U.S. patent application number 10/364587 was filed with the patent office on 2003-12-11 for scribing sapphire substrates with a solid state uv laser.
This patent application is currently assigned to New Wave Research. Invention is credited to Dere, Dan, Fang, Pei Hsien, Huang, Jih-Chuang, Liu, Jenn, Liu, Kuo-Ching, Lucero, Antonio, Middlebusher, Duane, Oltrogge, Steven, Pinkham, Scott.
Application Number | 20030226830 10/364587 |
Document ID | / |
Family ID | 26903235 |
Filed Date | 2003-12-11 |
United States Patent
Application |
20030226830 |
Kind Code |
A1 |
Liu, Kuo-Ching ; et
al. |
December 11, 2003 |
Scribing sapphire substrates with a solid state UV laser
Abstract
A process and system scribe sapphire substrates, by performing
the steps of mounting a sapphire substrate, carrying an array of
integrated device die, on a stage such as a movable X-Y stage
including a vacuum chuck; and directing UV pulses of laser energy
directed at a surface of the sapphire substrate using a solid-state
laser. The pulses of laser energy have a wavelength below about 560
nanometers, and preferably between about 150 in 560 nanometers. In
addition, energy density, spot size, and pulse duration are
established at levels sufficient to induce ablation of sapphire.
Control of the system, such as by moving the stage with a
stationary beam path for the pulses, causes the pulses to contact
the sapphire substrate in a scribe pattern at a rate of motion
causing overlap of successive pulses sufficient to cut scribe lines
in the sapphire substrate.
Inventors: |
Liu, Kuo-Ching; (Fremont,
CA) ; Fang, Pei Hsien; (Los Altos Hills, CA) ;
Dere, Dan; (Palo Alto, CA) ; Liu, Jenn;
(Fremont, CA) ; Huang, Jih-Chuang; (Santa Clara,
CA) ; Lucero, Antonio; (Fresno, CA) ; Pinkham,
Scott; (Bozeman, MT) ; Oltrogge, Steven;
(Belgrade, MT) ; Middlebusher, Duane; (San Jose,
CA) |
Correspondence
Address: |
HAYNES BEFFEL & WOLFELD LLP
P O BOX 366
HALF MOON BAY
CA
94019
US
|
Assignee: |
New Wave Research
Fremont
CA
|
Family ID: |
26903235 |
Appl. No.: |
10/364587 |
Filed: |
February 11, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10364587 |
Feb 11, 2003 |
|
|
|
10208484 |
Jul 30, 2002 |
|
|
|
6580054 |
|
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60387381 |
Jun 10, 2002 |
|
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Current U.S.
Class: |
219/121.68 ;
219/121.83 |
Current CPC
Class: |
B23K 26/0622 20151001;
B23K 26/073 20130101; H01L 33/0095 20130101; B23K 2101/40 20180801;
H01S 5/32341 20130101; B23K 26/364 20151001; B28D 5/0011 20130101;
B23K 2103/50 20180801; B23K 26/032 20130101; H01S 5/0201 20130101;
B23K 2103/36 20180801; B23K 26/40 20130101; H01L 21/78 20130101;
H01S 5/0213 20130101 |
Class at
Publication: |
219/121.68 ;
219/121.83 |
International
Class: |
B23K 026/38; B23K
026/03; B23K 026/14; B23K 026/10 |
Claims
What is claimed is:
1. A system for scribing a sapphire substrate, comprising: a laser
generating pulses of laser energy in a wavelength less than about
560 nanometers, with a pulse duration less than about 30
nanoseconds at a repetition rate of greater than 5 kHz; a stage
adapted to support, and move, a sapphire substrate; optics
directing the pulses to impact a sapphire substrate mounted on the
stage; and a control system coupled to the solid state laser and
the stage, the control system controlling the laser and stage, and
causing the pulses to impact the sapphire substrate in a scribe
pattern at a rate of motion causing overlap of successive pulses
sufficient to cut scribe lines in the sapphire substrate.
2. The system of claim 1, wherein the control system controls a
rate of motion of the stage, causing overlap of successive
pulses.
3. The system of claim 1, including an edge detection system which
detects edges of a substrate mounting on the stage during movement
of the stage;
4. The system of claim 1, including a debris exhaust system.
5. The system of claim 1, wherein the control system includes logic
to set up a scribe pattern.
6. The system of claim 1, wherein the stage includes a vacuum
chuck.
7. The system of claim 1, including a video system for viewing a
substrate mounted on the stage.
8. The system of claim 1, wherein the control system includes logic
to set up parameters including pulse repetition rate, pulse energy
and stage speed.
9. The system of claim 1, wherein the laser comprises a Q-switched
Nd:YAG laser.
10. The system of claim 1, wherein the laser comprises a Q-switched
Nd:YVO.sub.4 laser.
