U.S. patent application number 10/874566 was filed with the patent office on 2005-12-29 for bare aluminum baffles for resist stripping chambers.
Invention is credited to Chen, Anthony L., Egley, Fred D., Kang, Michael S., Kuo, Jack, Morel, Bruno, Outka, Duane, Shih, Hong.
Application Number | 20050284573 10/874566 |
Document ID | / |
Family ID | 35504326 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050284573 |
Kind Code |
A1 |
Egley, Fred D. ; et
al. |
December 29, 2005 |
Bare aluminum baffles for resist stripping chambers
Abstract
Bare aluminum baffles are adapted for resist stripping chambers
and include an outer aluminum oxide layer, which can be a native
aluminum oxide layer or a layer formed by chemically treating a new
or used bare aluminum baffle to form a thin outer aluminum oxide
layer.
Inventors: |
Egley, Fred D.; (Sunnyvale,
CA) ; Kang, Michael S.; (San Francisco, CA) ;
Chen, Anthony L.; (Pleasanton, CA) ; Kuo, Jack;
(Pleasanton, CA) ; Shih, Hong; (Walnut, CA)
; Outka, Duane; (Fremont, CA) ; Morel, Bruno;
(Santa Clara, CA) |
Correspondence
Address: |
BUCHANAN INGERSOLL PC
(INCLUDING BURNS, DOANE, SWECKER & MATHIS)
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
35504326 |
Appl. No.: |
10/874566 |
Filed: |
June 24, 2004 |
Current U.S.
Class: |
156/345.33 ;
216/37; 216/58 |
Current CPC
Class: |
H01J 37/32633 20130101;
H01J 2237/3342 20130101; G03F 7/427 20130101; C23C 8/02 20130101;
C23C 8/10 20130101; H01J 37/32357 20130101 |
Class at
Publication: |
156/345.33 ;
216/058; 216/037 |
International
Class: |
C23F 001/00; B44C
001/22 |
Claims
1. A bare aluminum baffle adapted for a plasma processing apparatus
comprising a resist stripping chamber and a remote plasma source
operable to supply reactive species into the resist stripping
chamber, wherein the baffle is configured to be supported by a
sidewall of the resist stripping chamber and form a top wall of the
resist stripping chamber, the baffle including gas passages for
distributing the reactive species.
2. The bare aluminum baffle of claim 1, comprising an outer
aluminum oxide layer forming the outer surface of the bare aluminum
baffle and having a thickness of about 50 angstroms to about 300
angstroms and a density of at least about 90% of the theoretical
density of aluminum oxide.
3. The bare aluminum baffle of claim 2, wherein the outer aluminum
oxide layer has a thickness of about 50 angstroms to about 100
angstroms and a density of at least about 95% of the theoretical
density of aluminum oxide.
4. The bare aluminum baffle of claim 1, comprising an outer native
aluminum oxide layer having a thickness of from about 25 to about
75 angstroms.
5. The bare aluminum baffle of claim 1, comprising an inner portion
and a peripheral portion, wherein the inner portion includes a
central projection and a plurality of concentrically arranged rows
of the gas passages surrounding the central projection, the central
projection includes an upper surface and a plurality of through
passages oriented at an acute angle relative to the upper surface
such that the through passages extend in radial outward directions
toward the peripheral portion, and the peripheral portion includes
a flange having holes adapted to receive fasteners to attach the
baffle to the sidewall.
6. The bare aluminum baffle of claim 1, wherein the bare aluminum
baffle is adapted to support a bare aluminum liner on a plurality
of liner supports on an upper surface of the bare aluminum baffle
such that the liner is adjacent to a cover of the resist stripping
chamber and a plenum is defined between a bottom surface of the
liner and an upper surface of the bare aluminum baffle when the
bare aluminum baffle is supported on the side wall, the plenum
being in fluid communication with the remote plasma source and the
resist stripping chamber.
7. The bare aluminum baffle of claim 1, which is of an aluminum
alloy.
8. The bare aluminum baffle of claim 1, which is circular shaped
and has a diameter which is larger than a width of the interior of
the resist stripping chamber so that a peripheral portion of the
baffle overlies the side wall when the baffle is supported on the
side wall of the resist stripping chamber.
9. A resist stripping apparatus, comprising: a resist stripping
chamber; a remote plasma source operable to generate a plasma and
introduce reactive species into the resist stripping chamber; and a
bare aluminum baffle according to claim 1 supported by a sidewall
of the resist stripping chamber and forming a top wall of the
resist stripping chamber.
