Title: Method of repairing an opaque defect on a mask with electron beam-induced chemical etching
Abstract: The present invention discloses a method of fabricating and repairing a mask without damage and an apparatus including a holder to mount a substrate; a stage to position the holder in a chamber; a pumping system to evacuate the chamber; an imaging system to locate an opaque defect in the substrate; a gas delivery system to dispense a reactant gas towards the defect; and an electron delivery system to direct electrons towards the opaque defect.
Patent Number: 6,897,157 Issued on 05/24/2005 to Liang, et al.
| Inventors:
|
Liang; Ted (Sunnyvale, CA);
Stivers; Alan (Palo Alto, CA)
|
| Assignee:
|
Intel Corporation (Santa Clara, CA)
|
| Appl. No.:
|
659961 |
| Filed:
|
September 10, 2003 |
| Current U.S. Class: |
438/710 |
| Intern'l Class: |
H01L 021/30.2 |
| Field of Search: |
438/710
430/5
510/376
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Niebling; John F.
Assistant Examiner: Stevenson; Andre′
Attorney, Agent or Firm: Chen; George
Parent Case Text
This is a Divisional Application of Ser. No. 09/895,511, filed Jun. 29, 2001,
which is presently pending.
Claims
1. A method comprising:
providing a substrate;
forming a layer over said substrate;
patterning said layer into a first region and a second region;
removing said layer in said first region;
inspecting said first region for an opaque defect;
forming a reactant gas over said opaque defect; and
directing electrons toward said opaque defect, said electrons inducing said reactant
gas to etch said opaque defect without ion bombardment.
2. The method of claim 1 wherein said reactant gas etches said opaque defect
without damage to said substrate.
3. The method of claim 1 wherein said opaque defect comprises chrome and said
reactant gas comprises chlorine and oxygen.
4. A method comprising:
providing a substrate;
forming a mirror over said substrate;
forming a buffer layer over said mirror;
forming an absorber layer over said buffer layer;
patterning said absorber layer into a first region and a second region;
removing said absorber layer in said first region;
inspecting said first region for an opaque defect;
dispensing a reactant gas over said opaque defect; and
scanning an electron beam over said opaque defect, said electron beam inducing
said reactant gas to react with said opaque defect without ion bombardment to form
a volatile byproduct.
5. The method of claim 4 wherein said opaque defect comprises an absorber and
said reactant gas comprises Xenon Fluoride (XeF
2).
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of semiconductor integrated circuit
manufacturing, and more specifically, to a method of fabricating and repairing
a mask with electron beam-induced chemical etching.
2. Discussion of Related Art
After coating photoresist on a semiconductor wafer, a scanner may be used to
expose the photoresist to radiation, such as deep ultraviolet (DUV) light with
nominal wavelength of 248 nanometers (nm), 193 nm, or 157 nm. The wafer is sub-divided
into contiguous identical fields and a reduction projection system is used to scan
light across a mask and onto each field. One or more integrated circuit (IC) chips
is fabricated in each field. The mask, which may be transmissive or reflective,
determines the pattern to be transferred to the photoresist as a result of the
exposure followed by a develop process.
Using a Phase-Shifting Mask (PSM) and Optical Proximity Correction (OPC) with
DUV light will allow printing of features with a critical dimension (CD) of 100-180
nm. However, Next Generation Lithography (NGL) is required to print features with
even smaller CD. Extreme Ultraviolet (EUV) lithography, a leading candidate for
NGL, uses exposure light with a central wavelength in the range of 10-15 nm.
An EUV scanner may have 4 imaging mirrors and a Numerical Aperture (NA) of 0.10
to achieve a CD of 50-70 nm with a depth of focus (DOF) of about 1.00 micrometer
(um). Alternatively, an EUV scanner may have 6 imaging mirrors and a NA of 0.25
to print a CD of 20-30 nm with a reduction in DOF to about 0.17 um.
A DUV or EUV mask is inspected for defects during fabrication. Repair of critical
defects is performed with a focused ion beam (FIB) tool having a Gallium liquid
metal ion source. A clear defect is covered up by depositing Carbon or a metal,
followed by trimming with gas-assisted etch (GAE). An opaque defect is repaired
with physical ion sputtering or GAE with ion bombardment. The process to remove
opaque defects should have adequate etch selectivity to the underlying layer. The
underlying layer is quartz in a transmissive mask for DUV or a buffer layer in
a reflective mask for EUV.