11. The system of claim 1, wherein the laser comprises a diode
pumped, Q-switched Nd:YVO.sub.4 laser operating at a third harmonic
wavelength of about 355 nanometers.
12. The system of claim 1, wherein the laser comprises a diode
pumped, Q-switched Nd:YAG laser operating at a third harmonic
wavelength of about 355 nanometers.
13. The system of claim 1, wherein the spot size is between 5 and
15 microns.
14. The system of claim 1, wherein the control system controls a
rate of motion of the stage, causing overlap of successive pulses,
wherein the overlap is in a range from 50 to 99 percent.
15. The system of claim 1, wherein the pulse rate is between about
10 kHz and 50 kHz.
16. The system of claim 1, wherein said energy density is between
about 10 and 100 joules per square centimeter, said pulse duration
is between about 10 and 30 nanoseconds, and the spot size is
between about 5 and 25 microns.
17. The system of claim 1, wherein the sapphire substrate has a
thickness, and the scribe lines are cut to a depth of more than
about one half said thickness.
18. The system of claim 1, including optics to linearly polarize
the pulses.
19. The system of claim 1, including optics to adjust polarization
of the pulses.
20. A system for scribing a sapphire substrate, comprising: a
Q-switched, solid state laser generating pulses of laser energy in
a wavelength between about 150 and 560 nanometers, pulse duration
less than about 30 nanoseconds and a spot size of less than 25
microns, at a repetition rate of greater than 10 kHz; a stage
adapted to support, and move, a sapphire substrate; optics
directing the pulses to impact a sapphire substrate mounted on the
stage; an edge detection system which detects edges of a substrate
mounting on the stage during movement of the stage; and a control
system coupled to the solid state laser, the stage and the edge
detection system, the control system controlling the laser and
stage, and responsive to the edge detection system, and causing the
pulses to impact the sapphire substrate in a scribe pattern at a
rate of motion causing overlap of successive pulses sufficient to
cut scribe lines in the sapphire substrate.
21. The system of claim 20, including a debris exhaust system.
22. The system of claim 20, wherein the control system includes
logic to set up a scribe pattern.
23. The system of claim 20, wherein the stage includes a vacuum
chuck.
24. The system of claim 20, including a video system for viewing a
substrate mounted on the stage.
25. The system of claim 20, wherein the control system includes
logic to set up parameters including pulse repetition rate, pulse
energy and stage speed.
26. The system of claim 20, wherein the laser comprises a
Q-switched Nd:YAG laser.
27. The system of claim 20, wherein the laser comprises a
Q-switched Nd:YVO.sub.4 laser.
28. The system of claim 20, wherein the laser comprises a diode
pumped, Q-switched Nd:YAG laser operating at a third harmonic
wavelength of about 355 nanometers.
29. The system of claim 20, wherein the laser comprises a diode
pumped, Q-switched Nd:YVO.sub.4 laser operating at a third harmonic
wavelength of about 355 nanometers.
30. The system of claim 20, wherein the spot size is between 5 and
15 microns.
31. The system of claim 20, wherein the overlap is in a range from
50 to 99 percent.
32. The system of claim 20, wherein the pulse rate is between about
20 kHz and 50 kHz.
33. The system of claim 20, wherein said energy density is between
about 10 and 100 joules per square centimeter, said pulse duration
is between about 10 and 30 nanoseconds, and the spot size is
between about 5 and 25 microns.
34. The system of claim 20, wherein the sapphire substrate has a
thickness, and the scribe lines are cut to a depth of more than
about one half said thickness.
35. The system of claim 20, including optics to linearly polarize
the pulses.
36. The system of claim 20, including optics to adjust polarization
of the pulses.
Description
RELATED APPLICATION DATA
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/208,484 entitled Scribing Sapphire Substrates with a
Solid State UV Laser filed Jul. 30, 2002, which is a
non-provisional filing of Provisional Application No. 60/387,381
entitled Scribing Sapphire Substrates With a Solid State UV Laser,
filed Jun. 10, 2002.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to systems and processes used
in manufacturing integrated device die, such as integrated circuit
and laser die, including diode laser die, formed on sapphire
substrates. More particularly, the present invention provides for
scribing sapphire substrates using solid state UV lasers, and
separating the scribed sapphire substrate into die.
[0004] 2. Description of Related Art
[0005] Sapphire Al.sub.2O.sub.3 is used as a substrate for a
variety of devices. The sapphire is a hard material that is
optically transmissive, electrically nonconducting and a good
conductor of heat. It has become the preferred substrate material
in manufacturing of laser diodes. In particular, blue laser diodes
and other structures based on gallium nitride GaN and related
materials are manufactured on sapphire substrates in large
volume.
