U.S. patent application number 10/604487 was filed with the patent office on 2005-01-27 for system and methods of altering a very small surface area.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Hamann, Hendrik F., Herschbein, Steven Brett, Marchman, Herschel Maclyn, Rue, Chad, Sievers, Michael Ray.
Application Number | 20050016954 10/604487 |
Document ID | / |
Family ID | 34079568 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050016954 |
Kind Code |
A1 |
Hamann, Hendrik F. ; et
al. |
January 27, 2005 |
SYSTEM AND METHODS OF ALTERING A VERY SMALL SURFACE AREA
Abstract
Very small scale altering of features of an existing pattern,
such as of an IC or photomask can be edited wherein a chemical
reactant and/or activating energy is localized to the site of the
target feature. In this manner, the alteration can be contained in
a highly localized area such that other portions of the pattern
remain substantially unaffected. The activating energy may be
delivered by far-field and/or near field techniques. In one
embodiment, the energy is converted into thermal energy at the site
by interaction with the apex of a probe where the apex is proximate
to the site. In another embodiment, the energy is converted to a
plasma by spaced electrodes at the apex of the probe in combination
with activating energy of at least two specifically selected
wavelengths. The method can be applied to the repair and/or
metrology of very small features of densely patterned substrates,
e.g., an integrated circuit, package, photomask, etc.
Inventors: |
Hamann, Hendrik F.;
(Yorktown Heights, NY) ; Herschbein, Steven Brett;
(Hopewell Junction, NY) ; Marchman, Herschel Maclyn;
(Poughquag, NY) ; Rue, Chad; (Poughkeepsie,
NY) ; Sievers, Michael Ray; (Poughkeepsie,
NY) |
Correspondence
Address: |
INTERNATIONAL BUSINESS MACHINES CORPORATION
DEPT. 18G
BLDG. 300-482
2070 ROUTE 52
HOPEWELL JUNCTION
NY
12533
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
New Orchard Road
Armonk
NY
|
Family ID: |
34079568 |
Appl. No.: |
10/604487 |
Filed: |
July 25, 2003 |
Current U.S.
Class: |
216/62 ;
430/5 |
Current CPC
Class: |
H01L 21/6708 20130101;
H01L 21/67069 20130101 |
Class at
Publication: |
216/062 |
International
Class: |
C23F 001/00 |
Claims
1. A method for altering a surface feature of an existing pattern
on a substrate, said method comprising (a) delivering a chemical to
a site proximate to a target feature to be altered, and (b)
providing activating energy at said site whereby a chemical
reaction and/or milling occurs, wherein said chemical delivery
and/or said providing of energy occurs only locally at said site
whereby said chemical reaction and/or milling occurs only locally
to said site, said reaction and/or milling resulting in alteration
of said feature.
2. The method of claim 1 wherein said chemical is delivered locally
to said site.
3. The method of claim 2 wherein said delivery is performed by
passing said chemical through a probe tip channel having an opening
placed proximate to said site.
4. The method of claim 2 wherein said delivery is performed by
placing a probe tip coated with said chemical proximate to said
site.
5. The method of claim 1 wherein said delivery is performed by
providing a fluid containing said chemical at said site.
6. The method of claim 1 wherein said activating energy is provided
by illuminating a probe tip proximate to said site.
7. The method of claim 6 wherein said probe comprises a non-metal
portion and a metal apex portion which causes localized scattering
of photons at said site resulting in near-field electromagnetic
field amplification.
8. The method of claim 7 wherein said apex is illuminated with an
energy source of wavelength at least about ten times greater than a
diameter of said apex.
9. The method of claim 6 wherein said probe tip comprises at least
two electrodes with a gap there between and said illumination
energy comprises coherent radiation at two wavelengths whereby
interaction between said electrodes and said illumination energy
causes formation of a plasma between said electrodes.
10. The method of claim 2 wherein said activation energy is
provided by directing far-field energy selected from the group
consisting of light, electron beam and ion beam.
11. The method of claim 1 wherein a second chemical is provided for
assisting in said reaction.
12. The method of claim 1 wherein said activation energy is
provided in the form of a beam and said reaction is locally
confined to an area narrower than a diffraction limit of said
beam.
13. The method of claim 5 wherein said chemical includes an
illumination sensitive material and said illumination sensitive
material is protected from said illuminating while being
delivered.
14. The method of claim 7 wherein said scattering results in the
imparting of thermal energy to said substrate at said site.
15. The method of claim 5 wherein said chemical is provided as an
ambient in a process chamber in which said substrate is placed.
16. The method of claim 5 wherein said chemical is provided as a
flow directed towards said site.
17. A system for altering a micron-scale or nanometer-scale surface
feature of an existing pattern on a substrate, said system
comprising: (a) a probe maneuverable to a site proximate to a
target feature to be altered, (b) a chemical source adapted to
provide delivery of a chemical to said site proximate to a target
feature to be altered, and (c) a energy source for providing
activating energy at said site, wherein said chemical source is
capable only of local chemical delivery and/or said energy source
is capable of providing of energy only locally at said site.
