U.S. patent application number 15/665173 was filed with the patent office on 2018-06-14 for method and apparatus for performing laser curved filamentation within transparent materials.
This patent application is currently assigned to ROFIN-SINAR TECHNOLOGIES INC.. The applicant listed for this patent is ROFIN-SINAR TECHNOLOGIES INC.. Invention is credited to S. Abbas HOSSEINI.
Application Number | 20180161916 15/665173 |
Document ID | / |
Family ID | 55073804 |
Filed Date | 2018-06-14 |
United States Patent
Application |
20180161916 |
Kind Code |
A1 |
HOSSEINI; S. Abbas |
June 14, 2018 |
METHOD AND APPARATUS FOR PERFORMING LASER CURVED FILAMENTATION
WITHIN TRANSPARENT MATERIALS
Abstract
Systems and methods are described for forming continuous curved
laser filaments in transparent materials. The filaments are
preferably curved and C-shaped. Filaments may employ other curved
profiles (shapes). A burst of ultrafast laser pulses is focused
such that a beam waist is formed external to the material being
processed without forming an external plasma channel, while a
sufficient energy density is formed within an extended region
within the material to support the formation of a continuous
filament, without causing optical breakdown within the material.
Filaments formed according to this method may exhibit lengths in
the range of 100 .mu.m-10 mm. An aberrated optical focusing element
is employed to produce an external beam waist while producing
distributed focusing of the incident beam within the material.
Optical monitoring of the filaments may be employed to provide
feedback to facilitate active control of the process.
Inventors: |
HOSSEINI; S. Abbas;
(Orlando, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROFIN-SINAR TECHNOLOGIES INC. |
Plymouth |
MI |
US |
|
|
Assignee: |
ROFIN-SINAR TECHNOLOGIES
INC.
Plymouth
MI
|
Family ID: |
55073804 |
Appl. No.: |
15/665173 |
Filed: |
July 31, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14742187 |
Jun 17, 2015 |
9757815 |
|
|
15665173 |
|
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03B 33/04 20130101;
C03B 33/07 20130101; C03B 33/0222 20130101; C03B 33/033 20130101;
B23K 2103/50 20180801; B23K 2103/54 20180801; B23K 26/38 20130101;
B23K 26/0624 20151001; B23K 26/0648 20130101; B23K 2103/166
20180801; B23K 26/0006 20130101; B23K 26/082 20151001; B23K 26/53
20151001; B23K 2103/16 20180801; B23K 2103/56 20180801; B23K
2103/42 20180801; B23K 2103/52 20180801 |
International
Class: |
B23K 26/00 20060101
B23K026/00; B23K 26/0622 20060101 B23K026/0622; B23K 26/06 20060101
B23K026/06; B23K 26/082 20060101 B23K026/082; B23K 26/38 20060101
B23K026/38; C03B 33/02 20060101 C03B033/02; C03B 33/033 20060101
C03B033/033; C03B 33/04 20060101 C03B033/04; C03B 33/07 20060101
C03B033/07 |
Claims
1-20. (canceled)
21. A method for machining a workpiece, comprising the steps of:
providing a laser beam having bursts of ultrafast laser pulses, the
workpiece being transparent to the laser beam; locating an optic in
the path of the laser beam that induces a cubic phase in the laser
beam; focusing the laser beam to form a distributed focus, the
distributed focus having a C-shape due to the cubic phase in the
focused laser beam; locating the workpiece such that at least a
portion of the C-shaped distributed focus is within the workpiece,
the focused laser beam having sufficient energy density to form a
continuous C-shaped filament within the workpiece, the continuous
filament inducing a C-shaped material modification in the
workpiece; and translating the workpiece laterally with respect to
the laser beam to form an array of C-shaped material modifications
that define a scribed path for cleaving the workpiece.
22. The method of claim 21, wherein the optic that induces the
cubic phase is selected from the group consisting of a cubic phase
plate, a cubic phase mask, and a spatial light modulator.
23. The method of claim 21, wherein the optic that induces the
cubic phase has two cylindrical lenses arranged at an angle to
introduce coma to the laser beam.
24. The method of claim 21, wherein the cubic phase produces an
Airy laser beam, the distributed focus of the Airy laser beam
having a C-shape.
25. The method of claim 21, wherein the distributed focus is formed
by at least one aberrated focusing element.
26. The method of claim 25, wherein the at least one aberrated
focusing element is an axicon.
27. The method of claim 26, wherein the focused laser beam is an
Airy-Bessel beam.
28. The method of claim 25, wherein the at least one aberrated
focusing element induces spherical aberration.
29. The method of claim 21, wherein the workpiece is made of a
material selected from the group consisting of a glass, a crystal,
a ceramic, and a semiconductor.
30. The method of claim 21, wherein a beam waist of the laser beam
is formed external to the workpiece.
31. The method of claim 21, wherein the filament is formed by
self-focusing of the laser beam due to the nonlinear Kerr
effect.
32. The method of claim 21, wherein the material modification is
one of the group consisting of defects, color centers, and micro
cracks.
33. The method of claim 21, wherein the material modification is a
cylindrical void.
34. The method of claim 33, wherein the cylindrical void is created
by radially compressing material about the continuous C-shaped
filament.
35. The method of claim 21, wherein the continuous C-shaped
filament with the workpiece has a length in the range of 100
micrometers to 10 millimeters.
36. The method of claim 21, wherein the continuous C-shaped
filament has a length exceeding about 1 millimeter.
37. The method of claim 21, wherein the ultrafast pulses have a
pulse duration of less than about 100 picoseconds.
38. The method of claim 21, further comprising the step of cleaving
the workpiece along the scribed path.
39. The method of claim 38, wherein the cleaving creates at least
one singulated part having at least one curved edge.
40. The method of claim 39, wherein the at least one curved edge
has a surface roughness of less than about 10 micrometers.
41. The method of claim 21 wherein each burst of ultrafast laser
pulses includes a plurality of pulses.
42. The method of claim 41 wherein each burst of ultrafast laser
pulses includes 2 to 20 pulses.
Description
[0001] This is a continuation of co-pending U.S. patent application
Ser. No. 14742187 filed Jun. 17, 2015. U.S. patent application Ser.
No. 14742187 filed Jun. 17, 2015 is incorporated herein in its
entirety by reference hereto.
FIELD OF THE INVENTION
[0002] The invention is in the field of laser filamentation within
transparent materials.
BACKGROUND OF THE INVENTION
[0003] The present disclosure is related to systems and methods for
the laser processing of materials. More particularly, the present
disclosure is related to systems and methods for the singulation
and/or cleaving of wafers, substrates, and plates that might
contain passive or active electronic or electrical devices created
thereon.
[0004] In the process, the filament is forced to curve in a profile
to form a facet with a C-shaped in cross-section profile. There is
huge demand in the brittle material industry to singulate samples
with a C-shaped in cross-section facet profile. The C-shaped in
cross-section facet profile is sometimes referred to herein as a
C-cut facet profile, a C-shaped (curved) facet profile, a C-shaped
facet path, a C-cut facet or just a C-cut.
[0005] Singulation of a wafer, substrate or plate having a C-cut
facet profile is performed in a single scan.
[0006] In current manufacturing, the singulation, dicing, scribing,
cleaving, cutting, and facet treatment of wafers or glass panels is
a critical processing step that typically relies on diamond or
conventional, ablative or breakdown (stealth) laser scribing and
cutting, with speeds of up to 30 cm/sec for displays as an
example.
[0007] In the diamond cutting process, after diamond cutting is
performed, a mechanical roller applies stress to propagate cracks
that cleave the sample. This process creates poor quality edges,
microcracks, wide kerf width, and substantial debris that are major
disadvantages in the lifetime, efficiency, quality, and reliability
of the product. The sharp edges on the top and bottom surfaces are
the source of potential chipping and crack development that can
cause material to break apart into pieces during transportation.
Generally edges are ground to remove any sharpness and this process
is known as the C chamfer grinding process or step. The C chamfer
grinding step is an extra processing step which necessitates
additional cleaning and polishing steps. The process uses
de-ionized water to run the diamond scribers and grinders and the
technique is not environmentally friendly since the water becomes
contaminated and requires filtration. Grinders and water refining
and filtration systems also occupy valuable manufacturing
space.
[0008] Laser ablative machining has been developed for singulation,
dicing, scribing, cleaving, cutting, and facet treatment, to
overcome some of the limitations associated with diamond cutting.
Unfortunately, known laser processing methods have disadvantages,
particularly in transparent materials, such as slow processing
speed, generation of cracks, contamination by ablation debris, and
moderated sized kerf width. Furthermore, thermal transport during
the laser interaction can lead to large regions of collateral
thermal damage (i.e. heat affected zones).
[0009] Laser ablation processes can be improved by selecting lasers
with wavelengths that are strongly absorbed by the medium (for
example, deep UV excimer lasers or far-infrared CO.sub.2 laser).
However, the aforementioned disadvantages cannot be eliminated due
to the aggressive interactions inherent in this physical ablation
process. This is amply demonstrated by the failings of UV
processing in certain LED applications where damage has driven the
industry to focus on traditional scribe and break followed by etch
to remove the damaged zones left over from the ablative scribe or
the diamond scribe tool, depending upon the particular work-around
technology employed.
[0010] Alternatively, laser ablation can also be improved at the
surface of transparent media by reducing the duration of the laser
pulse. This is especially advantageous for lasers that are
transparent inside the processing medium. When focused onto or
inside transparent materials, the high laser intensity induces
nonlinear absorption effects to provide a dynamic opacity that can
be controlled to accurately deposit appropriate laser energy into a
small volume of the material as defined by the focal volume. The
short duration of the pulse offers several further advantages over
longer duration laser pulses such as eliminating plasma creation
and therefor plasma reflections thereby reducing collateral damage
through the small component of thermal diffusion and other heat
transport effects during the much shorter time scale of such laser
pulses.