FIB may damage a mask during the scan to search for defects or during the repair
of defects. The repaired portions of the mask may be roughened by sputtering. Organic
contamination may be deposited on the surface of the mask. Gallium ions may be
implanted into underlying layers. Gallium absorbs strongly at 157 nm and at EUV
wavelengths, thus decreasing the transmission in a transmissive mask, such as a
157 nm DUV mask, or decreasing the reflectivity in a reflective mask, such as an
EUV mask. Underlying layers of the mask may be further damaged by knock-on of atoms
by Gallium.
Damage to a mask becomes more problematic as the CD of the features on the
mask shrinks. Lowering the acceleration voltage in the FIB will reduce the penetration
range of Gallium ions, but etch selectivity and spatial resolution are compromised.
Limiting imaging time and overscan area can reduce damage, but repair may also
be adversely affected. Post-repair treatment, such as wet etch of the quartz substrate
in a 157 nm DUV mask or the buffer layer in an EUV mask, will remove implanted
Gallium ions, but the underlying material may become pitted. If sufficient material
is removed, a phase error may also be introduced.
Thus, what is needed is an apparatus for and a method of fabricating and repairing
a mask without damage.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(
a)-(
d) are illustrations of a cross-sectional
view of an EUV mask blank formed according to the present invention.
FIGS. 2(
a)-(
d) are illustrations of a cross-sectional
view of an EUV mask formed according to the present invention.
FIG. 3 is an illustration of a cross-sectional view of an EUV mask of the present invention.
FIG. 4 is an illustration of a cross-sectional view of an apparatus for repairing
opaque defects with electron beam-induced chemical etch according to the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
In the following description, numerous details, such as specific materials, dimensions,
and processes, are set forth in order to provide a thorough understanding of the
present invention. However, one skilled in the art will realize that the invention
may be practiced without these particular details. In other instances, well-known
semiconductor equipment and processes have not been described in particular detail
so as to avoid obscuring the present invention.
A mask is used in lithography to print a desired pattern in photoresist on a
wafer.
Deep ultraviolet (DUV) lithography uses a transmissive mask for exposure with light
having a wavelength of 248 nm, 193 nm, or 157 nm. Extreme ultraviolet (EUV) lithography
uses a reflective mask for exposure since nearly all condensed materials are highly
absorbing in the EUV wavelength range of 11-15 nm.
The desired pattern is defined in a DUV mask by selectively removing portions
of an opaque Chrome layer to uncover a transparent quartz substrate. The desired
pattern is defined in an EUV mask by selectively removing portions of an absorber
layer to uncover a multilayer mirror on a substrate.
A DUV mask or an EUV mask is inspected for defects as part of the mask fabrication
process. The inspection is usually done with DUV light. A defect may appear clear
or opaque. A defect is considered critical if its size, shape, or location may
significantly affect the print fidelity and quality of the mask features in the
vicinity. A critical defect must be repaired or else the yield may be degraded
on the structure being fabricated with the mask. The present invention includes
an apparatus for and a method of repairing opaque defects on a DUV mask or an EUV
mask without damage to underlying layers.
Various embodiments of a method of fabricating and repairing an EUV mask
according to the present invention will be described. First, a substrate
1100
having a low coefficient of thermal expansion (CTE), a smooth surface, and a low
defect level is used as the starting material for an EUV mask of the present invention.
An embodiment is shown in FIG.
1(
a). The substrate
1100 may
be formed out of a glass-ceramic material with the desired properties.
Second, a multilayer (ML) mirror
1200 is formed over the substrate
1100 since an EUV mask operates on the principle of a distributed Bragg
reflector. An embodiment is shown in FIG.
1(
b). The ML mirror
1200
includes about 20-80 pairs of alternating layers of a high index of refraction
material
1210 and a low index of refraction material
1220. The thickness
uniformity should be better than 0.8% across the substrate
1100.
In one embodiment, the ML mirror
1200 includes 40 pairs of alternating
layers of a high index of refraction material
1210 and a low index of refraction
material
1220. The high index of refraction material
1210 may be
formed from about 2.8 nm thick Molybdenum while the low index of refraction material
1220 may be formed from about 4.1 nm thick Silicon. As needed, a capping
layer
1230, such as about 11.0 nm thick Silicon, may be formed over the
ML mirror
1200 to prevent oxidation of Molybdenum at the upper surface of
the ML mirror
1200 in an EUV mask. The ML mirror
1200 can achieve
a peak reflectivity of about 60-75% at the EUV central illumination wavelength
of about 13.4 nm.
