U.S. patent application number 09/759794 was filed with the patent office on 2001-07-05 for method for patterning thin films.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Florczak, Jeffrey M., O'Brien, Dennis P., Smithson, Robert L. W..
Application Number | 20010006766 09/759794 |
Document ID | / |
Family ID | 22869210 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006766 |
Kind Code |
A1 |
O'Brien, Dennis P. ; et
al. |
July 5, 2001 |
Method for patterning thin films
Abstract
Patterned articles, such as RFID antenna, are made by
subablation, a process comprising the steps of: A. providing a
substrate having a coating, such as a metal or metal oxide, and an
interface comprising the thin region where the coating and the
substrate are closest to each other; B. exposing at least one part
of the total area of the coating to a flux of electromagnetic
energy, Such as a focused excimer laser beam, sufficient to disrupt
the interface but insufficient to ablate the coating, and C.
removing the parts of the coating in registry with the portion of
the interface area that was disrupted, by means such as ultrasonic
agitation. The process has advantages over photo-resist processes
in that there is no residual chemical resist left on the product
and no undercutting of the pattern or image. It has advantages over
laser ablation processes in that higher throughput is possible at
the same energy level and there is no microscopic debris left on
the product surface.
Inventors: |
O'Brien, Dennis P.;
(Maplewood, MN) ; Florczak, Jeffrey M.;
(Maplewood, MN) ; Smithson, Robert L. W.;
(Minneapolis, MN) |
Correspondence
Address: |
Office of Intellectual Property Counsel
3M Innovative Properties Company
PO BOx 33427
St. Paul
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
22869210 |
Appl. No.: |
09/759794 |
Filed: |
January 12, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09759794 |
Jan 12, 2001 |
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09231428 |
Jan 14, 1999 |
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6203952 |
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Current U.S.
Class: |
430/325 ; 430/17;
430/9; 430/945 |
Current CPC
Class: |
G02B 19/0095 20130101;
G02B 19/0014 20130101; H05K 3/027 20130101; G03F 7/3014 20130101;
G02B 19/0052 20130101; G02B 27/0911 20130101; H01Q 7/00 20130101;
G02B 19/009 20130101; H01Q 1/2225 20130101; G03F 1/68 20130101;
G02B 27/09 20130101; G03F 7/34 20130101; B41M 5/262 20130101; G02B
27/0966 20130101; G03F 7/30 20130101 |
Class at
Publication: |
430/325 ; 430/9;
430/17; 430/945 |
International
Class: |
G03C 003/00; G03C
005/00 |
Claims
What is claimed is:
1. A method of making an imaged surface comprising: A. providing a
substrate having a coating and an interface comprising the region
where the coating and the substrate are closest to each other; B.
exposing at least one part of the total area of the coating to a
flux of electromagnetic energy sufficient to disrupt the interface
but insufficient to ablate the coating, and C. removing tie parts
of the coating in registry with the portions of the interface area
that was disrupted.
2. The method of claim 1 in which the substrate is polymeric.
3. The method of claim 2 in which the substrate is selected from
the group consisting of polyesters, polycarbonates, polyethylene,
polyamides, polyvinylchloride, polystyrene, polypropylene, and
polyimides.
4. The method of claim 1 in which the electromagnetic energy is
selected from the group consisting of light from a flash lamp and
laser radiation.
5. The method of claim 4 in which the electromagnetic energy is
laser radiation which is shaped and focused onto the coating
surface and has a fluence of between 30 and 99 percent of the
ablation threshold fluence.
6. The method of claim 5 in which the laser radiation is shaped to
a beam with an approximately rectangular cross section.
7. The method of claim 1 in which the adhesive force between the
coating and the substrate is between about 40 and 700 g/cm.
8. The method of claim 1 in which step B comprises exposing at
least part of the area of the substrate to electromagnetic
radiation in an arrangement in which there is a mask between the
substrate and the source of the electromagnetic radiation, the
distance between the mask and the substrate being referred to as a
path.
9. The method of claim 8 in which the path is no greater than 2
millimeters.
10. The method of claim 1 in which the coating is made of a
material selected from the group consisting of metals, metal
oxides, and metal alloys.
11. The method of claim 1 in which the coating is an organic
material.
12. The method of claim 10 in which the coating is selected from
the group consisting of copper, silver, nickel, chromium, tin,
gold, indium, aluminum and alloys thereof.
13. The method of claim 1 in which step C comprises a method
selected from: A. treating the coated substrate with ultrasonic
vibrations in a fluid medium until the parts of the coating in
registry with the disrupted parts of the interface are dislodged
from the surface of the substrate; B. contacting the surface of the
coated substrate with an adhesive sufficient to selectively lift
the )arts of the coating in registry with the disrupted parts of
the interface from the coated substrate but insufficient to lift
the parts of the coating in registry with parts of the interface
not disrupted from the coated substrate; and C. contacting the
surface of the substrate exposed to electromagnetic radiation with
a high velocity stream of a benign liquid or gas.
14. The method of claim 1 in which there is a tie layer at the
interface, and the parts of the tie layer congruent with the parts
of the coating removed in step C are also removed.