[0011] Femtosecond and picosecond laser ablation therefore offer
significant benefits in machining of both opaque and transparent
materials. However, in general, the machining of transparent
materials with pulses even as short as tens to hundreds of
femtoseconds is also associated with the formation of rough
surfaces, slow throughput and micro-cracks in the vicinity of
laser-formed kerf, hole or trench that is especially problematic
for brittle materials like alumina (Al.sub.2O.sub.3), glasses,
doped dielectrics and optical crystals. Further, ablation debris
will contaminate the nearby sample and surrounding devices and
surfaces. Recently, multi-pass stealth dicing has been disclosed.
In this approach each scan creates voids of about 50 .mu.m long and
by rotation of the incident beam and changing the focus of the
laser, multiple facet C-cuts are performed. This approach suffers
from the need to make multiple passes and precise rotation of the
laser head and focus changes for each C-cut and therefore results
in low processing throughput.
[0012] Short duration laser pulses generally offer the benefit of
being able to propagate efficiently inside transparent materials,
and locally induce modification inside the bulk by nonlinear
absorption processes at the focal position of a lens. However, the
propagation of ultrafast laser pulses (>5 MW peak power) in
transparent optical media is complicated by the strong reshaping of
the spatial and temporal profile of the laser pulse through a
combined action of linear and nonlinear effects such as
group-velocity dispersion (GVD), linear diffraction, self-phase
modulation (SPM), self-focusing, multiphoton/tunnel ionization
(MPI/TI) of electrons from the valence band to the conduction band,
plasma defocusing, and self-steepening.
[0013] These effects play out to varying degrees that depend on the
laser parameters, material nonlinear properties, and the focusing
condition into the material.
[0014] Although laser filamentation processing has been successful
in overcoming many of the limitations associated with diamond
cutting, as mentioned above, new demands for chamfer C cutting
encouraged invention of new methods and structure to successfully
implement filamentation photoacoustic compression scribing using
curved filaments.
SUMMARY OF THE INVENTION
[0015] Systems and methods are described for forming continuous
laser curved filaments in transparent materials. A burst of
ultrafast laser pulses or single laser pulse is propagated via a
custom optics cubic phase plate or mask to gain extensive cubic
phase then focused such that a beam waist is formed external to the
material being processed, such that a primary geometrical focus
does not form within the material, while a sufficient energy
density is formed within an extended region within the material to
support the formation of a continuous filament, without causing
optical breakdown within the material. An intense laser that gains
extensive cubic phase transforms to an Airy beam in far field.
Propagation of an Airy beam is first demonstrated by Siviloglou
(Phys. Rev. Lett. 99, 213901 2007) applying spatial light
modulator. An Airy beam tends to propagate in a parabolic
trajectory. As discussed by Papazoglou (Phes. Rev. A 81, 061807(R),
2010) it is possible to gain cubic phase via coma aberration which
is the nature of the lenses if they intercept the beam at an angle.
A spatial light modulator generally damage if an intense laser is
used and angled lens generally lose a lot of laser power. Since a
limited region of curved filament is desired it is preferable to
use a fixed cubic phase plate or mask to introduce sufficient phase
causing the beam to curve in the focus region. This creates a
curved filamentation inside the transparent material that assists
in singulation. As such, the facet is curved.
[0016] As stated above, curved facets are known as C-cuts. The
C-shaped in cross-section facet profile is sometimes referred to
herein as a C-cut facet profile, a C-shaped (curved) facet profile,
a C-shaped facet path, a C-cut facet or just a C-cut.
[0017] C-cut facets enhance bending strength and avoid formation of
chips or cracks. The prior art uses additional manufacturing steps
such as mechanical grinding to achieve C-cut facets.
[0018] Filaments formed according to this method may exhibit
lengths exceeding up to 10 mm with a 1:1 correspondence in the
length of the modified zone (in that the filament is the agent of
modification, so the modified zone tracks 1:1 with the extent of
the filament) and a taper-free profile when viewed with the long
axis in cross-section. In some embodiments, an uncorrected or
aberrated optical focusing element is employed to produce an
external beam waist while producing C-shaped filaments, for
example, a curved distributed focusing of the incident beam within
the material. Various systems are described that facilitate the
formation of C-shaped curved filament arrays within transparent
substrates for cleaving/singulation. Optical monitoring of the
filaments may be employed to provide feedback to facilitate active
control of the process.
[0019] Accordingly, in a first aspect, there is provided a method
of laser processing a transparent material, the method
comprising:
[0020] providing a laser beam comprising a burst of laser pulses or
single laser pulse;
[0021] providing a cubic phase mask in the beam path to induce
cubic phase in the laser pulses;
[0022] externally focusing the laser beam relative to the
transparent material to form a beam waist at a location that is
external to the transparent material;
[0023] wherein the laser pulses are focused such that a sufficient
energy density is maintained within the transparent material to
form a continuous laser C-shaped curved filament therein without
causing optical breakdown.
[0024] In another aspect, there is provided a method of processing
a transparent material, comprising the steps of:
[0025] providing a laser beam, said laser beam having a plurality
of bursts and each of said bursts include a plurality of
pulses;
[0026] generating an initial waist of said laser beam outside
(external to) said transparent material;
[0027] generating a weakly focused laser beam distributed within
said transparent material in a C-shaped curved path; and,
[0028] producing a spatially extended and spatially homogenous
C-shaped curved filament in said transparent material.
[0029] In another aspect, there is provided a method of processing
a transparent material, said transparent material has a metal layer
formed within or on a surface thereof, the laser beam is a
filament-forming laser beam, comprising the steps of:
[0030] prior to forming the continuous laser filament within the
transparent material;
[0031] providing a low-power laser beam comprising a burst of laser
pulses or single laser pulse by reducing the power of the
filament-forming laser beam below the threshold for the formation
of a filament within the transparent material, while maintaining
sufficient power to ablate the metal layer; and irradiating the
metal layer with the low-power laser beam at one or more locations
such that the metal layer is locally ablated by the laser beam
thereby producing one or more ablative markings within the metal
layer.
[0032] In another aspect, there is provided a transparent material
having a continuous laser C-shaped curved filament formed therein,
the continuous laser filament having a length exceeding
approximately 1 mm.
[0033] In another aspect, there is provided a transparent substrate
exhibiting a post-cleave or post-singulation break strength that
exceeds approximately 200 MPa.
[0034] In another aspect, there is provided a system for laser
processing a transparent material, the system comprising:
[0035] a laser source configured to provide a laser beam comprising
bursts of laser pulses;
[0036] a laser source configured to provide a laser beam comprising
a single pulse;
[0037] one or more focusing elements configured to externally focus
the laser beam relative to the transparent material to form a beam
waist at a location that is external to the transparent material
wherein the laser beam and the one or more focusing elements are
configured to produce a sufficient energy density within the
transparent material to form a continuous laser filament therein
without causing optical breakdown in a C-shaped curved profile;
[0038] means for varying a relative position between the laser beam
and the transparent material; and,
[0039] a control and processing unit operatively coupled to the
means for varying the relative position between the laser beam and
the transparent material, wherein the control and processing unit
is configured to control the relative position between the laser
beam and the transparent material for the formation of an array of
continuous laser filaments within the transparent material.
[0040] A further understanding of the functional and advantageous
aspects of the disclosure can be realized by reference to the
following detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] Embodiments of the disclosure will now be described, by way
of example only, with reference to the drawings, in which:
[0042] FIGS. 1A-E illustrate various optical configurations for the
formation of filaments.
[0043] FIGS. 1A and 1B illustrate the formation of filaments using
previously known methods involving the formation of a beam waist
within the material.
[0044] FIGS. 1C-1E illustrate various embodiments in which long
homogeneous filaments are formed by focusing the beam energy such
that it is "dumped" into a focus above and/or below the target
material (forming an "optical reservoir") in order to modulate the
amount of energy passed into the desired filament zone.
[0045] FIG. 1F is an example image of filaments formed according to
the methods disclosed herein, demonstrating the formation of a
spatially extended filament with a homogeneous and continuous
profile, where the depth and location of the filament within the
material is determined by the relative positioning of the beam
focus (each filament corresponds to a vertical offset of 25
microns).
[0046] FIG. 1G is a microscope image of a glass sample illustrating
the difference between the stealth dicing and filamentation
processing methods.
[0047] FIG. 2A depicts a long filament zone on the scales of
millimeters to tens of millimetres.
[0048] FIG. 2B illustrates the ability for the beam to pass through
intermediate layers without damaging them.
[0049] FIGS. 3A-3E illustrate the characteristics of an example
burst pulse train. In some embodiments the spacing between the
sub-pulses and the burst packets can be controlled, and the number
of pulses in the burst pulse train can be controlled.
[0050] FIG. 4A illustrates the optical configuration to curve the
filament reservoir resulting in curved filamentation.
[0051] FIG. 4B illustrates the C-shaped in cross-section facet
profile (C-cut edge).
[0052] FIG. 5A illustrates the Bessel-Airy beam configuration and
curved filament formation.
[0053] FIG. 5B illustrates the C-cut resulting from the structure
of FIG.5A.
[0054] FIGS. 6A-6C illustrate an example embodiment using a theta
stage for the positioning of the apparatus for the creation of
curved filament cleave planes. FIG. 6A is a side view of the
workpiece illustrating a C-shaped filament therein. The structure
of FIGS. 6A, 6B and 6C enables the production of parts with
C-shaped edges. For example, using the theta stage, a circular path
can be traced producing a part as shown in FIG. 6C with a cut-out
having a C-cut edge. FIG. 6B is a perspective view of the workpiece
illustrated in FIG. 6A. FIG. 6C illustrates a part cut from the
workpiece illustrated in FIGS. 6A and 6B with a circularly
extending C-shaped edge.
[0055] FIGS. 7A-7D illustrate an example embodiment showing the
formation of complex spline parts from curved targets by servoing
the z and "steering the beam" with adaptive optics, which are also
controlled by servo motors. The beam (FIG. 7A) and/or part (FIGS.
