U.S. patent application number 10/197384 was filed with the patent office on 2004-01-22 for composition and method for removing photoresist and/or resist residue using supercritical fluids.
This patent application is currently assigned to SCP Global Technologies Inc.. Invention is credited to Seghal, Akshey.
Application Number | 20040011386 10/197384 |
Document ID | / |
Family ID | 30442935 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040011386 |
Kind Code |
A1 |
Seghal, Akshey |
January 22, 2004 |
Composition and method for removing photoresist and/or resist
residue using supercritical fluids
Abstract
A method of removing photoresist and/or resist residue from a
substrate includes exposing the substrate to a supercritical fluid
in combination with a co-solvent mixture comprising an organic
solvent and an oxidizer. In one embodiment, the supercritical fluid
is supercritical carbon dioxide and the co-solvent mixture includes
1,2-Butylene Carbonate, Dimethyl Sulfoxide and hydrogen peroxide.
If desired, supercritical carbon dioxide in combination with a
second co-solvent mixture may be subsequently applied to the
substrate to rinse and dry the substrate. In one embodiment, the
second co-solvent mixture includes isopropyl alcohol.
Inventors: |
Seghal, Akshey; (Eagle,
ID) |
Correspondence
Address: |
STALLMAN & POLLOCK LLP
Suite 290
121 Spear Street
San Francisco
CA
94105
US
|
Assignee: |
SCP Global Technologies
Inc.
|
Family ID: |
30442935 |
Appl. No.: |
10/197384 |
Filed: |
July 17, 2002 |
Current U.S.
Class: |
134/26 ; 510/175;
510/505 |
Current CPC
Class: |
H01L 21/02101 20130101;
G03F 7/425 20130101; G03F 7/423 20130101; G03F 7/422 20130101; G03F
7/426 20130101 |
Class at
Publication: |
134/26 ; 510/175;
510/505 |
International
Class: |
C23G 001/02 |
Claims
What is claimed is:
1. A method of removing photoresist and/or resist residue from a
substrate, comprising the steps of: (a) providing a substrate
having photoresist material formed thereon; (b) exposing the
substrate to a supercritical fluid in combination with a co-solvent
mixture comprising an organic solvent and an oxidizer.
2. The method of claim 1 wherein the supercritical fluid is
supercritical carbon dioxide.
3. The method of claim 1 wherein the co-solvent mixture include an
aqueous fluoride.
4. The method of claim 3 wherein the aqueous fluoride is selected
from the group consisting of ammonium fluoride and hydrofluoric
acid.
5. The method of claim 1 in which the organic solvent is selected
from the group consisting of 1,2-Butylene Carbonate, Benzyl
Alcohol, Ethylene and Propylene Carbonate and mixtures thereof,
Dimethyl Sulfoxide, N-Methyl Pyrrolidone, Dimethyl Acetamide,
Dimethyl Formamide, Propylene Glycol and Propylene Glycol n-Butyl
Ether.
6. The method of claim 5, wherein the organic solvent includes
1,2-Butylene Carbonate.
7. The method of claim 5, wherein the organic solvent includes
Dimethyl Sulfoxide.
8. The method of claim 5, wherein the organic solvent includes
Benzyl Alcohol.
9. The method of claim 5, wherein the organic solvent includes
Propylene Carbonate, 1,2-Butylene Carbonate and Dimethyl
Sulfoxide.
10. The method of claim 5, wherein the organic solvent includes
Propylene Carbonate.
11. The method of claim 5, wherein the organic solvent includes
Propylene Carbonate and Dimethyl Sulfoxide.
12. The method of claim 5, wherein the organic solvent includes
Propylene Carbonate and Benzyl Alcohol.
13. The method of claim 5, wherein the organic solvent includes
1,2-Butylene Carbonate and Dimethyl Sulfoxide.
14. The method of claim 5, wherein the organic solvent includes
1,2-Butylene Carbonate and Benzyl Alcohol.
15. The method of claim 1 wherein the oxidizer is selected from the
group consisting of hydrogen peroxide, benzoyl peroxide, urea
peroxide and mixtures thereof.
16. The method of claim 15 wherein the oxidizer is 10 to 80%
hydrogen peroxide.
17. The method of claim 1 wherein the exposing step causes
stripping of photoresist material from the substrate.
18. The method of claim 1 wherein the exposing step cleans resist
residue from the substrate.
19. The method of claim 17, wherein the co-solvent mixture is a
first co-solvent mixture and wherein the method further includes
the step of, after step (b), exposing the substrate to a second
mixture comprising a supercritical fluid in combination with
isopropyl alcohol.
20. The method of claim 19 wherein the second co-solvent mixture
includes supercritical fluid in combination with isopropyl alcohol
and water.
21. The method of claim 19 wherein the step of exposing the
substrate to the second co-solvent mixture removes the first
co-solvent mixture from the substrate and dries the substrate.
22. The method of claim 1 wherein the substrate includes I-line
photoresist and wherein the method is for removing the I-line
photoresist.
23. The method of claim 1 wherein the substrate is a substrate
previously exposed to ion implantation.
24. The method of claim 1 wherein the substrate includes aluminum
lines formed thereon.
25. The method of claim 1 wherein the substrate includes at least
one integrated circuit device including low-dielectric constant
materials.
26. The method of claim 1 wherein the substrate includes at least
one integrated circuit device having high dielectric constant gate
materials.
27. The method of claim 1 wherein the substrate includes back
anti-reflective coating and wherein the method removes the back
anti-reflective coating from the substrate.
28. The method of claim 1 wherein the substrate includes deep UV
photoresist and wherein the method removes the DUV photoresist from
the substrate.
29. The method of claim 1 wherein the substrate includes post-ash
residues, and wherein the method includes removing the post-ash
residues from the substrate.
30. A composition for removing photoresist and/or resist residues
from a substrate, the composition comprising: a supercritical fluid
in combination with a co-solvent mixture comprising an organic
solvent and an oxidizer.
31. The composition of claim 30 wherein the supercritical fluid is
supercritical carbon dioxide.
32. The composition of claim 30 wherein the co-solvent mixture
include an aqueous fluoride.
