping rate. As such, the control of the
boundary layer thickness is used to regulate the diffusion of
reactive ozone to the surface of the wafer.
[0041] The surface layer thickness may range from a few molecular
layers (e.g., about 1 micron ), up to 100 microns, (typically
50-100 microns), or greater.
[0042] While ozone has a limited solubility in the heated deionized
water, the ozone is able to diffuse through the water and react
with photoresist at the liquid/resist interface. It is believed
that the presence of the deionized water itself further assists in
the reactions by hydrolyzing the carbon-carbon bonds of organic
deposits, such as photoresist, on the surface of the wafer. The
higher temperature promotes the reaction kinetics while the high
concentration of ozone in the gas phase promotes diffusion of ozone
through the boundary layer film even though the high temperature of
the boundary layer film does not actually have a high concentration
of dissolved ozone.
[0043] Elevated or higher temperatures means temperatures above
ambient or room temperature, that is temperatures above 20 or
25.degree. and up to about 200.degree. C.
[0044] Preferred temperature ranges are 25-150.degree., more
preferably 55-120.degree. or 75-115.degree. C., and still more
preferably 85-105.degree. C. In the methods described, temperatures
of 90-100.degree. C., and preferably centering around 95.degree. C.
may be used.
[0045] After the semiconductor workpieces 20 have been processed
through the reactions of the ozone and/or liquid with the materials
to the removed, the workpieces are subject to a rinse at 220 and
are dried at step 225. For example, the workpieces may be sprayed
with a flow of deionized water during the rinse at step 220. They
may then be subject to any one or more known drying techniques
thereafter at step 225.
[0046] In the described processes, elevated temperatures are used
to accelerate the reaction rates at the wafer surface. One manner
in which the surface temperature of the wafer may be maximized is
to maintain a constant delivery of heated processing liquid, such
as water or steam, during the process. The heated processing liquid
contacts and heats the wafer during processing. However, such a
constant delivery may result in significant waste of the water or
other processing liquid. In order to conserve water and achieve the
thinnest possible boundary layer, a "pulsed flow" of liquid or
steam may be used. In instances in which such a "pulsed flow" fails
to maintain the requisite elevated wafer surface temperatures, an
alternative manner of maintaining the wafer surface temperature may
be needed. One such alternative is the use of a "hot wall" reactor
that maintains the wafer surface and processing environment
temperatures at the desired level. To this end, the process chamber
may be heated by, for example, one or more embedded heated
recirculating coils, a heating blanket, irradiation from a thermal
source (e.g., and infrared lamp), etc.
[0047] In laboratory experiments, a 150 mm silicon wafer coated
with 1 micron of photoresist was stripped in accordance with the
teachings of the foregoing process. The processing chamber was
pre-heated by spraying deionized water that was heated to 95
degrees Celsius into the processing chamber for 10 minutes. During
the cleaning process, a pulsed flow of deionized water heated to 95
degrees Celsius was used. The pulsed flow included an "on time" of
approximately five seconds followed by an "off time" of 10 seconds.
The wafer was rotated at 800 rpm and the pulsed flow of deionized
water was sprayed into the processing chamber through nine nozzles
at a rate of 3 liters per minute. Ozone was injected into the
processing chamber through a separate manifold at a rate of 8
liters per minute at a concentration of 12 percent. The resultant
strip rate was 7234 Angstroms/min.
[0048] At a higher ozone flow rate, made possible by using a high
capacity ozone generator for injecting ozone into. the processing
chamber at a rate of 12 liters per minute and having a
concentration of 19 percent, the resultant strip rates can be
further increased to in excess of 8800 Angstroms/minute.
[0049] There are many benefits resulting from the use of the
semiconductor cleaning processes described above. One of the most
significant benefits is that the conventional 4-chem clean process
may be reduced to a two-chemical step process while retaining the
ability to remove organics, remove particulates, reduce metals and
remove silicon dioxide. Process times, chemical consumption, water
consumption and waste generation are all also significantly
reduced. A further benefit of the foregoing process is its
applicability to both FEOL and BEOL wafers and strip processes.
Laboratory tests indicate that there is no attack on metals such as
aluminum, titanium, tungsten, etc. A known exception is copper,
which forms a copper oxide in the presence of ozone. This oxide is
not a "hard" and uniform passivation oxide, such as the oxide that
forms on metals like aluminum. As a result, the oxide can be
readily removed.
[0050] A still further benefit is the higher ozone flow rates and
concentrations can be used to produce higher strip rates under
various processing conditions including lower wafer rotational
speeds and reduced temperatures. Use of lower temperatures (between
25 and 75.degree. C. and preferably from 25-65.degree. C. (rather
than at e.g., 95.degree. C. as described above) may be useful where
higher temperatures are undesirable.
[0051] One example where this is beneficial is the use of the
process with BEOL wafers, wherein metal corrosion may occur if the
metal films are exposed to high temperature de-ionized water.
