U.S. patent application number 16/456062 was filed with the patent office on 2019-11-14 for laser process with controlled polarization.
The applicant listed for this patent is Gentex Corporation. Invention is credited to Donald L. BAREMAN, David J. CAMMENGA, KURTIS L. GEERLINGS, Niels A. OLESEN.
Application Number | 20190344389 16/456062 |
Document ID | / |
Family ID | 67477525 |
Filed Date | 2019-11-14 |
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United States Patent
Application |
20190344389 |
Kind Code |
A1 |
GEERLINGS; KURTIS L. ; et
al. |
November 14, 2019 |
LASER PROCESS WITH CONTROLLED POLARIZATION
Abstract
A laser system includes a laser configured to provide a laser
beam and a laser delivery assembly including a waveplate. The laser
delivery assembly is positioned to receive the laser beam from the
laser and direct the laser beam toward a substrate to facilitate
forming a separation line within the substrate along a process
path. An instantaneous direction of the process path relative to a
direction of a crystalline plane of the substrate defines a process
path angle. The laser delivery assembly is configured to
selectively rotate at least one of the waveplate or the substrate
to control a polarization angle of the laser beam based on (i) an
instantaneous direction of polarization of the laser beam and (ii)
the process path angle.
Inventors: |
GEERLINGS; KURTIS L.;
(Zeeland, MI) ; BAREMAN; Donald L.; (Zeeland,
MI) ; CAMMENGA; David J.; (Zeeland, MI) ;
OLESEN; Niels A.; (Zeeland, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gentex Corporation |
Zeeland |
MI |
US |
|
|
Family ID: |
67477525 |
Appl. No.: |
16/456062 |
Filed: |
June 28, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14727668 |
Jun 1, 2015 |
10369663 |
|
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16456062 |
|
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62005211 |
May 30, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 26/0006 20130101;
B23K 2103/56 20180801; B23K 26/064 20151001; B23K 26/359 20151001;
C30B 29/20 20130101; C30B 33/02 20130101; H01S 3/0085 20130101;
G02B 27/286 20130101; G02B 5/3025 20130101; C30B 33/06 20130101;
G02B 26/06 20130101; B23K 26/53 20151001; B23K 26/0039 20130101;
G02B 5/3083 20130101 |
International
Class: |
B23K 26/359 20060101
B23K026/359; C30B 29/20 20060101 C30B029/20; C30B 33/02 20060101
C30B033/02; H01S 3/00 20060101 H01S003/00; G02B 5/30 20060101
G02B005/30; G02B 26/06 20060101 G02B026/06 |
Claims
1. A laser system comprising: a laser configured to provide a laser
beam; and a laser delivery assembly including a waveplate; wherein
the laser delivery assembly is positioned to receive the laser beam
from the laser and direct the laser beam toward a substrate to
facilitate forming a separation line within the substrate along a
process path; wherein an instantaneous direction of the process
path relative to a direction of a crystalline plane of the
substrate defines a process path angle; and wherein the laser
delivery assembly is configured to selectively rotate at least one
of the waveplate or the substrate to control a polarization angle
of the laser beam based on (i) an instantaneous direction of
polarization of the laser beam and (ii) the process path angle.
2. The laser system of claim 1, wherein the laser delivery assembly
is configured to selectively rotate the at least one of the
waveplate or the substrate such that the polarization angle and the
process path angle are the same along at least a portion of the
process path such that the instantaneous direction of the process
path and the instantaneous direction of polarization are
parallel.
3. The laser system of claim 1, wherein the laser delivery assembly
is configured to selectively rotate the at least one of the
waveplate or the substrate such that the polarization angle and the
process path angle are different along at least a portion of the
process path such that the instantaneous direction of the process
path and the instantaneous direction of polarization are
non-parallel.
4. The laser system of claim 1, wherein the separation line
includes a plurality of laser-induced channels positioned at a
plurality of spaced apart locations.
5. The laser system of claim 4, wherein the laser system is
configured to selectively rotate the at least one of the waveplate
or the substrate based on (i) the instantaneous direction of
polarization of the laser beam and (ii) the process path angle of
the instantaneous direction of the process path relative to the
direction of the crystalline plane of the substrate to prevent the
formation of microcracks between adjacent laser-induced
channels.
6. The laser system of claim 4, wherein the laser system is
configured to selectively rotate the at least one of the waveplate
or the substrate based on (i) the instantaneous direction of
polarization of the laser beam and (ii) the process path angle of
the instantaneous direction of the process path relative to the
direction of the crystalline plane of the substrate to cause the
formation of microcracks between adjacent laser-induced
channels.
7. The laser system of claim 1, wherein the laser delivery assembly
includes a motion device positioned to facilitate rotating the
waveplate.
8. The laser system of claim 1, wherein the laser delivery assembly
includes a base configured to support the substrate, wherein the
base is at least one of a movable base or a stationary base.
9. The laser system of claim 1, wherein the substrate is at least
partially transparent to the laser beam.
10. A laser system comprising: a laser delivery assembly including
a waveplate; wherein the laser delivery assembly is positioned to
receive a laser beam from a laser and direct the laser beam toward
a substrate to facilitate forming a separation line within the
substrate along a process path; wherein an instantaneous direction
of the process path relative to a direction of a crystalline plane
of the substrate defines a process path angle; and wherein the
laser delivery assembly is configured to selectively rotate at
least one of the waveplate or the substrate to control a
polarization angle of the laser beam based on (i) an instantaneous
direction of polarization of the laser beam and (ii) the process
path angle.