18. The system of claim 17 wherein said energy source is capable of
providing activation energy sufficient to cause a chemical reaction
and/or milling only locally to said site, said reaction and/or
milling resulting in alteration of said feature.
19. The system of claim 17 wherein said energy source is a source
of far-field energy selected from the group consisting of light,
electron beam and ion beam.
20. The system of claim 17 wherein said chemical source comprises a
channel in said probe for delivering said chemical.
21. The system of claim 17 wherein said chemical source comprise a
component from which at least a tip of said probe is made.
22. The system of claim 17 further comprising a source of a second
chemical for providing said second chemical at said site.
23. The system of claim 17 wherein said probe includes an opaque
coating such that said probe shields said chemical from said
activation energy while said chemical is being delivered to said
site.
24. The system of claim 17 wherein said probe comprises a
nonmetallic probe body and a metal-containing apex.
25. The system of claim 24 wherein said energy source is capable of
providing energy incident to said apex, and wherein said energy has
a wavelength at least about ten times greater than a diameter of
said apex wherein incidence of such energy causes localized
scattering and/or localized electromagnetic fields at said
site.
26. The system of claim 19 wherein source of activating energy
includes a far-field source comprising one or more wavelengths
selected from the range consisting of infrared to ultraviolet.
27. The system of claim 24 wherein said apex includes one or more
electrodes for coupling to one or more respective sources of
potential.
28. The system of claim 17 wherein said probe comprises an apex
including at least two open electrodes spaced by a gap, and said
source of activating energy is capable of providing coherent
radiation at two wavelengths whereby interaction between said
electrodes and said activating energy causes formation of a plasma
between said electrodes.
29. The system of claim 28 wherein said energy source includes a
laser and a light guide in or attached to said probe, said light
guide being adapted to guide light from said laser to said gap.
30. The system of claim 29 wherein said light guide is adapted to
guide a first wavelength of said coherent radiation, and said
energy source further includes an unguided beam adapted to
illuminate said gap with a second wavelength of said coherent
radiation.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The following applications (International Business Machines
Corporation) are related to the present application: U.S. patent
application Ser. No. 10/261,275, filed Sep. 30, 2002, titled "Tool
Having a Plurality of Electrodes and Corresponding Method of
Altering a Very Small Surface," and Attorney Docket No.
FIS920020170US1, titled "System and Method of Altering a Very Small
Surface Area By Multiple Channel Probe." The disclosures of these
applications are incorporated herein by reference.
BACKGROUND OF INVENTION
[0002] Current repair processes for integrated circuit (IC) chips
and lithographic reticles rely primarily on the use of focused
beams (ion, electron, and/or photons) to induce localized reactions
for etching or deposition of materials for when editing patterns.
Focused Ion Beam (FIB) tools have played a dominant role for most
repair applications as well as in failure analysis methods, due to
their superior spatial process confinement and reaction rates
(relative to scanning electron or photon beams). However, concerns
about energetic ion beam induced damage and contamination have
severely limited the applicability of FIB tools inside IC clean
rooms and lithographic mask production facilities. The more recent
use of non-legacy materials, such as copper metallization and low-K
dielectrics (polymers) in IC fabrication has also raised concerns
about the extendibility of present FIB technology for these
applications.
[0003] FIG. 1 illustrates such example, which is background to the
invention, but is not admitted to be prior art. As shown in FIG. 1,
a copper feature 10 of a substrate 20 lies under a plurality of
layers 12 of inter-level dielectric (ILD) material. Specifically,
the editing (i.e. cutting) of lower level metallization copper IC
features 10 by FIB tools has proved troublesome due to the tendency
of the copper milled by the tool to be redeposited on surfaces 14
of the entry hole 16 made by the tool (focused beam 15). Regions 11
where the copper remains or is redeposited are conductive and thus,
the desired degree of electrical isolation (i.e. the reason for
cutting the line) is not achieved. In addition, when ILD 12 is an
organic-based low-K polymer, it may become conductive in places 14
which are exposed to an energetic ion beam 15.
[0004] In addition, changes in the optical properties of
lithographic masks, known as staining, caused by gallium ions (the
source of ions in FIB tools is Ga+) and edge streaking
(river-bedding) are examples of problems being encountered with
FIB-based mask repair. In addition, there are no suitable beam
induced chemistries for complete volatilization of chrome (of which
opaque mask features are made) etch products. This forces one to
rely on mostly physical sputtering with the ion beam to edit chrome
mask features, which dramatically increases the amount (dose) of
gallium to the mask surface and hence staining (i.e. lower optical
transmission as well as phase error). Thus, a critical need exists
for a new tool and method for the working of micro-scale surfaces,
for example, for the repair of IC's and masks. At the same time,
the failure of existing in-line metrology techniques to provide
accurate three dimensional data for the development and control of
IC fabrication processes has highlighted the need for a tool
capable of sectioning a surface without causing damage or
contamination (Ga+ is a metal) to either the surface or to clean
room equipment and materials.
[0005] Scanning of focused laser beams has been used to induce
spatially localized chemical reactions to pattern various surfaces.