33. The composition of claim 32 wherein the aqueous fluoride is
selected from the group consisting of ammonium fluoride and
hydrofluoric acid.
34. The composition of claim 30 in which the organic solvent is
selected from the group consisting of 1,2-Butylene Carbonate,
Benzyl Alcohol, Ethylene and Propylene Carbonate and mixtures
thereof, Dimethyl Sulfoxide, N-Methyl Pyrrolidone, Dimethyl
Acetamide, Dimethyl Formamide, Propylene Glycol and Propylene
Glycol n-Butyl Ether.
35. The composition of claim 34, wherein the organic solvent
includes 1,2-Butylene Carbonate.
36. The composition of claim 34, wherein the organic solvent
includes Dimethyl Sulfoxide.
37. The composition of claim 34, wherein the organic solvent
includes Benzyl Alcohol.
38. The composition of claim 34, wherein the organic solvent
includes Propylene Carbonate.
39. The composition of claim 34, wherein the organic solvent
includes Propylene Carbonate and Dimethyl Sulfoxide.
40. The composition of claim 34 wherein the organic solvent
includes Propylene Carbonate and Benzyl Alcohol.
41. The composition of claim 34, wherein the organic solvent
includes 1,2-Butylene Carbonate and Dimethyl Sulfoxide.
42. The composition of claim 34, wherein the organic solvent
includes 1,2-Butylene Carbonate and Benzyl Alcohol.
43. The composition of claim 34, wherein the organic solvent
includes Propylene Carbonate, 1,2-Butylene Carbonate and Dimethyl
Sulfoxide.
44. The composition of claim 30 wherein the oxidizer is selected
from the group consisting of hydrogen peroxide, benzoyl peroxide,
urea peroxide and mixtures thereof.
45. The composition of claim 44 wherein the oxidizer is 10 to 80%
hydrogen peroxide.
46. A composition for removing photoresist and/or resist residue
from a substrate, the comprising including supercritical carbon
dioxide, 1,2-Butylene Carbonate, Dimethyl Sulfoxide and hydrogen
peroxide.
47. The composition of claim 46, further including ammonium
fluoride.
48. A composition for removing photoresist and/or resist residuel
from a substrate, the comprising including supercritical carbon
dioxide, Benzyl Alcohol, 1,2-Butylene Carbonate and hydrogen
peroxide.
49. The composition of claim 48, further including ammonium
fluoride.
50. A composition for removing photoresist and/or resist residue
from a substrate, the comprising including supercritical carbon
dioxide, Propylene Carbonate, Dimethyl Sulfoxide and hydrogen
peroxide.
51. The composition of claim 50, further including ammonium
fluoride.
52. A composition for removing photoresist and/or resist residue
from a substrate, the comprising including supercritical carbon
dioxide, Propylene Carbonate, Benzyl Alcohol and hydrogen
peroxide.
53. The composition of claim 52, further including ammonium
fluoride.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to supercritical fluids and,
in particularly, to compositions and methods using supercritical
fluids to remove photoresist and/or resist residues and associated
materials from semiconductor substrates.
BACKGROUND OF THE DISCLOSURE
[0002] During the process of fabricating semiconductor integrated
circuits, organic photoresist material may be applied to a
semiconductor substrate as a precursor to formation of features on
the substrate using photolithography techniques. Often additional
coatings, for example an anti-reflective coating known in the
industry as BARC [Back Antireflective Coating], are also applied to
the substrate to enhance the lithography process.
[0003] Once lithography is completed, the resist, BARC and other
coatings used for the lithography steps must be removed from the
substrate. A common technique for photoresist removal involves
placing the substrate in an asher and burning the resist and
associated coatings using a gaseous plasma. While the high
temperature in the plasma process chamber oxidizes the photoresist
and removes it, the plasma etch process leaves post-ash
residues--undesirable byproducts from the reaction of the plasma
gases, reactant species and the photoresist. These by-products are
generally referred to as "sidewall polymer," "via veil," "goat
horns," etc. and cannot be completely removed by the etch process.
Thus, the substrate must be subsequently placed in a wet cleaning
tool to remove byproducts of the plasma etch process, and then
rinsed and dried.
[0004] Moreover, the plasma etch procedure for resist removal is
less desirable for substrates having low dielectric constant (or
"low-k") films as insulating layers. These insulating layers, such
as SiO.sub.2 with carbon, are porous and are thus more likely to
absorb etch gases which can later out-gas and attack metal contacts
formed into the substrate (e.g., dual damascene copper).
[0005] Another currently used photoresist removal process includes
exposing the substrate to a liquid photoresist stripper containing
at least one polar solvent. At times, however, the byproducts of
the stripping process and the stripping solution itself may be left
behind in fine features formed in the substrate. Therefore,
additional steps of rinsing out the stripper and stripper residues
and drying the wafer must follow the wet stripping process.
[0006] In either method, at least two steps are needed for
photoresist and resist residue removal and separate steps are
needed to rinse and dry the wafer. It is highly desirable to
expedite and thereby reduce the cost of the resist removal process
by eliminating the need for follow-on cleaning and/or drying steps.
It would be desirable to carry out the resist and/or resist residue
removal and drying of the wafer in one step at low temperature.
[0007] Removing resist and/or resist residue, and drying of the
wafer in one step at low temperature is possible using the
compositions and methods disclosed herein for supercritical
processing. Supercritical conditions are created by a combination
of pressure and temperature of the environment above which a
substance enters its supercritical phase. In a supercritical state,
the substance has properties both of a liquid and a gas, i.e., the
liquid and gaseous states of matter exist together as a single
phase. FIG. 1 shows the conditions needed to achieve supercritical
conditions for carbon dioxide. Carbon dioxide has a critical
temperature of 31.degree. C. and a critical pressure of 72.8 atm.
Thus, when CO.sub.2 is subjected to temperature and pressure above
these critical conditions, it is in the supercritical state. A
substance that is in the supercritical state is known in the art as
a "supercritical fluid."