11. The laser system of claim 10, wherein the laser delivery
assembly is configured to selectively rotate the at least one of
the waveplate or the substrate such that the polarization angle and
the process path angle are the same along at least a portion of the
process path such that the instantaneous direction of the process
path and the instantaneous direction of polarization are
parallel.
12. The laser system of claim 10, wherein the laser delivery
assembly is configured to selectively rotate the at least one of
the waveplate or the substrate such that the polarization angle and
the process path angle are different along at least a portion of
the process path such that the instantaneous direction of the
process path and the instantaneous direction of polarization are
non-parallel.
13. The laser system of claim 10, wherein the substrate is at least
partially transparent to the laser beam.
14. The laser system of claim 10, wherein the separation line
includes a plurality of laser-induced channels positioned at a
plurality of spaced apart locations.
15. The laser system of claim 14, wherein the laser system is
configured to selectively rotate the at least one of the waveplate
or the substrate based on (i) the instantaneous direction of
polarization of the laser beam and (ii) the process path angle to
prevent the formation of microcracks between adjacent laser-induced
channels.
16. The laser system of claim 14, wherein the laser system is
configured to selectively rotate the at least one of the waveplate
or the substrate based on (i) the instantaneous direction of
polarization of the laser beam and (ii) the process path angle to
cause the formation of microcracks between adjacent laser-induced
channels.
17. The laser system of claim 10, wherein the laser delivery
assembly includes a base configured to support the substrate,
wherein the base is at least one of a movable base or a stationary
base.
18. The laser system of claim 10, wherein the laser delivery
assembly includes a motion device positioned to facilitate
selectively rotating the waveplate.
19. A laser system comprising: a laser; and a laser delivery
assembly including a waveplate; wherein the laser delivery assembly
is positioned to receive a laser beam from the laser and direct the
laser beam toward a substrate to facilitate forming a separation
line within the substrate along a process path; and wherein the
laser delivery assembly is configured to selectively rotate at
least one of the waveplate or the substrate to control a
polarization angle of the laser beam based on (i) an instantaneous
direction of polarization of the laser beam, (ii) an instantaneous
direction of the process path, and (iii) a direction of a
crystalline plane of the substrate.
20. The laser system of claim 19, wherein the separation line
includes a plurality of laser-induced channels positioned at a
plurality of spaced apart locations, and wherein the laser delivery
assembly is configured to selectively rotate the at least one of
the waveplate or the substrate to (i) selectively prevent the
formation of microcracks between adjacent laser-induced channels
and (ii) selectively cause the formation of the microcracks between
the adjacent laser-induced channels.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] This application is a Continuation of U.S. patent
application Ser. No. 14/727,668, filed Jun. 1, 2015, which claims
the benefit of and priority to U.S. Provisional Patent App. No.
62/005,211, filed May 30, 2014. The disclosures of each of the
foregoing applications are incorporated herein by reference in
their entireties, including their specifications, claims,
abstracts, and drawings, as if fully included herein.
TECHNICAL FIELD
[0002] The present disclosure generally relates to manufacturing
processes that use lasers and, more particularly, to processes that
use lasers to separate material into two or more separate portions
of material.
BACKGROUND
[0003] A substrate material can be separated into two or more
pieces by forming a plurality of laser-induced channels along a
process path located along an intended line of separation, as
taught by Bareman et al. in U.S. Pat. No. 8,842,358. A
laser-induced channel edge can be formed upon substrate separation
and can have a relatively smooth surface without the need for
post-processing operations such as grinding.
SUMMARY
[0004] In accordance with one or more embodiments, a laser system
includes a laser that produces a laser beam and a laser delivery
assembly that directs the laser beam toward a substrate. The laser
and laser delivery system are together configured to form
laser-induced channels in the substrate at a plurality of spaced
apart locations along a process path. The laser delivery assembly
includes an optical element that imparts the laser beam with a
direction of polarization that is controllable with respect to an
axis of the substrate when the substrate is supported by the system
for processing.
[0005] The direction of polarization of the laser beam may be
changeable and controllable with respect to an axis of the laser
system via movement of the optical element, and/or the orientation
of the substrate may be changeable and controllable with respect to
an axis of the laser system via movement of the substrate.
[0006] An angle between the direction of polarization of the laser
beam and the direction of the process path may be controllable
during formation of the laser-induced channels along the process
path. For example, the angle may be controllable and may vary by no
more than .+-.20 degrees along the process path, the angle may be
controllable and constant along the process path, the angle may
controllable and in a range from -20 degrees to 20 degrees along
the process path, and/or the angle may be controllable to be zero
along the process path. Additionally or alternatively, an angle
between the direction of polarization of the laser beam and a
crystalline plane of the substrate may controllable during
formation of the laser-induced channels along the process path.
[0007] The laser system may include a waveplate having an optical
axis with a controlled orientation with respect to the substrate
axis. For example, the system may be configured to rotate the
waveplate, the substrate, or both the waveplate and the substrate
to change said orientation.
[0008] In accordance with one or more embodiments, a method
includes the step of directing a laser beam of a laser system
toward a substrate that is at least partially transparent to the
laser beam, the laser system being configured to form laser-induced
channels in the substrate. The method further includes the step of
forming laser-induced channels in the substrate at a plurality of
spaced apart locations along a process path and the step of
controlling the direction of polarization of the laser beam with
respect to an axis of the substrate during the step of forming.