In such processing, chemicals needed for the reaction are activated
either directly by photolytic excitation, or indirectly through
conversion of photons into thermal energy. As shown in FIG. 2A, a
spot of light 22 is created at a desired site of a reaction by
focusing a beam 24 with conventional far-field optics. The spatial
extent of the reaction is confined by the size of the beam spot 22
on the surface. In many cases, pulsed laser beams can be used to
directly ablate material from the surface without any chemical
reactants. This occurs when the laser beam energy is focused to
within a small enough region spatially for achieving higher density
at the target surface and delivered within a very short time span
(i.e. pulsed), so that the material under such exposure conditions
will thermally evaporate. Selectivity is still achieved due to the
large difference in optical absorption and thermal properties
between chrome features and quartz mask substrate materials.
[0006] However, as shown in FIG. 2B, diffraction of the beam
through focusing mechanisms constrains the minimum dimension (focal
spot) 26 at which the beam spot may be formed. Patterns are created
on a surface by controlling the scanning of the focused laser beam
spot across the surface. While laser beam processing can support
reaction rates generally higher than that of FIB and electron beam,
the inability to spatially confine the reaction below the
diffraction limit of the beam poses a serious challenge to its use.
Another disadvantage of laser beam processing is the need to flood
the sample surface and possibly the entire process chamber with
gases needed to support the reaction. With the reaction-supporting
gases extending well beyond the desired reaction site, only
endothermic reactions can be confined, because only such reactions
do not spread beyond the energy source, i.e. the beam. Aberrations
and diffraction effects also limit the minimum spot sizes for
focused ion and electron beams, as well. A serious disadvantage
common to all existing beam techniques is the inability to confine
the energy vertically (i.e., along the axis of beam propagation) as
well as the inability to sense, in real-time, the actual surface
height during the modification process. This capability is very
important when editing three-dimensional structures, such as
phase-shifting mask features.
[0007] Near-field scanning optical microscopy (NSOM) is a technique
which permits imaging at a spatial resolution below the diffraction
limit of the illuminating source. This technique involves imaging
with evanescent optical modes, either by intensity collection, or
by illumination through a sub-wavelength aperture placed at the
apex of a scanned light guide or probe. In this technique, the apex
of the light guide or optical probe (acting as source, collector or
both) is brought very near the sample surface (typically using SPM
instrumentation) to create a localized spot of light. Super
resolution optical imaging is achieved beyond diffraction limits,
because lenses are never used to focus the light.
[0008] For inducing localized chemical processes with near-field
optical photons, a scenario involves illumination by an uncoated
light guiding probe. Light 39 is guided inside the probe 28 by
total internal reflection until it reaches the tapered region, and
escapes 33, as shown in FIG. 3A, then impinging as a spot 34 on the
surface. Chemicals adsorbed on the surface are then activated by
the light, which escapes from the tapered waveguide region. This is
similar to the light distribution from an uncoated optical fiber
probe in shear-force microscopy. Although simple, this approach
would result in fairly poor lateral resolution (at least hundreds
of nanometers).
[0009] Alternatively, one or more chemicals needed for a reaction
can be supplied through a hollow channel of a light guiding probe,
to spatially localize the reaction to the extent the chemical(s) is
distributed from the probe, as in a localized chemical delivery
probe technique. As shown in FIG. 3B, an optically opaque coating
36 can be applied to sidewalls of the light guiding probe 29 to
prevent light 37 from escaping before reaching an aperture 32
contained at the apex. The aperture can be made very small,
diameters of 20 nm having been reported. When the aperture is much
smaller than the wavelength of propagation of the light guide, only
evanescent near-field optical (NFO) modes 35 pass through the
aperture.
[0010] To promote a localized reaction on a surface, chemicals at
the location are exposed by near-field optical (hereinafter "NFO")
light emanating from the aperture. Since the NFO light spatially
confines the reaction in some measure, chemicals can be supplied as
an ambient, nozzle injected for surface adsorption, or locally
through a hollow light guiding localized chemical delivery probe
(LCDP). While NFO light guiding probes appear to spatially confine
photochemical processes better than the other described techniques,
their feasibility for repair and metrology is still problematic for
many reasons, primarily: (a) it is difficult to fabricate
consistently high quality nanometer scale NFO probe apertures; (b)
maximum intensity output is limited to aperture size; (c) apertures
are more susceptible to thermal and mechanical damage than solid
tips; (d) optical absorption by the metal coating generates heat
which can delocalize chemical reactions; (e) the conical shape of
the probe limits the aspect ratio of the sample topography that can
be scanned; and (f) resolution for imaging and processing in the
lateral dimension is limited (e.g., 20 nm).
[0011] Thus, there is a need for improved methods and tools for
altering features at small scale (e.g., .mu.m or nm scale) while
avoiding undesired side effects such as contamination, undesired
byproduct re-deposition, undesired thermal ablation and/or
undesired mechanical ablation. There is also a need for tools
capable of such process which are highly maneuverable, relatively
inexpensive and wear resistant. There is also a need for real-time
monitoring of 3D surface topography for end-pointing
etch/deposition modification processes.