[0006] One bottleneck in manufacturing of die on sapphire
substrates is the separation of the die from the substrate. Because
sapphire is very hard, the typical process requires the use of a
diamond tipped blade to scribe a pattern in the substrate. In one
common method, the sapphire substrate having an array of
semiconductor structures such as laser diodes formed thereon is
placed on an adhesive known as "blue tape," or "wafer tape." A
diamond blade is used to scribe the substrate. Mechanical stress is
used to crack the substrate along scribe lines. The tape carrying
the cracked substrate is then stretched to separate the die. A
robotic pick and place machine is used to remove the individual
die, having typical dimensions in a range of 200 to 500 microns on
a side, from the tape.
[0007] One major bottleneck in the manufacturing of the die is the
cutting process. The diamond blade requires the manufacturer to
allocate a relatively wide scribe line, referred to as a "street,"
(for example, 40 to 70 microns) on the substrate, reducing the
number of die manufacturable on a single substrate. In addition,
the diamond tip blade must be operated relatively slowly, requiring
as much as 1 and a half hours for a 2 inch diameter substrate.
Also, the diamond tips on the blade wear out and must be replaced
often, as much as one blade per wafer. Replacement of the blades
slows down the process of manufacturing. Also, the blades typically
have multiple tips, which must be carefully and precisely aligned
for proper cutting each time a new tip is brought on line, and each
time a new blade is installed. Finally, the mechanical scribing
process causes cracks, which can damage the die and reduce yields.
Typical yields for this process have been reported to be about
70%.
[0008] It is desirable, therefore, to provide a system and method
for scribing sapphire substrates in manufacturing die which is
faster, easier to use, minimizes the number of consumable parts,
allows for greater density and achieves greater yields than is
available using current technologies. Further, it is desirable that
such system be compact, safe to operate and low-cost.
SUMMARY OF THE INVENTION
[0009] The present invention provides a method and system for
manufacturing integrated device die, such as diode laser die, from
a sapphire substrate carrying an array of such integrated devices.
Particularly, the present invention is suitable for manufacturing
blue laser diodes based on gallium nitride structures. According to
the present invention, greater density and greater yield are
achieved, while also reducing the time required to separate the
individual die from the substrate. Furthermore, the present
invention is based on compact, low-cost machines, and otherwise
reduces the overall manufacturing costs for such integrated device
die.
[0010] The present invention provides a process including mounting
a sapphire substrate, carrying an array of integrated devices, on a
stage such as a movable X-Y stage including a vacuum chuck. Next,
pulses of laser energy are directed at a surface of the sapphire
substrate using a solid-state laser. The pulses of laser energy
have a wavelength below about 560 nanometers, and preferably
between about 150 and 560 nanometers. In addition, energy density,
spot size, and pulse duration are established at levels sufficient
to induce ablation of sapphire. Control of the system, such as by
moving the stage with a stationary beam path for the pulses, causes
the pulses to contact the sapphire substrate in a scribe pattern at
a rate of motion causing overlap of successive pulses sufficient to
cut scribe lines in the sapphire substrate.
[0011] Embodiments of the present invention produce laser pulses
having an energy density between about 10 and 100 joules per square
centimeter, a pulse duration between about 10 and 30 nanoseconds,
and a spot size between about 5 and 25 microns. The repetition rate
for the pulses is greater than 5 kHz, and preferably ranges from
about 10 kHz to 50 kHz or higher. The stage is moved at a rate of
motion causing overlap of the pulses in the amount of 50 to 99
percent. By controlling the pulse rate, the rate of motion of the
stage, and the energy density, the depth of the scribe line can be
precisely controlled. In embodiments of the invention, the scribe
lines are cut to a depth of about one-half the thickness, or more,
of the sapphire substrate, so that for an 80 micron thick
substrate, the scribe line is cut to a depth in the range of about
35 microns to, for example, 60 microns, and more preferably greater
than 40 microns.
[0012] In embodiments of the present invention, the solid-state
laser comprises a diode pumped, Q-switched, Nd:YVO.sub.4 laser,
including harmonic frequency generators such as nonlinear crystals
like LBO, so that output of the laser is provided at one of the
second, third, fourth and fifth harmonic frequencies of the 1064
nanometer line produced by the neodymium doped, solid-state laser.
In particular systems, the third harmonic frequency of about 355
nanometers is provided. In other embodiments, the solid-state laser
comprises a Q-switched, Nd:YAG laser, operating to provide one of
the harmonic frequencies as output.
[0013] In embodiments of the invention, the method includes
detecting edges of the sapphire substrate while directing pulses at
the substrate in the scribe pattern. In response to detected edges,
the system prevents the pulses of radiation from being directed off
of the substrate.
[0014] Embodiments of the present invention direct the pulses of
radiation at the backside of the substrate. This prevents damage
potentially caused by heat from reaching the active integrated
device die structures. Furthermore, it prevents debris from the
ablation process from contaminating the integrated devices on the
die.