Ion beam deposition (IBD) or direct current (DC) magnetron sputtering may be
used to form the ML mirror
1200 over the substrate
1100. IBD results
in less perturbation and fewer defects in the upper surface of the ML mirror
1200
because the deposition conditions may be optimized to smooth over a defect on the
substrate
1100. DC magnetron sputtering is more conformal, thus producing
better thickness uniformity, but any defect on the substrate
1100 will tend
to propagate up through the alternating layers to the upper surface of the ML mirror
1200.
Third, a buffer layer
1300 is formed over the upper surface of the
ML mirror
1200. An embodiment is shown in FIG.
1(
c). The buffer
layer
1300 may have a thickness of about 10-55 nm. The buffer layer
1300
may be formed from Silicon Dioxide, such as a low temperature oxide (LTO). A low
process temperature, typically less than about 150 degrees C., is desirable to
prevent interdiffusion of the alternating layers in the underlying ML mirror
1200.
Other materials, such as Silicon Oxynitride or Carbon, may be used to form the
buffer layer
1300. The buffer layer
1300 may be deposited by Radio
Frequency (RF) magnetron sputtering.
Fourth, an absorber layer
1400 is formed over the buffer layer
1300.
An embodiment is shown in FIG.
1(
d). The absorber layer
1400
may be formed from about 45-125 nm of a material that will attenuate EUV light,
remain stable during exposure to EUV light, and be compatible with the mask fabrication
process. The absorber layer
1400 may be deposited with DC magnetron sputtering.
Various metals, alloys, and ceramics may be used to form the absorber layer
1400. Metals include Aluminum, Chromium, Nickel, Tantalum, Titanium, and
Tungsten. Alloys include compounds of metals, such as Aluminum-Copper. Ceramics
include compounds of metals and nonmetals, such as borides, carbides, nitrides,
oxides, phosphides, silicides, and sulfides of metals. Examples include Nickel
Silicide, Tantalum Boride, Tantalum Germanium, Tantalum Nitride, Tantalum Silicide,
Tantalum Silicon Nitride, and Titanium Nitride.
The combination of absorber layer
1400, buffer layer
1300, ML mirror
1200, and substrate
1100 results in an EUV mask blank
1700.
An embodiment is shown in FIG.
1(
d). The EUV mask blank
1700
shown in FIG.
1(
d) may be further processed to produce an EUV mask
1800, an embodiment of which is shown in FIG.
2(
d).
First, an EUV mask blank
1700 is covered with a radiation-sensitive
layer, such as photoresist
1600. The photoresist
1600 has a thickness
of about 160-640 nm. A chemically-amplified resist (CAR) may be used. A desired
pattern is formed in the photoresist
1600 by selective exposure with sufficient
radiation of the appropriate wavelength, such as DUV light or electron beam, followed
by a wet or dry develop process. An embodiment is shown in FIG.
2(
a).
After developing the pattern in the photoresist
1600, the critical dimension
(CD) of the features is measured with an optical tool or a scanning electron microscope (SEM).
Reactive ion etch (RIE) may be used to transfer the pattern from the photoresist
1600 into the underlying absorber layer
1400. For example, an absorber
layer
1400 may be dry etched with a gas containing Chlorine, such as Cl
2
or BCl
3, or with a gas containing Fluorine, such as NF
3.
Argon may be used as a carrier gas. In some cases, Oxygen may be included. The
etch rate and the etch selectivity may be changed by modifying the configuration
of the reactor chamber and adjusting parameters such as power, pressure, substrate
temperature, and gas flowrate.
The buffer layer
1300 serves as an etch stop layer to help produce a good
etch profile in the overlying absorber layer
1400. Furthermore, the buffer
layer
1300 protects the underlying ML mirror
1200 from damage during
the etch of the overlying absorber layer
1400. The buffer layer
1300
also protects the underlying ML mirror
1200 from damage during any subsequent
repair to remove opaque defects in the absorber layer
1400.
