U.S. patent application number 09/340669 was filed with the patent office on 2001-12-13 for acid blend for removing etch residue.
Invention is credited to TOREK, KEVIN J., YATES, DONALD L..
Application Number | 20010051440 09/340669 |
Document ID | / |
Family ID | 23334444 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010051440 |
Kind Code |
A1 |
TOREK, KEVIN J. ; et
al. |
December 13, 2001 |
ACID BLEND FOR REMOVING ETCH RESIDUE
Abstract
A method for removing organometallic and organosilicate residues
remaining after a dry etch process from semiconductor substrates.
The substrate is exposed to a conditioning solution of phosphoric
acid, hydrofluoric acid, and a carboxylic acid, such as acetic
acid, which removes the remaining dry etch residues while
minimizing removal of material from desired substrate features. The
approximate proportions of the conditioning solution are typically
80 to 95 percent acetic acid, 1 to 15 percent phosphoric acid, and
0.01 to 5.0 percent hydrofluoric acid.
Inventors: |
TOREK, KEVIN J.; (MERIDIAN,
ID) ; YATES, DONALD L.; (BOISE, ID) |
Correspondence
Address: |
THOMAS J D'AMICO
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
2101 L STREET NW
WASHINGTON
DC
200371526
|
Family ID: |
23334444 |
Appl. No.: |
09/340669 |
Filed: |
June 29, 1999 |
Current U.S.
Class: |
438/745 ;
252/79.3; 257/E21.252; 257/E21.257 |
Current CPC
Class: |
H01L 21/02063 20130101;
C09K 13/08 20130101; H01L 21/31144 20130101; C11D 7/08 20130101;
C11D 11/0047 20130101; H01L 21/31116 20130101; C11D 7/265
20130101 |
Class at
Publication: |
438/745 ;
252/79.3 |
International
Class: |
H01L 021/302; H01L
021/461; C09K 013/08 |
Claims
What is claimed as new and desired to be protected by Letters
Patent of the United States is:
1. A method for removing dry etch residues from a semiconductor
substrate comprising the steps of: exposing a semiconductor
substrate having dry etch residues thereon to a conditioning
solution, wherein the conditioning solution comprises a solvating
acid, phosphoric acid, and hydrofluoric acid.
2. The method of claim 1, wherein the solvating acid is formic
acid.
3. The method of claim 1, wherein the solvating acid is a
carboxylic acid.
4. The method of claim 1, wherein the solvating acid is a mixture
of carboxylic acids.
5. The method of claim 1, wherein the solvating acid is acetic
acid.
6. The method of claim 5, wherein the acetic acid, phosphoric acid,
and hydrofluoric acid are present in the conditioning solution in
the approximate proportion of 80-95:1-15:0.01-5.0.
7. The method of claim 5, wherein the acetic acid, phosphoric acid,
and hydrofluoric acid are present in the conditioning solution in
the approximate proportion of 90-94:6-7:0.25-0.3.
8. The method of claim 5, wherein the acetic acid, phosphoric acid,
and hydrofluoric acid are present in the conditioning solution in
the approximate proportion of 91.5:6.5:0.27.
9. The method of claim 1, wherein the conditioning solution is a
solution of approximately 80 to approximately 90 percent acetic
acid, approximately 1 to approximately 15 percent phosphoric acid,
and approximately 0.01 to 5.0 percent hydrofluoric acid.
10. The method of claim 1, wherein the conditioning solution is a
solution consisting essentially of acetic acid, phosphoric acid,
and hydrofluoric acid.
11. The method of claim 1, wherein the conditioning solution is a
solution consisting essentially of approximately 80 to
approximately 95 percent acetic acid, approximately 1 to
approximately 15 percent phosphoric acid, and approximately 0.01 to
approximately 5.0 percent hydrofluoric acid.
12. The method of claim 1, wherein said exposure step is performed
at a temperature within the range of approximately 5 to
approximately 60 degrees Celsius.
13. The method of claim 1, wherein said exposure step is performed
at a temperature within the range of approximately 35 to
approximately 40 degrees Celsius.
14. The method of claim 1, wherein said exposure step is performed
at a temperature of approximately 38 degrees Celsius.
15. The method of claim 1, wherein said exposure step further
comprises immersing the substrate in the conditioning solution.
16. The method of claim 1, wherein said exposure step further
comprises dispensing the conditioning solution onto the
substrate.
