U.S. patent application number 14/273419 was filed with the patent office on 2014-08-28 for process for cleaning shield surfaces in deposition systems.
This patent application is currently assigned to SEMATECH, INC.. The applicant listed for this patent is ASAHI GLASS CO., LTD., SEMATECH, INC.. Invention is credited to Vibhu Jindal, Junichi Kageyama.
Application Number | 20140242500 14/273419 |
Document ID | / |
Family ID | 48903188 |
Filed Date | 2014-08-28 |
United States Patent
Application |
20140242500 |
Kind Code |
A1 |
Jindal; Vibhu ; et
al. |
August 28, 2014 |
Process For Cleaning Shield Surfaces In Deposition Systems
Abstract
A process for cleaning and restoring deposition shield surfaces
which results in a cleaned shield having a surface roughness of
between about 200 microinches and about 500 microinches and a
particle surface density of less than about 0.1 particles/mm.sup.2
of particles between about 1 micron and about 5 microns in size and
no particles less than about 1 micron in size and method for use
thereof is disclosed.
Inventors: |
Jindal; Vibhu; (Albany,
NY) ; Kageyama; Junichi; (Yokohama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEMATECH, INC.
ASAHI GLASS CO., LTD. |
Albany
Tokyo |
NY |
US
JP |
|
|
Assignee: |
SEMATECH, INC.
Albany
NY
ASAHI GLASS CO., LTD.
Tokyo
|
Family ID: |
48903188 |
Appl. No.: |
14/273419 |
Filed: |
May 8, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13365077 |
Feb 2, 2012 |
8734586 |
|
|
14273419 |
|
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Current U.S.
Class: |
430/5 ; 118/504;
451/38 |
Current CPC
Class: |
C23C 14/564 20130101;
B82Y 10/00 20130101; B82Y 40/00 20130101; B08B 7/04 20130101; G03F
1/60 20130101; G03F 1/22 20130101; C23C 14/34 20130101 |
Class at
Publication: |
430/5 ; 118/504;
451/38 |
International
Class: |
G03F 1/22 20060101
G03F001/22; B08B 7/04 20060101 B08B007/04; C23C 14/56 20060101
C23C014/56 |
Claims
1. A deposition shield, comprising: a shield having a surface
roughness of between about 200 microinches and about 500
microinches and a surface particle density of less than about 0.1
particles/mm.sup.2 of particles between about 1 micron and about 5
microns in size and no particles below about 1 micron in size, said
shield being fabricated by: roughening the surface of a stainless
steel shield by grit blasting the shield with fresh grit material;
loosening particles embedded in the roughened surface by etching
the surface with a chemical etch solution; and removing loosened
particles from the roughened surface by at least one of a high
pressure rinse and ultrasonication, to provide the shield with a
surface roughness of between about 200 microinches and about 500
microinches and a surface particle density of less than about 0.1
particles/mm.sup.2 of particles between about 1 micron and about 5
microns in size and no particles below about 1 micron in size.
2. An EUVL mask blank comprising: a layer deposited in a deposition
chamber having a shield with a surface roughness of between about
200 microinches and about 500 microinches and a surface particle
density of less than about 0.1 particles/mm.sup.2 of particles
between about 1 micron and about 5 microns in size and no particles
below about 1 micron in size, said shield being fabricated by:
roughening the surface of a stainless steel shield by grit blasting
the shield with fresh grit material; loosening particles embedded
in the roughened surface by etching the surface with a chemical
etch solution; and removing loosened particles from the roughened
surface by at least one of a high pressure rinse and
ultrasonication, to provide the shield with a surface roughness of
between about 200 microinches and about 500 microinches and a
surface particle density of less than about 0.1 particles/mm.sup.2
of particles between about 1 micron and about 5 microns in size and
no particles below about 1 micron in size.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/365,077, titled "Process For Cleaning Shield Surfaces
In Deposition Systems," filed Feb. 2, 2012, which is hereby
incorporated by reference in its entirety.
FIELD
[0002] The present disclosure relates to a process for cleaning
deposition system shields, and in particular, a process for
cleaning and restoring deposition system stainless steel shields
resulting in shields having a high surface roughness and low
particle residue and methods for the use of the cleaned shields
produced thereby.
BACKGROUND
[0003] A substrate deposition system may be used to process a
substrate with an energized gas, such as plasma. Typically, the
system includes a deposition chamber which encloses a process zone
into which a gas is introduced, a gas energizer to energize the
gas, and an exhaust to remove the energized gas. The deposition
chamber may, for example, be used to deposit material on the
substrate.