10. The resist stripping apparatus of claim 9, wherein the remote
plasma source includes a microwave generator adapted to emit
microwaves to excite a process gas into the plasma state.
11. A method of stripping resist from a substrate in a resist
stripping chamber, the method comprising: energizing a process gas
into the plasma state remotely from the resist stripping chamber
and supplying reactive species into the resist stripping chamber in
which a semiconductor substrate including a resist is supported on
a substrate support, the resist stripping chamber including a
sidewall and a bare aluminum baffle according to claim 1 supported
by the sidewall and forming a top wall of the resist stripping
chamber; and distributing the reactive species onto the substrate
through gas passages in the baffle so as to remove the resist from
the substrate.
12. The method of claim 11, wherein the baffle comprises an outer
aluminum oxide layer having a thickness of about 50 angstroms to
about 300 angstroms and a density of at least about 90% of the
theoretical density of aluminum oxide.
13. The method of claim 11, wherein the baffle comprises an outer
native aluminum oxide layer having a thickness of from about 25 to
about 75 angstroms.
14. The method of claim 11, wherein the process gas comprises
oxygen and fluorine.
15. A method of treating a bare aluminum baffle adapted for a
resist stripping chamber, comprising: a) treating a bare aluminum
baffle having a first outer aluminum oxide layer with a chemical
solution which is effective to remove contaminants and the first
outer aluminum oxide layer from the baffle to expose aluminum
material; and b) forming a second outer aluminum oxide layer on the
aluminum material, the second outer aluminum oxide layer having a
thickness of about 50 angstroms to about 300 angstroms and a
density of at least about 90% of the theoretical density of
aluminum oxide.
16. The method of claim 15, wherein the second outer aluminum oxide
layer has a thickness of about 50 angstroms to about 100 angstroms
and a density of at least about 95% of the theoretical density of
aluminum oxide.
17. The method of claim 15, wherein the first outer aluminum oxide
layer is a native aluminum oxide layer.
18. The method of claim 15, further comprising, between a) and b),
refinishing the surface of the bare aluminum baffle.
19. The method of claim 15, wherein the second aluminum oxide layer
is formed on the aluminum material by an electropolishing
procedure.
20. The method of claim 15, wherein the aluminum material is an
aluminum alloy.
Description
BACKGROUND
[0001] Semiconductor substrate materials, such as silicon wafers,
are processed by techniques including deposition processes, such as
chemical vapor deposition (CVD) or plasma-enhanced chemical vapor
deposition (PECVD) of metal, dielectric and semiconductor
materials; etching processes; and resist stripping processes.
[0002] Semiconductor integrated circuit (IC) processes include
forming devices on substrates. Conductive and insulating material
layers are deposited on the substrates. Resist can be applied as a
masking layer over the layer stack and patterned to protect
portions of the underlying material where etching is not desired.
After the etch process has been completed, the resist is removed
from the structure by a stripping technique, such as using organic
strippers, oxidizing-type strippers, or dry stripping by plasma
etching.
SUMMARY
[0003] Bare aluminum baffles are provided, which are adapted for a
resist stripping chamber of a plasma processing apparatus that
includes a remote plasma source to supply reactive species into the
resist stripping chamber. A preferred embodiment of the baffle is
configured to be supported by a sidewall of the resist stripping
chamber with a perforated surface of the baffle facing a
semiconductor substrate to be processed in the chamber. The
perforated surface of the baffle includes gas passages for
distributing the reactive species.
[0004] The bare aluminum baffle includes an outer aluminum oxide
layer forming an outer surface of the baffle. The outer layer
preferably has a thickness of about 50 angstroms to about 300
angstroms, and preferably having a density of at least about 90% of
the theoretical density of aluminum oxide. The outer aluminum oxide
layer can be a native aluminum oxide layer, or it can be formed by
chemically treating either a new or used bare aluminum baffle.
[0005] A preferred embodiment of a resist stripping apparatus
comprises a resist stripping chamber; a remote plasma source
operable to generate a plasma and introduce reactive species into
the resist stripping chamber; and a bare aluminum baffle supported
by a sidewall of the resist stripping chamber. The remote plasma
source preferably includes a microwave generator that emits
microwaves to excite a process gas into the plasma state.