[0009] The step of controlling may include changing the direction
of polarization with respect to an axis of the laser system, with
respect to an instant direction of the process path, and/or with
respect to a crystalline plane of the substrate. In some
embodiments the process path deviates from a straight line and may
be curvilinear or include multiple rectilinear segments oriented in
different directions. In some embodiments, the substrate comprises
or is sapphire. An angle between the direction of polarization and
the direction of the process path may be the same along the process
path, constant along the process path, and/or controlled within an
angular range along the process path. The step of controlling may
include passing the laser beam through a waveplate and rotating the
waveplate, the substrate, or both.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Illustrative embodiments will hereinafter be described in
conjunction with the appended drawings, wherein like designations
denote like elements, and wherein:
[0011] FIG. 1 is a schematic diagram of an illustrative laser
system;
[0012] FIG. 2. is a perspective view of an illustrative laser
system processing a substrate;
[0013] FIG. 3 is a perspective view of first and second portions of
the substrate of FIG. 2 after separation;
[0014] FIG. 4 is a schematic view of a portion of an illustrative
laser system, including an optical element;
[0015] FIG. 5 illustrates a laser-induced channel including an
array of self-focus damage volumes produced by a laser beam having
a direction of polarization;
[0016] FIG. 6A is a photographic image of a plurality of
laser-induced channels formed along a substrate process path with
no microcracks between adjacent laser-induced channels;
[0017] FIG. 6B is a photographic image of a plurality of
laser-induced channels formed along a substrate process path with
microcracks between adjacent laser-induced channels;
[0018] FIG. 6C is a photographic image of a plurality of
laser-induced channels formed along a substrate process path with
microcracks between adjacent laser-induced channels, along with
additional cracks and/or other substrate damage;
[0019] FIG. 7 is an illustrative crystal structure with multiple
crystalline planes;
[0020] FIG. 8 is a view of a wafer substrate illustrating an
example of relative orientations among a crystalline plane (C), the
direction of polarization of a laser beam (L), and the direction of
a process path (P);
[0021] FIG. 9 is an example of a wafer substrate with perpendicular
process paths for dicing the wafer; and
[0022] FIG. 10 is another example of a wafer substrate with
perpendicular process paths for dicing the wafer, with the process
paths oriented different than those of FIG. 9 with respect to the
crystalline plane of the wafer.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0023] With reference to FIG. 1, a laser system 100 is
diagrammatically illustrated. The illustrated embodiment includes a
laser 102 in optical communication with a laser delivery assembly
104. The laser delivery assembly 104 may include a laser path or
optics 106, a laser motion device 108, and a base 110, as shown,
and is configured to direct a beam of laser light (i.e., a laser
beam) emitted by the laser 102 toward a substrate 112 that is to be
processed.
[0024] The laser motion device 108 generally operates to change,
control, monitor and/or determine the relative location and/or
orientation of a portion of the laser beam that impinges the
substrate 112 and may do so via appropriate movement of the laser
beam and/or the substrate relative to a Cartesian coordinate system
and/or about various axes. For instance, the motion device 108 may
include servo motors, controllers, sensors, optical elements, and
other components configured to change the location and/or
orientation at which the laser beam impinges the substrate 112. The
motion device 108 may include its own optical elements separate
from the laser path or optics 106, which may be arranged between
the laser 102 and the motion device.
[0025] One process parameter of the laser system 100 that is
influenced by the motion device 108 is the speed or velocity at
which the laser beam moves with respect to the substrate 112. In
some embodiments, the motion device 108 is configured to move the
laser beam with respect to the substrate at a constant speed. More
particularly, with reference to FIG. 2, the motion device 108 (only
a portion of which is illustrated) can be configured to move the
laser beam 114 with respect to the substrate 112 so that a laser
spot 116 moves along a process path 118 at a constant speed. The
laser spot 116 is defined where the laser beam 114 impinges a
surface 120 of the substrate 112. Where the substrate 112 is at
least partially transparent to the particular wavelength of laser
light generated by the laser 102 (e.g., certain glass materials),
the impingement surface 120 may be considered an entry surface. As
used herein, the speed of the laser spot 116 is the magnitude of
the velocity of the laser spot 116 as measured along the process
path 118 in the instant direction of movement. In other words, when
the laser spot 116 is moving at a constant speed along the process
path 118, its speed may be increasing or decreasing in other
directions.
[0026] In the example illustrated in FIG. 2, the processed portion
of the process path 118 is indicated by a solid line, and the
unprocessed portion is indicated by a dotted line. The process
starting point is indicated at point A, and the starting direction
of movement is in the x-direction. Beginning at point A, the laser
spot 116 may move at a constant speed along the process path 118.
In this example, this means that the laser spot 116 moves away from
point A at the same constant speed in the x-direction and at a
different constant speed (i.e., zero) in the y-direction. Where the
process path 118 of FIG. 2 curves toward the y-direction, the speed
of the laser spot 116 decreases and increases in the respective x-
and y-directions while remaining constant along the process
path.
[0027] Moving the laser beam 114 and laser spot 116 at a constant
speed along the process path 118 is advantageous when the laser
system 100 is configured to deliver the laser beam to the substrate
in pulses at a designated frequency so that the locations at which
the laser affects the substrate material are evenly spaced along
the process path 118. For instance, with a laser system 100
configured with a pulse frequency of 100 kHz, movement of the laser
spot 116 along the process path 118 at a constant speed of 500
mm/sec results in laser pulses delivered to the substrate every 5
.mu.m along the process path 118. Other exemplary speeds are 250
mm/sec and 125 mm/sec, and other exemplary laser pulse frequencies
are 200 kHz and 400 kHz. Other laser movement speeds and pulse
frequencies are possible, and each can affect the spacing of
laser-induced channels or other laser-affected material portions
along the process path. It is also possible to vary the speed of
the laser spot 116 along the process path 118 and may be possible
to change the laser pulse frequency along the process path as
well.