[0004] The chamber components exposed to the energized gas are
often covered with removable shields which protect the surface of
the chamber components from the sputtered residues used to deposit
material on the substrate. The sputtered material coats the shield
which can be removed and replaced when the layer reaches a
thickness such that particles begin to flake off and contaminate
the process chamber. In subsequent processing cycles, the deposited
process residues can flake off of the shield surfaces and fall upon
and contaminate the substrate. Therefore, the shields must be
frequently periodically removed and cleaned of surface residue.
Manufacturers often use sandblasting to roughen the shield, which
allows them to run the sputtering chamber for longer periods of
time with out a shield change, reducing the down time of process
equipment. However, sandblasting leaves particle residue on the
surface of the shields which can increase the chances of
contamination of the substrate.
[0005] U.S. Patent Application Publication No. 2005/0089699 to Lin
et al. relates to a method for cleaning and refurbishing process
chamber components, such as a chamber shield having a coating. The
method includes immersing the shield in an acidic cleaning
solution, such as HF, HNO.sub.3, HCl, H.sub.3PO.sub.4, and
H.sub.2SO.sub.4, and/or a basic cleaning solution, such as KOH,
NH.sub.4OH, NaOH, and K.sub.2CO.sub.3, to remove process surface
residue and clean or remove at least a portion of the coating of
the shield. Optionally, the chemically cleaned surface can be
further cleaned by performing an ultrasonic cleaning step followed
by heating. The shield is then subject to a penetrative grit blast,
using particles having a grit mesh size of about 80 to 120, to
remove compounds between the underlying structure and the coating.
The cleaned surface is then subject to a texturizing grit blast,
using particles having a grit mesh size of about 24 to 70, to
provide a surface roughness of about 150 to 350 microinches.
Optionally, the texturized surface can be further cleaned by
performing an ultrasonic cleaning step followed by heating. Once
the surface of the shield has been cleaned and textured as set
forth above, a metal coating is applied by a deposition process.
The refurbished shield has coating having a thickness of about 152
to 508 microns and a surface roughness of about 1000 to 2000
microinches.
[0006] Thus, it is desirable to provide a process for cleaning
coated shields which minimizes the amount of flake-off of process
residue. It is further desirable to deposit low defect films on
substrates and provide a process for cleaning coated shields
resulting in a high surface roughness and low particle residue.
SUMMARY
[0007] One aspect of the present invention provides a method for
cleaning and restoring deposition chamber shields, including
roughening the surface of a stainless steel shield by grit blasting
the shield with fresh grit blasting material, loosening particles
embedded in the roughened surface by etching the surface with a
chemical etch solution, and removing loosened particles from the
roughened surface by at least one of a high pressure rinse and
ultrasonication, to provide the shield with a surface roughness of
between about 200 microinches and about 500 microinches and a
surface particle density of less than about 0.1 particles/mm.sup.2
of particles between about 1 micron and about 5 microns in size and
no particles below about 1 micron in size.
[0008] Another aspect of the present invention provides a cleaned
and restored deposition shield having a surface roughness of
between about 200 microinches and about 500 microinches and a
surface particle density of less than about 0.1 particles/mm.sup.2
of particles between about 1 micron and about 5 microns in size and
no particles below about 1 micron in size.
[0009] Another aspect of the present invention provides a EUVL mask
blank and a deposition method including providing in a deposition
chamber the cleaned and restored shield and depositing a layer on
the EUVL mask blank.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] These and other aspects of the present invention will become
apparent upon a review of the following detailed description,
accompanying claims, and appended drawings, which illustrate
examples of the invention, where:
[0011] FIG. 1 is a schematic side view of an embodiment of a shield
undergoing grit blasting in accordance with the present
invention;
[0012] FIG. 2 is a schematic side view of the shield of FIG. 1
following grit blasting to roughen the surface;
[0013] FIG. 3 is a schematic side view of the shield of FIG. 2
undergoing etching with a chemical etch solution to loosen the
embedded grit particles;
[0014] FIG. 4 is a schematic side view of the shield of FIG. 3
undergoing a high pressure rinse and/or ultrasonication to remove
the loosened particles;
[0015] FIG. 5 is a schematic side view of the shield of FIG. 4
showing a roughened and cleaned shield surface;
[0016] FIG. 6 is pair of SEM images of a shield surface cleaned
with a conventional cleaning process according to Comparative
Example A;
[0017] FIG. 7 is an SEM image of a shield surface cleaned with
conventional cleaning process according to Comparative Example A;
and
[0018] FIG. 8 is an SEM image of a shield surface cleaned according
to Example 1 of the present invention.