After completing the etch, the photoresist
1600 is removed and the CD
of the features formed in the absorber layer
1400 is measured with an optical
tool or with a scanning electron microscope (SEM). Whenever appropriate, an interferometer
may be used to measure the phase of the light signals in addition to the amplitude.
Then the mask is inspected for defects with a microscope or an automated inspection
tool. The mask inspection tools may combine optical techniques with scanning of
the mask to acquire images. A laser producing UV/DUV light is usually used as the
source of illumination. Typical wavelengths include, but are not limited to, 488
nm, 365 nm, 266 nm, 257 nm,
248 nm, 198 nm, and 193 nm. A shorter wavelength
provides better resolution and may be a better predictor of the lithographic consequences
of the defects that are found on the mask.
Defect inspection is generally performed by comparing two nominally identical
patterns printed in different portions of a mask (die-to-die) or comparing a pattern
printed on the mask and the corresponding layout data for the pattern (die-to-database).
A defect may be found in the absorber layer
1400 after pattern transfer
from the photoresist
1600. The defect may appear as a clear defect
1710
or as an opaque defect
1720. An embodiment is shown in FIG. 2 (
b).
In a clear defect
1710, the absorber layer
1400 should be present,
but it is completely or partially missing. In an opaque defect
1720, the
absorber layer
1400 should be absent, but it is completely or partially present.
A focused ion beam (FIB) tool may be used to cover a clear defect
1710
with
an opaque material
1730, such as Carbon. A clear defect may also be repaired
by ion beam-induced metal deposition from organometallic precursor gases. For example,
Tungsten may be deposited from Tungsten Hexacarbonyl or W(CO)
6 gas.
A post-deposition trim with gas-assisted etch (GAE) may be performed to eliminate
any overspray and to achieve the desired post-repair size for the opaque material
1730. Bromine gas or Chlorine gas may be used in the GAE. The deposited
opaque material
1730 need not have the same thickness as the chrome on a
transmissive mask or the absorber layer
1400 on a reflective mask. The deposited
opaque material
1730 should be compatible with the chemicals used to dean
the mask.
The present invention envisions using electron beam-induced chemical etching
to repair an opaque defect
1720 on a DUV mask or an EUV mask. Electron beam-induced
chemical etching has high selectivity to underlying layers because it is essentially
chemical, unlike FIB or GAE, which always have a physical component due to the
ion bombardment. Unlike with the ion beam in FIB, an electron beam will not damage
underlying layers by ion implantation or by knock-on of atoms. An embodiment is
shown in FIG.
2(
c).
In an EUV mask, a buffer layer
1300 covers and protects the ML mirror
1200
from damage during repair of the overlying absorber layer
1400. The thickness
required for the buffer layer
1300 depends on the quantity of material that
will be removed by the repair process. Consequently, a high etch selectivity allows
the use of a thin buffer layer
1300 on an EUV mask. A thin buffer layer
1300 results in a lower overall absorber stack that reduces shadowing and
improves imaging. A thin buffer layer
1300 also reduces the chances of generating
printable soft defects during the removal of the buffer layer
1300 after
completion of repair.
The buffer layer
1300 will increase light absorption over the ML mirror
1200 when the EUV mask
1800 is used to expose photoresist on a wafer.
The result is a reduction in contrast that will slightly degrade CD control of
the features printed in the photoresist on a wafer. In order to prevent this degradation,
the buffer layer
1300 is removed wherever it is not covered by the absorber
layer
1400.
The overlying absorber layer
1400 and the underlying ML mirror
1200
must not be damaged when the exposed portions of the buffer layer
1300 are
removed. A buffer layer
1300 formed from Silicon Dioxide may be dry etched
with a gas containing Fluorine, such as CF
4 or C
5F
8.
In some cases, Oxygen and a carrier gas, such as Argon, may be included. Alternatively,
a thin buffer layer
1300 may be wet etched since any undercut of the absorber
layer
1400 would then be small. For example, a buffer layer
1300
formed from Silicon Dioxide may be etched with an aqueous solution of about 3-5%
hydrofluoric acid. A combination of dry etch and wet etch may be used if desired.
The result of the process described above is an EUV mask
1800 having a
reflective region
1750 and an anti-reflective, or dark, region
1760.
An embodiment is shown in FIG.
2(
d).
Another embodiment of the present invention is an EUV mask
2700 as
shown in FIG.