[0006] A preferred embodiment of a method of stripping resist from
a semiconductor substrate in a resist stripping chamber is
provided, which comprises energizing a process gas into the plasma
state remotely from the resist stripping chamber, and supplying
reactive species into the resist stripping chamber in which a
substrate including a resist is supported on a substrate support.
The resist stripping chamber includes a sidewall and a bare
aluminum baffle forming a top wall and being supported by the
sidewall. The reactive species are distributed into the chamber
through the passages in the baffle to remove the resist from the
substrate.
[0007] A preferred embodiment of a method of treating a bare
aluminum baffle adapted for a resist stripping chamber is provided,
which comprises treating a bare aluminum baffle having a first
outer aluminum oxide layer with a chemical solution effective to
remove contaminants and the first outer aluminum oxide layer from
the baffle to expose aluminum material; and forming a second outer
aluminum oxide layer on the aluminum material. The second outer
aluminum oxide layer preferably has a thickness of about 50
angstroms to about 300 angstroms, and preferably has a density of
at least about 90% of the theoretical density of aluminum
oxide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 depicts an embodiment of a resist stripping chamber
including a preferred embodiment of the bare aluminum baffle.
[0009] FIG. 2 illustrates a preferred embodiment of the bare
aluminum baffle.
[0010] FIG. 3 illustrates a liner positioned on the bare aluminum
baffle shown in FIG. 2.
[0011] FIG. 4 illustrates an embodiment of a substrate that can be
processed in the resist stripping chamber shown in FIG. 1.
DETAILED DESCRIPTION
[0012] Plasma processing apparatuses for semiconductor substrates,
such as silicon wafers, include resist stripping chambers, which
are used in semiconductor device manufacturing processes to remove
resist (or "photoresist"), which is used as a mask for the
semiconductor structures. For example, resist is removed from
underlying layers after one or more of the layers have been etched
to form features in them. One technique that is performed in resist
stripping chambers to remove resist from semiconductor structures
is dry stripping, also referred to as "ashing," which uses plasma
dry etching techniques.
[0013] During a resist stripping operation, reactive species are
distributed over a substrate including a resist layer, which is
being processed inside the resist stripping chamber. It has been
found that baffles of materials including anodized aluminum, and
ceramics, such as quartz, silicon carbide and sapphire have certain
disadvantages. Anodized aluminum baffles include an outer oxide
coating formed by the anodic oxidation of aluminum materials in an
electrolyte. However, anodized layers formed by anodizing processes
include an inner layer and an outer layer, which can be undesirably
porous, of low density and include defects. Also, anodized layers
are thick, typically having a thickness of about 5,000 to 10,000
angstroms.
[0014] It has also been found that baffles of ceramic materials
have low thermal conductivity, making them prone to thermal shock
failure during semiconductor substrate processing, and also causing
them to have poor spatial temperature uniformity during resist
stripping, which reduces the uniformity of resist removal from
substrates. Ceramic baffles also are brittle and, consequently,
subject to breakage even during routine cleaning and handling
operations. Further, quartz baffles are consumable parts; i.e.,
their performance in resist stripping chambers degrades with
continued service.
[0015] In light of the above-described disadvantages associated
with using baffles of anodized aluminum and ceramic materials in
resist stripping chambers, further investigations have been
conducted to develop baffles of different materials for use in
resist stripping chambers. As a result of these investigations, it
has unexpectedly been determined that baffles of "bare aluminum"
can be used in resist stripping chambers without the
above-mentioned disadvantages of baffles of anodized aluminum and
ceramic materials. As used herein, the term "bare aluminum" means
an aluminum or aluminum alloy material that has a "native" outer
oxide layer, or such an aluminum or aluminum alloy material with a
thin outer aluminum oxide layer formed by an embodiment of the
methods described herein. As described herein, a "thin" outer
aluminum oxide layer preferably has a thickness of about 50
angstroms to about 300 angstroms, more preferably about 50
angstroms to about 100 angstroms. Native aluminum oxide layers form
naturally on aluminum materials when they are exposed to an
oxygen-containing atmosphere at ambient temperature. The term "bare
aluminum" as used herein does not include anodized aluminum
materials including an anodized aluminum oxide layer.