[0008] Supercritical fluids are desirable in the context of
integrated circuit fabrication for a variety of reasons. For
example, supercritical fluids have very low surface tension, which
enables them to achieve better effective contact with surfaces and
better penetration into high aspect vias and boundary layer films
than substances in the liquid state. The low viscosity of
supercritical fluids allows for relative fast mass transfer.
[0009] The industry trend is towards shrinking semiconductor device
structure geometries and other structure geometries into the
submicron range such as below 0.25 micron. Nevertheless, the
industry lacks a first-rate method of removing photoresist and/or
resist residue from high aspect ratio openings such as submicron
grooves, narrow crevices etc. without damaging the structure being
produced. Supercritical fluids are suitable for this purpose
because they can readily penetrate these high aspect ratio openings
and effectively remove resist and/or resist residues from them. In
addition, the supercritical fluid and/or co-solvent composition can
be exactly tailored to selectively attack only the resist and/or
residue without attacking the semiconductor device structures.
Moreover, it has been found that using supercritical fluids for
resist/residue removal can eliminate process steps thereby
increasing yield at a lower cost.
[0010] More specifically, resist and/or resist residue removal and
drying of the wafer in one step is possible by using supercritical
fluids in integrated circuit fabrication, providing a distinct
advantage over prior art methods requiring follow-on cleaning
and/or drying steps. This not only speeds up the wafer processing
but also results in a decreased consumption of solvents and/or
water used in cleaning, rinsing and drying. While this decreases
the chemical usage and disposal costs, corrosion of the IC
structure/stack is also reduced because of the small amounts of
co-solvent used in a controlled manner compared to the wafer being
immersed in a large bath for an extended period of time and then
subjected to further rinsing to remove the solvent. These
environmental benefits make supercritical cleaning of semiconductor
wafer substrates a desirable "green" process.
[0011] Supercritical CO.sub.2 ("scCO.sub.2") is a supercritical
substance suitable for integrated circuit fabrication because its
critical pressure and temperature are relatively easy to achieve,
and thus do not require high equipment and operating costs. It is
non-toxic and non-flammable, it is inert to inorganic materials
found on wafers, and it is not an ozone layer depleting chemical.
High purity grades of CO.sub.2 can be readily obtained and are
inexpensive.
[0012] Until now, however, the use of scCO.sub.2 in photoresist
removal processes has not been successfully achieved. This lack of
success is due to the fact that scCO.sub.2 itself is a very poor
solvent for polar residues such as resist and/or resist residues
found on wafer surfaces. Therefore, polar solvents (which are
necessary for the photoresist removal process) have limited
solubility in scCO.sub.2. Moreover, the polar solvents and the
scCO.sub.2 have vast differences in their densities, a condition
which prevents the substances from mixing evenly to a degree that
would allow uniform resist removal once the mixture was placed in
contact with a substrate. Nevertheless, some attempts have been
made to perform processes using supercritical fluids, including
scCO.sub.2, to remove photoresist and resist residues. Many of
these processes are not cost effective for commercial use in that
they require extended processing durations overly high energy
costs, or use of prohibitively large quantities of process
chemicals. Others expose substrates to temperatures and/or
pressures and/or chemical environments that can degrade the
electrical performance of the integrated circuits manufactured
using the substrates. Others may even result in damage to the
process equipment, such as amine stress corrosion cracking of the
pressure vessel which can occur when amines are used in the
presence of supercritical CO.sub.2. Still others are simply
ineffective at removing photoresist and/or resist residue.
[0013] As set forth in detail below, the present inventor has
developed compositions and methods which overcome these problems
and which allow for successful removal of photoresist and/or resist
residue using scCO.sub.2.
SUMMARY
[0014] A method of removing photoresist and/or resist residue from
a substrate includes exposing the substrate to a supercritical
fluid in combination with a co-solvent mixture comprising an
organic solvent and an oxidizer. In one embodiment, the
supercritical fluid is supercritical carbon dioxide and the
co-solvent mixture includes 1,2-Butylene Carbonate, Dimethyl
Sulfoxide and Hydrogen Peroxide. If desired, supercritical carbon
dioxide in combination with a second co-solvent mixture may be
subsequently applied to the substrate to rinse and dry the
substrate. In one embodiment, the second co-solvent mixture
includes isopropyl alcohol.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a phase diagram illustrating the supercritical
phase of carbon dioxide.
[0016] FIG. 2 is a simplified schematic representation of a
pressure chamber of a type which may be used in connection with the
composition and method described herein.
DETAILED DESCRIPTION
[0017] Disclosed herein are compositions and methods for removing
photoresist, and/or residues remaining after photoresist removal,
from substrates using supercritical fluids. It is readily apparent
to one skilled in the art that while the present invention is
described in terms of removing photoresist and/or the resist
residue, it is equally applicable to removing the photoresist and
the residue, or removing the photoresist only, or to removing the
residue only. For simplicity, the term "stripping" may also be used
to describe photoresist removal, and "cleaning" may be used to
describe removal of resist residue.
[0018] In one embodiment, a composition for removing photoresist
and/or resist residue includes a supercritical fluid such as
supercritical CO.sub.2 in combination with one or more co-solvents
and a method includes exposing one or more substrates to the
supercritical CO.sub.2 and co-solvent(s). The supercritical fluid
carries the co-solvent(s) into contact with the substrate and into
high aspect vias, allowing the co-solvent(s) to strip the
photoresist/residue. In another embodiment, a subsequent processing
step may be carried out in which a supercritical fluid carries a
second co-solvent into contact with a substrate and its high-aspect
vias, removing the first co-solvent and any by-products and rinsing
and drying the substrate.
[0019] If desired, the compositions and methods described herein
may be used without pressure cycling the system during the
photoresist/residue removal process and/or using amine-free,
non-toxic co-solvent mixtures. In one embodiment, photoresist
and/or photoresist residue are removed from a substrate in which
features are etched into a low dielectric constant material.
[0020] A preferred supercritical fluid used in the
composition/method is supercritical CO.sub.2, although it should be
appreciated that other components in supercritical form may be used
alone or in combination with each other or with supercritical
CO.sub.2. Such components may include, but are not limited to
supercritical forms of the following: Ar, He, CH.sub.4,
C.sub.2H.sub.6, n-C.sub.3H.sub.8, C.sub.2H.sub.4, CHF.sub.3,
N.sub.2, N.sub.2O, and the like. Throughout this discussion, the
term "supercritical component" may be used to describe the
supercritical substance before it has been brought to its
supercritical state.