3. An EUV mask
2700 includes an absorber layer
2400,
a thin buffer layer
2300, an ML mirror
2200, and a substrate
2100.
The EUV mask
2700 has a first region
2750 and a second region
2760.
The first region
2750 is reflective because the ML mirror
2200 is
uncovered. The second region
2760 is antireflective, or dark, due to the
absorber layer
2400.
First, the EUV mask
2700 of the present invention includes a substrate
2100, such as a glass-ceramic material, that has a low coefficient of thermal
expansion (CTE), a low defect level, and a smooth surface.
Second, a multilayer (ML) mirror
2200 is disposed over the substrate
2100. The ML mirror
2200 has about 20-80 pairs of alternating layers
of a high index of refraction material
2210 and a low index of refraction
material
2220.
In one embodiment, the ML mirror
2200 includes 40 pairs of a high index
of refraction material
2210 and a low index of refraction material
2220.
The high index of refraction material
2210 may be about 2.8 nm thick Molybdenum
while the low index of refraction material
2220 may be about 4.1 nm thick
Silicon. The ML mirror
2200 has a peak reflectivity of about 60-75% at a
central illumination wavelength of about 13.4 nm.
Third, an ultrathin buffer layer
2300 is disposed over the ML mirror
2200. The ultrathin buffer layer
2300 is about 10-55 nm thick. The
ultrathin buffer layer
2300 protects the underlying ML mirror
2200
from any damage during the etch of the overlying absorber layer
2400. The
ultrathin buffer layer
2300 also protects the underlying ML mirror
2200
from damage during repair to remove opaque defects.
The ultrathin buffer layer
2300 may be Silicon Dioxide, such as a low
temperature oxide (LTO). Other materials, such as Silicon Oxynitride or Carbon
may also be used for the ultrathin buffer layer
2300.
Fourth, an absorber layer
2400 is disposed over the ultrathin buffer
layer
2300. The absorber layer
2400 may be about 45-125 nm of a material
that will attenuate EUV light, remain stable during exposure to EUV light, and
be compatible with the mask fabrication process.
The absorber layer
2400 may include one or more metals, alloys, and ceramics.
Metals include Aluminum, Chromium, Nickel, Niobium, Tantalum, Titanium, and Tungsten.
Alloys include compounds of metals, such as Aluminum-Copper. Ceramics are compounds
formed from metals and nonmetals, such as borides, carbides, nitrides, oxides,
or suicides of various metals. Examples include Nickel Silicide, Tantalum Boride,
Tantalum Germanium, Tantalum Nitride, Tantalum Silicide, Tantalum Silicon Nitride,
and Titanium Nitride.
The present invention further envisions an apparatus
400 to repair an
opaque defect
405 on a DUV or EUV mask
410, by using electron beam-induced
chemical etching. An embodiment is shown in FIG.
4.
In the apparatus
400 claimed in the present invention, a mask
410
to be repaired is mounted on a holder
420. The holder
420 is positioned
in a chamber
470 by a stage
430. The stage
430 can rotate,
tilt, and move in different directions, such as along the x-axis, y-axis, and z-axis.
An imaging system
440 is used to locate an opaque defect
405 on the
mask
410. The imaging system
440 may include an electron column.
A gas delivery system
450 dispenses one or more gases from reservoirs
towards
the opaque defect
405 on the substrate
410 in the chamber
470.
The gases may be fed through one or more openings, such as nozzles, into the chamber
470. The desired flowrates are maintained by adjusting flow control valves.
Critical parameters include nozzle dimensions, tilt angle from nozzle to
mask, angular dispersion of gas dispensed, and distance from the opening of the
nozzle opening to the surface of the mask. Typical values include, but are not
limited to, 100-300 microns (um) for nozzle diameter, 45-70 degrees (from vertical)
for nozzle tilt angle, 5-25 degrees for angular dispersion, and 50-150 um for distance
from the nozzle opening to the mask surface.
The gases may include reactant gases and carrier gases. The choice of reactant
gases depends on the materials to be etched. In one embodiment of the present invention,
the reactant gases adsorb to the opaque defect
405 and become dissociated.
Argon is an example of a carrier gas.