Correspondingly, processing at ambient temperatures may be
preferred. The gain in strip rates not realized, as a result of not
using higher temperatures, is offset by increases in strip rate due
to the increased ozone flow rates and concentrations. The use of
higher ozone concentration can offset the loss of kinetic energy
from using lower temperatures.
[0052] With reference again to FIG. 3, it will be recognized that
process steps 205-215 may be executed in a substantially concurrent
manner. Additionally, it will be recognized that process steps
205-215 may be sequentially repeated using different processing
liquids. In such instances, each of the processing liquids that are
used may be specifically tailored to remove a respective set of
contaminants. Preferably, however, it is desirable to use as few
different processing liquids as possible. By reducing the number of
different processing liquids utilized, the overall cleaning process
is simplified and reducing the number of different processing
liquids utilized minimizes chemical consumption.
[0053] A single processing liquid may be used to remove organic
contaminants, metals, and particles in a single cycle of process
steps 205-215. The processing liquid is comprised of a solution of
deionized water and one or more compounds, such as HF or HCl, so as
to form an acidic processing liquid solution.
[0054] The steps and parameters described above for the ozone
processes apply as well to the ozone with HF and ozone process.
These processes may be carried out on batches of workpieces in
apparatus such as described in U.S. Pat. No. 5,544,421, or on
individual workpieces in an apparatus such as described in
PCT/US99/05676.
[0055] Typical chemical application times are in the range of 1:00
to 5:00 minutes. Compared to a 4-chem clean process time of around
20:00 minutes, the disclosed process with an HF and/or HCl
containing processing liquid becomes very attractive. Typical
H20:HF:HCl concentration ratios are on the order of 500:1:1 to
50:1:1, with and without HF and/or HC1. Higher concentrations are
possible, but the economic benefits are diminished. It is important
to note that gaseous HF or HCl could be injected into water to
create the desired cleaning chemistry as well. Due to differences
in processor configurations and desired cleaning requirements,
definition of specific cleaning process parameters will vary based
on these differences and requirements.
[0056] The process benefits include the following:
[0057] 1. Reduction in the amount and types of chemicals used in
the cleaning process.
[0058] 2. Reduction in water consumption by the elimination of the
numerous intermediate rinse steps required.
[0059] 3. Reduction in process time.
[0060] 4. Simplification of process hardware.
[0061] In the case of oxidizing and removing organic contamination,
conventional aqueous ozone processes show a strip rate on
photoresist (a hydrocarbon film) of around 200-700 angstroms per
minute. In the boundary layer controlled system of the disclosed
processes, the rate is accelerated to 2500 to 8800. angstroms per
minute in a spray controlled boundary layer, or higher when the
boundary layer is generated and controlled using steam at 15 psi
and 126 degrees C.
[0062] With reference to FIG. 4, there is shown yet a further
embodiment of the ozone treatment system 227. In the embodiment of
FIG. 4, one or more nozzles 230 are disposed within the treatment
chamber 15 to conduct ozone from ozone generator 75 directly into
the reaction environment. The heated treatment fluid is provided to
the chamber 15 through nozzles 40 that receive the treatment fluid,
such as heated deionized water, through a supply line that is
separate from the ozone supply line. As such, injection of ozone in
fluid path 60 is optional.
[0063] Another embodiment of an ozone treatment system is shown
generally at 250 in FIG. 5. In the system 250, a steam boiler 260
that supplies saturated steam under pressure to the process chamber
15 has replaced the pump mechanism. The reaction chamber 15 is
preferably sealed to thereby form a pressurized atmosphere for the
reactions. For example, saturated steam at 126 degrees Celsius
could be generated by steam boiler 260 and supplied to reaction
chamber 15 to generate a pressure of 35 psia therein during the
workpiece processing. Ozone may be directly injected into the
chamber 15 as shown, and/or may be injected into the path 60 for
concurrent supply with the steam. Using the system architecture of
this embodiment, it is thus possible to achieve semiconductor
workpiece surface temperatures in excess of 100 degrees Celsius,
thereby further accelerating the reaction kinetics. The steam
generator in FIG. 5 may be replaced with a heater(s) as shown in
FIGS. 1-4. While FIGS. 4 and 5 show the fluid and ozone delivered
via separate nozzles 40, they may also be delivered from the same
nozzles, using appropriate valves.
[0064] A still further enhancement that may be made to any one of
the foregoing systems is illustrated in FIG. 6. In this embodiment,
an ultra-violet or infrared lamp 300 is used to irradiate the
surface of the semiconductor workpiece 20 during processing. Such
irradiation further enhances the reaction kinetics. Although this
irradiation technique is applicable to batch semiconductor
workpiece processing, it is more easily and economically
implemented in the illustrated single wafer processing environment
where the workpiece is more easily completely exposed to the UV
radiation. Megasonic or ultrasonic nozzles 40 may also be used.
[0065] As described, the ozone gas may be separately sprayed, or
otherwise introduced as a gas into the process chamber, where it
can diffuse through the liquid boundary layer on the workpiece. The
fluid is preferably heated and sprayed or otherwise applied to the
workpiece, without ozone injected into the fluid before the fluid
is applied to the workpiece.