[0021] Supercritical CO.sub.2 is preferred because it is easily and
cheaply available in high purity grades and because its
supercritical conditions are achieved at moderate temperatures and
pressures. In addition, the zero dipole moment of CO.sub.2 ensures
that it is a poor solvent for polar substances until substantially
higher operating pressures (more than 4 times its critical
pressure) are used. At those high pressures, the solvating ability
of the scCO.sub.2 alone is so high that it will begin dissolving
parts of the semiconductor device structure along with the resist
and/or resist residue and loses its selective cleaning ability.
[0022] In the disclosed methods and compositions for resist
stripping and/or resist residue removal cleaning is accomplished
using a co-solvent mixture. This co-solvent mixture can be tailored
to selectively attack only the resist and/or resist residue without
damaging the sub-micron semiconductor device structures. The role
of scCO.sub.2 is to act as a pressurizing medium so that the
surface tension of the co-solvent mixture is decreased such that it
can penetrate the high aspect vias in sub-micron semiconductor
device structures. This leads to complete wetting of all surfaces
by the scCO.sub.2 and a small amount of the co-solvent mixture to
accomplish complete, uniform cleaning. The increased pressure of
the scCO.sub.2 system also increases the reaction kinetics of the
cosolvent mixture attack thereby accomplishing cleaning in a
shorter time.
[0023] The co-solvent mixture preferably includes one or more
organic solvent(s) for stripping the photoresist, and an oxidizer
for attacking the photoresist and dissolving the cross-linked bonds
in the photoresist. The oxidizer causes the co-solvent mixture to
dissolve the photoresist and/or resist residue layer by layer
rather than by undercutting it (as would occur with the
co-solvent(s) alone). The supercritical fluid carries the cosolvent
mixture into contact with the substrate and into high aspect vias,
allowing the polar co-solvent(s) to strip the photoresist and
allowing the oxidizer (if used) to attack the cross-linked bonds of
the photoresist. The co-solvent(s) and oxidizers may be added to
the supercritical component either before it is brought to its
supercritical state, or after it has been brought to its
supercritical state.
[0024] The organic solvent may be polar or non-polar, may be protic
or aprotic, maybe cyclic, branched or straight chained, and may
contain one or more functional groups. The organic solvent(s) could
be from a wide variety of representative classes such as:
[0025] Alcohols (Diacetone Alcohol, Benzyl Alcohol and Furfuyrl
Alcohol),
[0026] Amides (Formamide, Dimethyl Formamide, Acetamide and
Dimethyl Acetamide)
[0027] Carbonates (Including alkylene carbonates such as Ethylene,
Propylene or 1,2-Butylene Carbonate and mixtures thereof. Dialkyl
carbonates of the formula R--CO.sub.3--R' where R and R' may or may
not be the same group can also be used. Examples of dialkyl
carbonates are dimethyl carbonate and diethyl carbonate. The
dialkyl carbonates may be used singly or as mixtures of dimethyl-
and diethyl-carbonates. Mixtures of alkylene and dialkyl carbonates
may be also be used).
[0028] Chlorinated Hydrocarbons (Perchloroethylene,
Trichloroethylene, 1,1,1 Trichloroethane)
[0029] Ester solvents (Dibasic Ester Mix or DBE available
commercially from DuPont, N-Amyl Acetate)
[0030] Glycols (Ethylene, Propylene and Butylene Glycol, Methyl
Propanediol and Triethylene Glycol)
[0031] Glycol Ethers (Diethylene Glycol Butyl Ether, Dipropylene
Glycol Methyl Ether, Propylene Glycol Methyl Ether, Propylene
Glycol n-Butyl Ether and Dipropylene Glycol n-Butyl ether)
[0032] Ketones (Acetyl Acetone, Methyl Ethyl Ketone and Methyl
Isoamyl Ketone)
[0033] Lactams (piperidones such as N-Methyl Piperidone, N-Ethyl
Piperidone, Dimethyl Piperidone, Diethyl Piperidone, Dimethoxy
Piperidone, Diethoxy Piperidone and cyclohexyl analogues of these
piperidones such as N-Methyl-2-Pyrrolidone, N-Ethyl-2-Pyrrolidone,
N-(2-Hydroxyethyl)-2-Pyrrolidone,
N-2(Cyclohexyl)-2-Pyrrolidone)
[0034] Sulfur based solvents (Dimethyl Sulfoxide).
[0035] The oxidizer is preferably selected from the group of:
hydrogen peroxide (H.sub.2O.sub.2), benzoyl peroxide, urea
peroxide, nitrogen trifluoride, ozone, oxygen, halogens, sulfur
dioxide, and sulfur trioxide. Hydrogen peroxide having a
concentration of 10-80%, and most preferably 10-50%, is
particularly suitable for the process. Mixtures of peroxides and
carbonates (alkylene or dialkyl) have been found to make a stable,
single phase solution. Marquis et al. in U.S. Pat. Nos. 6,040,284
and 6,239,090 describe a number of single-phase solutions that are
formed by mixing peroxides and carbonates in different ratios that
are stable in composition. In addition, these solutions are
non-flammable, of low volatility and free of carcinogenic
chemicals. Normally concentrated solutions of hydrogen peroxide and
water are handled carefully as the peroxide is a strong oxidizer
and could pose a hazard. However, mixing hydrogen peroxide and
carbonate causes the concentration of hydrogen peroxide to decrease
(in the overall mix) thereby decreasing the hazardous nature of the
final composition and no special precautions need to be taken to
handle the composition.
[0036] The stability of the peroxide in the peroxide, water and
carbonate mixture, at room and at temperatures up to 50.degree. C.,
for long periods of time deserves special attention. This is in
direct contrast with the usual peroxide solutions used in the
semiconductor (and other) industries where peroxide concentration
in aqueous solutions decreases with time, the peroxide
decomposition being accelerated with increasing temperatures. A
single-phase solution is maintained when one or more organic
solvents are added to the peroxide, water and carbonate mixture, at
room and at temperatures up to 50.degree. C., for long periods of
time. This ensures that the oxidative power of the co-solvent mix
is retained for a long time and the efficacy of the mix to attack
and dissolve cross-linked photoresists does not diminish with time.