17. The method of claim 1, wherein said exposure step is performed
for a time sufficient to remove substantially all dry etch residues
from the substrate.
18. The method of claim 1, wherein said exposure step is performed
for approximately 60 seconds or longer.
19. The method of claim 1, wherein said exposure step is performed
for approximately 180 seconds or longer.
20. The method of claim 1, further comprising rinsing the substrate
after said exposure step.
21. The method of claim 20, wherein said rinsing step comprises
exposing the substrate to deionized water.
22. The method of claim 20, wherein said rinsing step comprises
exposing the substrate to an aqueous acid solution.
23. The method of claim 22, wherein the aqueous acid solution is a
solution of a carboxylic acid.
24. The method of claim 22, wherein the aqueous acid solution is a
solution of citric acid.
25. The method of claim 22, wherein the aqueous acid solution is a
solution of EDTA.
26. The method of claim 22, wherein the aqueous acid solution is a
solution of acetic acid.
27. The method of claim 22, wherein the aqueous acid solution is a
solution of an organic acid.
28. The method of claim 22, wherein the aqueous acid solution is a
solution of ascorbic acid.
29. The method of claim 22, wherein the aqueous acid solution is a
solution of carbonic acid.
30. The method of claim 22, wherein the aqueous acid solution is
buffered to a pH between approximately 4.0 and approximately
8.0.
31. The method of claim 20, wherein said rinsing step comprises
exposing the substrate to an organic solvent.
32. The method of claim 20, wherein the organic solvent is
propylene glycol.
33. The method of claim 20, wherein said rinsing step comprises
exposing the substrate to a solution containing an anti-etch
agent.
34. The method of claim 33, wherein the anti-etch agent is ammonium
lactate.
35. The method of claim 33, wherein the anti-etch agent is boric
acid.
36. The method of claim 20, wherein said rinsing step further
comprises immersing the substrate in a rinse bath.
37. The method of claim 36, wherein said rinsing step further
comprises agitating the rinse bath.
38. The method of claim 37, wherein the rinse bath is agitated with
megasonic energy.
39. The method of claim 37, wherein the rinse bath is agitated by
bubbling a gas through the rinse bath.
40. The method of claim 39, wherein CO.sub.2 is bubbled through the
rinse bath.
41. The method of claim 39, wherein N.sub.2 is bubbled through the
rinse bath.
42. A method for cleaning a wafer after a dry etch process
comprising the steps of: treating a wafer having at least one of
organometallic and organosilicate residues on exposed surfaces of
the wafer with a conditioning solution of a solvating acid,
phosphoric acid, and hydrofluoric acid until the residues are
removed from the wafer.
43. The method of claim 42, wherein the solvating acid is a
carboxylic acid.
44. The method of claim 42, wherein the solvating acid is acetic
acid.
45. The method of claim 42, further comprising rinsing the
substrate after said treating step.
46. The method of claim 42, wherein the solvating acid, phosphoric
acid, and hydrofluoric acid are present in the conditioning
solution in the approximate proportion of 80-95:1-15:0.01-5.0.
47. The method of claim 42, wherein the solvating acid, phosphoric
acid, and hydrofluoric acid are present in the conditioning
solution in the approximate proportion of 90-94:6-7:0.25-0.3.
48. The method of claim 42, wherein the solvating acid, phosphoric
acid, and hydrofluoric acid are present in the conditioning
solution in the approximate proportion of 91.5:6.5:0.27.
49. The method of claim 42, wherein the conditioning solution is a
solution consisting essentially of acetic acid, phosphoric acid,
and hydrofluoric acid.
50. The method of claim 42, wherein said treating step is performed
at a temperature within the range of approximately 5 to
approximately 60 degrees Celsius.
51. The method of claim 42, wherein said treating step is performed
at a temperature within the range of approximately 35 to
approximately 40 degrees Celsius.
52. The method of claim 42, wherein said treating step is performed
at a temperature of approximately 38 degrees Celsius.
53. The method of claim 42, wherein said treating step is performed
for approximately 60 seconds or longer.
54. A method for processing a substrate with patterned photoresist
on the substrate surface comprising the steps of: providing a
substrate with patterned photoresist on a surface of the substrate;
performing a dry etch process on the substrate; removing any
remaining photoresist from the surface of the substrate; and
exposing the substrate to a conditioning solution of a solvating
acid, phosphoric acid, and hydrofluoric acid.