15. An optic train comprising the following components arranged in
the order stated: A. a beam shaper comprising two half cylindrical
lenses with a focal length of at least 20 millimeters; B. a
homogenizer oriented to homogenize a beam orthogonally to the
direction of shaping effected by the beam shaper; and C. a
cylindrical lens.
16. The optic train of claim 15 in which the homogenizer comprises
a lenslet array arranged to homogenize a light beam entering the
array in one dimension.
17. An imaged article comprising a polymeric substrate bearing a
patterned image characterized by a substantial absence of A. heat
distortion; B. debris comprising the material of which the image is
made or decomposition products of such material; C. photo-resist;
and D. undercut of the image.
18. The imaged article of claim 17 in which the polymeric substrate
comprises a polyester.
19. The imaged article of claim 17 of which the patterned image is
an antenna.
Description
TECHNICAL FIELD
[0001] This invention relates the formation of an image or pattern
in an article such as a metal coated substrate. More specifically,
it relates to the formation of such an image or pattern using a
high energy source such as a laser or flash lamp.
BACKGROUND
[0002] Surface layer materials are often imaged or patterned for
many utilitarian purposes. The surface layers may include vacuum
deposited thin films, solution coatings, and electroless or
electroplated films Patterned conductive surface layers may find
use in both passive and active electronic circuits, display
components, antennas for radio frequency identification tags (RFD),
wireless local area networks (LAN), and proximity detectors as well
as antennas for communication such as pagers, cell phones, and
satellite reception. Optical surface layers may find application as
optical components such as diffractive optical elements and
security images, or in telecommunication applications as components
that can perform optical switching, modulation, and multiplexing or
demultiplexing.
[0003] There are techniques for forming patterns ill surface
layers. Two useful methods are chemical etching and laser ablation.
Images or patterns created by chemical etching are formed by
selectively dissolving the surface layer with the appropriate
chemicals or by energy ablation are formed by explosively detaching
and removing a thin surface layer in a selective manner to create
an image or pattern. However, each of these methods has
limitations.
[0004] Chemical etching is a multiple step process that may create
hazardous wvaste. Typically a chemical or photo-resist is applied
to selected parts of a surface that is to be patterned or imaged
Then, a chemical is applied on the entire surface and is able to
remove the coating (e.g. copper) exposed on the surface but not the
coating on the part of surface covered by the chemical or
photo-resist. The chemical solution containing the dissolved
surface layer material is then washed off of the imaged article.
The often hazardous solution is collected and treated in a safe
manner at some expense. This method is undesirable due to the
multiple process steps and the imaged article can have residual
photo-resist residue and undercut sidewalls of the image.
[0005] Contemporary methods of utilizing lasers to pattern or
micro-machine materials rely on the physical phenomena of ablation.
Energy ablation is a simpler process that does not involve
hazardous waste disposal. Typically, the surface layer of an
article to be imaged is exposed (for example through a mask) with
light pulses from a high-energy source, such as a laser or a flash
lamp. These pulses of energy are absorbed by parts of the surface
layer not covered by the mask, and the energy impacting the layer
causes a sudden increase in surface temperature for a short time.
The rapid rise in temperature causes the surface layer material to
explosively detach or eject from the substrate and create a pattern
corresponding to the mask pattern.
DISCLOSURE OF INVENTION
[0006] An improved method for imaging or patterning surface layer
materials has been created which comprises the steps of:
[0007] A. providing a substrate having a coating and an interface
comprising the thin region where the coating and the substrate are
closest to each other,
[0008] B. exposing at least one part of the total area of the
coating to a flux of electromagnetic energy sufficient to disrupt
the interface but insufficient to ablate the coating; and
[0009] C. removing the pails of the coating in registry with the
portion of the interface area that was disrupted.
[0010] The substrate can be any material suitable as a support for
a radiation-induced image. This process is particularly
advantageous for substrates that are susceptible to heat damage
such as some polymeric materials including polyester,
polycarbonate, polyvinylchloride, and polyimide. The coating can be
any imageable material that absorbs radiation. Typical coatings
include metals, metal alloys, and inorganic compounds such as metal
oxides and metal nitrides as well as organics. The flux of
electromagnetic energy may be from a light source such as a laser
or a short pulse width flash lamp.
[0011] The energy fluence is below the ablation threshold of the
surface coating but sufficient to disturb the interface between the
coating the substrate. Ablation threshold is the minimum energy
needed to ablate a coating from a substrate and is dependent on the
coating, substrate and wavelength of energy used. For purposes of
this description, the term disrupt, as applied to the interface,
means to affect the interfacial bonding between the substrate and
the coating so that this interface is weaker than the bonding in
the interface regions that have not been exposed to the energy
flux. This weakening of the interfacial bond is sufficient to allow
the removal of the coating in regions exposed to the energy flux as
described herein without removing coating from the unexposed
regions.
[0012] Less fluence, i.e., energy density at the coating surface,
is required to disturb or disrupt the interface than is required in
ablation processes, which implies greater throughput or output for
a given Source of electromagnetic energy flux. Also, there is
essentially no redeposition of coating material onto the work
piece, which alleviates any detrimental effects of the imaged
substrate associated with debris in the article produced.