[0015] Thus, embodiments of the invention include placing the top
surface of the substrate on an adhesive tape prior to scribing,
mounting the substrate with the adhesive tape on the stage, moving
the substrate under conditions causing ablation of the sapphire in
a scribe pattern on the backside of the substrate, and detecting
edges of the substrate during the scribing process to prevent the
pulses of radiation from impacting the adhesive tape.
[0016] The die defined by a scribe pattern are separated from the
sapphire substrate, by mechanically cracking the substrate along
the scribe lines, and using a pick and place robot or other
technology known in the art. In one embodiment, the sapphire
substrate is placed on an adhesive tape prior to scribing, and
after scribing the substrate is rolled or otherwise mechanically
manipulated to break the substrate along scribe lines in the scribe
pattern. The separated die remain adhered to the adhesive tape,
until separated using the pick and place robot, or other
technology.
[0017] Embodiments of the invention further provide for controlling
polarization of the laser pulses with respect to direction of
scribe lines in the scribe pattern. The polarization is controlled
so that the grooves are more uniform for scribe lines parallel to
different axes. Uniformity can be improved by random or circular
polarization of the pulses in some embodiments. More preferably,
polarization of the pulse is controlled so that the polarization is
linear and parallel to the scribe line being cut. It is found that
the quality of the groove being formed is more V-shaped with
parallel polarization, and more U-shaped with polarization that is
not aligned. V-shaped grooves are preferred for more uniform and
predictable breaking of the substrate during separation of the die.
Embodiments of the invention provide for control of the
polarization using a laser with an adjustable polarizer, such as a
half wave plate, in the optical path.
[0018] The invention also provides a system for scribing sapphire
which comprises a solid-state laser, as described above, a stage
adapted to support and move a sapphire substrate, optics directing
pulses to impact of sapphire substrate mounted on the stage, an
edge detection system which detects edges of substrate mounted on
the stage during movement of the stage, and a control system. The
control system in embodiments of the invention comprises a computer
system coupled to the solid-state laser, the stage, and the edge
detection system. The computer is responsive to the edge detection
system and parameters set by users to cause the pulses to impact of
the sapphire substrate in a scribe pattern at a rate of motion
causing overlap of successive pulses sufficient to cut scribe lines
in the sapphire substrate. Embodiments of the invention also
include a debris exhaust system coupled with the stage.
[0019] Embodiments of the invention include a user interface with
logic to set up the scribe pattern, and the operational parameters
including pulse repetition rate, stage velocity and energy levels
to establish scribe depth, scribe speed and other characteristics
of the process.
[0020] Other aspects and advantages of the present invention can be
seen on review of the drawings, the detailed description and the
claims, which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a simplified block diagram of a sapphire scribing
system according to the present invention.
[0022] FIG. 2 is a perspective view of a compact, portable sapphire
scribing system according to one embodiment of the present
invention.
[0023] FIG. 3 is a simplified block diagram including the laser
system and optics for the sapphire scribing system of the present
invention.
[0024] FIG. 4 is a simplified diagram of components of the edge
detection system according to the present invention.
[0025] FIG. 5 illustrates the overlapping of successive pulses
during the cutting of a scribe line.
[0026] FIG. 6 is a perspective view of the stage and debris exhaust
system of the sapphire scribing system according to the present
invention.
[0027] FIG. 7 illustrates a scribe pattern on a sapphire substrate
including an array of integrated laser diodes for cutting into die
according to the present invention.
[0028] FIGS. 8A-8C show a relationship between polarization of
laser pulses and scribe line scribing direction for uniform
V-shaped grooves.
[0029] FIGS. 9-16 are photographs showing experimental results of
the scribing process of the present invention.
DETAILED DESCRIPTION
[0030] A detailed description of embodiments of the present
invention is provided with reference to FIGS. 1 through 8A-8C, and
experimental results are shown in FIGS. 9-16.
[0031] FIG. 1 is a simplified block diagram of a sapphire scribing
system according to the present invention. In the embodiment shown,
a diode pumped, solid-state laser 10 generates high-density UV and
close-to-UV pulses at a repetition rate in the kHz range. In
preferred systems, the laser comprises a Q-switched Nd:YVO.sub.4
medium delivering third harmonic output as the stream of laser
pulses at a repetition rate greater than 10 kHz, with a pulse
duration of about 40 nanoseconds. The pulses are provided using an
optical delivery system 11 and turning mirror 12 to an ultraviolet
objective lens 13, which focuses the pulses on a sapphire substrate
14. The substrate 14 is supported on a vacuum chuck and X/Ystage
15. Preferably, the wafer is supported face down on an adhesive
wafer tape. A gas debris removing system 16 cooperates with a gas
exhaust system and vacuum 17 to remove debris generated by the
ablation of the sapphire substrate.