55. The method of claim 54, wherein the solvating acid is a
carboxylic acid.
56. The method of claim 54, wherein the solvating acid is acetic
acid.
57. The method of claim 54, further comprising rinsing the
substrate after said exposure step.
58. The method of claim 54, wherein the solvating acid, phosphoric
acid, and hydrofluoric acid are present in the conditioning
solution in the approximate proportion of 80-95:1-15:0.01-5.0.
59. The method of claim 54, wherein the solvating acid, phosphoric
acid, and hydrofluoric acid are present in the conditioning
solution in the approximate proportion of 90-94:6-7:0.25-0.3.
60. The method of claim 54, wherein the solvating acid, phosphoric
acid, and hydrofluoric acid are present in the conditioning
solution in the approximate proportion of 91.5:6.5:0.27.
61. The method of claim 54, wherein said step of exposing the
substrate to the conditioning solution is performed at a
temperature within the range of approximately 5 to approximately 60
degrees Celsius.
62. The method of claim 54, wherein said step of exposing the
substrate to the conditioning solution is performed at a
temperature within the range of approximately 35 to approximately
40 degrees Celsius.
63. The method of claim 54, wherein said step of exposing the
substrate to the conditioning solution is performed at a
temperature of approximately 38 degrees Celsius.
64. The method of claim 54, wherein said step of exposing the
substrate to the conditioning solution is performed for
approximately 60 seconds or longer.
65. A method for treating a semiconductor substrate to remove
residues remaining after a dry etch process comprising the steps
of: exposing a substrate with at least one of organometallic and
organosilicate residues on the substrate surface to a conditioning
solution of acetic acid, phosphoric acid, and hydrofluoric acid in
the approximate ratio 80-95:1-15:0.01-5.0.
66. A method for treating a semiconductor substrate to remove
residues remaining after a dry etch process comprising the steps
of: exposing a substrate with at least one of organometallic and
organosilicate residues on the substrate surface to a conditioning
solution of acetic acid, phosphoric acid, and hydrofluoric acid in
the ratio 90-94:6-7:0.25-0.3; and rinsing the wafer.
67. A method for treating a semiconductor substrate to remove
residues remaining after a dry etch process comprising the steps
of: exposing a substrate with at least one of organometallic and
organosilicate residues on the substrate surface to a conditioning
solution of a solvating acid, a phosphate source, and a fluorine
source; and rinsing the wafer.
68. A solution for use in removing residues remaining on a
semiconductor substrate after a dry etch process, said solution
comprising: acetic acid; phosphoric acid; and hydrofluoric
acid.
69. The solution of claim 68, wherein said solution consists
essentially of acetic acid, phosphoric acid, and hydrofluoric
acid.
70. The solution of claim 68, wherein said acetic acid, phosphoric
acid, and hydrofluoric acid are present in said solution in the
approximate proportion of 80-95:1-15:0.01-5.0.
71. The solution of claim 70, wherein said solution comprises
approximately 80 to approximately 95 percent acetic acid,
approximately 1 to approximately 15 percent phosphoric acid, and
approximately 0.01 to approximately 5.0 percent hydrofluoric
acid.
72. The solution of claim 68, wherein said acetic acid, phosphoric
acid, and hydrofluoric acid are present in said solution in the
approximate proportion of 90-94:6-7:0.25-0.3.
73. The solution of claim 72, wherein said solution comprises
approximately 90 to approximately 94 percent acetic acid,
approximately 6 to approximately 7 percent phosphoric acid, and
approximately 0.25 to approximately 0.3 percent hydrofluoric
acid.
74. The solution of claim 68, wherein said acetic acid, phosphoric
acid, and hydrofluoric acid are present in said solution in the
approximate proportion of 91.5:6.5:0.27.
75. The solution of claim 74, wherein said solution comprises
approximately 91.5 percent acetic acid, approximately 6.5 percent
phosphoric acid, and approximately 0.27 percent hydrofluoric acid.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the fabrication of
semiconductor devices and more particularly to a method for
cleaning a semiconductor substrate after the formation of dry etch
residues thereon.
BACKGROUND OF THE INVENTION
[0002] The importance of minimizing contamination during
semiconductor fabrication processes has been recognized since the
early days of the industry. As semiconductor devices have become
smaller and more complex, cleanliness requirements have become
increasingly stringent, especially for devices with submicron
critical dimensions, because the ability to reliably create
multi-level metallization structures is increasingly vital. The
importance of cleaning and conditioning steps during the device
fabrication process is also emphasized because small-scale residues
that may not have seriously affected the performance of devices
with large geometries may result in disabling defects in submicron
devices.