SUMMARY OF INVENTION
[0012] The invention provides methods and systems for altering a
features on a substrate (especially micron-scale or nanometer-scale
features, e.g., such as found in an integrated circuit or
photomask). The methods of the invention are characterized by
highly localized delivery of a chemical and/or activating energy to
the site of the target feature whereby the chemical reaction and/or
mechanical milling associated with the alteration is substantially
confined to the site. The systems of the invention are
characterized by the presence of a chemical source and an energy
source wherein at least one of the two is capable of highly
localized delivery.
[0013] In one aspect, the invention encompasses a method for
altering a surface feature of an existing pattern on a substrate,
the method comprising: (a) delivering a chemical to a site
proximate to a target feature to be altered, and (b) providing
activating energy at the site whereby a chemical reaction and/or
milling occurs, wherein the chemical delivery and/or the providing
of energy occurs only locally at the site whereby the chemical
reaction and/or milling occurs only locally to the site, the
reaction and/or milling resulting in alteration of the feature.
Preferred methods of local chemical delivery are (i) by passing the
chemical through a probe tip channel having an opening placed
proximate to the site or (ii) by placing a probe tip coated with
the chemical proximate to the site. A preferred method of
non-localized chemical delivery is by providing a fluid containing
the chemical at the site (e.g., as a fluid flow or as part of the
environment in the tool.
[0014] Preferred methods of delivering activating energy is
provided by illuminating a probe tip proximate to the site. In one
embodiment, the probe comprises a non-metal portion and a metal
apex portion which causes localized scattering of photons at the
site. In another embodiment, the probe tip comprises at least two
electrodes with a gap there between and the activating energy
comprises coherent radiation at two wavelengths whereby interaction
between the electrodes and activating energy causes formation of a
plasma between the electrodes. The method activation energy is
preferably provided by directing far-field energy selected from the
group consisting of light, electron beam and ion beam.
[0015] In another aspect, the invention encompasses a system for
altering a surface feature of an existing pattern on a substrate,
the system comprising: (a) a probe maneuverable to a site proximate
to a target feature to be altered,
[0016] (b) a chemical source being adapted to provide delivery of a
chemical to the site proximate to a target feature to be altered,
and (c) an energy source for providing activating energy at said
site, wherein the chemical source is capable only of local chemical
delivery and/or the energy source is capable of providing of energy
only locally at the site. The energy source is preferably a source
of far-field energy selected from the group consisting of light,
electron beam and ion beam. The chemical source preferably
comprises a channel in the probe for delivering the chemical, or a
component from which at least a tip of the probe is made. In one
embodiment, the probe comprises a non-metal portion and a metal
apex portion which causes localized scattering of photons at the
site. In another embodiment, the probe tip comprises at least two
electrodes with a gap there between and the activating energy
comprises coherent radiation at two wavelengths whereby interaction
between the electrodes and activating energy causes formation of a
plasma between the electrodes.
[0017] The site of the target feature is preferably to dimensions
of about 10 .mu.m in diameter to as small as 0.01 .mu.m or smaller.
The system and method are preferably applied to the repair and/or
metrology of very small features of densely patterned substrates,
e.g., an integrated circuit, package, reticle or photomask.
[0018] These and other aspects of the invention are described in
further detail below.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 illustrates a background method of etching a
substrate using a focused ion beam (FIB) tool.
[0020] FIGS. 2A, 2B illustrate optical diffraction limitations on
resolution for photo-chemical processing.
[0021] FIGS. 3A and 3B illustrate background methods for altering a
substrate using energy guiding probes.
[0022] FIGS. 4A, 4B and 5 illustrate systems and methods according
to a first group of embodiments of the invention.
[0023] FIGS. 6 and 7 illustrate systems and methods according to a
second group of embodiments of the invention.
[0024] FIGS. 8A and 8B graphically illustrate principles of the
invention to facilitate local generation of a micro-plasma at the
apex of a probe by mixing of light optical wavelengths.
[0025] FIGS. 9-10C illustrate embodiments of probes used to
generate micro-plasma.
[0026] FIG. 10D illustrates an embodiment including an array of
micro-plasma generated probes.
[0027] FIG. 11 illustrates a preferred embodiment of a system
including a probe for altering a very small surface area on a
substrate.
DETAILED DESCRIPTION
[0028] The invention provides methods and systems for altering a
features on a substrate (especially micron-scale or nanometer-scale
features, e.g., such as found in an integrated circuit or
photomask). The methods of the invention are characterized by
highly localized delivery of a chemical and/or activating energy to
the site of the target feature whereby the chemical reaction and/or
mechanical milling associated with the alteration is substantially
confined to the site. The systems of the invention are
characterized by the presence of a chemical source and an energy
source wherein at least one of the two is capable of highly
localized delivery.
[0029] A method of activating reactions to alter a very small
surface (as by milling, etching and/or depositing) with assistance
of far-field illumination will now be described. As shown in FIG.