[0032] A visible light source 18 and a turning mirror 19 deliver
white light through the objective lens 13 to the sapphire substrate
14. The edge detection electronics 20 is responsive to light
reflected via the objective lens 13 and turning mirror 21 to detect
edges of the substrate and prevent pulses of UV radiation from
being directed off of the substrate onto the backing wafer tape or
elsewhere. A camera 22 such as a charge coupled device camera is
focused on the wafer 14 and used to generate an image for
information processing and monitoring. Computer 23 is coupled to
the controllable components of the system, and causes the delivery
of the pulses, movement of the stage 15 and controls other
characteristics of the system to scribe the substrate in a scribe
pattern.
[0033] FIG. 2 is a perspective view of a sapphire substrate
scribing system in one embodiment of the invention. The diode
pumped solid-state laser is compact and low-cost so that it is
efficiently mounted on a cart as illustrated. The computer and
other system electronics are contained on the cart. The computer
keyboard 50 is mounted on a keyboard tray, which slides in and out
of the cart. A flat-panel display 51 is mounted on a swivel base,
so that it may be folded in during movement and storage of the
cart. The system includes a microscope 52, which enables viewing of
the wafer during the cutting process. Images generated by the
camera 22, and graphical user interface tools and other display
constructs are presented to the user using the display 51.
[0034] Generally, embodiments of the present invention are provided
as a semi-automatic turnkey system using a tabletop laser system
and computer mounted on a cart. The system provides for manual
loading and unloading of wafers. However, the invention
contemplates automated wafer loading and unloading systems as well.
Representative systems are adapted to receive two inch sapphire
wafers with die sizes, for example in the range of 250 microns by
250 microns. Smaller and larger die sizes are readily handled. The
wafer thickness ranges from about 80 to 200 microns, for typical
laser diode die, and is mounted face down on a 6.5 inch wafer metal
frame using adhesive wafer tape. The wafer metal frame is manually
placed on the stage and secured using a vacuum chuck. Manual
alignment of the wafer is possible using manual stage controls.
Software controlled scribe patterns are implemented with computer
control of the wafer stage, and controllable speed in the X- and Y-
directions. The system includes a class one laser system which
generate spot sizes less than 20 microns in operational conditions.
A groove is cut, preferably about 40 microns deep, and more
preferably greater than about 1/2 thickness of the sapphire
substrate. Nitrogen gas is used by the debris removing jet, and
evacuated using an exhaust pump. Throughput of the representative
system is about 1/2 hour per wafer, or greater. No damage is caused
to the wafer tape because of the edge detection process, supporting
greater yield in the die separation process.
[0035] The X/Y stage in one preferred system has a maximum speed of
100 mm per second, and a travel range of greater than 100 mm by 75
mm. The resolution of the stage alignment process is about one
micron. The accuracy over four inches of travel range is less than
4 microns. Repeatability of scribe lines provides for deviation of
less than three microns. The flatness of the stage is less than 1.5
microns deviation per inch. No rotation is required in some
embodiments. The vacuum chuck is at least 2.5 inches in diameter,
on a six inch platform, for holding a two inch wafer during
alignment and scribing.
[0036] The laser system in a preferred embodiment is a Q-switched,
diode pumped, third harmonic Nd:YVO.sub.4 providing an output at
355 nanometers wavelength. The laser provides one watt output power
at 20 kHz, and higher, electro-optically Q-switched output using
first pulse suppression. The pulses have a TEM.sub.00 intensity
profile with 10 to 15 micron, or smaller, diameter at 1/e.sup.2
peak magnitude spot size on the target surface. The laser pulse
duration is about 40 nanoseconds, or less and more preferably
between about 30 and 10 nanoseconds, for example about 16
nanoseconds. It is linearly polarized with external rotation
control of a half wave plate up to 45 degrees for alignment with
the crystalline structure of the sapphire for good and uniform
coupling of energy into the sapphire.
[0037] The basic structure of the laser system is like the
commercially available Acculase SS10 Laser System, by New Wave
Research, of Fremont, Calif., which is the assignee of the present
invention.
[0038] The computer system allows for automated control of the
laser and stage movement for defined cutting patterns, which can be
set up using the computer. A wafer map and cutting definition
function allows setup of the scribe pattern including rotation
control of the stage. Video overlay shows live video of the sample
within a software-controlled window to facilitate set up and
monitoring of the process. Control for the cutting parameters
including laser energy, repetition rate and stage speed are
provided via the user interface, giving the operator precise
control over the depth and quality of the scribing process. A
pattern alignment function allows the cutting pattern to be moved
in the X-, Y- and orthogonal directions to match the actual wafer
location during setup.
[0039] FIG. 3 is a basic layout of optical path for one embodiment
of the scribing system according to the present invention. The
optical path includes a laser 50, optics delivering the output of
the laser to a substrate 74 on the vacuum chuck 75 mounted on an
X-stage 76 and Y-stage 77. The laser includes a resonant cavity
defined by high reflector 51 and output coupler 59. A beam expander
52, laser medium rod 53, cylindrical lens 54, diode array 55, thin
film polarizer 56, thin film polarizer 57, and electro-optic
Q-switch 58 are included. The diode array is operated to pump the
rod 53 to induce resonance at the 1064 nm line for Nd:YVO.sub.4.