[0066] Alternatively, the ozone may be injected into the fluid, and
then the ozone containing fluid applied to the workpiece. In this
embodiment, if the fluid is heated, the heating preferably is
performed before the ozone is injected into the fluid, to reduce
the amount of ozone breakdown in the fluid during the fluid
heating. Typically, due to the larger amounts of ozone desired to
be injected into the fluid, and the low solubility of the ozone gas
in the heated fluid, the fluid will contain some dissolved ozone,
and may also contain ozone bubbles.
[0067] It is also possible to use aspects of both embodiments, that
is to introduce ozone gas directly into the process chamber, and to
also introduce ozone into the fluid before the fluid is delivered
into the process chamber. Thus, various methods may be used for
introducing ozone into the chamber.
[0068] The presently disclosed apparatus and methods may be used to
treat workpieces beyond the semiconductor workpieces described
above. For example, other workpieces, such as flat panel displays,
hard disk media, CD glass, etc, may also have their surfaces
treated using the foregoing apparatus and methods.
[0069] Although the preferred treatment liquid for the disclosed
application is deionized water, other treatment liquids may also be
used. For example, acidic and basic solutions may be used,
depending on the particular surface to be treated and the material
that is to be removed. Treatment liquids comprising sulfuric acid,
hydrochloric acid, and ammonium hydroxide may be useful in various
applications.
[0070] As described, one aspect of the process is the use of steam
(Water vapor at temperatures exceeding 100 C) to enhance the strip
rate of photoresist in the presence of an ozone environment.
Preliminary testing shows that a process using hot water at 95 C
produces a photoresist strip rate of around 3000-4000 angstroms per
minute. Performing a similar process using steam at 120-130 C
results in a strip rate of around 7000-8000 angstroms per minute.
However, the resultant strip rate is not sustainable.
[0071] The high strip rate is achieved only when the steam
condenses on the wafer surface. The wafer temperature rapidly
approaches thermal equilibrium with the steam, and as equilibrium
is achieved, there is no longer a thermal gradient to promote the
formation of the condensate film. This results in the loss of the
liquid boundary layer on the wafer surface. The boundary layer
appears to be essential to promote the oxidation of the organic
materials on the wafer surface. The absence of the liquid film
results in a significant drop in the strip rate on photoresist.
[0072] Additionally, once the steam ceases to condense on the wafer
surface, the reaction environment experiences the elimination of an
energy source to drive the reaction kinetics. As steam condenses on
the wafer surface, it must relinquish the heat of vaporization,
which is approximately 540 calories per gram. This energy then
becomes available to promote other reactions such as the oxidation
of carbon compounds in the presence of ozone or oxygen free
radicals.
[0073] In view of these experimental observations, a method for
maintaining the temperature of a surface such as a semiconductor
wafer surface, is provided to ensure that condensation from a steam
environment continues indefinitely, thereby enabling the use of
steam in applications such as photoresist strip in the presence of
ozone. Thus the formation of the liquid boundary layer is assured,
as well as the release of significant amounts of energy as the
steam condenses.
[0074] To accomplish this, the wafer surface must be maintained at
a temperature lower than that of the steam delivered to the process
chamber. This may be achieved by attaching the wafer to a
temperature-controlled surface or plate 350 which will act as a
heat sink. This surface may then be temperature controlled either
through the use of cooling coils, a solid-state heat exchanger, or
other means.
[0075] In a preferred embodiment, a temperature-controlled stream
of liquid is delivered to the back surface of a wafer, while steam
and ozone are delivered to an enclosed process region and the steam
is allowed to condense on the wafer surface. The wafer may be
rotated to promote uniform distribution of the boundary layer, as
well as helping to define the thickness of the boundary layer
through centrifugal force. However, rotation is not an absolute
requirement. The cooling stream must be at a temperature lower than
the steam. If the cooling stream is water, a temperature of 75 or
85-95 C is preferably used, with steam temperatures in excess of
100 C.
[0076] In another embodiment, and one which is relatively easy to
implement in a batch process, pulsed spray of cooling liquid is
applied periodically to reduce the wafer temperature. Steam
delivery may either be continuous or pulsed as well. The wafer may
be in any orientation and additives such as hydrofluoric acid,
ammonium hydroxide or some other chemical may be added to the
system to promote the cleaning of the surface or the removal of
specific classes of materials other than or in addition to organic
materials.
[0077] This process enables the use of temperatures greater than
100 C to promote reaction kinetics in the water/ozone system for
the purpose of removing organic or other materials from a surface.
It helps ensure the continuous formation of a condensate film by
preventing the surface from achieving thermal equilibrium with the
steam. It also takes advantage of the liberated heat of
vaporization in order to promote reaction rates and potentially
allow the removal of more difficult materials which may require
more energy than can be readily delivered in a hot water
process.
* * * * *