[0028] In the laser system 100 depicted in FIG. 2, the laser motion
device 108 includes an optical assembly 122 through or along which
the laser beam 114 travels on its way from the laser 102 to the
substrate 112. The motion device 108 may include other
non-illustrated components as well, such as a structural portion, a
motor portion, and/or other components. The optical assembly 122
includes one or more optical elements. Each optical element is
configured to change the direction, size, shape, energy density,
energy distribution, or other characteristic of the laser beam 114.
Some examples of optical elements include mirrors, reflectors,
lenses, magnifiers, diffusers, prisms, and apertures. In some
cases, an optical element can provide multiple beam-changing
functions. For example, a concave mirror may reflect or change the
direction of the laser beam while simultaneously focusing the
beam.
[0029] In embodiments where the substrate 112 is at least partially
transparent to the particular wavelength of the laser light from
the laser 102, it is possible to form a series of spaced-apart
laser-induced channels along the process path 118, with each of the
channels extending at least partially through the thickness of the
substrate (i.e., in the z-direction of FIG. 2). Laser-induced
channels are described in further detail below and are useful to
facilitate separation of the substrate 112 into separate portions,
such as inner and outer portions 124, 126, along a line of
separation defined at least in part by the process path 118. Each
laser-induced channel may be characterized by a columnar volume of
material within the substrate 112 along which the substrate
material has been damaged or otherwise altered. With the
application of chemical processes, physical stress, thermal stress,
time, or a combination thereof, cracks, (e.g., microcracks) may
form between adjacent laser-induced channels along most or all of
the length of the process path 118, and the substrate may be
severed or separated into two separate portions 124, 126, as shown
in FIG. 3. In this example, the process path 118 is a closed path
located within the perimeter or boundaries of the starting
substrate 112. In other examples, the process path 118 and
resulting line of separation extend to at least one edge of the
substrate 112.
[0030] When portions 124, 126 are initially separated, opposing
surfaces or edges 128, 130 are formed along each of the respective
separate portions. Each of the newly formed surfaces 128, 130 may
be referred to as a separation surface. When separated along a
series of laser-induced channels, the newly formed edges 128, 130
may be relatively smooth and absent sharp features, without the
need for post-processing such as grinding, even with substrates
such as glass, with which grinding of the edges is typically
required to remove sharp edges after traditional separation
techniques like mechanical scribing. Another characteristic of this
type of material separation or singulation is that it is
essentially a zero-kerf separation technique. In other words, in
contrast to most other laser scribing, cutting, or ablation
processes, the laser-induced channel separation process does not
remove any measurable amount substrate material--e.g., the outer
perimeter of inner portion 124 and the inner perimeter of outer
portion 126 are the same size and shape. Certain characteristics of
the separation surfaces 128, 130 (e.g., roughness) and of the
laser-induced channels along which the separation surfaces are
formed can be controlled via one or more laser process parameters.
As described further below, the direction of polarization of the
laser light is one such process parameter. Controlling the
direction of polarization of the laser light while forming
laser-induced channels is particularly useful with substrate
materials that include a crystalline component. For instance, it
has been found that the direction of polarization with respect to
the orientation of the crystalline structure can be controlled,
changed, optimized, or otherwise used to affect the extent of
damage associated with each and between each of the laser-induced
channel along the process path.
[0031] A brief description of the manner in which laser-induced
channels can be formed in a transparent or partially transparent
substrate is provided with reference to FIGS. 4 and 5. In the
example of FIG. 4, the optical assembly 122 of the laser system
includes optical element 132. The optical assembly 122 is
configured to receive the laser beam 114, alter a characteristic of
the laser beam, and emit the altered laser beam in a direction of
light propagation (parallel with the z-axis in this example), such
as toward the substrate 112. In the example of FIG. 4, the optical
assembly 122 includes a focusing optical element 132, such as a
lens, that narrows the laser beam 114, thereby increasing the power
density of the laser beam in the z-direction for some distance
beyond the optical assembly 122. The power density referred to here
is the average power per unit area, where the area is the
cross-sectional area of the beam measured in a plane perpendicular
with the direction of light propagation (i.e., the x-y plane in
FIG. 4). Without the substrate 112 in the path of the laser beam
114, the power density of the beam reaches a maximum along the
z-direction in a nominal or geometric focal region 134, beyond
which the power density of the beam decreases as the beam diverges
or diffuses. As used herein, the terms "power" and "energy" may be
used somewhat interchangeably, as skilled artisans will understand
that the two terms are related by time or duration. For instance,
the energy available from a laser beam of a particular power or
wattage within a particular amount of time is generally the product
of the laser power and the time. Thus, a timed pulse of laser
energy of a known power has an associated amount of available
energy.
[0032] The energy in a pulse of the laser beam 114 also has a
distribution along the direction of light propagation that is a
function of distance in the direction of light propagation. In
other words, the total amount of energy in a laser pulse of a
particular duration propagates through the optical assembly 122 and
is distributed at various distances from the last optical element
the beam encounters and in various corresponding amounts at each
distance. This energy distribution is referred to herein as the
focal energy distribution. As used here, a laser pulse refers to
both a single, uninterrupted pulse and to a rapid burst of pulses.