[0013] A reflective, absorptive or (diffractive mask defines the
desired pattern. As an example, opaque reflective regions and
transparent regions define the reflective mask patterns. When a
uniform energy flux is incident upon the mask, the energy is
reflected by the reflective regions and transmitted by the
transparent regions resulting in the exposure of the desired parts
of the coating material (corresponding to the pattern) to the
energy flux.
[0014] The coating that is over the disturbed part of the interface
is removed by a method such as contacting it with an adhesive roll,
exposing it to high velocity stream of a benign liquid or gas (eg.
air or water jet), or ultrasonic agitation in an aqueous solution.
As used in this paragraph, the term benign means characterized by
having no damaging effect (eg. by chemical reaction, corrosion, or
physical erosion) on the coating or substrate. This step of removal
of the coating over the disrupted area is relatively
inexpensive.
[0015] Imaged articles are also part of this invention. Inventive
articles comprising an imaged coating on a substrate are
differentiated from articles made by ablation by a substantial
absence of heat distortion and debris comprising the coating
material. They are also differentiated from articles made by
chemical or photo-resist process by a substantial absence of
photo-resist and absence of undercut of the image which can occur
with the chemical patterning process.
[0016] Applications that would benefit from this invention include
patterning of inorganic thin films for active and passive
electronic circuits, antennas for RFID tags, EMI shielding, patch
antenna, and biosensinig pattern arrays. Patterned optical surface
layers made by this invention could also find use in optical wave
guides, electro-optic filters and modulators, holograms, security
images, graphics and retroreflective materials. Patterned
transparent conductors on both rigid and flexible substrates would
find application in liquid crystal display (LCD) computer displays,
televisions, touch screens, heated and electrochromic windows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a pictorial view of the apparatus used to perform
the inventive method.
[0018] FIG. 2 is a plan view of an antenna made by the inventive
process.
[0019] FIG. 3 is a cross sectional view of the antenna of FIG.
2.
[0020] FIG. 4 is a back-scatter scanning electron photomicrograph
of an RFID antenna made by the inventive process at 102 X
magnification.
[0021] FIG. 5 is a back-scatter scanning electron photomicrograph
of an RFID antenna made by laser ablation at 102 X
magnification.
DETAILED DESCRIPTION
[0022] The inventors recognized that the light energy absorbed by
the work piece material in ablative processes caused thermal and
photochemical decomposition which resulted in gas byproducts
rapidly expanding and ejecting material fragments from the exposed
region. This requires relatively high fluences for complete
material removal and precautions to prevent material fragments from
depositing onto the work piece or adjacent optical elements.
[0023] The present invention allows fine resolution patterning with
minimal generation of debris, no use of hazardous chemicals, and
reduced process steps as compared to chemical etching techniques.
The inventive method takes advantage of the processing used during
ablation but eliminates the problem of debris generation and
deposition by reducing the energy densities below the ablation
threshold. The surface layer regions exposed to the electromagnetic
fluences have reduced adhesion to the substrate, allowing the
surface layer or coating to be removed by mechanical methods.
[0024] With reference to FIG. 1, one embodiment of the apparatus 1
which may be used to practice the inventive process includes:
energy source 30 which may be a laser; an optic train comprising
shutter 34, beam shaper 36, homogenizer 38, and cylindrical
converging lens 42; movable translation stage 24 on which is
mounted mask 26; and film handling subassembly 10 consisting of
protective web unwind and wind-up rollers 12 and 16 respectively,
idler rollers 18 and 19, work piece unwind and wind-up rollers 13
and 17 respectively, and idler rollers 14 and 15. In performing the
process: the coated substrate to be treated 20 is unwound from
roller 13, over idler rollers 14 and 15 and wound onto roller 17 so
that it is exposed to the rectangularly shaped laser beam 44; and
transparent protective web 22 is unwound from roller 12 past the
area where the laser beam 44 is incident and between coated
substrate 20 and mask 26 to permit comparison between the process
of the invention and a debris-prone ablation process without
ruining mask 26. The protective layer is not needed when only the
method of the invention is used.
[0025] During the exposure of mask 26, protective web 22 and coated
substrate 20 to laser beam 44, preferably protective web 22, coated
web 20 and mask 26 are moved at the same rate of speed in front of
laser beam 44 so that the whole area of the mask is exposed to the
laser beam substantially uniformly. This can be accomplished by
means within the skill of the art for moving translation stage 24
and advancing both coated substrate 20 and protective web 22. The
laser beam thus traverses over the whole area defined by the mask
in order to expose the coated substrate behind the mask. After the
area to be imaged has been exposed for sufficient lime to the
laser, the exposure is stopped (for example by shutting shutter 34)
and coated substrate 20 and protective web 22 are advanced on their
rollers so that a new area is available for processing Protective
web 22 is transparent to the electromagnetic energy of the beam
44.
[0026] Coated substrate 20 typically comprises a polymer web
substrate coated with a thin layer of material. The substrate can
be any material that can support an image. Because the process
operates at energy levels below that which may distort some
substrates, articles made with such substrates are particularly
benefited. Such substrates typically comprise a polymer web. Useful
polymers for the substrate are: polyester, polycarbonate,
polyethylene, polyamide, polyvinylchloride, polystyrene,
polypropylene or polyimide.