This is contrast to other photoresist stripper compositions in
which the stripper is not stable in composition and requires
additional steps of mixing the components just prior to use. In
that case there is a finite shelf and/or bath life of the stripper
and additional costs are involved in the disposal of unused
stripper mix.
[0037] The co-solvent mixture may be blended with additional
buffering agents (see Example 8), corrosion inhibitors, chelating
agents, surfactants and the like or may directly be used to effect
photoresist and/or photoresist residue removal in an scCO.sub.2
system.
[0038] For example, a first alternative embodiment adds an aqueous
fluoride to the preferred first co-solvent 1 mixture. In the first
alternative embodiment, the supercritical CO.sub.2, the solvent,
the oxidizer and the aqueous fluoride remove the photoresist and/or
resist residue generated in an etching or ashing step. Preferably,
the aqueous fluoride is selected from the group of fluoride bases
and fluoride acids. More preferably, the aqueous fluoride is
selected from the group consisting of aqueous ammonium fluoride
(NH.sub.4F) and aqueous hydrofluoric acid (HF).
[0039] Exposure of a substrate to the first co-solvent mixture may
be followed by a subsequent process step in which a supercritical
fluid carries a second co-solvent into contact with the substrate
and into high aspect vias. In this subsequent step, the second
co-solvent removes the co-solvent and any by-products, and rinses
and dries the substrate. Preferably, the second co-solvent is
selected from the group of monohydroxy alcohols such as Methanol,
Ethanol, Propanol and Benzyl Alcohol, isomers of these alcohols and
mixtures thereof. Alternatively, different mixtures of alcohol and
water may also be used. The mixture of alcohol and water may use a
single alcohol or blends of multiple alcohols added to water in
different ratios.
[0040] In one preferred embodiment, the first co-solvent mixture
(hereinafter the "co-solvent 1 mixture") includes 1,2-Butylene
Carbonate, Dimethyl Sulfoxide, and hydrogen peroxide, and the
second co-solvent mixture (hereinafter "co-solvent 2 mixture")
includes isopropyl alcohol. As discussed, inclusion of carbonates
in the mixture helps to maintain the stability of the co-solvent 1
mixture. Preferred carbonates are 1,2-Butylene Carbonate and
Propylene Carbonate.
[0041] Systems for carrying out the described process may be
configured in a variety of ways. One such system is schematically
shown in FIG. 2. The system includes a pressure chamber 10 capable
of withstanding temperatures and pressures at or above the critical
temperature and pressure of the supercritical substance to be used
in the process. The pressure chamber 10 functions as the process
chamber in which the substrate(s) are cleaned.
[0042] A supply of co-solvent 1 mixture is housed in first
reservoir 12, and co-solvent 2 mixture is housed in a second
reservoir 14. A co-solvent pump 15 is positioned to pump co-solvent
from first and/or second reservoirs 12,14 into a holding container
16, which is preferably heated by a heating tape 18. The
temperature of the co-solvent in the holding container is measured
by an internal RTD (resistive thermal device) probe 20. Carbon
dioxide (or another substance which serves as the supercritical
component in the process) is stored in reservoir 8. A pump 22 is
provided for pumping the CO.sub.2 into the system, through a heater
24, and into the pressure chamber 10. The pressure chamber 10
includes a drain valve 30 that allows fluid to be exhausted from
the chamber, and a pressure relief valve (not shown) that allows
pressure within the chamber to be reduced. Valve 30 is fluidly
coupled to a separator 32 that is vented to the atmosphere. The
separator allows the co-solvents to be separated from the
supercritical CO.sub.2 for potential re-use using a separation
process such as, for example, fractional distillation. The pressure
chamber 10 also includes a heating system and appropriate
temperature sensors and controllers (not shown) that function to
prevent "over temperature" conditions. One or more system
controllers (not shown) having software programmed for the desired
operations preferably control operation of the systems valves,
pumps etc.
[0043] During use, co-solvent mixture is pumped into a holding
container 16 and heated to a predetermined temperature by heating
tape 18. A substrate 26, having photoresist and/or resist residue
material that is to be removed is placed in pressure chamber 10 and
the chamber is sealed. Next, the CO.sub.2 is pumped from reservoir
8 through heater 24 (so as to heat the CO.sub.2 to a predetermined
temperature) and is into pressure chamber 10. When the desired
chamber pressure is achieved, the system software closes a valve 28
and prevents the flow of additional CO.sub.2 into the system. From
this time on, the chamber is preferably pressurized at the
operating pressure. This operating pressure is preferably much
greater than the critical pressure for CO.sub.2 (1070 psi) and is
typically on the order of 1800 psi.
[0044] When the co-solvent 1 chemistry in the holding container 16
has reached the predetermined temperature, it is introduced into
the process chamber 10 where it contacts the substrate. After the
substrate has been exposed to the co-solvent 1 mixture for the
desired amount of time, the co-solvent 1 mixture may be rinsed from
the substrate surface by using pure supercritical fluid directed
onto the substrate. This is accomplished by opening a valve 30 that
connects the process chamber 10 to a separator 32. The separator is
vented to atmosphere by opening valve 30 to subject the fluid
inside the pressure chamber 10 to a pressure differential, causing
the fluid to flow from the pressure chamber into the separator 32.
Valve 28 is simultaneously opened by the software routine to let
fresh scCO.sub.2 into the system such that the pressure inside the
process chamber 10 is maintained.