7B, 7C)) can be rotated, tilted or otherwise manipulated to create
a very wide process window and capability for producing parts with
complex surface curvature. FIG. 7D provides an example
implementation of such an embodiment, showing a glass part
processed via filament formation to exhibit a rounded edge.
[0056] FIG. 8A illustrates an example embodiment in which a
multilayer substrate can be cut or processed in single pass,
C-cutting of all layers.
[0057] FIG. 8B illustrates the processing of a two layer laminated
glass substrate having a C-cut in each layer.
[0058] FIG. 8C illustrates the processing of a two layer laminated
glass substrate having a C-cut in each layer but having an offset
cut.
DETAILED DESCRIPTION OF THE INVENTION
[0059] Various embodiments and aspects of the disclosure will be
described with reference to details discussed below. The following
description and drawings are illustrative of the disclosure and are
not to be construed as limiting the disclosure. Numerous specific
details are described to provide a thorough understanding of
various embodiments of the present disclosure. However, in certain
instances, well-known or conventional details are not described in
order to provide a concise discussion of embodiments of the present
disclosure.
[0060] As used herein, the terms, "comprises" and "comprising" are
to be construed as being inclusive and open ended, and not
exclusive. Specifically, when used in the specification and claims,
the terms, "comprises" and "comprising" and variations thereof mean
the specified features, steps or components are included. These
terms are not to be interpreted to exclude the presence of other
features, steps or components.
[0061] As used herein, the term "exemplary" means "serving as an
example, instance, or illustration," and should not be construed as
preferred or advantageous over other configurations disclosed
herein.
[0062] As used herein, the terms "about" and "approximately" are
meant to cover variations that may exist in the upper and lower
limits of the ranges of values, such as variations in properties,
parameters, and dimensions. In one non-limiting example, the terms
"about" and "approximately" mean plus or minus 10 percent or
less.
[0063] Unless defined otherwise, all technical and scientific terms
used herein are intended to have the same meaning as commonly
understood to one of ordinary skill in the art. Unless otherwise
indicated, such as through context, as used herein, the following
terms are intended to have the following meanings.
[0064] As used herein, the term "filament modified zone" refers to
a filament region within a substrate characterized by a region of
compression defined by the optical beam path.
[0065] As used herein, the phrases "burst", "burst mode", or "burst
pulses" refer to a collection of laser pulses having a relative
temporal spacing that is substantially smaller than the repetition
period of the laser. It is to be understood that the temporal
spacing between pulses within a burst may be constant or variable
and that the amplitude of pulses within a burst may be variable,
for example, for the purpose of creating optimized or
pre-determined filament modified zones within the target material.
In some embodiments, a burst of pulses may be formed with
variations in the intensities or energies of the pulses making up
the burst.
[0066] As used herein, the term "transparent" refers to a material
having an absorption spectrum and thickness such that at least a
portion of the incident beam is transmitted in the linear
absorption regime. For example, a transparent material may have a
linear absorption spectrum, within a bandwidth of the incident
beam, and a thickness, such that the percentage of light
transmitted through the material is greater than 10%, greater than
25%, greater than 50%, greater than 75%, greater than 80%, greater
than 85%, greater than 90%, greater than 95%, greater than 98%, or
greater than 99%, as the case may be.
[0067] As used herein, the phrase "geometric focus" refers to the
calculated or estimated focus produced by an optical focusing lens
or assembly, where the calculation is made without incorporating or
considering nonlinear effects within the material being processed
(e.g. with a beam waist position determined according to the simple
lens equation). This phrase is used to distinguish between the
expected location of the optical focus based on the position of the
lenses, and the optical constriction events created within the
material being processed that are caused by non-linear beam
refocusing, which provides, in effect, a quasi-Rayleigh length on
the order of up to approximately 10 mm.
[0068] As used herein, the term "photoacoustic drilling" refers to
a method of machining a target (generally by cutting or drilling of
a substrate from a solid by irradiating it with a lower pulse
energy light beam than is used in ablative drilling or cutting
techniques. Through the processes of optical absorption followed by
thermoelastic expansion, broadband acoustic waves are generated
within the irradiated material to form a pathway of compressed
material about the beam propagation axis (common with the axis of
the orifice) therein that is characterized by a smooth wall
orifice, a minimized or eliminated ejecta and minimized micro crack
formation in the material.
[0069] Airy beam refers to a laser pulses that are propagated
through a spatial light modulator, combination of angled lenses or
phase plate to gain a substantially cubic phase. An airy beam pulse
is a special kind of pulse with cubic phase that does not diffract
and propagate in a parabolic arc trajectory in the far field. Using
a single lens applies a Fourier transform to the pulse and changes
the arc trajectory formation to the near field (geometrical focus
of the lens).
[0070] A Bessel beam is a non-diffractive beam that can be
generated using an axicon. It has a long depth of focus ideal to
elongate the focus to guide the intense ultrafast beam towards
filamentation.
[0071] An Airy-Bessel beam refers to pulses that have a substantial
cubic phase that focuses using axicon to form an elongated curved
focuses.
[0072] The main objective of the present invention is to provide
fast, reliable and economical non-ablative laser machining to
initiate orifices (stopped/blind or through orifices) in the target
material that may be initiated below or above a single or multiple
stacked target material by curved filamentation by a burst(s) of
ultrafast laser pulses. Ultra short lasers offer high intensity to
micromachine, to modify and to process surfaces cleanly by
aggressively driving multi-photon, tunnel ionization, and
electron-avalanche processes. The issue at hand is how to put
enough energy in the transparent material of the target, less than
that used in ablative drilling, but beyond the critical energy
level to initiate and maintain photoacoustic compression so as to
create a filament that modifies the index of refraction at the
focal points in the material and does not encounter optical
breakdown (as encountered by the prior art ablative drilling
systems) such that continued refocusing of the laser beam in the
target material can continue over long distances, enough so that
even multiple stacked substrates can be drilled simultaneously with
negligible taper over the drilled distance, a relatively smooth
orifice wall and can initiate from above, below or within the
target material all in a curved configuration as such after
cleaving the sample facet having a C-shaped in cross-section
profile.
Laser Filamentation
[0073] Laser filaments can be formed in transparent materials using
ultrafast laser pulses that are focused within the material. For
example, as taught in Patent Cooperation Treaty Application No.
PCT/CA2011/050427, titled "Method of Material Processing by Laser
Filamentation", filaments can be formed by focusing, with an
objective lens, a burst-train of short duration laser pulses inside
a transparent substrate. The burst of laser pulses produces
internal microstructural modification with a shape defined by the
laser filament volume. By moving the sample relative to the laser
beam during pulsed laser exposure, a continuous trace of filament
tracks is permanently inscribed into the glass volume as defined by
the curvilinear or straight path followed by the laser in the
sample.
[0074] As noted in PCT Application No. PCT/CA2011/050427, it is
believed that filaments (also referred to as "plasma channels") are
produced by the weak focusing of laser pulses having a high
intensity and short duration, such that the pulses can self-focus
by the nonlinear Kerr effect due to the formation of a plasma. This
high spatio-temporal localization of the light field can deposit
laser energy in a long and narrow channel, while also being
associated with other complex nonlinear propagation effects such as
white light generation and formation of dynamic ring radiation
structures surrounding this localized radiation. PCT Application
No. PCT/CA2011/050427 teaches that laser filaments may be formed
over length scales on the order of hundreds of microns by focusing
the laser beam such that the focal point (e.g. initial beam waist)
lies within the material.
[0075] In contrast to known filament forming methods, the present
disclosure provides methods for forming spatially extended and
spatially homogeneous curved filaments in transparent materials.
According to one embodiment, a burst of ultrafast laser pulses is
focused such that an external beam waist is formed outside the
target material and weak distributed focusing of the incident beam
occurs within the target material in an arc configuration, thereby
forming a high density electric field within the material and
creating a zone of compression along the incident path of the
laser. This zone of compression results in a phase change
(confirmed by etch rate experiments) in a narrow curtain of
material extending uniformly and radially from the center of the
propagation axis.
[0076] As described further below, the length and position of the
filament is readily controlled, for example, by the positioning of
the focusing apparatus, the cubic phase plate or mask, the
numerical aperture of one or more focusing elements, the laser
pulse energy, wavelength, duration and repetition rate, the number
of laser pulses and bursts applied to form each filament track, and
the optical and thermo-physical properties of the transparent
medium. Collectively, these exposure conditions (power, repetition
rate, translation speed and the degree to which the wavefronts has
been distributed/aberrated to extend the interaction zone) can be
manipulated to create sufficiently long and intense filaments to
extend or nearly extend over the full thickness of the processed
material.
[0077] Accordingly, embodiments disclosed herein harness short
duration bursts of laser pulses (preferably with a pulse duration
less than about 100 ps) to generate a filament inside a transparent
medium. The method avoids plasma generation such as through optical
breakdown that can be easily produced in tight optical focusing
conditions as typically applied and used in femtosecond laser
machining (for example, as disclosed by Yoshino et al.,
"Micromachining with a High repetition Rate Femtosecond Fiber
Laser" (2008), Journal of Laser Micro/Nanoengineering Vol. 3, No. 3
pgs. 157-162).
[0078] In the weak and distributed focusing embodiments disclosed
herein, the nonlinear Kerr effect is believed to create an extended
laser interaction focal volume that exceeds the conventional depth
of field, overcoming the optical diffraction that normally diverges
the beam from the small self-focused beam waist. It is in this
so-called filament zone, formed via distributed or extended
focusing, that the material undergoes a phase transition induced by
photo-acoustic compression, in a substantially symmetrical,
substantially curved cylindrical region centered about the axis of
beam propagation in the material.
[0079] This modification requires energy densities above a certain
characteristic threshold for each material, ideally chosen by the
highest threshold of the materials present in a non-homogeneous
complex stack. This modification can occur at normal and non-normal
angles of incidence relative to the top of the substrate and
persist for distances only limited by the power available in the
incident beam.