4A, in a first preferred embodiment, far-field illumination 40 is
supplied to a desired reaction site 42 on a surface of a substrate
44 (e.g., IC, component, package, photomask, reticle, etc.). Also
supplied thereto is one or more chemicals 46 (gas, liquid, or both)
to assist the reaction from an output aperture 48 of a localized
chemical delivery probe (LCDP) 50. One or more other chemicals 52
for supporting or assisting the reaction may also be supplied as an
ambient or through directed flow to the desired reaction site. A
chemical 46 is provided to the reaction site 42 through a channel
50 in such probe, and occupies only a very limited area including
the desired reaction site. Far-field illumination 40 is then
supplied to promote creation of a reactive species. Etching or
deposition on the surface is then promoted by the induced reaction.
The reaction is spatially confined because the LCDP probe spatially
limits the distribution of the reaction-supporting chemical.
Because the reaction is spatially confined by the extent of
chemical distribution, the extent of the far-field illumination may
be broader than the extent of chemical distribution.
[0030] In a further preferred embodiment, the method of the
invention may be used to support deposition of a light sensitive
polymer to the reaction site 42. In such case, an opaque coating 54
is preferably applied to the sidewall of the probe 50 so that a
polymer dispensed to the reaction site 42 through probe 50 does not
begin curing prior to exiting aperture 48.
[0031] In another preferred embodiment, as illustrated in FIG. 4B,
a solid probe LCDP having a tip 60 is used to provide highly
localized delivery of a chemical to assist in a reaction to a site
proximate to the target feature. Such solid probe LCDP can be
fabricated from a variety of materials (e.g., from one or more
metals, silicon, glass, a polymer, etc.) such as needed for the
particular application. A chemical for assisting in the reaction
may be provided as a component material of at least a tip 60 of the
solid probe, or alternatively, carried in liquid phase or solid
phase form as a coating 62 applied to tip 60. Solid coatings 62 may
be applied to the tip 60 by sputtering or evaporative deposition,
or other suitable technique. The coating 62 may include a chemical
which, when activated, provides a reactive species. Alternatively,
or in addition thereto, a chemical of the coating 62 may be a
catalyst for the desired reaction. When the coating 62 supplies
only a catalyst, a second chemical is preferably distributed to the
site in a less localized manner, e.g., as by chemical ambient or as
a generalized flow directed toward the surface. Preferably, the
highly localized delivery of such chemical spatially confines the
reaction to dimensions smaller than the diffraction limit of the
activating energy source.
[0032] If desired, the chemical may be carried by tip 60 by dipping
the tip 60 into a source of the chemical, and then carrying the
wetted tip 60 to the site proximate to the target feature where
activation energy is present. In another variation, a solid probe
having a wet liquid chemical layer on the tip 60 slowly releases
the chemical to the surface of the tip, as by the flow of a small
quantity of a liquid chemical from a reservoir (not shown) above
the apex slowly down to the apex in a quantity which spatially
confines the reaction.
[0033] The activating energy may act directly and/or indirectly (by
causing surface heating at the target site) to activate one or more
chemicals to support or assist in the desired reaction. Direct
activation provides better spatial localization and/or control,
while surface heating may permit a higher reaction rate. In a
preferred embodiment of the invention, tuning of reaction rate vs.
confinement may be possible through adjustment of activating energy
source properties, e.g., by selecting the focusing and/or intensity
properties of the activating energy source (e.g., far-field
illumination) to fit the need at hand.
[0034] FIG. 5 illustrates a system for repair/editing a surface of
a feature of a pattern on a substrate. A substrate 510 containing
the feature to be edited rests on a movable stage 512 for initial
coarse positioning of the substrate 510 and optical navigation
under a high-NA (numerical aperture) objective lens microscope 514
to surface 520. High NA optical microscope viewing/imaging allows
one to see where the tip 516 of the probe tool 518 is relative to
the feature to be edited on the substrate, even if the feature to
be edited is below surface 520 (e.g., when the substrate includes
one or more optically transparent layers above the feature of
interest). The separation between the tip 516 and surface 520 is
then actively regulated via surface force feedback (from transducer
522) and control electronics 524. In a preferred embodiment, a
reservoir source of chemical 528 is coupled through one or more
ducts 530 for supplying the fluid by the probe tool tip 516 to the
surface 520. Preferably, the duct(s) 530 provide chemical to a
channel of probe tool 518 such that the location of chemical
delivery to the substrate 510 is controlled in connection with the
above-described method for positioning the tip 516 proximate to the
site of the target feature.
[0035] In a preferred embodiment the tip 516 may include
transparent guiding means 540 coupled to a source 550 of activating
energy (e.g., far-field illumination) to the site at surface 520.
Alternatively, far-field illumination may be provided externally to
the body of the probe 518 by an illuminating source 560, outputting
a focused beam of light, electron beam or ion beam to the site at
surface 520.
[0036] In a preferred embodiment, a system may be adapted for a
particular application, such as the repair of a copper feature on
an IC, which may be buried beneath one or more layers of
inter-level dielectric (ILD). In such case, the system may include
multiple probe tools, e.g., a first probe tool having a tip adapted
to etching the ILD above the copper feature, and a second probe
tool having a tip adapted to editing the copper feature. In such
case, the ILD can be selectively etched out, leaving existing metal
patterns, by the first probe tool in which the reaction may be
promoted over a somewhat larger area of the IC (e.g., 5 to 50 times
larger diameter) than the area in which the second probe tool
subsequently edits the copper feature. When the second probe tool
edits the existing copper feature, any copper redeposited thereby
(as a byproduct of the editing process) is distributed in very
small amounts over a large area. Consequently, any redeposited
copper is much less likely to form deposits which are attached and
continuous, such as could cause conductive shorting of exposed
metal patterns.