[0016] FIG. 1 depicts an exemplary embodiment of a resist stripping
chamber 10 in which a preferred embodiment of the bare aluminum
baffle 50 is mounted. The resist stripping chamber 10 includes a
side wall 12, a bottom wall 14 and a cover 16. The walls 12, 14 and
the cover 16 of the resist stripping chamber 10 can be of any
suitable material, such as anodized aluminum, or bare aluminum. The
cover 16 is preferably pivotably attached by hinges to the side
wall 12 to allow the cover 16 to be opened to access the interior
of the resist stripping chamber 10 to remove the bare aluminum
baffle 50 for cleaning or replacement, or for other purposes. The
resist stripping chamber 10 includes vacuum ports 18 in the bottom
wall 14.
[0017] The resist stripping chamber 10 also includes a substrate
support 20 on which a semiconductor substrate 22, such as a wafer,
is mounted during resist stripping. The substrate 22 includes a
resist that provides a masking layer for protecting underlying
layers of the substrate 22 during the resist stripping process. The
underlying layers can be of conductive, insulative and/or
semiconductive materials. The substrate support 20 preferably
comprises an electrostatic chuck adapted to clamp the substrate 22.
The substrate support 20 preferably includes a heater, such as a
resistive heating element, adapted to maintain the substrate 22 at
a suitable temperature during the resist stripping process,
preferably from about 200.degree. C. to about 300.degree. C., more
preferably from about 250.degree. C. to about 300.degree. C. The
substrate 22 can be introduced into and removed from the resist
stripping chamber 10 through a substrate entry port 26 provided in
the sidewall 12. For example, the substrate 22 can be transferred
under vacuum into the interior of the resist stripping chamber 10
from an etching chamber located proximate the resist stripping
chamber.
[0018] In the embodiment, a remote plasma source 30 is arranged in
fluid communication with the resist stripping chamber 10. The
plasma source 30 is operable to produce plasma and to supply
reactive species into the interior of the resist stripping chamber
10 through a passage 32 connected to the resist stripping chamber
10. The reactive species remove resist from the substrate 22
supported on the substrate support 20. The illustrated embodiment
of the plasma source 30 includes a remote energy source 34 and a
stripping gas source 36. The energy source 34 can be any suitable
source and is preferably a microwave generator. Exemplary
apparatuses including a microwave generator are available from Lam
Research Corporation located in Freemont, Calif. In a preferred
embodiment, the microwave generator operates at a frequency of 2.45
GHz, and preferably has a power in the range of about 500 to about
1500 W, more preferably in the range of about 1000 to about 1500 W.
Microwaves, represented by arrow 38, are produced by the microwave
generator 34 and propagated through a waveguide 40 into the passage
32.
[0019] The gas source 36 is operable to supply process gas,
represented by arrow 42, into the passage 32, where the gas is
energized into the plasma state by the microwaves produced by the
energy source 34. Reactive species pass through an opening 44 into
the interior of the resist stripping chamber 10.
[0020] The reactive species are distributed in the resist stripping
chamber 10 by a bare aluminum baffle 50 located between the cover
16 and the substrate support 20 before the reactive species flow
onto the substrate 22 and strip the resist. The substrate 22 is
preferably heated by a heater located in the substrate support 20
during resist stripping. Waste products generated during resist
stripping are pumped out of the resist stripping chamber 10 through
the exhaust ports 18.
[0021] As shown in FIG. 2, the bare aluminum baffle 50 is
preferably a circular, one-piece body of bare aluminum. The resist
stripping chamber 10 is preferably cylindrical for single wafer
processing. When adapted to be installed in a cylindrical resist
stripping chamber 10, the bare aluminum baffle 50 preferably has a
diameter larger than the width, e.g., diameter, of the interior of
the resist stripping chamber 10 so that the baffle can be supported
by the side wall 12. The bare aluminum baffle 50 includes an inner
portion having a raised central portion 52 with an upper surface 54
and through passages 56. In the illustrated embodiment of the bare
aluminum baffle 50, the central portion 52 includes six
circumferentially spaced-apart passages 56. The number of passages
56 can be either more or less than six in other embodiments. In the
embodiment, ultraviolet (UV) radiation that passes through the
passage 32 impinges on the upper surface 54 in a direction
generally perpendicular to the upper surface. The passages 56 are
preferably oriented at an acute angle relative to the upper surface
54 to prevent a direct line of sight for the UV radiation to pass
through the bare aluminum baffle 50. Consequently, the UV radiation
is reflected from the upper surface 54 and the walls of the
passages 56 so that it does not damage the substrate 22.