In a DUV transmissive mask
410, an opaque defect
405 may include
materials such as chrome, chrome oxide, chrome nitride, or chrome oxynitride. The
underlying layer may include quartz. An electron delivery system
460 may
be used to induce a reactant gas, such as chlorine (Cl
2) and oxygen
(O
2), to chemically etch the opaque defect
405 relative to the
underlying layer with a selectivity of 2:1 or more.
In an EUV reflective mask
410, an opaque defect
405 may include
absorber layer material such as Tantalum Nitride. The underlying layer may include
buffer layer material such as Silicon Dioxide. An electron delivery system
460
may be used to induce a reactant gas, such as Xenon Fluoride (XeF
2)
or Carbon Tetrafluoride (CF
4) or Fluorine (F
2), to chemically
etch the opaque defect
405 relative to the underlying layer with a selectivity
of 10:1 or more. Volatile byproducts, such as Tantalum Fluoride, may be removed
from the chamber
470 by a pumping system
480.
When an opaque defect
405 includes a Carbon-containing material, an electron
delivery system
460 may be used to induce a reactant gas, such as water
vapor (H
2O) or Oxygen (O
2), to chemically etch the opaque
defect
405 relative to the underlying layer with a selectivity of 10:1 or
more. For example, a Carbon etch may be used to repair an opaque defect
405
on an EUV mask
410 that has a conductive buffer layer containing Carbon.
A Carbon etch may also be used to repair an opaque defect
405 in a photoresist
pattern on a mask
410 to increase the patterning yield and to reduce rework.
Furthermore, a Carbon etch may be helpful in the more difficult repair that is
required after a mask
410 has gone through additional processing.
The electron delivery system
460 used to induce chemical etching may resemble
an electron column used to image a sample in a SEM except that the focusing and
scanning controls for the electron beam are more sophisticated. In particular,
critical parameters, such as beam current, pixel spacing, dwell time, scan rate,
refresh time, and retrace time, may be controlled by a computer to optimize etch
rate, etch geometry, etch uniformity, and surface roughness.
The electron delivery system
460 directs electrons towards the opaque
defect
405 on the mask
410 in the chamber
470. The electron
delivery system
460 may include a focusing system to provide a highly focused
electron beam. In one embodiment, highly focused means that the electron beam size
is smaller than the range of the secondary electrons. In another embodiment, highly
focused means that the electron beam size is smaller than about 30% of the size
of the smallest critical defect to be repaired. In general, an electron beam has
a typical tail diameter of about 5-125 nm.
The electron delivery system
460 uses a low acceleration voltage, such
as in the range of 0.3-3.0 keV, to limit the lateral spread of emitted electrons
at the surface of the mask
410. A low voltage also minimizes surface charging.
The emitted electrons include secondary electrons and backscattered electrons.
A chemical etch of an opaque defect
405 is induced when secondary electrons
interact with the reactant gas that is adsorbed and dissociated on the surface
of the mask
410. If desired, the secondary electron current may be monitored
to detect the etch endpoint.
In most cases, the electron beam-induced chemical etch is reaction-limited and
not mass transfer-limited. The chemical etching of the opaque defect
405
by the reactant gas produces volatile byproducts that dissociate from the mask
and may be removed from the chamber
470 holding the mask
410. A pumping
system
480 evacuates gases and volatile materials from the chamber
470,
thus creating a vacuum inside the chamber
470.
The electron beam-induced chemical etch rate of the opaque defect
405
depends on the partial pressure of the reactant gas and the current density of
the electron beam. The pressure in the chamber
470 may be about 0.001-0.200
milliTorr (mT) globally and about 0.500-10.000 mT locally over the opaque defect
405 being repaired on the mask
405. The beam current may be about
0.050-1.000 nanoAmperes (nA). The electron beam-induced chemical etch rate usually
depends on the yield of the secondary electrons. The etch rate is usually at a
maximum for an acceleration voltage of about 1.0 keV or less.
Many embodiments and numerous details have been set forth above in order to
provide a thorough understanding of the present invention. One skilled in the art
will appreciate that many of the features in one embodiment are equally applicable
to other embodiments. One skilled in the art will also appreciate the ability to
make various equivalent substitutions for those specific materials, processes,
dimensions, concentrations, etc. described herein. It is to be understood that
the detailed description of the present invention should be taken as illustrative
and not limiting, wherein the scope of the present invention should be determined
by the claims that follow.
Thus, we have described an apparatus for and a method of fabricating and repairing
a mask without damage.
*