The output beam is directed to turning mirror 60 and turning mirror
61 through spherical focal lens 62 through nonlinear crystal 63.
The nonlinear crystal 63 produces a second harmonic and passes the
second harmonic along with the primary line through spherical focal
lens 64 to a second nonlinear crystal 65. The second nonlinear
crystal produces a third harmonic output, among others, which is
delivered to turning mirror/filter 66 and turning mirror/filter 67
and half lambda wave plate 68. The wave plate 68 is motorized and
acts as a controllable polarizer for the output beam. The wave
plate 68 is used to align the polarization of the output beam with
respect to the scribing direction to make a grooves cut by the
laser pulses uniform in the X- and Y-directions. The third harmonic
output, at a wavelength of about 355 nanometers, is delivered to
optics including turning mirror 69, beam expander 70, turning
mirror 71, turning mirror 72 and objective 73 to the sapphire
substrate 74. The objective lens 73 is a 20X lens in this
embodiment.
[0040] The nonlinear crystal 63 used for second harmonic generation
can be made of a variety of materials, preferably LBO, BBO or KTP.
Likewise, the nonlinear crystal 65 used for third or higher
harmonic generation can be made of a plurality of materials,
preferably LBO or BBO. In one preferred system, LBO is utilized for
both nonlinear crystals 63 and 65.
[0041] Rod 53 in one preferred system is a Nd: YVO.sub.4
solid-state laser medium. This material allows for shorter pulse
durations and higher Q-switch repetition rates than other suitable
materials, such as Nd:YAG or Nd:YLF. However, other solid-state
laser media, including without limitation, Nd:YAG, Nd:YLF, and
other media suitable for generation of ultraviolet and
close-to-ultraviolet pulses at high repetition rates, are utilized
in some embodiments. Preferred output wavelengths for the
solid-state Nd-based media includes the second, third, fourth and
fifth harmonics of the infrared 1064 nm line, within a range of
about 560 nanometers to about 150 nm. Higher wavelengths into the
visible range may not be as efficient for ablation of sapphire,
while wavelengths below 150 nm require an evacuated optical path
for efficient operation.
[0042] FIG. 4 illustrates the edge detection system used in
preferred embodiments of the present invention. The system includes
a white light source 81 which provides light through turning mirror
82 and objective lens 84 to the sapphire substrate 85 on wafer tape
86, or other mounting media. Reflected light passes through
objective lens 84, turning mirror 83, turning mirror 82 and is
deflected by turning mirror 87 through a spherical focal lens 88 to
a photodetector 89. The photodetector 89 is coupled with the
computer system, and its output indicates edge detection. The edge
of the wafer is detected based on the significant difference of
light contrast between the wafer surface 85 and the wafer tape 86
or other low reflectivity materials on which the wafer is mounted.
The computer system stops the motion of the stage upon receipt of
the edge detection signal, preventing laser pulses from being
directed off the side of the stage.
[0043] FIG. 5 illustrates the overlapping of laser spots according
to the present invention. At high repetition rates, as the stage
moves the wafer, pulses emitted by the laser system overlap. Thus,
a first pulse 90 is overlapped by a second pulse 91 which in turn
is overlapped by second pulse 92 and so on. The amount of overlap
determines in part the depth of the scribe lines. For a repetition
rate about 10 kHz and stage speeds are between 2.5 mm/sec and 5.0
mm/sec, the overlap can easily be controlled in a range of about 50
to 99 percent. The overlap can be obtained by the following example
calculation:
Laser spot size.about.10 micron, diameter
Stage speed.about.2.5 mm/sec
[0044] Then there is a (10 micron/(2.5 mm/sec)=4.0.times.10.sup.-3
sec overlap on a single spot 10 microns in diameter. The number of
pulses that overlap the spot (shot density) is then (10000 pulses
per see).times.(4.times.10.sup.-3 sec)=40. A shot density of 40 is
equal to an overlap of 97.25%.
[0045] FIG. 6 provides a perspective of the stage 100, objective
lens 101 and debris removal jet 102 in one embodiment of the
invention. The stage 100 includes a vacuum chuck 103 centered on a
movable plate 104. A movable plate 104 includes manual adjustment
knob 105 for the Y-direction and a similar adjustment knob (not
shown) for the X-direction. Also, the movement of the stage is
automatically controllable. The jet 102 is arranged to deliver air
or nitrogen gas into the region of the ablation in order to remove
debris. A vacuum (not shown) withdraws the gas with the debris from
the region of the wafer.
[0046] In a representative system, the repetition rate is
controllable within a range of 20 to 50 kHz, with a stage speed
ranging up to 8 to 10 mm per second. Other combinations of
repetition rate and stage speed will be developed according to the
needs of a particular implementation.