[0022] The bare aluminum baffle 50 also includes through passages
58 arranged between the central portion 52 and a peripheral portion
60. The passages 58 are adapted to distribute reactive species in a
desired flow pattern into the interior of the resist stripping
chamber 10. As shown in FIG. 2, the passages 58 preferably are in
the form of concentrically-arranged rows of holes. The passages 58
preferably have a round cross section and preferably increase in
cross-sectional size (e.g., diameter) in the radial outward
direction of the bare aluminum baffle 50 from the central portion
52 toward the peripheral portion 60.
[0023] As shown in FIG. 2, the peripheral portion 60 of the bare
aluminum baffle 50 includes a flange 62 having circumferentially
spaced-apart holes 64 for receiving fasteners 66, e.g., threaded
bolts (FIG. 1), to attach the bare aluminum baffle 50 to the top
surface 68 of the side wall 12 of the resist stripping chamber 10.
The bare aluminum baffle 50 can be detached from the side wall 12
and removed from the resist stripping chamber 10 to treat or
replace the bare aluminum baffle, as desired.
[0024] The bare aluminum baffle 50 is of aluminum or an aluminum
alloy, such as 6061 aluminum, which comprises by weight from about
96 to about 99% Al, about 0.8 to about 1.2% Mg, about 0.4 to about
0.8% Si, Cu, Cr, and optionally Fe, Mn, Zn and/or Ti.
[0025] A liner 70 is adapted to be supported on the upper surface
72 of the bare aluminum baffle 50 to minimize the deposition of
materials on the bottom surface of the cover 16 during resist
stripping processes. Circumferentially spaced-apart spacers 65 are
provided on the upper surface 72 to support the liner 70 and form a
plenum 74 therebetween (FIG. 1). The spacers 65 can be of any
suitable material, and are preferably of "TEFLON." The liner 70
includes a centrally located passage 44 through which reactive
species pass from the passage 32 into the plenum 74. The liner 70
is preferably made of bare aluminum, such as 6061 aluminum.
[0026] The bare aluminum baffle 50 can be a "new" baffle that has
not been used in a resist stripping chamber and includes a native
aluminum oxide outer layer, or a "used" baffle, i.e., a baffle that
has been previously used in a resist stripping chamber and includes
either a native outer aluminum oxide layer or a thin outer aluminum
oxide layer formed by an embodiment of the methods described
herein. Such "new" and "used" bare aluminum baffles can be treated
by the methods described herein to produce a thin outer aluminum
oxide layer. In other words, "used" bare aluminum baffles can be
recovered by performing the methods described herein. "Recovered"
bare aluminum baffles including a thin outer aluminum oxide layer
can be reinstalled in resist stripping chambers and reused for
resist stripping processing.
[0027] As explained above, new bare aluminum baffles including a
native outer aluminum oxide layer can be used in resist stripping
chambers. The native outer aluminum oxide layer preferably has a
thickness of from about 25 to about 75 angstroms. Before new bare
aluminum baffles are installed in a resist stripping chamber, they
are preferably treated to remove residual contaminants, such as
lubricants, resulting from the manufacturing of the baffles.
[0028] According to another preferred embodiment of the bare
aluminum baffles, new bare aluminum baffles that include a native
outer aluminum oxide layer can be treated by removing the native
outer aluminum oxide layer, thereby leaving only the aluminum base
material; and then forming a thin outer aluminum oxide layer on the
exposed surface of the aluminum material. The native outer aluminum
oxide layer is removed if it is determined to have insufficient
properties for use in a resist stripping chamber, e.g., the native
outer aluminum oxide layer has an insufficient density, thickness
and/or uniformity. The outer aluminum oxide layer formed after
removing the native outer aluminum oxide layer preferably is a
single layer; preferably has a thickness of about 50 angstroms to
about 300 angstroms, more preferably about 50 angstroms to about
100 angstroms; and preferably has a density of at least about 90%,
more preferably at least about 95%, of the theoretical density of
aluminum oxide. Accordingly, the thin aluminum oxide layer has
reduced porosity than anodized aluminum oxide layers. Also, thick
anodized aluminum oxide layers can include undesirable
intermetallic inclusions, such as SiMg or MgSiFe, which reduce
their quality.