[0003] Dry etch processes play a key role in developing multi-level
metallization structures on semiconductor substrates. The step of
transferring the desired pattern from the photoresist into the
substrate is often accomplished via a dry etch process. While dry
etch processes are effective for selectively etching the substrate
in only the areas not masked by photoresist, these processes have a
tendency to leave behind residues on the substrate. Although these
residues may serve a beneficial role during a dry etch process,
they are undesirable after the completion of the dry etch process.
In back end of the line processes, where both dielectrics, such as
SiO.sub.2, and metals, such as Al or W, are present, the residues
left behind by dry etch processes may include both organometallic
and organosilicate species. These undesirable post-etch residues
are often difficult to remove without damaging the desired
substrate features.
[0004] Current methods for removing dry etch residues have met with
only limited success. Traditional cleans involving aqueous acid
solutions can not provide a general solution for removing these
residues, as these processes are not suitable for processing in the
presence of metal lines. Current strategies often involve treating
substrates with solutions containing hydroxylamine (NH.sub.2OH) and
an organic chelating agent. These methods have shown some
effectiveness but have significant drawbacks. These types of
solutions can cause corrosion of exposed metal on the wafer and
usually require long processing times at temperatures near 100 C.
These hydroxylamine solutions are also expensive, as the chemicals
are not only expensive to purchase but also typically require
specialized disposal.
[0005] As the removal of dry etch residues grows increasingly
troublesome in microelectronic device manufacture, there is a need
for an effective method of removal of these residues which can be
easily implemented in standard wafer processing equipment and has
reduced costs for chemical purchase and disposal.
SUMMARY OF THE INVENTION
[0006] The present invention provides a method for removing
organometallic and organosilicate residues from a semiconductor
substrate following a dry etch process. A substrate previously
subjected to a dry etch process is exposed to a conditioning
solution to remove residues remaining after the dry etch. The
conditioning solution is a solution of a suitable carboxylic acid,
such as acetic acid, phosphoric acid, and hydrofluoric acid. The
substrate is exposed to the solution for a period of time
sufficient to remove the dry etch residues. After exposure, the
substrate can be rinsed with either deionized water or with an
aqueous acidic solution.
[0007] Additional advantages and features of the present invention
will be apparent from the following detailed description and
drawings which illustrate preferred embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic cross-sectional view of a substrate
with dry etch residues near a sample device feature.
[0009] FIG. 2 is a schematic cross-sectional view of a substrate
undergoing the process of a preferred embodiment of the
invention.
[0010] FIG. 3 shows the substrate of FIG. 2 at a processing step
subsequent to that shown in FIG. 2.
[0011] FIG. 4 shows the substrate of FIG. 2 at a processing step
subsequent to that shown in FIG. 3.
[0012] FIG. 5 shows the substrate of FIG. 2 at a processing step
subsequent to that shown in FIG. 4.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] In the following detailed description, reference is made to
the accompanying drawings which form a part hereof, and in which is
shown by way of illustration specific embodiments in which the
invention may be practiced. These embodiments are described in
sufficient detail to enable those skilled in the art to practice
the invention, and it is to be understood that structural and
chemical changes may be made without departing from the spirit and
scope of the present invention.
[0014] The terms "wafer" and "substrate" are to be understood as
including any semiconductor-based structure having an exposed layer
which may be effectively cleaned by the process of the present
invention. Typically this will include semiconductor-based
structures which have been dry-etched and have resultant
organometallic and/or organosilicate residues on an exposed layer,
but other structures may also be beneficially treated by the
present inventive method. "Wafer" or "substrate" may include
silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology,
doped and undoped semiconductors, epitaxial layers of silicon
supported by a base semiconductor foundation, and other
semiconductor structures. Furthermore, when reference is made to a
"wafer" or "substrate" in the following description, previous
process steps may have been utilized to form regions or junctions
in the base semiconductor structure or foundation. In addition, the
semiconductor need not be silicon-based, but could be based on
silicon-germanium, germanium, or gallium arsenide.