[0047] FIG. 7 shows a magnified view of an active surface of a
sapphire substrate having an array of laser diodes formed thereon.
Spaces, or streets, about 80 microns wide are left between the
individual laser diodes to allow room for scribing. However, the
white dots should not be cut so the effective street width is less.
In FIG. 7, grooves (dark lines within the streets) are machined
having a width of 10-15 microns, on the top surface for perspective
of the relative widths. In a preferred system, the backside of the
wafer is scribed. In a typical system according to the prior art,
the streets must be wide enough to accommodate diamond tipped
blades. In these prior art systems, such streets have been between
at least 40 wide. With the system of the present invention with a
spot size in the range of 10 microns, and the precision available,
the streets can be reduced to 20 or 30 microns in width or less.
This significantly increases the density of devices that can be
made on a single substrate and improves throughput in manufacturing
process for the die.
[0048] As described above, a representative system is based on a
Nd:YVO.sub.4 or Nd:YAG laser medium operated at its third harmonic
wavelength of 355 nanometers. Theoretically there is very little
absorption at this wavelength in a sapphire crystal. However, under
a very high intensity flux of laser light, greater than a Giga Watt
per cm squared, for example, it is believed that non-linear
absorption occurs causing the coupling of the laser energy into the
sapphire material. This coupling with sufficient energy density
causes ablation of sapphire. In addition, the laser pulses are
highly overlapped during processing as described. The advantages of
overlapping the laser pulses during micro-machining include not
only improving the smoothness of the machined groove, but also
enhancing the laser coupling efficiency into the sapphire
material.
[0049] FIGS. 8A-8C illustrate control of linear polarization of the
laser pulses with respect to the scribing direction on the sapphire
substrate. The half wave plate 68 described above with respect to
FIG. 3 is used to control polarization of the pulses in order to
optimize the coupling of laser energy to the sapphire, and the
uniformity of the grooves in the X- and Y-directions.
[0050] FIG. 8A illustrates an UV laser 200 which generates a
linearly polarized output beam on line 201 aligned vertically, for
example in the plane of the paper, as indicated by arrow 202. The
polarization may be established intra-cavity as shown in FIG. 3.
Alternative systems may include a polarizer outside the cavity. The
pulses proceed to half wave plate 203, which is aligned vertically
in a Y-direction, parallel with the polarization 202. After half
wave plate 203, the pulses remain aligned vertically as indicated
by arrow 204. The pulses proceed through focus lens 205 maintaining
vertical polarization as indicated by arrow 206. The polarization
is aligned with the machining direction of a scribe line 207
parallel with a Y-axis.
[0051] FIG. 8B illustrates the layout of FIG. 8A, with like
components having the same reference numbers. In FIG. 8B, half wave
plate 203 is rotated 45 degrees relative to the position of FIG.
8A. The rotation of the half wave plate 203 causes the polarization
of the pulses to rotate 90 degrees as indicated by arrow 208,
extending for this example into the paper. The pulses proceed
through focus lens 205 maintaining their polarization as indicated
by arrow 210. The polarization 210 is aligned with the machining
direction of a scribe line 211 parallel with a X-axis.
[0052] FIG. 8C illustrates laser polarization direction relative to
the cutting or machining direction of the scribe line. Thus, a
scribe line 215 consists of the sequence of overlapping pulses
aligned in a cutting direction 216. The laser polarization
direction 217 in the preferred system is parallel with the cutting
direction 216. The alignment of polarization parallel with the
cutting direction is found to produce uniform V-shaped grooves. The
V-shaped grooves allow for more uniform separation of the die than
can be achieved with grooves that are more U-shaped, or that are
less uniform.
[0053] Two important requirements for the sapphire scribing system
are the throughput and the cutting depth of the wafer. The cutting
depth of sapphire is dependent on the overlap and the energy
density. It is required, typically, to cut at least half way
through the wafer. In one available Nd:YAG laser embodiment, a 10
kHz repetition rate and maximum energy density 40 j/cm2 are
achieved, and used for scribing according to the present invention.
FIGS. 9-16 are photographs of experimental results of the scribing
process using this Nd:YAG embodiment, showing the depth and V-shape
of the grooves that can be achieved in representative systems. The
figures show cross-sections of sample sapphire wafers having
thicknesses of about 80 microns, with laser cut grooves more than
half the thickness of the wafer. In these examples, an energy
density is controlled in a range of about 22.5 to 40.0 j/cm2, and a
stage speed in a range of about 2.5 to 5.0 mm/sec.