DETAILED DESCRIPTION
[0019] During the sputtering process, such as manufacturing mask
blank for extreme ultraviolet lithography ("EUVL"), metallic
material is deposited on the substrate as well as the shields used
to protect the deposition chamber surfaces. Metallic materials
adhere to the shield surfaces and over time tend to flake off the
shields onto the substrates and contaminate the substrates. To
minimize contamination from the shields, they are periodically
removed and cleaned.
[0020] The present invention relates to a process for cleaning
stainless steel shield surfaces. The process results in a cleaned
shield having a surface roughness of between about 200 microinches
and about 500 microinches and a surface particle density of less
than about 0.1 particles/mm.sup.2 of particles between about 1
micron and about 5 microns in size. Preferably, the shield surfaces
are cleaned to a surface roughness of between about 240 microinches
and about 400 microinches, more preferably between about 260
microinches and about 350 microinches, and further preferably
between about 280 microinches and about 320 microinches.
Preferably, the shield surfaces are cleaned such that there is no
particle residue on the surface below about 1 micron in size.
[0021] When the surface roughness of the reconditioned shields is
less than about 200 microinches, the surface is too smooth. During
use of these shields in a deposition process, defects coming from
the shields and deposition on the shields are increased. The
deposition film growth of deposited material on shields will cause
stress buildup with time. The stress is relieved by cracking of the
thin film deposition which causes particle generation. The
resulting particles end up as defects on the substrate. Therefore,
it is desirable to increase the surface roughness of the shield so
as not to let stress build up as the deposited thin film is
discontinuous. One method to increase surface roughness is to grit
blast the surface. However, when the shield surface is grit blasted
to a roughness of more than about 500 microinches, the defects
coming from the shields and depositing on the substrate are
increased. This is due to large particles, such as Al.sub.2O.sub.3,
that reside on the shields as a result of the grit blasting process
to generate such a high surface roughness shield surface.
[0022] Surface roughness is defined as R.sub.a which is the
arithmetic average of the absolute values of the collected
roughness data points. These values characterize the surface based
on the vertical deviations of the roughness profile from the mean
line. The average roughness, R.sub.a, is expressed in units of
height, which is typically expressed in "millionths" of an inch and
is also referred to as "microinches". The surface roughness for
such high roughness can be determined by electronic gauges, e.g.,
Mitutoyo Surftest SJ-201, where a stylus records the vertical
movement along the surface measuring the displacement. The vertical
displacement of the stylus is further amplified, recorded and
processed to calculate the roughness value.
[0023] More than 100 shield parts inside a typical deposition
system line the process chamber and protect internal components
during deposition. These parts are coated with Mo, Si, and Ru
material during every marathon. Therefore, the shields are removed
and their surfaces cleaned afterwards. A marathon is the time
period from one maintenance procedure to the next. The restoration
of shield surfaces after cleaning is important and has been shown
to significantly influence the resulting defects of the final mask
blank. The surface of the shield must be very rough to enable the
starting shield to decrease the Si family particle defect count.
The Si family defect count is the total count of Si and Si/Mo
defects. The defect count is the number of defect particles
deposited on the blank from a deposition procedure. Additionally,
any residual contaminants remaining on the shields, from either the
deposition or the cleaning process, should be minimized after the
cleaning treatment so that no further defects are added to the
blank during the deposition.
[0024] Conventional chemical treatments that can etch the
deposition cleanly have been demonstrated. However, such treatment
will also smooth the shield surfaces, which is not desirable. A
typical shield surface roughness achieved by conventional chemical
treatment procedures is less than 20 microinches, which is an order
of magnitude less than that achieved by the present invention. A
physical cleaning process, such as grit blasting the shields, can
be used to roughen the surface after chemical removal of the
deposited material, but this process leaves a substantial amount of
particle residue embedded in the surface. This particulate residue
then becomes a particle source for defects during the deposition
marathon. The limitations of conventional chemical and physical
cleaning procedures make cleaning the shield surfaces a
challenge.