[0080] Furthermore, it is believed that optical breakdown does not
occur in the material during processing, as this would create
discrete damage centers instead of the long continuous and
homogenous filament modified zones of the present disclosure. While
laser energy deposited along the filaments leads to internal
material modification that can be in the form of defects, color
centers, stress, microchannels, microvoids, and/or micro
cracks--experimental results have shown that the modification is
substantially uniform and symmetric in its appearance, with an
interior surface that is substantially homogenous in its physical
characteristics. This is believed to be achieved by presenting a
very high intensity electric field that possesses a very uniform
energy distribution along the length of the filament.
Formation of Extended Straight Filaments via Distributed Focusing
of Laser Beam
[0081] In contrast to the methods and apparatus disclosed in PCT
Application No. PCT/CA2011/050427, the present disclosure provides
methods, apparatus and systems for the controlled formation of
filaments in transparent materials using an optical focusing
configuration in which the incident beam is directed onto the
material such that an external waist is formed and such that the
beam energy is focused in a distributed manner throughout a region
within the material. It is believed that the distributed focusing
configuration without the formation of an internal beam waist
provides conditions that sustain the formation of the laser
filament over longer distances, with more controllable geometries
and mechanical properties, as further described below.
[0082] Referring now to FIG. 1A, a focusing arrangement disclosed
in PCT/CA2011/050427 is illustrated, in which focusing lens 100 is
employed to focus a burst of ultrafast laser pulses within a
material 110 for the formation of a filament 120. Focusing lens 100
is positioned relative to material 110 such that the focus of lens
100 is located within material 110. Incident beam 130 is focused by
focusing lens 100 to form converging beam 140, which is focused
within material 110 and maintains a focused configuration, forming
filament 120 prior to expanding and de-focusing. As described
above, the confinement of the optical power within material 110,
while forming filament 120, is achieved through self-focusing via
self-phase modulation. Beam 140 expands beyond the filament forming
region due to loss of optical beam power, such that self-phase
modulation is no longer sufficient to support self-focusing and to
counter the defocusing caused by the presence of the heating and
subsequent index change in the target material. As shown in FIG.
1B, this method can result in the formation of a filament 120
within material 110 having a length on the scale of hundreds of
microns.
[0083] FIG.1C illustrates an example embodiment of spatially
extended filament generation in a transparent material through the
distributed focusing of a burst of ultrafast laser pulses. Unlike
the configuration shown in FIG. 1A, in which incident beam 130 is
focused by focusing lens 100 to form a well-defined initial waist
within material 110, the configuration shown in FIG. 1C employs
distributed focusing element 150 to focus incident beam 160 such
that the resulting converging beam 165 is focused to an initial
external waist 175, and is also weakly focused in a distributed
manner within material 115. The external formation of the initial
waist prevents excessive focusing and optical breakdown within the
material, avoiding deleterious effects such as optical breakdown.
The distributed focusing configuration causes the focused beam to
be directed onto material 115 such that the optical power is
extended over a range of locations, unlike known methods in which
external focusing produces a narrow external plasma channel,
thereby distributing the incident laser within material 115, as
opposed to forming a waist within the material with a tight and
well-defined location. Such a distributed focusing configuration is
capable of producing a filament 170 having controlled geometrical
properties and a length on the millimeter scale. Distributed
focusing element 150 may include one or more lenses that are formed
(e.g. ground or molded) to produce what appears to be a distributed
focus (not necessarily an evenly distributed focus), with a waist
residing above or in front of the surface of the material, adjacent
to a surface of the material, providing a very weakly focused spot
at the material surface in the absence of an external plasma
channel In one embodiment, the waist is located at an offset of at
least approximately 10 .mu.m from an external surface of the
material. In another embodiment, the waist is located at an offset
of at least approximately 20 .mu.m from an external surface of the
material. In another embodiment, the waist is located at an offset
of at least 50 .mu.m from an external surface of the material.
Accordingly, the present embodiment avoids the need to form a
primary beam waist within the material by altering the focal
properties of the lenses, offering a wide range of processing
options, such that an external waist is formed above, below or, for
example, in between layers of target materials in an interstitial
space.
[0084] Without intending to be limited by theory, it is believed
the distributed focusing configuration of the present disclosure
produces longer filaments due to the spatial replenishment of the
optical beam power from the additional focal regions. As optical
power within the narrow filament forming region is initially
depleted during beam propagation, through interaction with the
complex (non-linear) index changes formed via the nonlinear
processes, additional optical power is provided by the distributed
focusing of the beam along its length, such that the beam can
propagate further in a self-focused manner while forming the
filament, prior to defocusing. As noted above, in some embodiments
this approach produces the desired self-focusing and compression
without actually forming plasma.
[0085] Referring again to FIG. 1C, the illustrated example
embodiment is shown with focusing element 150 positioned such that
a least a portion of the converging beam 165 is focused in front of
material 115, for example at location 175 in FIG. 1C. In
particular, in the example implementation shown, the high numerical
aperture rays encountering distributed focusing element 150 are
focused in front of material 115. By focusing a portion of the
incident optical power in front of material 115, the intensity
profile formed immediately within the material is not too high or
too low, which therefore allows the formation of a filament having
a substantially uniform cross section over its length.
[0086] As noted above, the advantage of creating a beam waist above
or in front of the material, instead of below, lies in the desire
to avoid exceeding the optical breakdown threshold of the material.
It also enables a larger process window by giving the user more
options relative to process set-up and sample configuration.
[0087] FIG. 1D illustrates an alternative example embodiment in
which distributed focusing element 150 is positioned such that a
portion of converging beam 180 is focused behind material 115 at
location 185 for forming filament 190. Referring now to FIG. 1E,
another example embodiment is illustrated in which distributed
focusing element 150 is positioned such that a portion of
converging beam 191 is focused in front of material 115 (e.g. at
location 192), and another portion of converging beam 191 is
focused behind material 115 (e.g. at location 193), for forming
filament 194. In this configuration, a greater length and still
maintain enough energy along the path through the target to create
acoustic compression from the electric field induced heating
effects formed by the laser. This embodiment may be employed to
enable a higher degree of control and depth in forming filaments.
As shown in FIG. 1D, such an embodiment may be useful in forming
filaments throughout the material, through transparent substrates
with thicknesses of millimeters to tens of millimeters. The benefit
of the distributed focusing configuration employed in methods
disclosed herein can be understood as follows. If the incident beam
is focused to a waist within the material, the filament progression
stops after a short distance, as in the previously known methods.
However, if the incident power is focused outside of the material,
forming an optical reservoir, and the material is allowed to act as
the final lens as it undergoes thermally induced changes in the
index (complex index in particular), then the filament can be
formed with a substantially homogeneous cross sectional profile,
and spatially extended over millimeters in length, as illustrated
in FIG. 1F, which demonstrates the formation of homogeneous
filaments with lengths exceeding 1 mm in soda lime glass. FIG. 1F
further illustrates the control of relative vertical positioning of
the filaments by varying the axial position of the beam focus (each
filament corresponds to an offset of 25 microns). Such processing
can produce high quality edges which are substantially absent of
large chips. (for example, chips>10 .mu.m).
[0088] FIG. 1G is a microscopic image of a glass substrate
processed and cleaved according to the stealth dicing method. A
filament array had also been formed in a direction perpendicular to
the stealth dicing line (the sample shown had not yet been cleaved
according to the filament array line). As shown in FIG. 1G stealth
dicing line 20 shows the telltale signs of optical breakdown, which
produces a very smooth top edge, but a very rough face overall. The
roughness of the faced edge obtained by cleaving along the stealth
dicing line was found to be 53 microns in the vertical direction
and 85 microns in the horizontal direction. In contrast, filament
10 illustrates a continuous material modification extending through
the substrate, facilitating cleavage that results in a smoother
facet. As described below, the cleavage of the sample along the
filament array line can produce surface roughness values on the
order of 1 to 10 microns for glass materials.
[0089] As described in further detail below, the filaments formed
according to the methods disclosed herein can be formed with a
length that is much longer than previously reported filaments.
Furthermore, the present methods can be employed to produce
filaments that are continuous, radially symmetric and uniform in
dimension. A key consideration for the formation of extended
filaments within the transparent material is the supply of the
requisite fluence, treated below, while at the same time avoiding
the optical breakdown threshold of the material. It has been found
that the filament length is tied into the total energy supplied to
the material and the material's linear absorption.
[0090] For example, filaments 3 mm long can be formed in
borosilicate glass using the following conditions: an average power
of approximately 50W; a wavelength of 1064 nm; a pulse width of
less than approximately 50 picoseconds; a burst profile of
approximately 5 pulses, a pulse profile decreasing in amplitude,
increasing in amplitude, and/or level in amplitude; and a spot size
of approximately 10 .mu.m.
[0091] The position of the stop and start of the filament can be
controlled by selecting the position of the geometric focus, or
beam waist, as predicted by the geometrics of the lens group or
focusing assembly. The balance between power and size, also
explained below, provides the ability to avoid the formation of a
beam waist within the material.
[0092] FIGS. 2A and 2B show the flexibility can be achieved by
controlling the location of the beam waist focus. FIG. 2A depicts a
long filament zone 250 on the scales of millimeters to tens of
millimeters (not to scale; filaments of up to 10 mm have been
produced by the inventor). The ability for the beam to pass through
layers without damaging them is illustrated. The critical diameter
range 260 (which may vary, for example, accordingly for each
material, focusing conditions, and laser power) is also indicated,
which is defined as the range of laser spot diameters above which
filaments do not form and below which optical damage occurs. In one
example implementation, the critical diameter range for soda lime
glass has been found to lie near 8 .mu.m. The critical ratio is
also noted, which equals the ratio of the diameter of the incident
laser spot on the material to the diameter of the filament. For
example, in one example range, the critical ratio may vary between
approximately 0.01 and 1000; in another example range, the critical
ratio may vary between approximately 0.01 and 10, in another
example range, the critical ratio may vary between approximately 10
and 50, in another example range, the critical ratio may vary
between approximately 50 and 500, and in another example range, the
critical ratio may vary between approximately 1 and 1000.