[0015] The following detailed description is, therefore, not to be
taken in a limiting sense, and the scope of the present invention
is defined by the appended claims. When referring to solutions
described herein, the term "percent" refers to the percent measured
by weight, e.g., a 90% acetic acid solution is 90% by weight acetic
acid.
[0016] Referring now to the drawings, where like elements are
designated by like reference numerals, FIG. 1 depicts a
semiconductor wafer 20 in an intermediate processing stage of a
fabrication process. The wafer 20 comprises a substrate 22 with
devices 24 located thereon. The devices 24 are covered by a
dielectric layer 26 of SiO.sub.2, BPSG, or other suitable material
which has a top surface 28. A device feature that has been formed
by a dry etch process is formed on the substrate 22, either on or
in the dielectric layer 26. For exemplary purposes, the device
feature will be illustrated and described as a trench 30, which may
be a via, but it should be understood that the invention is not
limited thereto.
[0017] The trench 30 is formed in the dielectric material, and has
sidewalls 32 and a bottom surface 34, which may be composed of a
metal such as aluminum or tungsten. The wafer 20 of FIG. 1 has been
subjected to a dry etch process followed by a photoresist ashing or
stripping process. Due to the dry etch process residues 40, which
may be, for example, organosilicate or organometallic residues, are
present on the top surface 28 of the dielectric layer 26 and on the
sidewalls 32 of the trench 30. If not removed, the residues 40
could prevent proper deposition of subsequent layers in the trench
30 or on the dielectric layer 26.
[0018] An embodiment of the present invention for removing residues
is illustrated by FIGS. 2 through 5. This embodiment uses a
conditioning solution to cleanse the substrate surface after
performance of a dry etch. The conditioning solution is a solution
of phosphoric acid, hydrofluoric acid, and a solvating acid. The
solvating acid is composed of one or more carboxylic acids. In a
preferred embodiment, the solvating acid is acetic acid. In another
embodiment, the solvating acid is formic acid. In other
embodiments, the solvating acid may be composed of a mix of
carboxylic acids, such as a mixture of formic acid and acetic acid.
The substrate 22 is exposed to the conditioning solution for a
period of time sufficient to remove residues 40 from the substrate
surface while minimizing the amount of material removed from
exposed surfaces, such as metal lines, vias, or dielectric
layers.
[0019] Referring to FIG. 2, the process of the present invention
begins subsequent to the formation of devices 24, which may be
transistors, capacitors, word lines, bit lines, or the like, on a
substrate 22 of a wafer 20, and the formation of a dielectric layer
26 on the substrate 22. The dielectric layer 26 may be a silicon
dioxide, borophosphosilicate glass (BPSG), phosphosilicate glass
(PSG), borosilicate glass (BSG) or other dielectric layer, and may
be deposited by chemical vapor deposition or other suitable
means.
[0020] FIG. 3 depicts the next step of the process, in which a
photoresist 42 is formed on the top surface 28 of the dielectric
layer 26 by suitable means such as spinning. The photoresist 42 is
patterned and developed, and a dry etch process is performed using
the patterned photoresist. After the dry etch process has been
performed, and the photoresist has been removed by means such as
ashing or stripping, residues 40 remain on the top surface 28 of
the dielectric layer 26, and inside the trench 30, as shown in FIG.
4.
[0021] The wafer 20 is then subjected to the cleansing process of
the present invention. The wafer 20 is exposed to a conditioning
solution by any suitable method, which is typically a wet
processing method. Suitable methods may involve immersion of the
wafer 20, either singly or in combination with other wafers, into a
bath containing the conditioning solution, or by dispensing of the
conditioning solution onto one or more wafers 20 as a stream or
spray, so long as such dispensing of the conditioning solution
results in exposure of the surface of the substrate to the
conditioning solution for the desired length of time. Other methods
of treating substrates with the conditioning solution will be
apparent to those skilled in the art. The wafer 20 is exposed to
the conditioning solution for a time sufficient to remove residues
40 from the top surface 28 of the dielectric layer 26 and from the
sidewalls 32 and bottom surface 34 of the trench 30. Residues 40
may be organometallic residues, organosilicate residues, other
post-etch residues, or a combination of these residues. The
cleansing method of this invention is effective for removal of
these residues when present individually or in combination.