[0054] The energy density and stage speed for FIGS. 8 to 15 are as
follows:
1 Fig. 9: 22.5 j/cm.sup.2/2.5 mm/sec Fig. 10: 30.0 j/cm.sup.2/2.5
mm/sec Fig. 11: 40.0 j/cm.sup.2/2.5 mm/sec Fig. 12: 40.0
j/cm.sup.2/3.0 mm/sec Fig. 13: 40.0 j/cm.sup.2/3.5 mm/sec Fig. 14:
40.0 j/cm.sup.2/4.0 mm/sec Fig. 15: 40.0 j/cm.sup.2/4.5 mm/sec Fig.
16: 40.0 j/cm.sup.2/5.0 mm/sec
[0055] It can be seen from the FIGS. 9 to 16 that the cutting depth
is larger than half wafer thickness for the stage speed between 2.5
mm/sec and 5 mm/sec. A sapphire scribing system using a
Nd:YVO.sub.4 medium operates readily at 20 to 50 kHz, and a maximum
energy density can be 45.about.50 j/cm2. To keep the same cutting
depth and increase the throughput, the stage speed can be increased
to 8.about.10 mm/sec, for this system.
[0056] In one embodiment, computer software is provided to
engineers and operators for managing scribing operations as a step
in manufacturing of laser diode die. The software operates at two
levels in this example, designated an engineering interface and an
operator interface. At the engineering interface level, the
engineer has the ability to control the following:
[0057] Fire the laser
[0058] Change the rep rate
[0059] Change power (from 0 to 100%)
[0060] Adjust the coax light
[0061] Continuous, burst or single shot firing
[0062] Create reference point (two point for XY, and three points
for XYZ)
[0063] Ability to re-coordinate: Save, recreate and move a map on a
different wafer to coincide with previously determined reference
points.
[0064] Create wafer map: which controls the following
[0065] Manipulate wafer map by changing horizontal and vertical
spacing
[0066] Size of the wafer scribe pattern
[0067] Explode scribe pattern to individual lines: Take a wafer and
make it into several individual lines
[0068] Translate or rotate patterns
[0069] Laser setting: which controls the following:
[0070] Speed of the stage
[0071] Rep rate
[0072] Polarization
[0073] Laser power (0-100%)
[0074] Number of passes
[0075] Depth of passes
[0076] Explode lines: which controls the following
[0077] Move each line individually
[0078] Change all setting individually
[0079] Translate or rotate lines individually
[0080] Ability to save and recall
[0081] Stop and begin at the beginning of any line
[0082] Ability to turn ON and OFF the vacuum and nitrogen air
[0083] Calibrate the edge detection
[0084] With the operator interface, the user will control the
following:
[0085] Vacuum control (Load the wafer mechanism)
[0086] Place a new map from the tools library
[0087] Ability to rotate the map
[0088] Run the system
[0089] Abort if needed
[0090] The present invention provides a process for manufacturing
laser diode die, and other integrated device die, formed on
sapphire substrates. Procedures according to embodiments of the
invention include the following:
[0091] 1) laying out and forming laser diodes in an array on an
active surface of a sapphire substrate, with individual laser
diodes separated by streets having a width less than 40 microns,
and preferably around 25 microns or less;
[0092] 2) placing the sapphire wafer with the active surface facing
down on wafer tape on a metal frame;
[0093] 2) placing the taped wafer with a metal frame on the vacuum
chuck of the wafer stage, and turning on the vacuum to secure the
wafer and tape to the stage;
[0094] 3) moving the wafer to a home position by controlling the
stage
[0095] 4) automatically, or semi-automatically, aligning the wafer
position to coordinates established by the computer setup;
[0096] 5) setting up a scribe pattern based on wafer and die size
and layout parameters;
[0097] 6) automatically, or semi-automatically, setting up the
lighting levels for edge detection;
[0098] 7) setting up stage speed, laser polarization and laser
power for the required cutting depth;
[0099] 8) turning on the debris removing system;
[0100] 9) starting the process of laser scribing based on the
scribing pattern on one line parallel to one axis;
[0101] 10) continuing the process on other lines and axes, while
controlling polarization, until the wafer is finished;
[0102] 11) causing the stage to return to an exit position, turn
off the vacuum, and removing the wafer from the chuck;
[0103] 12) cleaning wafer with high-speed air or other gas jet to
remove laser machining induced debris;
[0104] 13) applying mechanical pressure to break the wafer along
the scribe lines; and
[0105] 14) stretch the wafer tape for separation and transport
using a pick and place system to other mounting apparatus.
[0106] The procedures outlined above are carried out using the
systems described above, or similar systems.
[0107] Accordingly, the present invention provides a significantly
improved scribing process and system for use with sapphire
substrates. The process and system are low-cost, high yield, and
high throughput compared to prior art sapphire scribing
technologies.
[0108] While the present invention is disclosed by reference to the
preferred embodiments and examples detailed above, it is to be
understood that these examples are intended in an illustrative
rather than in a limiting sense. It is contemplated that
modifications and combinations will readily occur to those skilled
in the art, which modifications and combinations will be within the
spirit of the invention and the scope of the following claims.
* * * * *