For instance, a laser operating at a pulse frequency of 100 kHz may
deliver a particular amount of energy (i.e., the product of the
laser power and total pulse time) 100,000 times per second--i.e.,
once every 10 .mu.s. Depending on the amount of energy delivered
every 10 .mu.s, it may be delivered in a single uninterrupted pulse
or in a plurality of pulses on the nanosecond scale.
[0033] Where the substrate 112 is at least partially transparent to
the particular wavelength of laser light, self-focusing of the
light beam can occur due to the Kerr effect. Generally, the Kerr
effect is the change in the refractive index of a material in
response to an electric field. The optical Kerr effect is the case
in which the electric field is due to the light itself. In such
cases, the index of refraction of the material increases as a
function of increasing light intensity. As the refractive index
increases, the beam of light is focused further due to the
differential increase in index in the center of the beam. This
focusing, called self-focusing, causes a further increase in the
intensity, and a corresponding further increase in the index of
refraction. In a scenario in which this self-focus process is not
limited by another process, the beam of light may cause a
catastrophic self-focus event in which an internal volume of the
substrate is damaged once a certain intensity threshold is reached.
The threshold may be specific to the material composition, and the
intensity may be a particular amount of energy per unit mass or
volume. Thus, placing a Kerr material in the path of the beam 114
alters the focal energy distribution of the beam away from the
nominal condition due to both its linear index of refraction and
its non-linear effects.
[0034] When the focal energy distribution of the beam is such that
the damage threshold of the substrate material is reached at a
distance from the final optic that is within the thickness of the
substrate, an array of one or more self-focus damage volumes is
formed approximately along a line and about an axis in the
direction of light propagation (z-direction in FIG. 4). This array
of one or more self-focus damage volumes is referred to as a
laser-induced damage channel or a laser-induced channel. In some
cases, the array of damage volumes is sufficiently large in number
and/or the individual damage volumes of the array are sufficiently
large in size that the resulting laser-induced channel extends
through the entire thickness of the substrate. The spacing between
individual damage volumes and/or the size of the individual damage
volumes along a particular laser-induced channel may be related to
the focal energy distribution. For instance, as the energy density
along a focal region decreases, the damage spots that make up the
laser-induced channel can have a lower apparent presence (e.g.,
smaller, spaced farther apart, present over a smaller portion of
the substrate thickness, and/or less visible). As the energy
density along a focal region increases, the damage spots of the
laser-induced channel can have a greater apparent presence (e.g.,
larger, spaced closer together, present over a larger portion of
the substrate thickness and/or more visible). As used here, a focal
region is defined between two planes spaced different distances
from the final optical element. The focal region may be located
generally along the line of light propagation, but the light may be
focused along a focal path that deviates from the line of light
propagation or the direction of light propagation. The
laser-induced channel need not be perpendicular to the surface
plane of the optical element nor parallel to the line of light
propagation.
[0035] FIG. 5 depicts an example of a laser-induced channel 136
comprising a plurality of self-focus damage volumes 138 extending
through the thickness of a Kerr material substrate 112. In this
particular example, the damage volumes 138 are spaced non-uniformly
in the direction of the material thickness. In other examples, the
damage volumes 138 can be arranged more uniformly in the direction
of material thickness. For instance, the laser optics can be
customized or otherwise configured to provide a uniform focal
energy distribution at the desired portion of the substrate
thickness. Linear ray tracing or non-linear ray tracing can be used
to design the laser optics to distribute the available energy in
any desired manner to produce damage volumes distributed as
desired, whether uniformly, non-uniformly, only partially through
the thickness of the substrate, at or away from the entry and/or
exit surfaces of the substrate, etc. The size of the individual
self-focus damage volumes 138 can be affected or controlled as
well, such as by increasing the power in a particular laser pulse
to increase the size of the damage volumes or decreasing the power
to decrease the size of the damage volumes. The radial size or
effective diameter (i.e., width in the x and/or y direction in FIG.
5) of each laser-induced channel can be affected by affecting the
size of the damage volumes.
[0036] FIG. 5 also depicts the direction of polarization L of the
laser beam 114. The electric field component of a single light wave
140 is schematically illustrated. Multiple light waves 140 may
combine to form the laser beam 114, which is characterized by a
direction of propagation--in the direction of the z-axis of the
reference frame in this case. The direction of polarization L is
perpendicular to the direction of propagation. The light wave 140
shown in FIG. 5 is polarized in the x-direction of the reference
frame. Stated differently, the electric field component of the
light wave 140 shown in FIG. 5 oscillates in a plane parallel with
the x-z plane of the reference frame.
[0037] It should be understood that a light beam is the result of
any number of combined waves and that there are an infinite number
of different combinations of waves that yield the same resultant
light beam. Once multiple light waves are combined to form the
beam, the individual waves that were combined are no longer
discernible. In other words, the wave 140 of FIG. 5 is used for
purposes of illustration of the direction of polarization of the
laser beam 114 and may be thought of as a resultant waveform
representing the laser beam for this purpose. In this example, the
laser beam 114 is linearly polarized in the x-direction. Laser
light may be provided by the above-described laser 102 (FIGS. 1 and
2) as a linearly polarized beam 114. The laser system may include a
polarizer, for example as part of the laser path 106 or motion
device 108 of the laser delivery assembly 104 (see FIG. 1), through
which the laser beam 114 passes for polarization. A polarizer
absorbs or reflects, depending on the type of polarizer, the
portion of the beam with a direction of polarization that does not
match the optical axis of the polarizer. A polarizer may be
considered an optical element as defined above.