[0093] As shown in FIG. 2B, the incident beam 270, focused by final
lens 275, can be made to pass through one or more substantially
transparent layers 272 above the desired target location of the
filament zone, without forming either a focus or any filaments,
with an external waist 290 that is formed beyond the final layer
276. Filaments 280, 280 then form within one or both layers 274,
276 and not in transparent layer 272 (as a result of the critical
(requisite) fluence not being achieved in layer 272)
[0094] Critical fluence is achieved in layers 274, 276 as
illustrated in FIG. 2B along the incident path through the target
stack.
[0095] In order to control the fluence in the incident beam, the
power contained within the beam diameter at the surface of the
material can be altered, programmed in fact, by varying the size of
the beam diameter. In particular, there is a correlation between
the transparent material, the critical (required) fluence (power)
and filament formation efficacy.
[0096] In one example implementation, the properties of the
filaments can be controlled by varying the first incident fluence
(the fluence on the first incident surface) and the energy
contained within each sub pulse. It will be understood that in
embodiments involving multiple surfaces upon which the laser is
incident (described further below), each surface will have its own
fluence, and each fluence will depend upon the first incident
fluence due to absorption and scattering.
[0097] It has been found that an incident spot size of
approximately 100 .mu.m leads to filaments with a diameter of 2.5
.mu.m and a length of several mm. Some characteristics of the
filament can be controlled by changing the pulse energy and spot
size ratio. Different materials have different propensities toward
extended filament formation.
[0098] In order for the filament to create a continuous and
substantially uniform channel, the energy intensity must also be
such that once deposited, the burst pulse induced intensity,
refreshed at the burst pulse frequency rate, is capable of forming
a shock wave of the requisite intensity to radially compress the
material. Once this phase change occurs (or in certain materials,
simply a density change), the filament zone functions as a cleavage
plane, either immediately, after some programmable delay or via the
application of a subsequent cleavage step. A suitable energy can be
empirically determined for a given material by producing filaments
at various beam energies, observing or measuring the filament
depth, and selecting a beam energy that produces filaments of a
suitable length. In one non-limiting example implementation, the
energy in the incident beam (the energy of all pulses in a burst)
may be between approximately 10 .mu.J and approximately 2000
.mu.J.
[0099] It will be understood that a wide range of laser beam
parameters may be varied to obtain filaments with different
characteristics and properties. Furthermore, the beam parameters
suitable for forming a filament with a given set of properties will
vary among different materials. The present disclosure provides
some example ranges of beam parameters that may be employed to form
filaments in some selected materials. Such example ranges are not
intended to be limiting, and it will be understood that other
ranges may be suitable for forming filaments with other properties
in the example materials, or in other materials.
[0100] It is to be understood that the burst repetition rate,
together with the translation speed of the material relative to the
incident beam, defines the spacing between neighboring filaments.
In one non-limiting example, this range may be from approximately 1
kHz to approximately 2 MHz.
[0101] As shown in FIGS. 1C to 1E, the incident beam is focused
such that the focal volume is distributed over an extended region
within the sample. The distributed focal volume may be sufficiently
longer than the Rayleigh range obtained from a non-distributed
focusing element having a similar or equivalent numerical aperture.
For example, the focal region under distributed focusing may be
20%, 30%, 50%, 100%, 200%, 500%, 1000% or greater than the
corresponding Rayleigh range obtained without distributed
focusing.
[0102] The distributed focal volume may be sufficiently long that
the filament formed by the beam under distributed focusing
conditions is significantly longer than the filament that would be
formed from a non-distributed focusing element having a similar or
equivalent numerical aperture. For example, the filament formed
under distributed focusing may be 20%, 30%, 50%, 100%, 200%, 500%,
1000% or greater than the corresponding filament formed without
distributed focusing.
[0103] It is to be understood that the distributed focal assembly
may include one or more optical components/elements, such as an
optical train including two or more optical components. In one
embodiment, the distributed focal assembly is configured to focus
the optical beam in a non-distributed manner in one lateral
dimension, and to focus the beam in a distributed manner in the
other lateral dimension.
[0104] With appropriate beam focusing, manipulating the focal
length or beam expansion ratio, for instance, laser filaments can
terminate and cause the laser beam to exit the glass bottom surface
at high divergence angle such that laser machining or damage is
avoided at the bottom surface of the transparent plate. It is also
possible to create filaments in the middle of a multi-sheet stack,
without inducing damage in the sheets located above and below the
target sheet, but while damaging the top and bottom surface of the
target sheet, as described further below.
[0105] In some embodiments, the long filament length may be created
by a combination of negative and positive lenses that optimize the
filling of the apertures on each optical element, maintaining high
power efficiency within the optical train and maintains laser
intensity to radially compress the target material as has been
previously described.
Example Distributed Focusing Element: Aberrated Element
[0106] In some embodiments, the distributed focal assembly may
include one or more optical components configured to induce
aberrations in the focused optical beam, such that the focused
optical beam is focused in a distributed manner over a longitudinal
focal volume without forming a waist within the material.
[0107] One or more optical components may include spherical
aberration. In some embodiments, the distributed focal assembly may
include one or more aberrated optical components, and one or more
substantially non-aberrated optical components. In some
embodiments, aberrations are induced by the distributed focal
assembly in one dimension. In other embodiments, aberrations are
induced by the distributed focal assembly in two dimensions.
[0108] Long filaments can be created by the use of an aberrated
optical assembly (one or more aberrated optical elements) such that
a long series of quasi-focal points can be achieved, even though no
beam-waist forms within the material due to the distortion wrought
by the target itself and the electric field heating created along
the incident axis. Creating a large spot with >1 .mu.m diameter
and creating at least one external beam waist (a "reservoir
region"), in front of the target material and/or behind it (as
illustrated in FIGS. 1C-1E, enables "dumping" energy into focal
spots outside the target material or layer, where a beam waist is
formed in the air without forming a plasma channel in the air, and
no ablative work is accomplished.
[0109] The present embodiment provides a beam path with non-uniform
distribution of energy outside of the material, while also forming
a uniform beam path contained within the target material that
produces a filament containing no beam waist along its length.
[0110] Using one or more aberrated elements, one can choose to
distribute the energy in such a fashion as to avoid the beam waist
event within the material and yet create a uniform filament and
"dump" the extra energy into one, two or more external waist
regions, without forming an external plasma channel, in order to
maintaining the required fluence to promote filament formation,
long uniform modification and avoid optical breakdown. In other
words, the strong focus of the one or more aberrated elements may
be employed to act as an external beam dump, and the remaining rays
may be employed to create a strong burst pulse filament within the
material.
[0111] The aberration of an optical focusing component, assembly,
or system may be measured in waves (or fractions thereof, related
to the wavelength of light being used). For example, the aberration
may be specified according to the ratio of waves not arriving at
the same spatial point (or volume) as defined by the ideal lens to
the ratio of waves arriving at the same point. In some non-limiting
example implementations, the aberration in the optical focusing
assembly may be greater than approximately 0.1% aberration and less
than approximately 80% aberration.
[0112] The nature of the aberration can be variable provided the
energy density at the first incident surface stays above that
required to form filaments and below the optical breakdown
threshold for the target material. In one particular example, the
optical elements can be formed such that two primary foci form,
separated by at least a distance corresponding to the thickness of
the target material(s) or layer(s). See, for example, FIG. 1E.
Burst Pulse Characteristics
[0113] It has been found that the use of burst pulses in a
distributed focusing configuration supports the formation of long
filaments (such as, but not limited to, filaments having a length
>15% of the total target material thickness, for example, in
glass applications, a length >100 .mu.m and up to >10 mm),
with homogenous properties (for example, filaments having
substantially the same diameter over a substantial length thereof,
and substantially the same diameter at the entrance and exit faces
of the material for filaments that traverse the material
thickness). It is possible to make a filament using a single pulse
but the effect of heat accumulation using a burst of laser pulses
is outstanding. Similarly, material scribing that can be done with
40 W ps laser would need at least 60 W if a single pulse regime is
used. Importantly, a 40 W scribed line using burst pulses will
cleave much easier than a 60 W scribed line using a single pulse
both scribed at the same speed. The distributed focusing of a burst
of pulses also supports the formation of smooth surfaces after
cleaving along a filament array. For example, the beam and focusing
conditions disclosed herein have been employed to provide segmented
samples with cut face surface roughness (Ra) that is less than
approximately 10 .mu.m, and sometimes as low as 200 nm, or less.
Such filaments can be formed in brittle materials.
[0114] FIGS. 3A-3E illustrate multiple embodiments showing the
temporal nature of the burst pulses 350 and the degree of control
the laser source can provide on the timing and sequencing of the
pulse. FIGS. 3A and 3B illustrates the optional control over burst
repetition rate 360 and inter-pulse temporal spacing 375. For
example, the timing between the pulses can be controlled by
manipulating the EO switch timing, to create various multiples of
the main oscillator signal, generating the variable pulse timing.
FIG. 3B is an example illustration showing the degree of
variability over which the pulses can be delivered and a schematic
of the pulses being generated within the laser head 370. It is to
be understood that in some embodiments, the pulses could be
modulated along the optical train, for example, by inclusion of an
optical switch or electro-optical switch to develop user selectable
pulse (and or pulse envelopes) profiles (rising or falling or
equal), changing the amplitude of the energy in the pulse (and/or
pulse envelopes) and deciding to what degree it is divided among
smaller burst pulses where the total number of pulses is user
selectable.
[0115] As shown in FIG. 3C, the user/operator may manipulate the
pulse profile 380 to control the process based on the desired
material properties of the parts generated in a system equipped
with such a laser and associated optics.