[0037] In another preferred embodiment, a system as in FIG. 5 may
be used to repair of a transmissive defect in a photomask (a
feature of a mask which shifts the phase of the light transmitted
therethrough and/or attenuates the light). Such defects occur in
the clear (light transmissive) portions of the mask, rather than in
opaque features, e.g. the chrome patterns of a mask. A system as
shown in FIG. 5 is particularly adapted to the repair of
transmissive defects in masks because the reaction used in the
repair can be spatially confined by the extent of chemical
distribution provided by the probe 518 where probe 518 is an LCDP.
Thus, the highly localized chemical delivery limits the repair to
only the desired location and depth.
[0038] In a second group of embodiments, activating energy is
introduced to the site of interest, by far-field illumination onto
the apex of a probe, where the apex has properties that stimulate
near-field scattering to produce highly localized energy at the
reaction site. Far-field illumination that is not scattered by the
near-field enhancement effect of the probe tip apex, may
nevertheless assist in the reaction by imparting thermal energy to
the reaction site, such as may assist in promoting the rate of the
reaction and the removal of subsequent products.
[0039] FIGS. 6 and 7 illustrate embodiments using near field
scattering. Polarized light 610 from a far-field source (e.g., a
laser), external to the probe body 630 is focused onto a metal
scattering object 620 on the apex of a probe 630 in close proximity
to a reaction site 640 on a surface of a substrate 650. Such
far-field illumination preferably includes one or more wavelengths
selected from range consisting of the infrared to the ultraviolet.
Enhancement of the near-field energy results when the diameter of
the metallic scattering object 620 is made smaller than one tenth
of the wavelength of the far-field illuminating source 610. Further
enhancement of the field can be achieved if a material
discontinuity is introduced at the apex, such as when the
scattering object 620 is metallic and body 630 of the probe is a
nonconductor (e.g., glass) or semiconductor (e.g., silicon). Thus,
far-field illumination onto the metal scattering object 620 in
close proximity to the reaction site 640 invokes highly localized
enhancement of the electromagnetic field 660. The incident
far-field illumination 610 also provides a background spot of
far-field intensity 670 around the highly localized enhanced
near-field 660 region. The near field scattering preferably acts to
perturb the energy level at a very specific point above that which
is required for the chemical process to begin. The chemical (gas,
liquid, or both) 615 can be introduced as an ambient, directed
towards the reaction site 660 by nozzles onto the surface, or
through a hollow channel of the probe body.
[0040] Examples of hollow LCDP probes and solid, chemical-coated
LCDP probes are shown in FIGS. 7A and 7B, respectively. In such
probes, a chemical for promoting the reaction is delivered, in a
highly localized manner, to the reaction site 720 either through a
channel 730 inside the probe, or as a solid phase chemical or
liquid phase chemical carried as a coating 722 on the surface of a
solid probe. A solid LCDP probe, not having an interior chemical
channel, can be fabricated from a variety of materials (e.g.,
metals, silicon, glass, a polymer, etc.) as needed for the
particular application.
[0041] The metal electrode 710 of the probe shown in FIG. 7A and
electrodes 712, 714 of the probe shown in FIG. 7B at the LCDP apex
region act as apertureless near-field optical scattering objects
with which to enhance the near field energy. As illustrated in FIG.
7B, further enhancement of the near field energy may be possible if
the electrodes 712, 714 of the probe, are closely spaced to form a
dipole and placed in close proximity to the desired reaction site
720. If desired, when deposition or etching of large areas is
desired, one can increase the background energy level of the
far-field illumination 770 above the reaction threshold to
essentially perform laser beam based processing.
[0042] A third group of embodiments of the invention employ
localized plasma generation as show in FIGS. 8A and 8B. In FIG. 8A,
a micro-plasma is generated by the mixing of two different
wavelengths (i.e., two different frequencies) of coherent radiation
(e.g., laser light) at the apex of a probe in close proximity to a
highly localized site of interest 820. A plasma can be sustained
when an inert gas and/or a reactant is present. Reactive species
can be produced locally when a chemical (gas, liquid or both) is
provided to the surface of the sample, either by local distribution
to the probe apex or in the ambient. Proximity of the plasma source
810 to the sample surface is then determined by control of the
probe position. Due to the probe having gapped electrodes which
establish and control the position of the plasma, the plasma is
established at the probe apex 816 regardless of the probe's
proximity to the sample. If desired, a DC bias can be applied to
the substrate in order to accelerate the generated reactive species
towards the substrate surface.