[0025] The present inventors have found that analysis of the
deposited mask blank defects indicates that maintaining surface
roughness and leaving no particulates on the surface of the shields
after cleaning can minimize these defect types. With these
objectives, shield cleaning treatments were initiated resulting in
the development of a shield cleaning treatment with grit blast
materials, such as Al.sub.2O.sub.3, SiC, SiO.sub.2, and
Si.sub.3N.sub.4 to maintain surface roughness, followed by
post-cleaning methods to remove embedded particles on the shield
surface that can provide higher surface roughness with less than
about 0.1 particles/mm.sup.2 of particles between about 1 micron
and about 5 microns and no particles less than about 1 micron in
size on the surface.
[0026] The process in accordance with the present invention for
cleaning and restoring deposition shield chambers includes grit
blast and etching techniques. In one embodiment, the overall
process includes the following steps: (a) pre-cleaning the surface
(optional), (b) grit blast (high pressure, low working distance and
use of fresh grit for every part) to obtain a very rough surface,
(c) FeCl.sub.3 etch to undercut and loosen the remaining particles,
(d) KOH etch to etch surface particles (optional), (e)
post-cleaning of etched surface (optional), (f) high pressure rinse
to remove loosened particles, and/or (g) an ultrasonic step to
remove loosened particles.
[0027] Grit size refers to the size of the particles of abrading
materials embedded in for example sandpaper. Several different
standards have been established for grit size. These standards
establish not only the average grit size, but also the allowable
variation from the average. The two most common are the United
States CAMI (Coated Abrasive Manufacturers Institute, now part of
the Unified Abrasives Manufacturers' Association) and the European
FEPA (Federation of European Producers of Abrasives) "P" grade. The
FEPA system is the same as the ISO 6344 standard.
[0028] Grit blasting is a physical process in which grit blast
materials such as, Al.sub.2O.sub.3 or alternatively hard materials
like SiC or SiO.sub.2 are blasted with high pressure to roughen the
target surface, as shown in FIG. 1. The high pressure often breaks
the grit material and leaves the residue embedded on the shield
surface as shown in FIG. 2. Typically, the surface is grit blasted
to a surface roughness of at least about 200 microinches,
preferably at least about 250 microinches, so that after cleaning,
a surface roughness of between about 200 microinches and about 500
microinches can be attained. Because these embedded Al.sub.2O.sub.3
particles are prominent sources of defect particles on EUVL mask
blank during deposition, a follow-up cleaning procedure to remove
embedded Al.sub.2O.sub.3 particles on the shield surface is
employed. The cleaning procedure provides surface roughness between
about 200 microinches and about 500 microinches with only a few
small Al.sub.2O.sub.3 particles left on the surface. The bigger
grit particles were deeply embedded in the surface giving low
probability to be particle adders during deposition system.
[0029] The FeCl.sub.3 etch step undercuts the surface and loosens
adhered particles, as shown in FIG. 3, which enables subsequent
removal. The pressure wash and/or ultrasonic step removes the
loosened particles from the surface, as shown in FIG. 4. The
process yields a surface having between about 200 microinches and
about 500 microinches roughness with a surface particle density of
less than about 0.1 particles/mm.sup.2 of particles between about 1
micron and about 5 microns in size and no particles below about 1
micron in size, as shown in FIG. 5. The surface roughness of the
cleaned surface can be determined by the stylus based measurements
as described above. The particle size distribution can be
determined by characterizing the surface under scanning electron
microscope (SEM), model Altura 835, available from the FEI Company,
Hillsboro, Oreg.