[0027] Some of these would not normally be in the form of roll
goods as shown in FIG. 1. Indeed, the substrates may be in a
variety of forms depending on the application. Some useful forms
include, for example, flat films or foils in sheet or roll form,
rods, fibers beads, wafers, panels, platters, and non-woven webs.
These forms can be prepared from a wide variety of materials. Not
all materials can be prepared in all of the forms, but persons
skilled in the art of material processing will be able to determine
the possibilities for the various material sets.
[0028] The substrate may be organic or inorganic. Inorganic
substrate materials include silica based glasses, ferrous and
nonferrous metals, ceramics, semiconductors such as silicon,
germanium, gallium arsenide, gallium nitride, and other metal
inorganics such as aluminum oxide and titanium dioxide.
[0029] One substrate polymer that has been used in making this
invention is PETG polyester from Eastman Chemical Company,
Kingsport, Tenn. It is a clear, amorphous copolyester based on
poly(ethylene terephthalate) having a density of 1.27 g/cm.sup.3
and is useful for making heat laminated cards such as RFID cards.
Other polymers which can be heat laminiated (eg. polyesters coated
with one or more vinyl polymer layers) would also be useful
substrates for such applications.
[0030] Onto the substrate, an imageable material is coated to the
desired thickness for a particular application. This coating may be
a single or multiple layers. Depending upon the material
composition, a wide variety of techniques can be used to coat. For
example, for thin metallic film coatings, vacuum evaporative or
sputtering deposition techniques are widely known in the art to
produce excellent film properties. For organic film coatings, a
number of solution coating methods are well known, such as gravure,
slot, and kiss coating. Persons skilled in the art of coating and
materials processing will be able to select the appropriate coating
techniques for the specific coating materials and substrates.
Materials with imageable characteristics include both organic and
inorganic materials. By way of example, inorganic materials with
useful characteristics include metal films such as copper, silver,
gold, nickel, chromium, till, indium, aluminum; metal alloys such
as NiFe, AgZn; oxide films such as indium-tin-oxide, silicon
dioxide, silicon monoxide, zinc oxide, aluminum oxide; and other
inorganic films such as lithium niobate, magnesium fluoride, zinc
sulfide, and calcium fluoride. Organic coatings include acrylate,
polycarbonate, and epoxy-based polymers.
[0031] The coating may contain organic and inorganic materials to
provide optical, electrical, structural or aesthetic features.
Coating layers to provide appropriate optical properties may
include oxides such as germanium oxide, silicon dioxide, silicon
monoxide, lithium niobate, and/or LiTaO.sub.3, sulfides such as
ZnS, and fluorides such as calcium fluoride and magnesium fluoride.
Aesthetic features could be provided by alloys, oxides, and
nitrides such as niobium oxide, tantalum oxide, silver-zinc alloys,
and titanium nitrides.
[0032] There may also be a tie layer in the interface between the
coating and the substrate, which alters the adhesion of the coating
to the substrate. The tie layer would be of a material different
from that of either the coating or the substrate, and it is an
important advantage of the inventive process that such a tie layer
can be removed at the same time as the coating layer. In
conventional wet etching processes, a separate process step with
different chemicals can be required to remove a tie layer.
[0033] The energy source is one that is able to generate a
sufficient range of fluence to the coating surface to result in
adequate disruption of the coating-substrate interface. Suitable
energy sources include lasers and flashlamnps. The operating
wavelengths of lasers can go from the ultraviolet (UV) to the
infrared. Two classes of lasers are described that are particularly
useful for this process.
[0034] Excimer lasers are high power lasers that can generate high
fluence light in the ultra-violet frequency range. Their lasing
capability is based upon the excitation of specific diatomic gas
molecules In particular, excimer lasers constitute a family of
lasers, which emit light in the wavelength range of 157-355 nm. The
most common excimer wavelengths and respective diatomic gases are
XeCl (308 nm), KrF (248 nm) and ArF (193 nm). The lasing action
within an excimer is the result of a population inversion in the
excited dimers formed by the diatomic gases. Pulse widths are
typically in the 10s to 100s of nanoseconds resulting in high
energy, short pulse width pulses. These characteristics of the
excimner laser can lead to subablative or ablative processing
conditions for materials with significant absorption within the
excimer excitation range depending on the energy output chosen.
[0035] Solid state lasers are high power lasers that can generate
concentrated light beams from the infrared to the ultra-violet
wavelength range. A selected portion of these solid state lasers is
based on materials and involves the doping of neodenium into a
solid host such as yittrium-aluminium-garnet (YAG),
yittrium-lithium-fluoride (YLF), and yittrium vanadate (YVO.sub.5).
These particular materials lase at a fundamental wavelength in the
infrared wavelength range of 1.04 to 1.08 .mu.m. This lasing can be
extended to shorter wavelengths through the use of nonlinear
optical crystals such as lithium triborate (LBO) or potassium
titanyl phosphate (KTP). As an example, the fundamental 1.06 um
radiation from a neodinium doped YAG laser can be frequency doubled
to a wavelength of 532 nm or frequency tripled to 355 nm using
these nonlinear crystals. Like the excimers, the characteristics of
the solid state laser can lead to subablative (ie. at energy levels
below the ablation threshold) or ablative processing conditions for
materials with absorption in the useable wavelength ranges.