[0043] Open electrodes (not shown in FIG. 8A or 8B) are located in
the apex 816 of the probe 818. The electrodes generate a plasma
when coherent radiation of at least two different frequencies is
provided thereto and a fluid (e.g. inert gas and/or reactant) is
present. The electrode gap has a nonlinear, exponential current
transfer function, not unlike that of a forward-biased
semiconductor diode. In other words, the output current of the
gapped electrodes is an exponential function of the voltage which
is input thereto. When coherent radiation at two different
frequencies is provided to the gapped electrodes, the two wave
functions are multiplied together, analogous to the frequency
mixing which occurs in a tuner of a radio receiver. The mixing
process results in output at two dominant frequencies: one
frequency at the sum of the two different input frequencies, and a
second one being at the difference between the two different input
frequencies. It is the second, difference frequency, obtained by
the exponential transfer characteristic of the gapped electrodes
that provides an oscillating electric field for generating a plasma
at apex 816 of probe 818. Tuning the difference between the
radiation frequencies can produce radio and/or microwave radiation,
such frequencies being preferred for plasma processing. The
RF/microwave radiation is then used to ionize various gas species
to create a plasma. Localization to a confined micro-plasma volume
at the probe apex is accomplished by choice of tip electrode
geometry. Preferably, the micro-plasma volume is not quite as wide
as the separation between the electrodes in the probe apex, due to
sheath regions.
[0044] Referring to FIG. 8B, a desired density of electron current
830 is established in close proximity to the reaction site on a
surface of the substrate 835 by irradiating the probe apex with two
different frequencies of coherent radiation 831, 832 (e.g. laser,
maser, or coherent radio frequency). Molecules of an inert gas or
reactant gas are introduced to the volume surrounding and including
the probe apex (not shown). When the gas provided is an inert gas,
e.g. argon, the highly localized plasma 834 can be used to
mechanically mill a very small surface area in close proximity to
the probe. When the gas provided is a reactant, the highly
localized plasma confines the desired reaction to the region of the
substrate in close proximity thereto, due to the short lifetime of
the reactive species.
[0045] A first plasma probe of the third group of embodiments is
illustrated in FIG. 9A. Tip 900 of the probe has a diameter on the
order of 1 mm or less, and includes a first electrode 910 and a
second electrode 920, which are open, i.e., not in conductive con
tact with each other or any other conductor at the apex 930. A
insulator 940 separates the first electrode 910 from the second
electrode 920. In this embodiment, first and second electrodes 910,
920 are coaxial, first electrode 910 having a smaller diameter and
arranged concentrically inside second electrode 920. First and
second electrodes 910, 920 have a gap between them which is
preferably about 3 microns to as small as 0.01 microns or less.
This spatial arrangement produces an electron current which is
radially symmetric. At apex 930, first electrode 910 extends beyond
second electrode 920. This arrangement produces an electric field
having lines of electric flux extending into the volume near apex
930 outside of tip 900.
[0046] FIG. 9B illustrates a variation of this embodiment in which
first electrode 911 at apex 932 is recessed relative to second
electrode 921. In this variation, more of the lines of electric
flux remain within cavity 934 within tip 901, and less remain
outside of tip 901. First and second electrodes 911, 921 are
configured in such manner that lines of the electric flux are
oriented in generally lateral direction (i.e., not at a high angle
thereto) thereby assisting vertical confinement of the reaction.
Preferably, apex 932 is coated with one or more protective layers
to prevent damage to tip 901 if particularly aggressive chemical
processes are to be induced.
[0047] FIG. 9C illustrates a further embodiment of a plasma probe.
In this embodiment, the tip 950, of diameter on the order of 1 mm
or less, has two parallel electrodes 952 and 954, respectively. As
in the previous embodiment, electrodes 952 and 954 are open, that
is, not in conductive contact with each other or any other
conductor at apex 956. Insulative material 957 helps mechanically
support electrodes 952, 954 while insulating them from each other
and unwanted contact with an external conductor. First and second
electrodes 952, 954 have a gap between them preferably similar to
the gap for the first plasma probe described above.
[0048] FIG. 9D illustrates another plasma probe embodiment having a
tip 960 of diameter on the order of 1 mm or less in which first and
second electrodes 962, 964 are arranged in parallel, but also
arranged in arc fashion over an underlying insulator 966 of tip
960. The gap between first and second electrodes 962, 964 is
preferably similar to the gap for the first plasma probe described
above. Fabrication of tip 960 may be simplified. For example, an
insulator 966 can be coated with a conductive film, and the
conductive film then etched in two lines extending down tip 960 to
apex 968 form two open electrodes 962, 964.
[0049] FIG. 10A illustrates yet another probe embodiment having a
tip 1000 which includes not only first and second open electrodes
1010, 1020, but also one or more channels 1030 for delivering a
fluid or gas to the apex 1002. An insulator 1004 separates the open
electrodes 1010, 1020 from each other, while also helping to
mechanically support them and hold them in relation to each other.
The channel(s) 1030 delivers a fluid reactant to apex 1002. The
fluid which may contain one or more chemicals helpful in assisting
the reaction or controlling it.
[0050] FIG. 10B illustrates another embodiment in which the center
electrode has tip 1040 and an open volume 1050 which are recessed
within outer electrode 1010.
[0051] As an alternative to delivering a reactant chemical via a
channel 1030 of the probe tip 1000, tip 1000 may form a solid type
LCDP probe, including a solid chemical or chemical coating 1035 for
assisting in the reaction.