[0030] In accordance with one embodiment of the present invention,
after the deposition process the used shields are soaked in a
deposition stripping tank of etchant. Suitable etching solutions
include about 10% HF+about 50% HNO.sub.3 in water at 50.degree. C.,
preferably, the % of HF can vary from about 5% to about 25% while
HNO.sub.3 can vary from about 30% to about 60%. The soak time can
vary between about 30 minutes and about 120 minutes, depending on
different shield parts selected, at a temperature of between about
50.degree. C. and about 80.degree. C. The shields are soaked in the
solution long enough to make sure that deposition is removed as
confirmed by naked eye observation. Shield parts receive different
amounts of deposition after every run, which requires variability
in the etching time at this step of the process. The shields can be
exposed to stainless steel recycle pickle agent, such as
HF+HNO.sub.3+H.sub.2O (about 1:1:1 mixture) for about 30 seconds to
about 30 minutes, preferably, the mixture of HF can vary from about
10% to about 40%, while HNO.sub.3 can vary from about 10% to about
40%, and H.sub.2O can vary from about 10% to about 40%. After
removal of deposition material, the shields are grit blasted with
grit material, such as Al.sub.2O.sub.3, of grit size 80 at a
pressure of from about 30 psi to about 75 psi, preferably about 40
psi to about 50 psi, more preferably about 45 psi. The shields can
be grit blasted a second time with Al.sub.2O.sub.3 grit material of
grit size 16 at a pressure of from about 30 psi to about 75 psi,
preferably about 40 psi to about 50 psi, and more preferably about
45 psi. Each shield part is blasted with new grit material, as
shown in FIG. 1, since the grit tends to break down to smaller and
smaller sizes if recycled. The breakdown of the grit into smaller
sizes adds more small particle size residue and reduces the
roughness of the blasted surfaces. After a post grit blast
inspection, making sure the uniformity looks good on the shield
parts, the shield parts can be exposed to high pressure water
rinse, preferably at a temperature of from about 50.degree. C. to
about 80.degree. C., a pressure of from about 1 kPa to about 5 kPa,
and from a time of from about 10 minutes to about 50 minutes, more
preferably at a pressure of about 2 kPa for a rinse time of about
30 minutes at a temperature of about 50.degree. C. The shield parts
are soaked in an FeCl.sub.3 solution for from about 90 minutes to
about 120 minutes, preferably an FeCl.sub.3 solution of from about
20% to about 80% mixed with water. The soaking process undercuts
the stainless steel to remove Al.sub.2O.sub.3 embedded particles
and surface particle residue, as shown in FIG. 3. Optionally, the
shield can be additionally etched in a KOH solution of from about
20% to about 80% mixed with water for between about 90 minutes and
about 120 minutes to undercut the stainless steel to remove
embedded grit particles and surface particle residue. The shield
parts can again be exposed to a stainless steel recycle pickle
agent, such as HF+HNO.sub.3+H.sub.2O (about a 1:1:1 mixture) for
about 30 seconds to about 30 minutes, preferably about 5 minutes.
Preferably, the mixture of HF can vary from about 10% to about 40%
while HNO.sub.3 can vary from about 10% to about 40%. The shield
parts can be soaked in from about 30% to about 75% for about 30
seconds to about 30 minutes, preferably about 40% HNO.sub.3 for
about 10 minutes. As shown in FIG. 4 the shield parts can be
exposed to a high pressure water rinse, according to the conditions
noted above, preferably at a pressure of about 2 kPa for a rinse
time of about 30 minutes at a temperature of about 50.degree. C.
After that the shield parts are baked in an oven at about
300.degree. C. for about 1 hour and then a high pressure rinse of
water can be performed. The shield parts can be ultrasonicated, as
shown in FIG. 4, at about 5 kHz and then at about 20 kHz for
between about 5 minutes and about 20 minutes, preferably between
about 1 kHz to about 1 MHz. The process provides shields with a
surface roughness of from about 200 microinches to about 500
microinches with a surface particle density of less than 0.1
particles/mm.sup.2 of particles between about 1 micron and about 5
microns in size and no particle residue below about 1 micron in
size, as shown in FIG. 5. The shield parts are then vacuum baked
and packed for storage or delivery.
[0031] A mask blank is a laminate before patterning, to be used for
the production of a photomask. An EUVL mask blank has a structure
wherein a reflective layer to reflect EUV light and an absorber
layer to absorb EUV light are formed in this order on a substrate
made of, e.g., glass. As the reflective layer, a Mo/Si multilayer
reflective film is usually employed wherein a molybdenum (Mo) film
as a low refractive index layer and a silicon (Si) film as a high
refractive index layer are alternately laminated to increase the
light reflectance when the layer surface is irradiated with EUV
light.
[0032] For the absorber layer, a material having a high EUV light
absorption coefficient, specifically a material containing chromium
(Cr) or tantalum (Ta) as the main component, is employed.
[0033] A protective layer is usually formed between the reflective
layer and the absorber layer. Such a protective layer is provided
for the purpose of protecting the reflective layer so that the
reflective layer will not be damaged by the etching process carried
out for the purpose of forming a pattern in the absorber layer.
Accordingly, for the protective layer, it is preferred to employ a
material not susceptible to influence by the etching process.
Further, the protective layer is required not to lower the
reflectance of EUV ray, since the reflective layer of the mask
blank is irradiated with EUV light in a state where the protective
layer is formed. For these reasons, as the constituting material
for the protective layer, Ru or a Ru compound (such as RuB, RuNb or
RuZr) is preferred.