[0045] After rinsing the process chamber 10 and substrate 26 in
fresh scCO.sub.2 (for a duration of, for example, 15 seconds),
co-solvent 2 is also introduced into the process chamber 10 via the
holding container 16 from the co-solvent 2 reservoir 12. Alternate
cycles of (1) rinsing the process chamber 10 and substrate 26 in
pure scCO.sub.2 and (2) exposing the substrate to co-solvent 2 may
be repeated to dry the wafer. During the entire duration of this
rinsing phase, valve 30 is open to drain all the fluid contents of
the process chamber 10 into the separator and valve 28 is open to
let fresh scCO.sub.2 into the system to maintain the system
pressure. After the desired number of rinsing cycles of scCO.sub.2
and co-solvent 2, valve 28 is closed and valve 30 is kept open to
depressurize the chamber. After depressurization, a cleaned and dry
photoresist and/or resist residue free substrate, 26, is removed
from the process chamber 10.
[0046] Preferably, the pressure chamber is not de-pressurized
between application of the co-solvent 1 mixture and application of
the co-solvent 2 mixture. This allows the entire process to be
performed as a single step, without pressure-cycling the
system.
[0047] The substrate is supported within the pressure chamber in a
manner that allows the front and/or front and back surfaces of the
substrate to be exposed to fluids within the chamber. The pressure
chamber may be configured to support a single substrate or multiple
substrates.
[0048] The composition and methods described herein are highly
beneficial in that they can achieve thorough stripping of
photoresist materials (including I-Line, BARC, DUV, 193 nm) and
their photoresist residue (also called "post-ash residue") created
in a plasma chamber. The substrates treated using the disclosed
compositions and methods may have various features which include
(but are not limited to) aluminum metal lines, high dielectric
("high k") gate materials such as platinum, high aspect vias,
and/or features etched into copper/low k dielectric substrate
materials. It should be noted that the term "integrated circuit
device" may be used herein to describe integrated circuit devices
in various stages of completion. Moreover, although semiconductor
substrates are primarily discussed herein, the composition and
method may also be used for other types of substrates, such as
liquid crystal displays.
[0049] The near zero surface tension of the supercritical fluid and
reduced surface tension of the co-solvent mix allow penetration of
the supercritical fluid and/or the cosolvent into high aspect ratio
structures that are commonly found in integrated circuits. Without
complete co-solvent penetration, residue removal from the bottom
and the sidewalls of high aspect ratio structures is not possible.
This process has been shown to work for removing blanket
photoresist films that may have been hardbaked (e.g. to drive off
the solvent and improve the adhesion of the photoresist material to
the substrate surface and/or the barrier layer). Some of the
hardbaked photoresist may be further cross-linked under high
intensity UV lamps to achieve 100% cross-linking of the
photoresist. A 100% cross-linked photoresist structure improves the
intended performance of the photoresist but makes the photoresist
very difficult to remove.
[0050] In addition, the disclosed compositions and methods are
suitable for use on substrates (including the photoresist covering
part of the substrates) that were implanted with Group III or Group
V elements of the periodic table. This process is called doping and
is intended to create surface layers, over certain select areas of
the wafer, that have different conductivity from the bulk silicon
substrate. Following the ion implantation step(s), the photoresist
has a hard outer crust covering a jelly like core. The hard crust
dissolves at a much slower rate than the underlying photoresist and
therefore, implanted photoresists are considered some of the most
challenging resists to remove. Typically, in the prior art, implant
levels greater than 1.times.10.sup.14 atoms/cm.sup.2 are removed by
a two-step process requiring plasma ashing in an O.sub.2 plasma
followed by removal of residues created in the plasma process in a
stripping bath. Using the disclosed compositions/methods of
scCO.sub.2 cleaning, one can remove very high implant levels
photoresist (5.times.10.sup.15 atoms/cm.sup.2) and come out with a
dry, photoresist free wafer surface in a single step that is less
harsh on the environment and the substrate itself than the
multi-step processes currently used in the industry.
[0051] Following are examples that illustrate certain embodiments
of practicing the present invention. It should be understood that
these are intended as examples only, and are not intended to limit
the scope of the claims. The examples were carried out using a test
bed apparatus that differed from the apparatus of FIG. 2. Although
a preferred apparatus would perform the disclosed method on an
entire substrate or substrates, in each example the test bed
apparatus performed each the described methods on a single-die cut
from a substrate. For this reason, it should be noted that the
quantities of substances used and the exposure times given will
differ for when one or more complete substrates are being
treated.
EXAMPLE 1
[0052] In a first example, a substrate having a hard baked I-line
photoresist that was DUV stabilized using UV lamps to achieve 100%
cross-linking was placed in the process chamber. A co-solvent 1
composition of 40% (by weight) 1,2-Butylene Carbonate, 30% Dimethyl
Sulfoxide, and 30% of 30% hydrogen peroxide was mixed at a
temperature of 55.degree. C.
[0053] The 1,2-Butylene Carbonate was selected for its high
solvency and the fact that it makes a single-phase solution with
hydrogen peroxide. Propylene Carbonate may be substituted for the
1,2-Butylene Carbonate (and vise versa) in this and the following
examples. The hydrogen peroxide was selected for its ability to
attack the cross-linked bonds of the photoresist, and the dimethyl
sulfoxide was selected for its ability to carry out photoresist
stripping. This mixture was made to flow into the process chamber
and onto-the substrate at a rate of 8 g/min for-approximately 90
seconds. Supercritical carbon dioxide was caused to flow into the
chamber with the co-solvent 1 at a flow rate of 72 g/min to have a
total fluid flow rate into the process chamber at 80 g/min. The
temperature and pressure within the chamber were 110.degree. C. and
165 bar, respectively. After 90 seconds, the flow of carbon dioxide
into the chamber was suspended, and the flow rate of the co-solvent
1 was increased to 80 g/min for approximately 20 seconds.
[0054] Next, flow of co-solvent 1 was terminated and the
back-pressure regulator was turned off, leaving the substrate in a
static dwell of co-solvent and supercritical carbon dioxide at 165
bar and 110.degree. C. to affect photoresist stripping. Although
fluids may alternatively be made to flow through the chamber during
the exposure period, a static dwell is preferable in that is
minimizes chemical usage. The substrate was then allowed to dwell
in the chamber for approximately 4 minutes and 40 seconds. After
the dwell time, the back-pressure regulator was turned on, and
supercritical carbon dioxide was allowed to flow onto the substrate
to flush the first-co-solvent from the substrate for a period of 30
seconds.