[0052] In another embodiment (FIG. 10C), a plurality of tools,
constructed according to the third group of embodiments, are
arranged in an array 1060. The array may be brought into close
proximity to a substrate surface 1062, such that a larger area of
the substrate can be modified (e.g., repaired) simultaneously. For
providing the two different coherent radiation frequencies, two
different narrowband sources may be used (e.g., lasers).
Alternatively, a single source arranged in an interferometric
configuration may be used to provide coherent radiation
simultaneously at two different frequencies.
[0053] Possible configurations for providing the coherent radiation
to the gapped electrodes include: (i) laser light from uncoated
fiber/capillary core, (ii) focused spot from a far-field objective
lens, (iii) combined optical fiber and objective lens; and (iv)
near-field aperture of a coated, light guiding probe.
[0054] A plasma is established and sustained between electrodes at
the probe apex while the fluid (inert or chemical reactant) is
introduced and activated. Mechanical milling, etching and/or
deposition then occurs if the probe is brought into sufficient
proximity of the target surface. Protective coatings can be added
near the tip of the probe to protect the probe body from the
particular chemical process induced. The farthest protruding
electrode is preferably grounded, so that incidental contact with
the substrate will not cause electrical shorting on conductive
surface regions. In some instances, however, it may be desirable to
use shorting to terminate the process on conductive features. The
electrodes are preferably configured such that the current density
only has lateral components, therefore achieving extreme vertical
confinement (i.e., along the probe axis direction). A small enough
electrode separations, tunneling currents (instead of field
emission) can be used for inducing plasmas. Utilization of
tunneling currents further improves spatial confinement of the
chemical reaction in three dimensions.
[0055] The probes of the invention can be moved into close
proximity to the site proximate to the target feature using
apparatus that is available currently for the positioning of a
scanned probe microscope (SPM).
[0056] FIG. 11 illustrates a probe of the third group of
embodiments in a system for controlling movement thereof in close
proximity to a surface to be worked. A substrate 1110 rests on a
movable stage 1112 for initial coarse positioning of the substrate
1110 and optical navigation under a high-NA (numerical aperture)
objective lens microscope 1114 to the surface 1120. High-NA optical
microscope viewing/imaging allows one to see where tip 1116 is
relative to the feature of interest on the substrate, even if the
feature of interest is below top surface 1120 (cases when the
substrate includes one or more optically transparent layers above
the feature of interest). The separation between tip 1116 and
surface 1120 is then actively regulated via surface force feedback
(e.g., from transducer 1122) and control electronics 1124. Tip 1116
preferably includes a transparent guiding means 1140 coupled to a
source 1150 to transmit one or both of the coherent radiation
frequencies (e.g., laser beam) to probe apex 1116 for generating
the micro-plasma. Alternatively, one or both of the frequencies of
coherent radiation may be provided externally to the body of probe
1118 (e.g., by an illuminating source 1160) using a focused laser
beam, maser beam, beamed radio frequency, electron beam, ion beam,
etc. If desired, a biasing voltage may be applied to substrate 1110
by source 1170 for the purpose of accelerating ions from the plasma
to surface 1120.
[0057] In a preferred embodiment, a reservoir source of fluid 1128
is coupled through one or more ducts 1130 for supplying the fluid
to the surface to be worked on the substrate 1110. Preferably the
duct(s) 1130 provide fluid into a channel of micro-tool 1118 such
that the location of fluid delivery to substrate 1110 is controlled
in connection with the above-described method for positioning tip
1116 proximate to surface 1120. Alternatively, a chemical for
promoting a reaction can be supplied to the substrate as a solid
component or coating of a solid LCDP type probe 1118, or supplied
to surface 1120 as an ambient, or by flow directed towards the
desired reaction site.
[0058] If it is desired to induce mechanical milling, preferably a
non-reactive gas (e.g., not reactive with the surface to be
treated) can be supplied to surface 1120 and ionized locally by
probe 1118. The choice of non-reactive gas may depend on the
substrate composition; for example, when an oxide layer is to be
processed, nitrogen and oxygen can be considered suitable
non-reactive gases for such purpose. Generally, nitrogen, helium or
argon are preferred gases.
[0059] Mechanical milling may be performed with or without
assistance of a concurrent chemical reaction involving the surface
1120. For example, a highly localized reactive ion beam etch
process can be performed, spatially confined by the plasma
generated by probe 1118, when both a chemically reactive species
and an inert gas are present. Anisotropy and reaction rate can be
tuned by adjusting the relative pressures of the chemical reactant
and the inert gas, as well as the biasing voltage 1170 applied to
substrate 1110.
[0060] It should be understood that the probes and systems of all
three groups of embodiments can generally be used to perform the
method of the invention. In a preferred implementation of the
methods of the invention using probes from the third group of
embodiments, removal of reaction products can also be mechanically
assisted by the tool, either by intermittent contact of the tip
with the substrate or by electrostatic force exerted between tip
and sample surface. Doing so increases the rate and anisotropy of
the etch in a similar fashion to the mechanical sputter mill
component of FIB GAE processes.
* * * * *