[0036] An alternative light source to the excimer laser is a short
pulse linear excimer, ultraviolet flash lamp. Typically, such a
lamp would include a transparent quartz lamp tube with a wall
thickness of about 1 mm having an internal bore of about 3 to 20 mm
in diameter. Such flash lamps can be as long as 30 cm. Electrodes
preferably made of tungsten are sealed into the ends of the lamp
tube which is filled with a noble gas such as xenon. The flash lamp
is pulsed in the range of 1 to 20 Hz by applying a high voltage in
the range of 5 to 40 KV to the electrodes using a capacitor bank.
The charge ionizes the xenon atoms to form a plasma which emits a
broadband of radiation ranging in wavelength from about 200 nm to
about 800 nm. The flash lamp can include a reflector placed
partially around the tube to shape and guide the radiation from the
lamp toward the mask and workpiece.
[0037] Linear flash lamps are capable of producing high intensity,
high fluence energy output at shorter wavelengths in relatively
short pulses of about 5 .mu.sec. For example, it has been found
that a xenon linear flash lamp, with a broadband spectral output
can provide a useful energy density of between about 1.0 and 1.5
J/cm.sup.2 during a pulse of about 2 and 6 .mu.sec.
[0038] Each coating and substrate system has fluence levels defined
as the ablation threshold and the subablation threshold. The
ablation threshold fluence is the minimum energy per unit area that
must be absorbed by the coating to cause the coating to explosively
decompose or ablate from the substrate. The subablation threshold
fluence is the minimum energy per unit area required at the coating
surface to heat the coating sufficiently to disrupt the interface
between the coating and the substrate but not ablate it.
Subablation occurs just below the ablation threshold fluence and
extending down to the subablation threshold fluence.
[0039] Adhesion of the coating to the substrate is also important.
The adhesion must be sufficient so that the coating in registry
with the undisrupted interfacial regions is not removed by the step
that removes the coating in registry with the disrupted interfacial
regions. Since disruption of the interface generally reduces the
adhesion between the coating and the substrate, satisfactory images
result when the adhesive force between the unexposed coating and
the substrate is within the range of about 40 to 700 g/cm as
measured by Method B described hereinafter.
[0040] The laser 30 shown in FIG. 1 and used in some of the
experiments which led to this invention was an excimer laser from
which emanates laser beam 32 having approximately a rectangular
cross section with an aspect ratio of about 3:1. The excimer laser
produces a short pulse (eg. 20 nanoseconds) beam with sufficient
fluence (measured in milli-Joules/cm.sup.2) to disrupt the
interface The high density energy of the excimer laser is available
over a relatively large area, as compared to other lasers.
[0041] The beam shaper 36 functions principally to reshape the top
and bottom edges of the laser beam in order to increase usable
pulse energy. The beam 32 exits the laser with a gaussian energy
profile with a reduction of energy density away from the beam axis.
The beam shaper changes the energy profile to be more rectangular,
sometimes referred to as a top hat profile Beam shapers are
commercially available, one embodiment being available from Optec,
in Site du Grand Hornu, Belgium The beam shaper preferably has a
focal length of at least 20 mm. In one embodiment of a beam shaper,
the active lenses are plano-convex lenses with a local length of
240 mm. The width element (at 50 mm) was sufficient to span the
entire width of a raw laser beam 33 mm wide. The height element of
the lenses (at 12.5 nm) was equal to at least half of the beam
height (11 mm). The beam shaper elements act upon the top and
bottom edges of the raw excimer beam to redirect them vertically
toward the beam center.
[0042] The homogenizer 38 functions to divide and overlap a
sufficient number of segments of beam 32 to make the resulting beam
40 homogeneous in the horizontal direction (across the beam from
one side to the other). Point-to-point fluctuations in energy
distribution can be reduced by nixing various parts of the excimer
laser beam with each other using, for example an array of lenslets
oriented vertically through which the beam passes Homogenization
can increase the useful portion of the excimer beam 40. A number of
homogenizers are known in the art, as taught in Industrial Excimer
Lasers, 2.sup.nd ed., Basting, D)., ed., Lambda Physik GmbH,
Gottingen, Germany. One useful homogenizer contained a lenslet
array of seven cylindrical, plano-convex lenses with a focal length
of 16 mm. The width of each element was 5 mm, and the length (38
mm) was sufficient to span the height of the beam (11 mm). The
lenslets were side-by-side to cover the entire width of the raw
beam and homogenize it in the horizontal direction.
[0043] Laser beam 40 expands in cross section over the distance
between laser 30 and cylindrical lens 42, but cylindrical lens 42
concentrates the intensity of the entire beam 40. The beam exiting
lens 42 has substantially less height (for example about 10 times
less) than the beam 40 which entered lens 42. One useful embodiment
was a plano-convex lens with a focal length of 103 mm. Its width
was 38 mm, and its length was 350 mm making it sufficiently large
to accept an entire reshaped and homogenized beam. The cylindrical
lens 42 is made of a highly transmissive material such as fused
silica. Thus, the beam shaper 36 and cylindrical lens 42 affect the
vertical profile of the laser beam, and the homogenizer 38 effects
homogenization orthogonal to the vertical.