[0055] Next, a second co-solvent consisting of isopropyl alcohol,
at room temperature, was made to flow onto the substrate surface at
a rate of 40 g/min, together with supercritical carbon dioxide
which was also flowing into the chamber at 40 g/min, for a total
fluid flow into the chamber of 80 g/min. This flow continued for
approximately 90 seconds, after which the flow of the second
co-solvent was terminated. Flow of supercritical carbon dioxide
continued for an additional two minutes, after which the substrate
was removed from the chamber. The substrate was found to be
completely free of photoresist, and the substrate and the chamber
were thoroughly dried.
EXAMPLE 2
[0056] In the second example, the co-solvent mix is unchanged but
is introduced into the process chamber in higher amounts at the
start of the run and the complete process is run without any static
dwell in the process chamber. A substrate having a hard baked
I-line photoresist that was DUV stabilized using UV lamps to
achieve 100% cross-linking was placed in the process chamber. A
co-solvent I composition of 40% (by weight) 1,2-Butylene Carbonate,
30% Dimethyl Sulfoxide, and 30% of 30% hydrogen peroxide was mixed
at a temperature of 50.degree. C. This mixture was made to flow
into the process chamber and onto the substrate at a rate of 20
g/min for approximately 30 seconds. Supercritical carbon dioxide
was caused to flow into the chamber with the co-solvent 1 at a flow
rate of 60 g/min to have a total fluid flow rate into the process
chamber at 80 g/min. Subsequently the co-solvent 1 flow rate was
decreased to 2.4 g/min and the supercritical carbon dioxide flow
rate increased to 77.6 g/min. for the next 3 minutes and 30
seconds. The operating temperature and pressure within the chamber
were 110.degree. C. and 165 bar, respectively.
[0057] Next, flow of co-solvent 1 was terminated and supercritical
carbon dioxide, at a flow rate of 80 g/min., was allowed to flow
onto the substrate to flush the first-co-solvent from the substrate
for a period of 30 seconds.
[0058] Next, a second co-solvent consisting of isopropyl alcohol,
at room temperature, was made to flow onto the substrate surface at
a rate of 40 g/min, together with supercritical carbon dioxide
which was also flowing into the chamber at 40 g/min. for a total
fluid flow into the chamber of 80 g/min. This flow continued for
approximately 90 seconds, after which the flow of the second
co-solvent was terminated. Flow of supercritical carbon dioxide
continued for an additional two minutes, after which the substrate
was removed from the chamber. The substrate was found to be
completely free of photoresist, and the substrate and the chamber
were thoroughly dried.
EXAMPLE 3
[0059] The third example is similar to Example 2, but differs in
that a different cosolvent 1 composition was used. A substrate
having a hard baked I-line photoresist that was DUV stabilized
using UV lamps to achieve 100% cross-linking was placed in the
process chamber. A co-solvent 1 composition of 40% (by weight)
1,2-Butylene Carbonate, 40% Benzyl Alcohol, and 20% of 30% hydrogen
peroxide was mixed at a temperature of 50.degree. C. This mixture
was made to flow into the process chamber and onto the substrate at
a rate of 20 g/min for approximately 45 seconds. Supercritical
carbon dioxide was caused to flow into the chamber with the
co-solvent 1 at a flow rate of 60. g/min to have a total fluid flow
rate into the process chamber at 80 g/min. Subsequently the
co-solvent 1 flow rate was decreased to 2.4 g/min and the
supercritical carbon dioxide flow rate-increased to 77.6 g/min. for
the next 3 minutes and 15 seconds. The operating temperature and
pressure within the chamber were 110.degree. C. and 165 bar,
respectively.
[0060] Next, flow of co-solvent 1 was terminated and supercritical
carbon dioxide, at a flow rate of 80 g/min., was allowed to flow
onto the substrate to flush the first-co-solvent from the substrate
for a period of 30 seconds.
[0061] Next, a second co-solvent consisting of isopropyl alcohol,
at room temperature, was made to flow onto the substrate surface at
a rate of 40 g/min, together with supercritical carbon dioxide
which was also flowing into the chamber at 40 g/min for a total
fluid flow into the chamber of 80 g/min. This flow continued for
approximately 90 seconds, after which the flow of the second
co-solvent was terminated. Flow of supercritical carbon dioxide
continued for an additional two minutes, after which the substrate
was removed from the chamber. The substrate was found to be
completely free of photoresist, and the substrate and the chamber
were thoroughly dried.
EXAMPLE 4
[0062] The fourth example utilized the same co-solvent 1
composition as used in Example 2, but the composition was used on a
substrate having different characteristics. In this example, the
blanket photoresist layer removed was a 6000 .ANG. thick DUV 5
photoresist layer on top of a polysilicon layer which covers a
silicon dioxide layer on top of the silicon wafer substrate. The
photoresist was subjected to a high dose implant of boron at 10 keV
to a dosage level of 3.times.10.sup.15 atoms/cm.sup.2. A co-solvent
1 composition of 40% (by weight) 1,2-Butylene Carbonate, 30%
Dimethyl Sulfoxide, and 30% of 30% hydrogen peroxide was mixed at a
temperature of 50.degree. C. This mixture was made to flow into the
process chamber and onto the substrate at a rate of 8 g/min for 4
minutes. The co-solvent 1 mixture was carried into the process
chamber by supercritical carbon dioxide at a flow rate of 72 g/min
to have a total fluid flow rate into the process chamber at 80
g/min. The operating temperature and pressure within the chamber
were 110.degree. C. and 165 bar, respectively.
[0063] A 4-minute exposure of the photoresist film to the
co-solvent 1 mixture was found to have completely dissolved the
photoresist by visual observation (no edge exclusion was visible)
and verified by ellipsometry.
[0064] Although the drying step was not performed, the result is
expected to be the same as was achieved in Examples 1-3. The
primary modification to Example 4 as compared with Example 2 was
that the ion implant process created a level of organic
contamination that traditionally has been more difficult to remove
by liquid chemicals only.