[0116] FIG. 3D illustrates the ability to control the net energy
delivered to the material, based on the integrated power in the
burst. FIG. 3E illustrates the ability to control the number of
pulses in a given burst 390. In one example implementation, the
burst of laser pulse is delivered to the material surface with a
pulse train containing between 2 and 20 sub pulses into which the
laser pulse is divided. This division may be created within the
laser head according to one of several known approaches. It is to
be understood that any one or more of the pulse parameters shown in
FIGS. 3A-3E may be employed to control the formation of filaments
within the processed material.
Materials
[0117] The filamentation methods disclosed herein may be employed
for the processing of a wide range of materials that are
transparent to the incident laser beam, including glasses,
crystals, selected ceramics, polymers, liquid-encapsulated devices,
multi-layer materials or devices, and assemblies of composite
materials. Substrates processed according to the methods disclosed
herein may include glasses, semiconductors, transparent ceramics,
polymers, transparent conductors, wide bandgap glasses, crystals,
crystalline quartz, diamond, and sapphire, rare earth formulations,
metal oxides for displays and amorphous oxides in polished or
unpolished condition with or without coatings.
[0118] It is further to be understood that the spectral range of
the incident laser beam is not limited to the visible spectrum, but
may also lie in the vacuum ultraviolet, ultraviolet, visible,
near-infrared, or infrared spectra. For example, silicon is
transparent to above 1300 nm light but opaque to visible light.
Thus, laser filaments may be formed, for example, in silicon with
short pulse laser light generated at above 1300 nm wavelength
either directly (e.g. viadoped fiberlasers) or by nonlinear mixing
(e.g. via optical parametric amplification) in crystals or other
nonlinear medium. Suitable performance can be expected with light
ranging from 1200-3000 nm for a wide array of brittle materials,
such as Si, SiC, GaAs, GaN, and other compound and complex compound
semiconductors (for example, II-VI and similar band gap engineered
materials) as well as display-related compounds, such as ITO, IPS,
IGZO, etc.
Pulse Energies and Power
[0119] In order to form filaments and to sustain self-focusing, the
pulse energy is selected to be within the nonlinear regime, such
that burst generated filament formation is possible. According to
one non-limiting example, it has been found that for the processing
of soda lime glasses, pulse energies between approximately 10 .mu.J
and 2 mJ are suitable for achieving the electric field intensity
needed to reach a state where it can be sustained for self-focusing
to occur. In some example implementations, the average power of the
laser may lie within approximately 3 W and 150 W (or more),
although it will be understood that the average power required for
filament formation will depend on the pulse energies, number of
pulses per burst, and repetition rate, for example.
[0120] In one example embodiment, the pulse repetition rate may
range between 10 kHz and 8 MHz in terms of the pulse repetition
frequency as defined by the pulse picked oscillator. These may be
subsequently down-selected into bursts of less energy and delivered
to the material with sub-pulse spacing equal to 1 fs or greater, up
to 1 millisecond. In some example embodiments, the laser possess a
beam quality, M.sup.2, of less than approximately 5. An M.sup.2 of
approximately 1 may be employed, for example, in embodiments where
the optical components are configured to create more than one focal
point along the axis, and while less strict M.sup.2 embodiments can
be tolerated to the extent that the downstream optics are
compensating for the beam's native shape. In some example
embodiments, in which a filament is to be formed throughout the
thickness of the material, the laser beam should be transmitted
through the material (including any intervening gaps of
inhomogeneous and dissimilar materials) with a transmitter power
exceeding a pre-selected threshold (for example, at least
approximately 50%) in order to provide sufficient luminous
intensity along the beam path.
Collimation, Focal Length, Clear Aperture
[0121] In some embodiments, the optical train of the system
includes one or more optical components for collimating the beam
prior to focusing, in order to accommodate a variable path length
between the distributed focusing element and the laser source. In
some example embodiments, the numerical aperture of the collimating
components is between approximately 0.1 and 0.88 NA, with an
effective focal length between approximately 4.5 mm and 2.0 m. In
some example embodiments, the diameter of the clear aperture may be
between approximately 2 and 10 mm.
Filament Formation Mechanisms
[0122] The present methods for forming filaments therefore support
new material processing applications for transparent materials that
were hitherto not possible. Extremely long, C-shaped (curved)
filaments are generated, by virtue of burst mode timing and
distributed focusing.
[0123] Known laser processing methods, such as those employed in
the Stealth Dicing and the Accuscribe systems, are driven by
modifications such as those by the Yoshino et al. ["Micromachining
with a High repetition Rate Femtosecond Fiber Laser" (2008),
Journal of Laser Micro/Nanoengineering Vol. 3, No. 3 pgs. 157-162],
are processes governed primarily by optical breakdown, where the
primary mode of material removal is ablation via small explosions
creating voids of variable lateral dimensions and of limited
longitudinal length. Optical breakdown is the result of a tightly
focused laser beam inside a transparent medium that forms a
localized and dense plasma around the geometrical focus created by
the material to be singulated. The plasma generation mechanism is
based on initial multi-photon excitation of electrons; followed by
inverse Bremsstrahlung, impact ionization, and electron avalanche
processes. The Columbic explosion is responsible for creation of
the localized voids and other modifications described in the
literature. Such processes and systems, underscore the refractive
index and void formation processes described above [US6154593; SPIE
Proceedings 6881-46,], and form the basis of most short-pulse laser
applications for material processing. In this optical breakdown
domain, the singulation, dicing, scribing, cleaving, cutting, and
facet treatment of transparent materials has disadvantages such as
slow processing speed, generation of cracks, low-strength parts,
contamination by ablation debris, and large kerf width--all of
which require further processing to complete the part's journey to
assembly into handheld electronic devices such as computers,
tablets and/or phones.
[0124] In contrast, laser filamentation processing and the systems
disclosed herein overcome the disadvantages of the previously known
methods for internal laser processing of transparent materials, and
can avoid ablation or surface damage (if desired), dramatically
reduce kerf width, avoid crack generation, and speed processing
times for such scribing applications. Further, high repetition rate
lasers equipped with regenerative amplifiers and fast electro-optic
switching allow for the enhancement of the formation of laser beam
filaments with minimal heat accumulation and other transient
responses of the material on time scales much faster (smaller in
time) than thermal diffusion out of the focal volume (typically
<10 microseconds). The focal volume produced according to the
methods of the present disclosure can be manipulated by optical
components in the beam path to extend many times the calculated
depth of focus (DOF).
[0125] As shown in the examples below, using picosecond pulse
bursts, the pulses focus in a distributed manner, it remains
confined for an axial distance ranging from approximately 20 .mu.m
to approximately 10 mm, depending on the fluence of the laser
pulses, and depending on the process conditions chosen. This
enables dense, localized sonic pressure formation useful for via
drilling with substantially zero taper, in materials where
substantially non-ablative processes are responsible for removing
or compressing most of the material.
[0126] Without intending to be limited by theory, it is believed
that the filaments are produced by weak focusing, high intensity
short duration laser light, which can self-focus by the nonlinear
Kerr effect, thus forming a so-called filament. This high
spatio-temporal localization of the light field can deposit laser
energy in a long narrow channel, while also being associated with
other complex nonlinear propagation effects such as white light
generation and formation of dynamic ring radiation structures
surrounding this localized radiation.
[0127] Heating by the rapid laser pulses temporarily lowers the
refractive index in the center of the beam path causing the beam to
defocus and break up the filament. The dynamic balance between Kerr
effect self-focusing and index shifting modulated defocusing can
lead to multiple re-focused laser interaction filaments through to
formation of a stable filament.
[0128] Unlike known methods of filament modification, embodiments
disclosed herein support the formation of continuous filaments that
are extendable over a wide range of depths within a substrate. For
example, in some embodiments, filaments are produced such that they
are substantially continuous in nature along their path. This is to
be contrasted with known filament processing methods that produce
disconnected, discreet damage centers with insufficient radiation
intensity (laser fluence or power) to affect any changes in the
material. Accordingly, embodiments described below include methods
for forming a continuous zone of photo acoustic compression along
the path of a processing beam, such that the material properties of
the substrate differ compared to regions not exposed to this
phenomenon. In some embodiments, a continuous via is formed within
the substrate by a radially uniform compression of material within
the substrate.
[0129] On the simplest level, the filamentation process is believed
to depend mainly on two competing processes. First, the spatial
intensity profile of the laser pulse acts like a focusing lens due
to the nonlinear optical Kerr effect. This causes the beam to
self-focus, resulting in an increase of the peak intensity. This
effect is limited and balanced by increasing diffraction as the
diameter decreases until a stable beam diameter is reached that can
propagate distances many times longer than that expected from a
simple calculation of the confocal beam parameter (or depth of
focus) from this spot size. The other key distinguishing feature is
the extremely small filament size achieved by this technique.
[0130] The regime of filament formation disclosed herein is new.
Filaments with a length well in excess of those previously obtained
using prior filament forming methods are described herein. For
example, according to selected embodiments of the present
disclosure, radially compressive filaments--wherein the material is
compressed revealing a cylindrical void extending through the
entire thickness of the material--with a length of 10 mm or longer
may be formed in suitably transparent media. Without intending to
be limited by theory, the mechanism appears to involve a shockwave
compression created by rapid heating via tightly spaced successive
pulses of laser light (the burst pulse phenomenon) centered along
the beam propagation axis in the material. Provided that the
filament forming beam has sufficient intensity, it is capable of
crossing air gaps and gaps of material with substantially lower
indices of refraction (real and complex) and forming filaments when
entering other transparent layers. White light generation and x-ray
emission confirm the highly non-linear processes at work. Gurovich
and Fel [ArXiv 1106.5980v1], writing about related phenomena,
observed shock wave formation in the presence of ionic and electron
collisions in a medium.
[0131] The photoacoustic nature of the filament forming process
resides in deep ablative drilling studies carried out by Paul, et
al. [Proceedings SPIE vol. 6107, 610709-1 (2006)] wherein their
method of measurement involved a photoacoustic signal generated by
void formation using multiple laser pulses. The present approach,
involving the distributed focusing of bursts, generates an even
more intense photoacoustic signal while avoiding material ablation
common to other techniques. Furthermore, although a mildly thermal
entrance and exit are formed at the initial and final surfaces of
the target materials, the internal surfaces of the filament are
substantially free from any disturbances associated with ablative
micromachining.