[0044] Preferably, mask 26 is made of a base material that is
highly transparent to the excimer laser beam. The base material can
for example be coated with a protective overlay that is reflective
to the wavelengths of electromagnetic energy used. For example, the
base material of the mask can be synthetic fused silica, and the
protective overlay can be aluminum. The aluminum can be vacuum
deposited onto the fused silica base material to a depth of
approximately 600 nm. The pattern of the mask is formed in the
protective overlay by standard semiconductor industry
photolithographic and wet etch processing techniques.
[0045] The parts of the optic train 30, 34, 36, 38, 42 and mask 26
can be aligned properly using a camera and taking accurate
measurements of distance and height. The initial height of mask 26
call be adjusted by means of translation stage 24 a device known to
those skilled in the art The distance between the cylindrical lens
42 and the front of the coated substrate 20 is one parameter that
determimes the width of the incident laser beam and the fluence or
energy density the distance between mask 26 and coated substrate 20
is referred to as the path. The path is preferably no greater than
2 mm long, more preferably about 50 to 100 micrometers long.
[0046] FIG. 2 depicts an example of a product which can be made by
the inventive process and which itself is inventive. It is a
patterned copper coating 46 on a polymeric substrate 52 which call
serve as an RFID antenna. RFID is widely used to identify things or
people and in electronic article surveillance. The series of
generally rectangular, stripe-like regions 48 are the pairs of the
coating (eg. copper) which were unexposed to the electromagnetic
energy flux and remained adhered to substrate 52. The lines 49
separating regions 48, the area in the middle of the pattern, and
the region outside of the pattern of stripe-like rings in a
generally rectangular array correspond to parts of the coated
substrate not protected by the mask and from which the coating was
removed in the process. In the cross-sectional view of FIG. 3, one
can see that the stripe-like regions 48 are raised above the
surface of the substrate 52 from which the remainder of the coating
has been removed.
[0047] FIGS. 4 and 5 demonstrate the cleanliness advantage of the
inventive articles. FIG. 4 shows basically no debris in the field
of view which is an area of an inventive patterned substrate from
which metal had been removed after treatment in accordance with the
process of this invenition. On the other hand, FIG. 5 shows metal
debris and stripes left in an exposed area of the same type of
metal coated substrate which had been patterned by laser
ablation.
[0048] The invention will be further clarified by the following
examples which are exemplary and not intended to limit the scope of
this invention. In the experimental work, the following test
methods were used.
[0049] A spectrophotometer was used to determine the optical
wavelength and energy source appropriate for disruption of an
interface. The coated surface layer of the coated substrate was
placed under a spectrophotometer, Model Lambda 900 available from
Perkin-Elmer Norwalk, Conn., and the absorption of the surface
coating was measured as a function of wavelength. Generally, a
wavelength between 200 nm and 2 .mu.m would be selected at which
the coating had the most absorption. An energy source was then
chosen based in part on whether wavelengths in the operating range
of wavelengths for the source were sufficiently absorbed by the
coating. A rough measure of sufficiency would be that absorption
was sufficient to ablate the coating.
[0050] Adhesion between the coating layer and the substrate layer
was evaluated by two methods and will be called the interlayer
adhesion. The methods were used to determine whether the
inter-layer adhesion is sufficient to permit selective removal of
the coating over the disrupted interface while not removing the
coating over the interface that was not disrupted. Method A was a
qualitative test and Method B was a quantitative test.
[0051] In Method A, two different pressure-sensitive adhesive (PSA)
tapes, each approximately 15 cm by 12 mm, were applied to the
surface of the coating on the coated substrate. Tape 1 was a PSA
tape having relatively weak adhesion, acrylate-based Scotch Brand
No. 810 Magic Tape and Tape 2 was a PSA tape having relatively
strong adhesion, Kraton.TM. block copolymer based Scotch Brand No.
396 Box Sealing Tape. A 5 cm wide roll weighing 1.5 kg was passed
once over each tape such that each tape had one end that was not
adhered to the coating surface. The tapes were allowed to rest for
about one minute. The free end of each tape was then gripped by
hand and the tape was peeled back from the surface at approximately
180 degrees and at a speed of approximately 2 cm per second. If the
coating was removed by Tape I, the interlayer adhesion was likely
to be insufficient. The coating over even the interface that was
not disrupted was likely to be removed together with that over the
disrupted interface. If the coating was not removed by Tape 2, the
interfacial adhesion was likely to be too great to permit the
coating over the disrupted interface to be removed by subsequent
removal techniques of the invention.
[0052] In Method B, the force required to remove the coating from
the substrate was measured. Metallic coatings on a substrate may
require specially made test samples having a greater thickness than
used for an application to prevent premature tearing of the coating
during testing. Test strips having surface strips of coating
material (eg. copper) that were 5 mm wide were prepared. One end of
the coating surface strip was manually separated from the substrate
by means of a thin blade (eg. a scalpel). The sample was then
adhesively affixed to a staging system that allowed horizontal
movement in response to a vertical peel of the coating at 90
degrees from the substrate. Peel was performed smoothly with a
force measuring device (Instron.TM. Model 1122 available from
Instron Corp., Canton, Mass.) operated at a speed of approximately
0.17 cm per second. If the adhesive force between the coating and
substrate was between about 40 and 700 g/cm, suitable patterning
could be accomplished with this invention.