[0022] The wafer 20 may then be rinsed to prepare the substrate for
a subsequent process step. In one embodiment, the substrate is
rinsed with deionized water. In a preferred embodiment, the
substrate may be exposed to an acidic rinse composed of an aqueous
solution of a suitable acid. Carboxylic acids such as citric acid,
acetic acid, or EDTA (ethylene diamine tetraacetic acid) are
preferred for this embodiment. Other organic acids which are not
carboxylic acids may also be used, such as ascorbic acid.
[0023] In another embodiment, the aqueous acid solution may be
buffered to raise the pH of the solution to any desired pH level up
to approximately pH 8. In yet another embodiment, anti-etch agents
may be added to the rinse bath, such as ammonium lactate or boric
acid. In another embodiment, the substrate may be rinsed by
exposing the wafer to an organic solvent, such as an alcohol, a
polyhydric alcohol (such as propylene glycol), a ketone, or a
fluorocarbon. In another embodiment, the rinse may be carried out
in a bath and the rinse bath may be agitated by introduction of a
gas. The agitating gas may be CO.sub.2, N.sub.2, or other gases
which can be conveniently introduced into the rinse bath for
agitation. In yet another embodiment, the solution may be agitated
using megasonic energy. In still another embodiment, the solution
may be agitated by manual or robot-controlled shaking of the vessel
containing the rinse bath.
[0024] Use of the acidified rinse or buffered rinse greatly reduces
the potential for unwanted consumption of the desired substrate
materials after exposing the wafer to the conditioning solution. In
embodiments where rinsing is accomplished with a rinse bath, a gas
may be bubbled through the rinse bath. When the gas is CO.sub.2,
introduction of the gas provides another means for acidifying the
rinse water as well due to the formation of carbonic acid. When the
rinse is already acidified, however, inert gases such as N.sub.2
exhibit similar effectiveness to CO.sub.2. In some applications of
this method, either the wafer may not be susceptible to the
unwanted consumption of the substrate or additional loss of
substrate material may not be critical. In these cases the wafer
may be rinsed with deionized water.
[0025] In still another embodiment, the wafer 20 may be pre-rinsed
with a non-aqueous solvent prior to the rinse step. In one
embodiment, the non-aqueous solvent is a polyhydric alcohol, such
as propylene glycol. In another embodiment, the wafer is pre-rinsed
with the same non-aqueous solvent used in the conditioning
solution. After pre-rinsing the wafer with a non-aqueous solvent,
the wafer may be rinsed with any of the rinses described above.
[0026] The exact nature and length of the rinse step may vary
depending on the next process step the substrate will undergo. The
wafer 20 may be spin-dried after rinsing, if appropriate. The final
structure of the wafer 20 with the residue removed is shown in FIG.
5. Further steps to create a functional circuit from the wafer 20
may now be carried out.
[0027] In a preferred embodiment, the conditioning solution is a
solution of acetic acid, phosphoric acid, and hydrofluoric acid. By
weight, the conditioning solution is predominantly composed of
acetic acid, and is preferably approximately 80 to approximately 95
percent acetic acid. The conditioning solution also contains
approximately 1 to approximately 15 percent phosphoric acid and
approximately 0.01 to approximately 5.0 percent hydrofluoric acid.
A preferred conditioning solution comprises approximately 90 to
approximately 94 percent acetic acid, approximately 6 to
approximately 7 percent phosphoric acid, and approximately 0.25 to
approximately 0.3 percent hydrofluoric acid. A particularly
preferred conditioning solution comprises about 91.5 percent acetic
acid, about 6.5 percent phosphoric acid, about 0.27 percent
hydrofluoric acid. In all of the above conditioning solutions, the
balance of the solution weight is made up by water. In many
embodiments, the conditioning solution is prepared by combining
stock acid solutions which contain water, so a small amount of
water may be present in the conditioning solution. It is preferred,
however, that the water content of the conditioning solution be as
low as possible.
[0028] In other embodiments, a suitable conditioning solution may
be prepared by other combinations of chemicals. Although HF is
preferred, other fluorine sources may be effectively employed
within the scope of this invention. For example, NH.sub.4F might be
employed as the fluorine source as long as the NH.sub.4F was
compatible with the other components selected for the conditioning
solution. Similarly, H.sub.3PO.sub.4 is not the only source of
phosphate contemplated within the inventive method. For example,
phosphate salts which could dissociate to yield
H.sub.2PO.sub.4.sup.-, HPO.sub.4.sup.2-, or PO.sub.4.sup.3- might
be appropriate depending on the other components in the
conditioning solution. HF and H.sub.3PO.sub.4, however, are
particularly preferred and convenient choices for the fluorine
source and the phosphate source.