[0038] Other types of optical elements that can affect the
polarization and/or the direction of polarization of the laser beam
include waveplates, such as a half-wave plate (.lamda./2 plate) or
a quarter-wave plate (.lamda./4 plate). The direction of
polarization L of linearly polarized light passing through a
half-wave plate may be changed depending on the alignment of the
direction of polarization of the incoming light with the optical
axis of the waveplate. When the direction of polarization of the
incoming light is aligned or perpendicular with the optical axis of
a half-wave plate, the direction of polarization of outgoing light
is the same as the incoming light. When the direction of
polarization of the incoming light is off-axis, the direction of
polarization of the outgoing light is different from that of the
incoming light. With a half-wave plate in particular, the direction
of polarization of linearly polarized light passing through the
plate normal to the plate surfaces changes by twice the angle
between the direction of polarization of the incoming light and the
optical axis of the waveplate. For instance, if the angle between
the direction of polarization of the incoming light and the optical
axis of the waveplate is 45 degrees, the direction of polarization
of the outgoing light is changed by 90 degrees. Stated differently,
the direction of polarization of the incident light rotates about
the propagation axis by twice its angle to the optical axis of the
plate.
[0039] In the particular case of a quarter-wave plate, linear
polarized light is transformed to elliptically polarized light when
the incoming direction of polarization is unaligned and
non-perpendicular to the optical axis. When the direction of
polarization of the incoming light is at a 45 degree angle with the
optical axis of the plate, the outgoing light is circularly
polarized. Conversely, circularly polarized light can be linearized
through a quarter-wave plate. Half-wave and quarter-wave plates are
common types of waveplates, but other types of waveplates or
non-waveplate optical elements can be used to affect the direction
of polarization of the laser beam.
[0040] The direction of polarization L of the laser beam 114 can
affect the above-described laser-induced channels 136, the
individual damage volumes 138, the portion of the substrate between
individual laser-induced channels, and/or the separation surfaces
128, 130 (FIG. 3) defined along the process path. This is
particularly true with substrate materials that include a
crystalline component, crystalline substrates, and single-crystal
substrates. For example, the direction of polarization L of the
laser light with respect to a crystalline plane of the substrate
112 can affect the size of the self-focus damage volumes 138, the
presence or absence of microcracks between adjacent laser-induced
channels, and/or the overall amount of damage along the process
path.
[0041] FIGS. 6A-6C include photographic images of a top-view (i.e.,
showing the entry surface) of three different pluralities of
laser-induced channels 136 formed along respective process paths of
substrates 112. In these examples, each substrate is made from the
same type of material and comprises a crystalline component. More
specifically, each substrate 112 in the examples of FIGS. 6A-6C is
sapphire, which is a crystalline substrate and which, in this
particular example, is a single-crystal sapphire substrate. A
crystalline plane of the substrate lies in a known orientation,
defining a direction C at the intersection of the crystalline plane
and the substrate entry surface. It has been determined that the
relative orientations of the crystalline plane of the substrate,
the direction of polarization of the laser beam, and/or the
instantaneous direction P of the process path can affect certain
characteristics of the laser-induced channels. For instance, in
FIGS. 6A-6C, each respective plurality of laser-induced channels
136 is formed in the respective substrate 112 using a pulsed laser
beam with the same power per pulse, the same number of pulses per
individual channel location, the same pulse frequency and speed
along the process path (resulting in the same inter-channel
spacing), and the direction of polarization of the laser beam in
the same direction with respect to the coordinate system (x-y-z) of
the laser system. The direction of polarization of the laser beam
is not shown in FIGS. 6A-6C, but it changes with respect to the
orientation of the crystalline plane by the same amount as the
direction of the process path in these examples. Also in the
illustrated examples, the referenced crystalline plane of the
substrate is perpendicular with the opposite surfaces of the
substrate, such that the orientation of the crystalline plane can
be described more simply as a lying in direction C.
[0042] As indicated in FIGS. 6A-6C, the overall amount of damage
associated with the laser-induced channels formed in the substrate
is a function of the direction C of the crystalline plane with
respect to the direction P of the process path and/or the direction
of polarization L of the laser beam. In the example of FIG. 6B,
microcracks 142 are formed between each pair of adjacent
laser-induced channels 136 with the crystalline plane in the
illustrated offset direction C with respect to the process path
direction P and direction of polarization L of the laser beam.
Here, the direction C of the crystalline plane is at a 45-degree
angle with respect to the direction P of the process path. The
processed substrate of FIG. 6A, where the direction C of the
crystalline plane is parallel with the direction P of the process
path, does not include such microcracks between adjacent
laser-induced channels 136. In the example of FIG. 6C, where the
direction C of the crystalline plane is perpendicular to the
direction P of the process path, the substrate 112 includes
microcracks between adjacent laser-induced channels 136 along with
additional cracks and/or other substrate damage that is not
necessarily located along or in alignment with the process path.
Overall greater amounts of substrate damage may be generally
associated with greater roughness along the separated edges and/or
less effort required to separate the substrate portions from each
other.