Examples 1-3
Comparative Examples 1-2
[0053] A metal-coated substrate was exposed to sufficient radiation
of an energy source to disrupt the interface between the metal and
the substrate. The metal-coated substrate consisted of an organic
polymer substrate (PETG, containing TiO.sub.2 filler and having a
thickness of 125 micrometers (elm) and available from VPI, Chebogan
Falls, Wis.) coated with a metal (copper, evaporation-coated with
an electron beam in a vacuum to a thickness of 250 nm) and had an
ablation threshold of 325 mJ/cm.sup.2 and a subablation threshold
fluence of 190 mJ/cm.sup.2.
[0054] A laser light beam was formed by an ultraviolet energy
source (Model LPX 315 150 watt Excimer laser available from Lambda
Physik of Germany) utilizing krypton fluoride (Kids) gas to produce
ultraviolet radiation at 248 nm. The source was operated to form a
beam with a repetition rate of 75 Hz, a pulse width of 10 ns and an
energy output of 750 mJ per pulse. The beam was passed through an
optic train composed of a beam shaper (Model HY-120 Excimer Laser
Beam Shape, manufactured by Optec S. A., I Hornu, Belgium) followed
by an homogenizer and then a single plano-convex lens. The
homogenizer was an array of plano-convex cylindrical lenses each
with a focal length of 16 mm. The single lens was a plano-convex
cylindrical lens with a focal length of 103 mm. The laser beam was
expanded horizontally to about 20 cm prior to entering the single
plano-convex cylindrical lens. The distance between the metal
surface of the metal-coated substrate and the surfaces of the beam
shaper, homogenizer and cylindrical lens that was closest to the
metal surface was 670 mm, 620 mm, and 93 mm, respectively. The
resulting shaped beam was incident on the copper coating surface
with a beam cross section 200 mm in length and 0 76 mm in
width.
[0055] This very long and narrow beam passed from the optic train
through a patterning mask (made of an EQZ grade vised silica plate
available From Hoya, Corp., Shelton, Conn.) that was vacuum-coated
with aluminum in a thickness of approximately 600 nm and imaged by
selectively removing aluminum with standard photolithographic and
wet etching techniques). The beam then passed through a protective
web (OPP grade 7 .mu.m thick polypropylene available from Bolmet
Inc., Dayville, Conn.) that was adjusted to be in contact with the
metal surface and spaced 25 .mu.m from the patterning mask. The
beam energy density or fluence was 220 mJ/cm.sup.2 at the copper
surface (as measured by an apertured Joulemeter, model ED-500 from
Gentec Inc., Quebec, Canada) sufficient to disrupt the interface
between the metal and the substrate.
[0056] The relative positions of the patterning mask and the
metal-coated substrate with respect to the shaped beam were
controlled by a linear translation stage (Model OFL-1515 available
from NEAT Technologies, Lawrence, Massachusetts). The translation
stage was moved at a linear rate of 5.9 cm/sec. The final beam
profile was overlapped by 12% for successive pulses. Both the
protective web and Cu/PETG substrate were moved parallel to the
direction of the mask travel and at 5.9 cm/sec to form a resulting
exposed rectangular area of about 8.7 cm x 5.5 cm. Within the
rectangular area, the pattern of the mask could be visually seen by
comparing the exposed and unexposed portions of the sample. The
metal surface that had been exposed through the mask appeared dark
in comparison to the unexposed metal surface that had been covered
by the mask, but none of the copper was removed by the excimer
radiation.
[0057] Samples of exposed metal-coated substrate were then placed
in a water bath at a temperature of 20.degree. C. with two
immersible ultrasonic transducers (Model LP 610-6 Immersible
Ultrasonic Transducers excited by a Model EMLX 30-12 generator both
available from Branson Cleaning Equipment Co., Shelton, Conn.). The
metal surfaces of the samples were placed about 18 mm from the
transducers for about 4 seconds with the oscillation amplitude of
the transducers limited to 18 .mu.m (0.7 mils) peak-to-peak to
remove the metal at the disturbed regions of the copper/PETG
interface. This ultrasonic treatment resulted in the complete
removal of the exposed copper but not the unexposed copper. The
pattern in the copper coating had good resolution. The fine
features were as small as 75 .mu.m wide metal lines and 75 .mu.m
wide spaces. Also, there were no electrical shorts between the
lines or voids within the lines.
[0058] Examples 2 and 3 were made and tested as in Example 1 except
the fluence was approximately 200 and 300 mJ/cm.sup.2,
respectively. The pattern in the copper coating had good
resolution. The fine features were as small as 75 .mu.m wide metal
lines and 75 .mu.m wide spaces. Also, there were no electrical
shorts between the lines or breaks within the lines.
[0059] For comparison, Comparative Examples 1 and 2 were made like
Example 1 except for the output energy of the laser Comparative
Example 1 was exposed to a fluence of 150 mJ/cm.sup.2, and
Comparative Example 2 was exposed to a fluence of 400 mJ/cm.sup.2
respectively. The exposed metal in Comparative Example 1 was not
removed because the fluence used was insufficient to disrupt the
interface. In Comparative Example 2, electrical shorts were
observed in the patterned copper because the fluence was sufficient
to ablate the metal and some of the ablated molten metal
re-deposited onto the metal coated surface of the sample.