[0029] Residue removal with the conditioning solution may be
performed at temperatures of approximately 5 to approximately 60
degrees Celsius. Temperatures below 5 degrees Celsius may be used,
but are not as favorable due to decreased residue removal speeds.
As a result, at lower temperatures the conditioning solution may
need to be applied to the substrate for longer periods of time,
leading to lower throughput in a production setting. Additionally,
the tendency of acetic acid to solidify near room temperature may
provide a lower limit to the temperatures which may be used.
Temperatures above 60 degrees Celsius may also be used, but at
higher temperatures the vapor pressure of the conditioning solution
may become significant. This can lead to excessive fume production
when the method is performed in an wet bench environment.
Preferably, the substrate is exposed to the conditioning solution
at a temperature of approximately 35 to approximately 40 degrees
Celsius. Exposing the substrate to the conditioning solution at a
temperature of approximately 38 degrees Celsius is a particularly
preferred embodiment of this invention.
[0030] Preferably, the substrate is exposed to the conditioning
solution for a period of time sufficient to remove any undesirable
dry etch residues from the surface of the substrate. This may
involve an exposure of the substrate to the conditioning solution
for periods of time ranging from about 60 seconds to about 180
seconds or longer depending on the exact nature of the substrate,
the residues targeted for removal, and the process temperature.
Longer exposure times allow for greater removal efficiency of the
dry etch residues but will also lead to lower throughput in a
production setting. Also, depending on the exact nature of the
substrate, longer exposures to the conditioning solution may
eventually lead to removal of material from exposed features on the
surface of the substrate, such as metal lines, vias, or dielectric
surfaces. As a result, the optimal amount of time for exposure of a
substrate to the conditioning solution will be substrate dependent.
The preferred exposure time could be near 60 seconds, near 180
seconds, or a longer or shorter period of time depending on the
exact nature of the target substrate.
[0031] Without being bound by any particular theory, it is
currently believed that several factors contribute to the
effectiveness of this method for removing dry etch residues. It is
believed that the acetic acid, or other solvating acid, plays a
role by passivating the surface of exposed metal lines, especially
aluminum lines, which are on the surface of the substrate. It is
believed that the phosphoric acid and hydrofluoric acid play
complementary roles of aiding in the removal of organometallic and
organosilicate residues, respectively.
[0032] It is also believed that the acetic acid, or other solvating
acid, plays a further role in the conditioning solution. Due to the
high concentration of carboxylic acid (>80%), the effective pH
of the conditioning solution is below 1. As a result, the
hydrofluoric acid present in the conditioning solution tends to
exist as molecular HF and H.sub.2F.sub.2, as opposed to undergoing
dissociation into H.sup.+, F.sup.-, HF.sup.2-, or any of the other
likely species produced when HF dissociates in solution. By
preventing dissociation of the HF present in the conditioning
solution, the HF is forced to remain in its molecular form which
generally reacts much more slowly with substrate materials such as
SiO.sub.2 or the aluminum lines likely to be exposed on a substrate
surface. This depression of the reaction rate greatly reduces the
potential for damage to the desired substrate features during
exposure of the substrate to the conditioning solution.
[0033] An alternate theory which could explain the lack of
reactivity with the aluminum lines is that the nature of the
conditioning solution suppresses the solubility of aluminum
fluoride. Aluminum fluoride is one of the likely products of any
reaction involving aluminum lines on the surface of the substrate.
Lowering the solubility of aluminum fluoride might cause this
reaction product to build up at the surface of the aluminum lines
and prevent further reaction.
[0034] As can be seen from the embodiments described herein, the
present invention encompasses processes of removing dry etch
residues from substrates having exposed areas of both metal and
dielectric. The substrate is treated with/exposed to a conditioning
solution composed of a solvating acid (typically acetic acid),
phosphoric acid, and hydrofluoric acid. The conditioning solution
efficiently removes organometallic, organosilicate, and other dry
etch residues with minimal impact on exposed features on the
substrate surface.
[0035] The above description and drawings are only illustrative of
preferred embodiments which achieve the objects, features and
advantages of the present invention. It is not intended that the
present invention be limited to the illustrated embodiments. Any
modification of the present invention which comes within the spirit
and scope of the following claims should be considered part of the
present invention.
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