[0029] According to another preferred embodiment of the bare
aluminum baffles, used bare aluminum baffles that include a native
outer aluminum oxide layer can be recovered by a treatment process
that includes steps of removing surface contaminants and the native
outer aluminum oxide layer from the baffle, thereby leaving only
the aluminum base material; and then forming a thin outer aluminum
oxide layer on the exposed surface of the aluminum base material.
The outer aluminum oxide layer preferably is a single layer;
preferably has a thickness of about 50 angstroms to about 300
angstroms, more preferably about 50 angstroms to about 100
angstroms; and preferably has a density of at least about 90%, more
preferably at least about 95%, of the theoretical density of
aluminum oxide.
[0030] According to another preferred embodiment, used bare
aluminum baffles that include a thin outer aluminum oxide layer
formed by embodiments of the methods described herein can be
treated to remove contaminants on the outer aluminum oxide layer
and also to remove the outer aluminum oxide layer itself, and then
to form a new outer aluminum oxide layer on the resulting aluminum
base material. This treatment can be performed when desirable,
thereby allowing the as-treated bare aluminum baffle to be re-used
in a resist stripping chamber. For example, the treatment can be
performed when it is determined that there has been a reduction in
the resist strip rate, strip non-uniformity across the wafer,
and/or the occurrence of particle deposition on substrates
processed in the resist stripping chamber containing the bare
aluminum baffle. The treatment can be performed one or more times,
i.e., the bare aluminum baffle can be recovered at least once.
[0031] In another preferred embodiment, the bare aluminum baffle
including the as-formed aluminum oxide layer can be post-treated to
remove micro-contaminants, particles and defects from the aluminum
oxide layer.
[0032] According to a preferred embodiment, new and used bare
aluminum baffles are treated by a chemical treatment process that
includes removing surface contaminants and the native aluminum
oxide layer from new or used bare aluminum baffles, or a
previously-formed thin aluminum oxide layer and contaminants from
used bare aluminum baffles. A thin aluminum oxide layer is formed
on the aluminum base material after the aluminum oxide layer is
removed. Depending on various factors including the composition of
the resist, the composition of the layers of the substrate, and the
process gas mixture used for stripping resist from the substrate,
contaminants deposited on the exposed surface of the bare aluminum
baffle can include, for example, carbon, Ti, TiF.sub.4 and
AlF.sub.3. The chemical treatment process comprises steps of
removing surface contaminants and the native or previously-formed
thin outer aluminum oxide layer to expose the aluminum base
material, and then forming a thin aluminum oxide layer on the
aluminum base material. The chemical treatment process preferably
also includes steps of refinishing the surface of the aluminum base
after removing the aluminum oxide layer, and treating the
refinished surface of the bare aluminum baffle to remove
contaminants prior to forming the thin aluminum oxide layer.
[0033] According to a preferred embodiment of the chemical
treatment process, a new or used bare aluminum baffle is initially
cleaned to remove deposits. Such deposits can include organics from
stripping photoresist from substrates, as well as other substances,
such as Ti, TiF.sub.4 and AlF.sub.3. The cleaning preferably
includes first using a suitable alkaline cleaning solution, such as
Nova 120 solution available from Henkel Surface Technologies
located in Madison Heights, Mich. This solution is a non-silicated,
alkaline cleaning solution containing sodium tetraborate and
proprietary additives. The bare aluminum baffle is preferably
immersed in the solution for about 5 to about 15 minutes at a
temperature of about 110.degree. F. to about 130.degree. F.,
followed by rinsing with the bare aluminum baffle with water for
about 3 to about 5 minutes to remove the solution from it.
[0034] In the embodiment, the bare aluminum baffle outer surface
preferably is then etched using a suitable alkaline etching
solution, such as Nova SC603B solution available from Henkel
Surface Technologies. This solution is an alkaline etching solution
containing primarily sodium hydroxide and proprietary additives.
The bare aluminum baffle is preferably immersed in the solution for
about 30 seconds to about 2 minutes at a temperature of about
110.degree. F. to about 130.degree. F., followed by rinsing with
water for a sufficient amount of time to remove the solution from
the bare aluminum baffle, typically about 5 minutes to about 10
minutes. The rinsing water is preferably ultrapure water having a
resistivity of at least about 15 Mohm-cm at about ambient
temperature.
[0035] In the embodiment, the outer surface of the bare aluminum
baffle is then de-oxidized using a suitable solution, such as Nova
310A & B solution available from Henkel Surface Technologies.