[0043] It is noted that FIGS. 6A-6C are merely illustrative and
that the angle between the direction P of the process path and the
direction C of the crystalline plane is not necessarily
determinative of or correlated to the amount of substrate damage,
at least because the direction of polarization of the laser beam is
the same in each of the illustrated examples and could be different
with respect to the direction P of the process path in other
examples. Additionally, in the particular examples of FIGS. 6A-6C,
the crystalline plane is the C-plane of the single crystal
sapphire, and the results may vary in other examples. For instance,
a single crystal sapphire substrate has other crystalline planes,
such as an A-plane and an R-plane, as shown in the representative
crystal cell structure of FIG. 7. Other crystalline substrates may
have other cell or lattice structures that define different
crystalline planes.
[0044] TABLE I qualitatively summarizes results obtained from
forming laser-induced channels along a process path in a
single-crystal sapphire substrate with the direction of
polarization L of the laser beam at various angles with respect to
the C-plane of the sapphire and with the direction P of the process
path at various angles with respect to the C-plane of the sapphire.
The TABLE I entries indicate the extent of substrate damage
associated with the laser-induced channels produced with various
combinations of process path angles and polarization angles. The
extent of damage is categorized by the presence or absence of
microcracks between adjacent laser-induced channels. Where no
microcracks were present between adjacent laser-induced channels,
such as in the example of FIG. 6A, the table entry is "none." Where
microcracks were present between substantially all adjacent
laser-induced channels, such as in the example of FIG. 6B, the
table entry is "all." Where microcracks were present between only
some pairs of adjacent laser-induced channels, the table entry is
"some." Where microcracks were present between substantially all
adjacent laser-induced channels and the substrate had additional
chipping or damage in the vicinity of the process path, such as in
the example of FIG. 6C, the table entry is "all +."
TABLE-US-00001 TABLE I Process Path Polarization Angle Angle
0.degree. 45.degree. -45.degree. 90.degree. Circular 0.degree. none
some none none none 45.degree. some/all none none all none
-45.degree. some/all some none all none 90.degree. all+ all all+
none/some all
[0045] To obtain the results in TABLE I, laser-induced channels
were produced in single-crystal sapphire wafers with the C-plane in
a known orientation and direction. The "Process Path Angle" is the
angle formed between the process path and the direction of the
C-plane--i.e., the angle between directions P and C. The
"Polarization Angle" is the angle formed between the direction of
polarization of the laser beam and the direction of the
C-plane--i.e., the angle between directions L and C. FIG. 8
illustrates an example where the polarization angle is 0.degree.
and the process path angle is 45.degree..
[0046] For each polarization angle in TABLE I, pluralities of
laser-induced channels were produced along straight process paths
in the x-direction and the y-direction of the laser system and
along process paths at .+-.45 degrees with respect to the x-y axes.
The direction of polarization L of the laser beam was varied using
a half-wave plate placed in the path of the laser beam so that the
laser beam passed through the waveplate before impinging the
substrate. The waveplate was rotated with respect to the laser
system to change the direction of polarization L of the laser beam
as desired. A quarter-wave plate was used with some samples to
change the incoming linearly polarized laser beam to a circularly
polarized laser beam. The same focusing optics and laser power were
used for all samples, with laser power output selected to
differentiate between the process path directions--i.e., too much
laser power may cause extensive damage at all process path and
laser polarization directions, while too little laser power may not
cause microcracks or laser-induced channels at all process path and
laser polarization directions.
[0047] As confirmed by the TABLE I results, the extent of substrate
damage associated with the laser-induced channels is a function of
the direction of polarization and/or the direction of the process
path with a substrate having a crystalline component. Thus, one
possible result, when separating portions of such a substrate along
a line of laser-induced channels, is inconsistent roughness along
the separated edges if the direction of polarization is not
controlled as a process variable. For instance, if the process path
is not along a straight line (as in the example of FIGS. 2 and 3),
an as-generated laser beam having a constant direction of
polarization along the entire process path may produce
laser-induced channels with the extent of substrate damage
(inter-channel microcracks, damage volume size, etc.) dependent on
the process path direction. The resulting separated edges may have
different amounts of roughness and/or different amounts of
separation effort may be required along different edges.
[0048] In the process of producing laser-induced-channels in a
closed profile for purposes of singulating a shape as in FIG. 3,
the process path 118 ranges from 0.degree. to 360.degree. with
respect to crystal orientation. As shown in TABLE I, there may be
no constant polarization angle that produces the same level of
damage along the process path. When it is desirable to have
consistent damage around the entire shape--whether for consistent
edge roughness, evenly distributed separation effort, or some other
reason--the polarization angle can be varied depending on the
instant direction of the process path to achieve the desired extent
of damage associated with the laser-induced channels.
[0049] In some cases, the result of FIG. 6B is preferred along the
entire process path, as the microcracks between all laser-induced
channels can allow for easy separation and a relatively smooth
edge. In other cases, the absence of inter-channel microcracks as
in FIG. 6A is preferred, such as when the processed substrate must
be handled prior to separation. In still other cases, microcracks
plus extraneous damage as in FIG. 6C is preferred, such as when
very low separation effort or high edge roughness is desired. It is
also possible that different roughness or separation efforts are
desirable along different edges of a separated substrate, or that
only a portion of a separated edge is desirably rough or smooth.
Controlling the polarization direction of the laser beam can
predictably achieve any of these results.