EXAMPLE 5
[0065] The fifth example utilized the same co-solvent 1 composition
as used in Example 2, but the composition was used on a substrate
having different characteristics. The blanket photoresist layer
removed was a 6000 .ANG. thick DUV 5 photoresist layer on top of a
polysilicon layer which covers a silicon dioxide layer on top of
the silicon wafer substrate. The photoresist was subjected to a
high dose implant of arsenic at 20 keV to a dosage level of
2.times.10.sup.15 atoms/cm.sup.2. A co-solvent 1 composition of 40%
(by weight) 1,2-Butylene Carbonate, 30% Dimethyl Sulfoxide, and 30%
of 30% hydrogen peroxide was mixed at a temperature of 50.degree.
C. This mixture was made to flow into the process chamber and onto
the substrate at a rate of 8 g/min for 5 minutes. The co-solvent 1
mixture was carried into the process chamber by supercritical
carbon dioxide at a flow rate of 72 g/min to have a total fluid
flow rate into the process chamber at 80 g/min. The operating
temperature and pressure within the chamber were 110.degree. C. and
165 bar, respectively.
[0066] A 5-minute exposure of the photoresist film to the
co-solvent 1 mixture was found to have completely dissolved the
photoresist by visual observation (no edge exclusion was visible)
and verified by ellipsometry.
[0067] Although the drying step was not performed, the result is
expected to be the same as was achieved in Examples 1-3. The
primary modification to Example 5 as compared with Example 2 was
the presence of a level of organic contamination that traditionally
has been more difficult to remove by liquid chemicals only.
EXAMPLE 6
[0068] The sixth example utilized the same co-solvent 1 composition
as used in Example 2, but the composition was used on a substrate
having different characteristics. The blanket photoresist layer
removed was a 6000 .ANG. thick DUV 5 photoresist layer on top of a
polysilicon layer which covers a silicon dioxide layer on top of
the silicon wafer substrate. The photoresist was subjected to a
high dose implant of arsenic at 10 keV to a dosage level of
3.times.10.sup.15 atoms/cm.sup.2. A co-solvent 1 composition of 40%
(by weight) 1,2-Butylene Carbonate, 30% Dimethyl Sulfoxide, and 30%
of 30% hydrogen peroxide was mixed at a temperature of 50.degree.
C. This mixture was made to flow into the process chamber and onto
the substrate at a rate of 8 g/min for 6 minutes. The co-solvent I
mixture was carried into the process chamber by supercritical
carbon dioxide at a flow rate of 72 g/min to have a total fluid
flow rate into the process chamber at 80 g/min. The operating
temperature and pressure within the chamber were 110.degree. C. and
165 bar, respectively.
[0069] A 6-minute exposure of the photoresist film to the
co-solvent 1 mixture was found to have completely dissolved the
photoresist by visual observation (no edge exclusion was visible)
and verified by ellipsometry.
[0070] Although the drying step was not performed, the result is
expected to be the same as was achieved in Examples 1-3. The
primary modification to Example 6 as compared with Example 2 was
the presence of a level of organic contamination that traditionally
has been more difficult to remove by liquid chemicals only.
EXAMPLE 7
[0071] The seventh example utilized the same co-solvent 1
composition as used in Example 2, but the composition was used on a
substrate having different characteristics. The blanket photoresist
layer removed was a 6000 .ANG. thick DUV 5 photoresist layer on top
of a polysilicon layer which covers a silicon dioxide layer on top
of the silicon wafer substrate. The photoresist was subjected to a
high dose implant of arsenic at 5 keV to a dosage level of
5.times.10.sup.15 atoms/cm.sup.2. A co-solvent 1 composition of 40%
(by weight) 1,2-Butylene Carbonate, 30% Dimethyl Sulfoxide, and 30%
of 30% hydrogen peroxide was mixed at a temperature of 50.degree.
C. This mixture was made to flow into the process chamber and onto
the substrate at a rate of 8 g/min for 6 minutes. The co-solvent 1
mixture was carried into the process chamber by supercritical
carbon dioxide at a flow rate of 72 g/min to have a total fluid
flow rate into the process chamber at 80 g/min. The operating
temperature and pressure within the chamber were 110.degree. C. and
165 bar, respectively.
[0072] A 6-minute exposure of the photoresist film to the
co-solvent 1 mixture was found to have completely dissolved the
photoresist by visual observation (no edge exclusion was visible)
and verified by ellipsometry.
[0073] Although the drying step was not performed, the result is
expected to be the same as was achieved in Examples 1-3. The
primary modification to Example 7 as compared with Example 2 was
the presence of a level of organic contamination that traditionally
has been more difficult to remove by liquid chemicals only.
EXAMPLE 8
[0074] The substrate used in the eighth example included a via
structure which contained a low k dielectric layer. Prior to the
experiment, photoresist was removed using an asher, leaving
post-ash residues in the via structure. The specific chemistry
employed was the following: 39.93% (by weight) 1,2-Butylene
Carbonate, 39.93% Dimethyl Sulfoxide, and 29.94% of 30% hydrogen
peroxide and 0.2% of 40% ammonium fluoride. This mixture was made
to flow into the process chamber and onto the substrate at a rate
of 8 g/min for 5 minutes. The co-solvent 1 mixture was carried into
the process chamber by supercritical carbon dioxide at a flow rate
of 72 g/min to have a total fluid flow rate into the process
chamber at 80 g/min. The operating temperature and pressure within
the chamber were 43.degree. C. and 165 bar, respectively.
[0075] A 5-minute exposure of the post ash residues to the
co-solvent 1 mixture was found to have completely dissolved and
removed the post ash by SEM analysis. SEM photo of various die
locations showed that complete residue removal was achieved with no
attack of the semiconductor structure geometries.
[0076] Although the drying step was not performed, the result is
expected to be the same as was achieved in Examples 1-3. The
primary modification to Example 8 as compared with Example 2 was
the type of organic contamination (post ash residue) that had to be
removed.
[0077] All patents, patent applications, and publications disclosed
herein are incorporated by reference in their entirety, as if
individually incorporated. The foregoing detailed description and
examples have been given for clarity of understanding only. No
unnecessary limitations are to be understood therefrom. The
invention is not limited to the exact details shown and described,
for variations obvious to one skilled in the art will be included
within the invention defined by the claims.
* * * * *