The bare aluminum baffle is preferably immersed in the solution for
a sufficient amount of time to remove the outer aluminum oxide
layer from the bare aluminum baffle, typically from about 5 to
about 10 minutes. The solution is preferably at about ambient
temperature. The bare aluminum baffle is then rinsed, preferably
with ultrapure water, for a sufficient amount of time to remove the
solution, typically about 5 to about 10 minutes. The rinsed bare
aluminum baffle is dried using, for example, clean dry air or
filtered nitrogen.
[0036] After removing the aluminum oxide layer, the bare aluminum
baffle preferably is refinished to form a desired surface roughness
for use in the resist stripping chamber. For example, the
refinished surface roughness can be about 15 to about 20
microinches. The bare aluminum baffle can be refinished using any
suitable abrasive, such as abrasive paper including an aluminum
oxide abrasive, e.g., a 220-grit abrasive paper. Coarser or finer
abrasive paper can also, or alternatively, be used depending the
desired surface finish of the bare aluminum baffle. The bare
aluminum baffle can be rotated during resurfacing to enhance the
uniformity of the surface finish. The resurfaced bare aluminum
baffle is rinsed, preferably using ultrapure water, for a
sufficient amount of time to remove loose particles from the bare
aluminum baffle surface, typically about 5 to 10 minutes. The
rinsed bare aluminum baffle is dried using, for example, clean dry
air or filtered nitrogen.
[0037] In the embodiment, contaminants remaining on the bare
aluminum baffle surface from the refinishing are removed;
preferably first using a suitable alkaline cleaning solution, such
as Nova 120. The bare aluminum baffle is preferably soaked in the
solution for about 5 to about 15 minutes at a temperature of about
110.degree. F. to about 130.degree. F. The bare aluminum baffle is
then rinsed, preferably with ultrapure water for about 3 to about
10 minutes, to remove residual alkaline cleaning solution from the
bare aluminum baffle.
[0038] After the alkaline cleaning step, the bare aluminum baffle
is cleaned with an acid cleaning solution to form an aluminum oxide
layer on the bare aluminum baffle, which following the completion
of this step will continue to grow in air. Any suitable acid
cleaning solution can be used. A preferred acid cleaning solution
contains a mixture of about 0.25% phosphoric acid and about 0.05%
hydrofluoric acid. The bare aluminum baffle is preferably immersed
in an acid cleaning solution for about 1 to about 3 minutes at
about ambient temperature. The bare aluminum baffle is then rinsed,
preferably with ultrapure water for about 3 to 10 minutes, to
remove residual acid cleaning solution from the bare aluminum
baffle.
[0039] In the embodiment, the bare aluminum baffle is preferably
then ultrasonically cleaned in ultrapure water in a suitable clean
environment, preferably a class 1000 clean room. The water is
preferably at about ambient temperature. After ultrasonic cleaning,
the bare aluminum baffle is preferably rinsed with ultrapure water
and then dried using, for example, clean dry air or filtered
nitrogen.
[0040] In another preferred embodiment, new and/or used bare
aluminum baffles can be treated by a process that includes removing
surface contaminants and either a native outer aluminum oxide layer
or a previously formed thin outer aluminum oxide layer, and then
forming a thin outer aluminum oxide layer on the bare aluminum
baffle by an electropolishing procedure. In the embodiment, the
contaminants and outer aluminum oxide layer can be removed by the
steps described above.
[0041] After the outer aluminum oxide layer has been removed from
the bare aluminum baffle to expose the aluminum base material, the
bare aluminum baffle is electropolished by placing the bare
aluminum baffle in an electropolishing tank containing a suitable
acid solution, preferably containing at least phosphoric acid. The
electropolishing conditions can be selected to produce an aluminum
oxide layer having a desired thickness, preferably from about 50 to
about 100 angstroms. The aluminum oxide layer preferably has a
density of at least about 90%, more preferably at least about 95%,
of the theoretical density of aluminum oxide. Typically, the
electropolishing can be conducted for about 30 seconds to about 5
minutes to produce an aluminum oxide layer of the desired
thickness.
[0042] In the embodiment, the bare aluminum baffle having an outer
aluminum oxide layer is preferably rinsed in deionized water and
ultrasonically cleaned in ultrapure water in a clean environment,
such as a class 10,000 or 1000 clean room. The bare aluminum baffle
is then dried, preferably using nitrogen or ultrapure air.