[0034] In the production of an EUVL mask blank, a sputtering method
is preferably employed for the formation of the Mo/Si multilayer
reflective film, the protective layer and the absorber layer for
such reasons that a uniform film thickness can easily be obtained,
the takt time is short, the film thickness can easily be
controlled, etc. Here, for the formation of the Mo film and the Si
film constituting the Mo/Si multilayer reflective film, and the
protective layer, an ion beam sputtering method is preferably used,
and for the formation of the absorber layer, a magnetron sputtering
method is preferably employed.
[0035] The sputtering method is a film-forming method wherein a
sputtering target surface is bombarded by charged particles to beat
out sputtered particles from the target so that the sputtered
particles are deposited on a substrate disposed to face the target
thereby to form a thin film. For a sputtering target to be used for
such a film forming method, it is common to apply a structure
wherein a target main body made of a film-forming material is held
by a substrate so-called a backing plate.
EXAMPLES
[0036] The invention will be further illustrated with reference to
the following specific examples. It is understood that these
examples are given by way of illustration and are not meant to
limit the disclosure or the claims to follow.
Comparative Example A
[0037] A conventional physical cleaning process, such as grit
blasting used shields, was performed to roughen the surface after
chemical removal of the deposited material. This process left a
substantial amount of particle residue embedded in the surface.
Used stainless steel shield parts were cleaned by the following
process. The shield parts were grit blasted with 80 grit size under
a pressure of 30 psi. The grit surface residue was then blown off
with dry air. The shield parts were then immersed in HCl (20%) for
5 minutes. After spray rinse with de-ionized water, the parts were
blown dry with dry air. The cleaned shields had a surface roughness
of from 125 to 150 microinches and a surface particle density of
100 particles/mm.sup.2. FIG. 6 shows a pair of SEM images and FIG.
7 shows an SEM image of shield surfaces cleaned with a conventional
cleaning process according to Comparative Example A.
Example 1
[0038] Cleaning of used shields--After the deposition, the used
stainless steel shields were soaked in a deposition stripping tank
of etchant (10% HF+50% HNO.sub.3 in water at 50.degree. C.) for 30
minutes. The shields were then exposed to stainless steel recycle
pickle agent HF+HNO.sub.3+H.sub.2O (1:1:1 mixture) for 20 minutes.
The shields were then grit blasted with Al.sub.2O.sub.3 grit
material of grit size 80 at a pressure of 45 psi. The shield parts
were then again grit blasted with 16 grit size at 45 psi. Each
shield part is blasted with new grit material each time. After the
post grit blast inspection, to make sure the uniformity looks good
on the shield part, the shield parts were then exposed to high
pressure water rinse. The shield parts were then soaked in
FeCl.sub.3 solution of 50% mixed with water for 120 minutes to
undercut the stainless steel to remove Al.sub.2O.sub.3 embedded
particles and surface particle residue. The shield parts were again
exposed to stainless steel recycle pickle agent
HF+HNO.sub.3+H.sub.2O (1:1:1 mixture) for 5 minutes. Shield parts
were then soaked in 40% HNO.sub.3 for 10 minutes. Then the shield
parts were exposed to high pressure water rinse. The shield parts
were then baked in an oven at 300.degree. C. for 1 hour and then a
high pressure water rinse was performed. The shield parts are
further ultrasonicated for 5 mintues at 5 kHz and then 5 minutes at
20 kHz. The process provided shields having a surface roughness of
from about 280 to about 300 microinches with a surface particle
density of less than 0.1 particles/mm.sup.2 of particles between
about 1 micron and about 5 microns in size and no particle residue
below about 1 micron in size. FIG. 8 shows an SEM image of a shield
surface cleaned according to Example 1 of the present
invention.
[0039] The present invention provides cleaned and surface restored
shields having the following qualities: (a) a roughness of at least
about 200 microinches, (b) little or no surface particle residue,
and (c) would not generate particles under ion beam deposition.
Example 2
[0040] The restored shields of Comparative Example A and Example 1
were each placed in separate deposition chambers. 150 EUVL mask
blanks were produced in each chamber. These blanks for each chamber
were examined for defects and the ratio of the average defect count
per target for shields cleaned in Comparative Example A compared to
those of Example 1 was determined to be a ratio of about 10.8 to
1.
[0041] While the invention has been described with preferred
embodiments, it is to be understood that variations and
modifications are to be considered within the purview and the scope
of the claims appended hereto.
* * * * *