[0132] It is further noted that the extreme pressures associated
with solid state machining using plasma assisted laser ablation are
reported by Kudryashov, et al. [Appl. Phys. Lett. 98, 254102
(2011)]. In their work they report plasma temperatures of 90eV with
corresponding pressures of 110 GPa. At these levels, there is
sufficient energy to setup a compression wave inside the material.
The present approach utilizes much closer burst spacing and has the
advantage of creating an even hotter beam axis center over a
shorter period of time, where the thermal shockwave outpaces any
latent thermal effects rendering compression modified environs
faster than the formation of any heat affected zone (HAZ) or melt.
Inspection of the radiative processes that occur according to the
present methods illustrates that not only is Bremsstrahlung
observed, but also ultrasonic transients as well. By virtue of
optical adjustment and changes in geometric focus location, the
extent and the "stop-start" characteristics of this photoacoustic
modification in the material can be controlled--even if multiple
layers with gaps comprise the target material. The character of the
edges so produced, is fundamentally distinct from those produced
using slower, ablative processes that do not depend upon uniform
modification of the physical and chemical properties of the
materials so exposed.
Curved Filamentation
[0133] Filamentation is based on construction of a cylindrical
corridor of light that carries laser energy and is known as a
reservoir. The reservoir is responsible for pumping energy to the
core of the propagation where the plasma channel is forming. When
this reservoir is in a curved configuration it is conducive to the
formation of a curved filament resulting in formation of a curved
curtain in the modified zone inside the material when the sample or
the laser head is moved. It is possible to curve the filament using
Airy beam propagation inside the material. Using a spatial light
modulator technique, an airy beam can be produced, but due to the
high intensity of pulses used to form the filament, the costly
modulator is damaged frequently and is not a viable industrial
solution for the formation of curved filaments. Introducing
considerable coma in the beam using a combination of two
cylindrical lenses placed at an angle is one workable solution to
induce cubical phase in the beam and indeed freedom in rotation
helps to make the amount of phase change adjustable but it loses a
lot of the input pulse energy via extra optics and angle optics
surface reflection.
[0134] Knowledge of the cubic phase that is sufficient to make the
curved filament is on the order of 10 pi to 20 pi and it is more
practical to use custom made fixed cubic phase plate or mask optics
that can be produced cheaply and robustly. The only major drawback
is the phase change is constant. Constant phase change is desired
for fixed curvature in the cuts.
[0135] FIG. 4A illustrates an optical setup. Cubic phase plate or
mask 401 is located in the beam path 403 before the aberrated
focusing element 402. A schematic side edge view of the sample 406
is shown in FIG. 4B after being C-cut 407 and cleaving using the
apparatus of FIG. 4A. Cleaving is the act of separating the part to
be removed from the part that is manufactured (the part that is to
be kept). FIG. 4A illustrates incoming beam 403 which enters the
cubic phase mask 401. Cubic phase mask 401 changes the phase and
provides a constant output phase change 404 which is acted upon
aberrated focusing element 402.
[0136] Instead of using aberrated focusing optics to elongate the
focus it is possible to use an axicon. An axicon transforms the
Gaussian beam to a Bessel-Gaussian beam. The Bessel-Gaussian beam
has tendency to make an elongated focus. As shown in FIG. 5A, the
laser beam propagates through the cubic phase mask 401 and then
focuses via axicon lens 501 generating an Airy-Bessel-Gaussian beam
502. The Airy-Bessel-Gaussian beam 502 has the property of a curved
elongated focus. Using ultrafast laser pulses of the incident beam
403 will result in formation of curved filaments 503, 503 when the
pulses are focused inside transparent sample 506. Pulses will start
self-focusing in the curved reservoir corridor forming curved
filaments 503, 503. By moving the sample or the focusing optics
with respect to each other with pitches more than 2 .mu.m but less
than 10 .mu.m it is possible to arrange the curved filaments 503,
503 beside each other. Unlike most laser processing such as stealth
dicing or ablation, filaments 503, 503 form if there is no overlap
between distinct pulses. Clearly this is to avoid diffraction of
the reservoir by previously modified zones. Of course using a burst
that has a very high frequency such as 30 MHz to 60 MHz will help
guide multiple pulses in each burst to a single location to form
burst curved filaments. Heat accumulation using a burst is helpful
to make solid phase change inside the material resulting in easy
cleaving of the sample. Without loss of generality it is possible
to use a single pulse instead of a burst of pulses, but to have the
same effect the per pulse energy of the laser needs to be multiple
times larger if a single pulse is used to form the filament. In the
filament forming region photo-acoustic compression takes place
causing the transparent material to be modified. FIG. 5B is
schematic view of the side edge of the C-cut 507 after cleaving.
Cleaving is the act of separating the part to be removed from the
part that is manufactured (the part that is to be kept).
Singulation
[0137] In some embodiments, the aforementioned curved filament
forming methods and apparatus is employed for the singulation of
transparent materials. The laser induced index change created
during the aforementioned filamentation process may be employed to
produce a filament array for singulating parts with substantially
or effectively no weight loss in the material being singulated.
[0138] In one example implementation, a method of singulation may
include loading, aligning, mapping and irradiating the substrate
with one or more bursts of pulses of a laser Airy beam having a
distributed or stretched focus, wherein the substrate is
substantially transparent to the laser beam, and wherein the one or
more of pulses have an energy and pulse duration selected to
produce a filament. An array of curved filaments is formed by
translating (moving) the transparent material substrate relative to
the focused laser beam. Moving the transparent material substrate
produces additional filaments in desired locations. The filament
array thus defines an internally scribed path for cleaving the
substrate. These arrays can exist in one or more dimensions around
the line of translation, and can be formed in straight or curved
profiles, where an example curved profile 605 is shown in FIG.
6.
[0139] The filaments may be formed such that they extend over a
substantial fraction (for example, more than approximately 15% of
target material, and typically greater than 50 .mu.m, or in some
cases, greater than 1 mm or even 10 mm) of the target material.
[0140] In some embodiments, the methods disclosed herein involve
lateral translation of the focused laser beam to form an array of
closely positioned filament-induced modification tracks. This
filament array defines a pseudo-continuous curtain of modifications
inside the transparent medium without generating laser ablation
damage at either of the top or bottom surfaces (unless specifically
desired). This curtain renders the irradiated material highly
susceptible to cleaving when only very slight pressure (force) is
applied, or may spontaneously cleave under internal stress. The
cleaved facets may be devoid of ablation debris, show minimal or no
microcracks and microvents, and accurately follow the flexible
curvilinear or straight path marked internally by the laser with
only very small kerf width as defined by the self-focused beam
waist.
[0141] In some embodiments, for selected materials and processing
conditions, once a filamentation array is formed in the transparent
substrate, only small mechanical pressure may be required to cleave
the substrate into two parts on a surface shape that is precisely
defined by the internal laser-filamentation curtain. In certain
materials and especially in chemically strengthened glasses, the
separation event may be spontaneous, requiring no further steps to
affect singulation.
[0142] The user selectable process conditions may be chosen to vary
the time interval between exposure and separation from 0 seconds
(immediately separates upon exposure) to an infinite number of
seconds (requires a follow-on step of some kind to complete the
singulation process).
[0143] In some embodiments, the substrate may be cleaved using one
or more of the following: additional laser processing steps,
physical heating, cooling, and/or mechanical means. It has been
found that when a filament array is formed according to the
aforementioned filament generation methods, the cleavage step
requires far less applied force and produced superior edge quality
relative to known approaches. Depending upon the nature of the
material, the process of scribing and separation (singulation) may
take place in a single step requiring no further exposure to any
forces or thermo-mechanical tension.
[0144] In some embodiments, the filament array may be formed such
that the filaments touch (e.g. are tangential to one another; e.g.
for filaments circular in the distribution about the beam center or
axis of incidence) or are separated by a user-selectable distance,
which can be variable. In some embodiments, the distance between
filaments forming the array is constant. In other examples, the
properties of the material may be such that improved singulation is
obtained for filament arrays that are formed with variable spacing
along the perimeter of the shape to be removed or cut. The suitable
filament spacing for efficient cleaving will thus generally be
determined by the characteristics of the material and the
requirements of the application, including the physical/electrical
properties of the singulated part. In addition to the varying beam
parameters such as pulse width, pulse-to-pulse separation within a
burst, burst repetition rate, wavelength, and pulse energy, the
polarization state may be varied by utilizing a polarization
rotation element (such as a waveplate) and varying the degree of
rotation from about 1 degree to about 80 degrees and from random
polarization to linear polarization to circular polarization or to
some mixture of the two during processing as required by the
desired end result. It is observed that edge quality and therefore
post-singulation edge strength can be modulated by using this
technique, as well as others.
[0145] As noted above, the laser source may include a burst pulse
laser, for example, a pulsed laser with a regenerative amplifier,
but other burst pulse systems may be employed. For example, in one
embodiment, a multi-pass amplifier equipped with a fast
electro-optic switch, either internally or externally mounted, may
be employed to deliver the beam to the substrate via computer
controlled steering (and optional focus mechanisms and polarization
control), and the substrate may be translated relative to the
focused laser beam with a constant velocity along the path of
exposure. In some embodiments, the tangential velocity may be
constant when forming curved portions of a filament array, such as
when forming filament arrays at corners, such that the array of
filaments so created is constant in its spatial irradiance, dose
and temporal characteristics. In other embodiments, computer
control may be employed to translate the beam relative to a fixed
substrate. In other embodiments, the computer control may be
employed to control the motion of both the beam and the
substrate.
[0146] For example, the translation rate employed to form the
filament array may be determined according to the velocity of a
simple linear stage supporting the substrate, or may be determined
according to the combination of the stage velocity and the beam
velocity, in the case of a scanning system based on telecentric or
non-telecentric final objectives, depending upon the desired
process.