[0043] Bare aluminum baffles having a native aluminum oxide outer
layer or a thin aluminum oxide outer layer formed by preferred
embodiments of the methods described above can be used in resist
stripping chambers without causing metallic contamination of
substrates, such as semiconductor wafers, reduced resist stripping
rates, or reduced resist strip uniformity. The bare aluminum
baffles can provide resistance to oxidation and/or erosion by etch
process gases, including fluorinated gases.
[0044] The bare aluminum baffles can provide certain advantages as
compared to bare aluminum baffles of ceramic materials and anodized
aluminum. Particularly, the bare aluminum baffles have higher
thermal conductivity than ceramic baffles, which can eliminate
thermal shock problems and provide better temperature uniformity in
the bare aluminum baffles, which in turn can improve resist strip
uniformity on substrates. Aluminum is also less expensive than
high-purity ceramic materials. As compared to anodized aluminum
baffles, the bare aluminum baffles have an outer aluminum oxide
layer, which is a single layer, and which is thinner and of higher
density than the anodized layers of such anodized aluminum
baffles.
[0045] An exemplary embodiment of a substrate 22 that can be
processed in the resist strip chamber 10 is shown in FIG. 4. The
substrate 22 is depicted after metal etching has been completed,
but before resist stripping has been performed. In other
embodiments, other layers can be provided above, below or between
the layers shown. Further, not all of the layers shown in FIG. 4
need be present and some or all may be substituted by other
different layers.
[0046] The substrate 22 includes a base substrate 102, typically of
silicon. An oxide layer 104, such as SiO.sub.2, is formed on the
substrate 102. One or more barrier layers 106 of, e.g., Ti, TiN,
TiW or the like, can be formed between the oxide layer 104 and an
overlying metal layer 108.
[0047] The metal layer 108 can comprise, e.g., tungsten, aluminum
or an aluminum alloy, such as Al--Cu, Al--Si, or Al--Cu--Si. The
substrate 22 also can include an antireflective coating (ARC) layer
110 of any suitable material, such as TiN or TiW. A patterned
resist layer 112 is provided over the ARC layer 110. Processing
byproducts 120 are shown on the walls.
[0048] The process gas used to form the remote plasma includes
oxygen, which is excited into a plasma state that dissociates
O.sub.2 into oxygen radicals and ion species, which are flowed into
the interior of the resist stripping chamber 10 and react with
(i.e., oxidize or "ash") the resist layer 112 on the substrate 22.
The rate at which the photoresist is removed by the strip process
is referred to as the "strip rate." The process gas can have any
suitable composition, such as an oxygen-containing gas mixture,
such as an O.sub.2/N.sub.2, O.sub.2/H.sub.2O,
O.sub.2/N.sub.2/CF.sub.4, or O.sub.2/N.sub.2/H.sub.2O gas mixture.
The gas mixture preferably comprises O.sub.2, N.sub.2, and a
fluorine-containing component, such as CF.sub.4 or C.sub.2F.sub.6.
N.sub.2 can be added to the gas mixture to enhance selectivity with
respect to the photoresist material as compared to a second
material, such as a barrier and/or underlying material. As used
herein, the term "selectivity" with respect to photoresist material
as compared to a second material is defined as the ratio of the
photoresist etch rate to the etch rate of the second material.
[0049] Preferred gas mixtures can contain, for example, by total
gas volume, from about 40% to about 99%, preferably from about 60%
to about 95%, and more preferably from about 70% to about 90%
O.sub.2; from about 0.5% to about 30%, preferably from about 2.5%
to about 20%, and more preferably from about 5% to about 15% of
fluorine-containing gas; and from about 0.5% to 30%, preferably
about 2.5% to 20%, and more preferably about 5 to 15% of N.sub.2.
During resist stripping, the total flow rate of the process gas is
preferably in the range of from about 500 to about 6000 sccm, more
preferably from about 2000 to about 5000 sccm, and the pressure in
the resist stripping chamber 10 is preferably in the range of about
200 mTorr to about 10 Torr.
[0050] The present invention has been described with reference to
preferred embodiments. However, it will be readily apparent to
those skilled in the art that it is possible to embody the
invention in specific forms other than as described above without
departing from the spirit of the invention. The preferred
embodiment is illustrative and should not be considered restrictive
in any way. The scope of the invention is given by the appended
claims, rather than the preceding description, and all variations
and equivalents which fall within the range of the claims are
intended to be embraced therein.
* * * * *