[0050] A laser system as set forth above may thus be constructed
with special attention paid to the direction of polarization of the
laser beam. For instance, the laser system may include an optical
element that imparts the laser beam with a direction of
polarization that is controllable with respect to an axis of the
substrate when the substrate is supported by the system for
processing. This substrate axis with respect to which the direction
of polarization is controllable may be an axis of the reference
frame of the process path, for example. Or it may be a substrate
axis aligned with or having a known orientation with respect to a
crystalline plane of the substrate. In some embodiments, the system
is configured so that the direction of polarization of the laser
beam is controllable with respect to an axis of the laser system,
such as a stationary base of the laser system. In such a system, a
substrate can be mounted to the system for processing with a
crystalline plane and/or a process path reference frame axis having
a known orientation with respect to the system axis. The system can
be configured to control or change the direction of polarization of
the laser beam with respect to a desired substrate axis along a
process path or to have a different constant direction of
polarization for a different process path. The control and/or
change can be effected via movement of the optical element (e.g.,
by rotation, translation, or tilting of the optical element) and/or
by movement of the substrate by the system.
[0051] In some embodiments, an angle between the direction of
polarization of the laser beam and the direction of the process
path is controllable during formation of the laser-induced channels
along the process path--i.e., while the laser spot moves along the
process path. For instance, this angle may be controllable within a
range of .+-.5 degrees, .+-.10 degrees, .+-.20 degrees, or .+-.30
degrees, to list a few examples. In one example, the system is
configured so that this angle changes so that the direction of
polarization is the same as the instant direction of the process
path (i.e., the angle is zero) or the same as the instant direction
of the process path within an angular range such as those noted
above. In another example, the angle is non-zero and constant or
constant within the angular range. The same control and/or change
may be exercised with the direction of polarization of the laser
beam with respect to a crystalline plane of the substrate--for
instance, when the substrate is mounted to the system for
processing with the crystalline plane in a desired or known
orientation with respect to a system axis.
[0052] The advantages of polarization control are not limited to
enclosed profile shapes. Benefits can be realized even with
straight line process paths, as is apparent from the some of the
differences in the extents of damage in TABLE I between
perpendicular process paths. In one example, a single-crystal
sapphire wafer is diced by producing laser-induced channels along a
plurality of straight process paths in a first direction and along
another plurality of straight process paths in a second direction
perpendicular to the first direction, as in FIG. 9.
[0053] As is apparent from TABLE I, if the polarization angle is
not considered in conjunction with the direction of dicing,
inconsistent separated edges could be the result. For instance, if
the polarization angle is 0.degree. for all process paths, the
substrate will be easy to separate and have rough edges along the
x-direction (90.degree.) process paths, but will be difficult to
separate along the y-direction (0.degree.) process paths. Whereas,
if the polarization direction is changed to 90.degree. for the
process paths in the x-direction, more uniform damage will be
produced in both directions. A constant polarization direction of
90.degree. in both the x- and y-directions would also be more
consistent than a constant polarization direction of 0.degree..
With the particular laser power and parameters used to generate the
data of TABLE I, orienting the perpendicular process paths as in
FIG. 10 with a polarization angle of 90.degree. would achieve the
result of FIG. 6B along all edges.
[0054] In one embodiment, laser-induced channels are formed with
the polarization angle and the process path angle substantially the
same along the entire process path. Stated differently, the
direction of polarization of the laser beam is always aligned with
the process path. This technique can produce consistent
laser-induced channels and associated substrate damage along the
entire process path and corresponds to the 0/0, 45/45, -45/-45, and
90/90 pairings in TABLE I. In this embodiment, sensitivity of the
process to the direction of the crystalline plane may also be
reduced or removed. With consistency among all process path
directions achieved, laser power may then be increased or decreased
to adjust the overall amount of consistent damage along the process
path or paths.
[0055] An embodiment of the laser system includes a waveplate, such
as a half-wave plate, located so that the laser beam passes through
the waveplate at some location between the laser and the substrate.
The waveplate is configured to rotate about the axis of propagation
of the laser beam to change the direction of polarization of the
laser beam as desired. The waveplate may be an optical element of
the optical assembly 122 (FIG. 2) and move together with other
optical elements, such as a focusing lens, with respect to the
substrate. In another example, the waveplate is located between the
substrate and the final optical element of the optical assembly and
is not configured for translational movement with respect to the
substrate or other laser system components. A laser system
controller may control the rotation of the waveplate and allow an
operator to select a fixed rotational position for the waveplate,
or change the rotational position of the waveplate based on the
direction of the process path. In one particular example, the
waveplate is a half-wave plate that is configured to rotate by an
amount corresponding to one-half the angle of the instantaneous
process path direction. Thus, if the process path changes direction
by 90 degrees, the waveplate rotates by 45 degrees. In this manner,
the angle between the direction of polarization of the laser beam
and the process path direction may remain substantially constant
(such as 0.degree.) for the length of the process path.
[0056] It is to be understood that the foregoing description is of
one or more preferred exemplary embodiments of the invention. The
invention is not limited to the particular embodiment(s) disclosed
herein, but rather is defined solely by the claims below.
Furthermore, the statements contained in the foregoing description
relate to particular embodiments and are not to be construed as
limitations on the scope of the invention or on the definition of
terms used in the claims, except where a term or phrase is
expressly defined above. Various other embodiments and various
changes and modifications to the disclosed embodiment(s) will
become apparent to those skilled in the art. All such other
embodiments, changes, and modifications are intended to come within
the scope of the appended claims.
[0057] As used in this specification and claims, the terms "for
example," "for instance," and "such as," and the verbs
"comprising," "having," "including," and their other verb forms,
when used in conjunction with a listing of one or more components
or other items, are each to be construed as open-ended, meaning
that the listing is not to be considered as excluding other,
additional components or items. Other terms are to be construed
using their broadest reasonable meaning unless they are used in a
context that requires a different interpretation.
* * * * *