Example 4
[0060] This example illustrated the effect of a different energy
source on image characteristics.
[0061] Example 4 was made in a manner similar to Example 1 except a
different energy source and optical train were used, some of the
conditions were changed, and a different cleaning method was used.
The energy source was an infrared laser (Model 2660 Nd:YAG Infrared
Laser available from Excel Technology Inc., Hauppauge, N.Y.)
operating at a wavelength of 1.06 .mu.m, a repetition rate of 2000
Hz, an energy per pulse of 0.6 mJ, and a pulse width of 200 ns. The
laser light incident on the metal coating was a dot or point, in
contrast to the line or narrow rectangle of light in example 1 (as
shown in FIG. 1). The optical trail consisted of only a round
plano-convex lens with focal length of 10 cm. There was no beam
shaper, homogenizer, or cylindrical lens. No mask and no protective
web were used. The resulting fluence reaching the metal surface was
determined from the energy output of the laser as measured by a
joulemeter (Model J3-09 available from Molectron, Inc. Portland,
Oreg.) and the area irradiated on the surface of the metal and was
calculated to be 350 mJ/cm.sup.2, below that needed to ablate the
metal from the substrate for this wavelength. The translation stage
was moved at a speed of 20 cm/s to result in a 20% overlap between
successive pulses on the metal surface. Parallel line patterns were
exposed with spacing between lines achieved by cross-web movement
of the second axis of the translation stage after each pass of the
laser.
[0062] The copper was not removed from the PETG surface by the YAG
infrared laser exposure, but the areas exposed to the infrared
radiation could be detected by the difference in reflectivity from
the unexposed regions. The exposed areas of the metal layer were
removed with the following technique. A pressure-sensitive adhesive
coated roll was moved over the metal coating side of the metal
coated substrate with one pass. The roll was 20 cm wide and weighed
about 4.5 kg. Visual inspection of the 50 .mu.m wide lines and
spaces on the metal-coated film showed that the metal was
completely removed over exposed regions where the interface was
disrupted and completely intact over regions where the interface
was not disrupted.
Example 5
[0063] This example illustrated the use of a metal oxide coating on
the substrate.
[0064] Example 3 was made as in Example 1 except that a metal oxide
coated substrate was used and the energy output was reduced to
about 650 mJ. The metal oxide coated substrate consisted of
polyester that had been sputter coated with indium tin oxide to
achieve a conductivity of 80 Ohms/square and available as No. OFC80
from Courtaulds Performance Films Inc., Canoga Park, Calif. The
optical train was configured to shape the incident excimer laser
beam into a 150 mm by 0.89 mm rectangle at the metal oxide surface.
The energy from the excimer laser was adjusted to achieve a
calculated fluence of about 80 mJ/cm.sup.2 in tills rectangle,
below the ablation threshold of 90 mJ/cm.sup.2 that is needed to
ablate this coating from this substrate for this wavelength. The
final beam profile was overlapped by 10% for the successive pulses.
The subsequent pattern had good resolution with fine features as
small as 50 .mu.m wide lines and spaces.
Example 6
[0065] This example illustrated the use of a different substrate
class.
[0066] Example 6 was made as in Example 1 except that a different
substrate was used and the fluence was reduced. (energy level was
about 650 mJ). The metal coated substrate consisted of polyimide
(50 .mu.m thick film available as Kapton.TM. E from DuPont Inc.,
Circleville, Ohio) that had been sputter coated with copper to
achieve a coating thickness of approximately 250 nm. The resulting
subablation fluence used to disrupt the coating substrate interface
was calculated to be 170 mJ/cm/.sup.2, below the ablation threshold
of approximately 300 mJ/cm.sup.2 that is needed to ablate the metal
from the substrate for this wavelength. The subsequent pattern had
good resolution with fine features as small as 75 .mu.m wide lines
and spaces.
Example 7
[0067] This example illustrated the use of ail organic coating.
Example 7 was made in a manner similar to example I except the
material and laser conditions were different. A clear acrylate
coating (available from Spray On, division of Sherwin Williams Co.,
Bedford Heights, Ohio, product number #02000) was sprayed onto a
poly(ethylene terephtalate) (PET) substrate to a coating thickness
of 3 .mu.m. The coating was allowed to cure at ambient conditions
for one hour. This coating/substrate system had an ablation
threshold of 100 mJ/c.sup.2. The laser energy was adjusted to
obtain an energy output of 450 mJ per pulse and yield an energy
fluence of 65 mJ/cm.sup.2 sufficient to disrupt the interface
between the acrylate and PET substrate. The acrylate coating was
not removed from the PET surface by the excimer laser exposure, but
the areas exposed to the radiation could be detected by a
difference in reflectivity from the unexposed regions. Ultrasonic
treatment resulted in the complete removal of the exposed acrylate
but not the unexposed acrylate. The pattern in the arcylate coating
had good resolution The fine features were as small as 75 .mu.m
wide lines and 75 .mu.m wide spaces.
[0068] While certain representative embodiments and details have
been discussed above for the purpose of illustrating the invention,
it will be apparent to those skilled in the art that various
changes and modifications may be made in this invention without
departing from its true spirit or scope which is indicated by the
following claims.
* * * * *