[0147] The translation rate may be selected to produce
user-selectable filament spacing on a micron scale, depending, for
example, upon the desired characteristics (physical, optical,
electrical, chemical, thermal, etc.) of the materials thus
singulated. Accordingly, by varying one or more of the processing
parameters in real-time, filament arrays with locally controlled or
tailored properties may be formed--i.e. arrays of filaments where
the properties of the filaments vary spatially among different
regions of the material, thereby spatially modifying properties of
the material itself This aspect of laser processing has not been
achievable using previously known laser singulation approaches and
systems. Indeed, the present method of forming arrays with
locally-controlled properties may be employed for a wide range of
applications. A non-limiting list of example properties that may be
locally controlled according to the present filamentation process
include electrical performance, light output and post-singulation
break strength.
[0148] Properties of the beam of laser pulses employed to form the
filament array may varied according to pre-selected, and computer
controlled, process parameters, in order to provide sufficient beam
intensity within the substrate to cause self-focusing of the laser
beam. For example, the laser beam may be controlled such that the
filament is formed at all points along the beam axis within the
material to be processed. In other words, the beam properties may
be controlled as to exceed a particular characteristic energy level
to create acoustic compression within the substrate(s), thus
rendering it (them) singulated or ready to be so, depending upon
the nature of the target materials.
[0149] In some embodiments, the filament arrays are formed by
filaments that are substantially symmetric about their longitudinal
axis (usually the incident axis of the laser beam). The length of
the filament may be controllable (for example, from approximately
100 .mu.m to over 10 mm) by changing the process parameters, such
as power, focusing characteristics and beam shape, which are
controlled machine parameters. Varying such parameters may result
in a change in the characteristics associated with the
photoacoustic modification created in the material.
[0150] An important distinction exists between chirped pulses and
the burst pulses employed in the methods of the present disclosure,
both in terms of how they are generated, but also in terms of the
energy characteristics of each, with the burst machining method
exhibiting much greater flexibility in processing, particularly
when coupled with a scanner and the appropriate focusing optics to
render telecentric behavior over a defined field size.
[0151] In one embodiment, a system is provided for auto-focusing of
the filament forming beam in real-time. For example, in some
implementations, the beam can be moved at high rates of speed using
galvanometers and/or acoustic optical deflectors to steer the beam
in a coordinated manner fully under computer control.
[0152] FIGS. 6A-6C illustrate an example embodiment using a theta
stage for the positioning of the apparatus for the creation of
curved filament cleave planes. FIG. 6A is a side view of the
workpiece 610 illustrating a C-shaped filament 602 therein. The
structure of FIGS. 6A, 6B and 6C enables the production of parts
with C-shaped edges. For example, using the theta stage, a circular
path 605 can be traced producing a part as shown in FIG. 6C with a
cut-out having a C-cut edge 695. FIG. 6B is a perspective view of
the workpiece 610 illustrated in FIG. 6A. FIG. 6C illustrates a
generally disk-shaped part 690 cut from the workpiece illustrated
in FIGS. 6A and 6B with a circularly extending C-shaped edge 695.
Scribed release lines 621, 622, 623, and 624 are created by the
filamentation apparatus and process described and shown herein. The
scribed release lines enable the release/separation of the part 690
from the workpiece.
[0153] FIGS. 6A-6C show the curved cut out approach for making
internal features with C-shaped (curved) edges requiring no post
singulation processing to achieve the desired curved result. In
FIGS. 6A-6C, the beam track is accomplished via rotation around the
theta axis 600 with a fixed incidence Airy laser beam, equal to the
slope desired on the final part edge 695. This non-limiting
embodiment enables curve cutting and translation of the rotary
stage as an apparatus to support the creation of complex cutouts
via filament arrays. Due to mechanical lockage, scribed release
lines of 621, 622, 623, 624 are needed to release the desired disk
690 with curved edges from the main workpiece 610. Scribed release
lines 621, 622, 623, and 624 are created by the filamentation
apparatus and process described and shown herein.
[0154] The aforementioned apparatus, with multi-axis rotational and
translational control, may be employed for the purpose of bringing
the beam on to the work piece(s) at variable focus positions,
non-normal angles of incidence and at variable, recipe controlled
positions to create curvilinear zones of filament arrays, for the
purpose of singulating the parts into component pieces, cutting out
closed-form shapes and creating products such as cover glass for
mobile devices with high break strength, which is presently not
possible using the techniques currently employed by the device
manufacturers.
[0155] Those skilled in the art will recognize that all of these
axes are not required for all applications and that some
applications will benefit from having simpler system constructions.
Furthermore, it is understood that the apparatus shown is but one
example implementation of the embodiments of the present
disclosure, and that such embodiments may be varied, modified or
hybridized for a wide variety of substrates, applications and part
presentation schemes without departing from the scope of the
present disclosure.
Apparatus for Complex Spline Processing
[0156] In some embodiments, a system for forming a curved filament
within a substrate according to the methods disclosed above may
include a rotary stage and an automated gimbal mounted final
objective (gamma axis, .gamma.), coupled with coordinated Z
position control, for rendering complex spline parts. Such an
embodiment supports the creation of high bend strength parts at
high yield and without need for further refinement or post
processing.
[0157] FIGS. 7A, 7B and 7C illustrate processing of samples with a
complex spline surface 700, from which parts may be cut of
arbitrary shape with normal or non-normal beam incidence across the
entire perimeter of the part shape as dictated by the desired
characteristics of the part after it has been singulated (e.g.
strength, conductivity, electrical efficiency of devices
therein/thereon, etch resistance or efficacy, etc.).
[0158] Coordinated rotation as indicated by theta and gamma about
the Z, Y axes, respectively with appropriate translation in the XY
plane coupled with auto focus for constant objective lens spacing,
can be employed to generate parts with user-selectable (over a
reasonable range) properties depending upon the application of the
part and its required/desired performance envelope. The optics (not
shown in FIGS. 7A-7D) and/or the part 900 being processed may be
translated and/or rotated to achieve the desired part.
[0159] FIG. 7A illustrates rotation about the Z axis as indicated
by the Greek letter .theta. and FIG. 7A illustrates rotation about
the Y axis as indicated by the Greek letter .gamma.. Reference
numeral 712 illustrates the incident beam whose characteristics and
qualities have been described above. FIG. 7A is not illustrated
with stage 705.
[0160] FIG. 7B illustrates complex spline 700 on stage 705 capable
of rotation about the Y axis as indicated by the Greek letter
.gamma.. FIG. 7C illustrates the translation and/or rotation of the
part 700 being processed via a stage 705. FIG. 7D provides an
example implementation of such an embodiment, showing a glass part
706 processed using a curved filament formation to exhibit a C-cut
shaped edge. 707.
Processing of Multiple Layers
[0161] In other embodiments, multi-level curved filaments can be
produced across several layers of glasses separated by transparent
gas or other transparent materials, or in multiple layers of
different transparent materials. The substrate may include two or
more layers, wherein a location of a beam focus of the focused
laser beam is selected to generate filament arrays within at least
one of the two or more layers.
[0162] For example, the multilayer substrate may comprise
multi-layer flat panel display glass, such as a liquid crystal
display (LCD), flat panel display (FPD), and organic light emitting
display (OLED). The substrate may also be selected from the group
consisting of autoglass, tubing, windows, biochips, optical
sensors, planar lightwave circuits, optical fibers, drinking glass
ware, art glass, silicon, III-V semiconductors, microelectronic
chips, memory chips, sensor chips, electro-optical lenses, flat
displays, handheld computing devices requiring strong cover
materials, light emitting diodes (LED), laser diodes (LD), and
vertical cavity surface emitting laser (VCSEL).
[0163] Alternatively, the location of a beam focus of the focused
laser beam may be first selected to generate filament arrays within
a first layer of the two or more layers, and the method may further
comprise the steps of: positioning a second beam focus to create an
index change within a second layer of the two or more layers;
irradiating the second layer and translating the substrate to
produce a second array defining a second internally (internal to
the stack, not the individual layers) scribed path for cleaving the
substrate. The substrate may be irradiated from an opposite side
relative to when irradiating the first layer. The substrate may be
further illuminated from top and bottom or from multiple angles of
incidence, either in concerted or subsequent process steps.
Furthermore, prior to irradiating the second layer, a position of
the second beam focus may be laterally translated relative a
position of the beam focus when irradiating the first layer. A
second focused laser beam may be used to irradiate the second
layer. This beam can be supplied by the system from a single source
or a second source. Multiple beams operating in concert can
therefore process multiple substrates in parallel.
[0164] FIG. 8A illustrates how multiple stacks of materials 835
(optionally having gaps 840, 841, 842 having larger or smaller
refractive index, n) can be singulated by the formation of curved
filament zones 831, 832, 833, 834 within the materials by an Airy
beam 825. In addition, conditions may be chosen to affect ablation
at intermediate 850 and terminal 851 interfaces of the stacks. This
is primarily adjusted by controlling the onset of filament
formation, typically a set distance from the final objective lens,
to coincide with the Z position of the target layer wherein
filament formation is desired. By adjusting the Z height of the
part or optic, a high degree of control can be afforded the user in
determining where the curved filament first forms. Also changing
the cubic phase mask having different phase characteristics will
affect the filament bend curvature.
[0165] FIG. 8B shows an example implementation of an embodiment in
which a double layer laminated glass substrate was processed using
curved filament formation in a single pass for each layer at a
speed of 0.5 m/s. In some embodiments, by controlling the laser
exposure to only form filaments in the solid transparent layers,
one can avoid ablation and debris generation on each of the
surfaces in the single or multi-layer plates. This offers
significant advantages in manufacturing, for example, where thick
glasses or delicate multilayer transparent plates must be cleaved
with smooth and crack free C-cut facets. The embodiment of FIG. 8C
presents laminated samples where offset is needed between the
layers. A clear example would be a display where offset is needed
for LCD driver installation.
* * * * *