Precision Materials Processing Using Diode-Pumped Solid-

State (DPSS) Lasers

Bruce B. CraigCREOL/College of Optics

Affiliates Day, April 1st, 2005

2

Spectra-Physics Mountain View, CA

3

Outline

• Overview of Diode-Pumped Solid State Laser Technology

• Review of Market for Diode-Pumped Solid State Lasers

• Applications overview • Ultrafast materials processing

4

DiodeReceptacle

Diode Pump

Pump DiodeArray

Diodes

Laser Diode Controller

5

Diode Lasers

• Very efficient (≈50%)• solid state, long

lifetime (≈104 hrs)• used in CD players,

telecommunicationsbut

• imperfect beam quality

• no energy storage

6

Laser Diode Process

Epitaxial Layer Growth

Wafer Fab Assembly

Test/Burn-inFiber Coupling

Customer

Negative Contact

Substrate

Positive Contact

Cleaved Facet Mirror

CladdingLight Emission

Active Medium

Vertically Integrated of High Power Gallium-Arsenide III-V Semiconductor Lasers

7

Fiber-Coupled Diodes

• Couple the diode light into a multi-mode fiber• Place the diode, thermal control and power supply

in a separate box from the laser• Easy to replace the diode• Industry standard

Laser Diode Coupling Lenses

Optical Fiber

8

Diode-Pumped Lasers

• Must now deal with the beam quality out of the fiber

Laser Diode Mode Volume

Gain Region

TEM00 Mode Volume

9

Direct diodesystems

Semiconductor Lasers

Q-switched 532nmQ-switched 1064 nm

FCbarModules

Q-switched UV

CW 1064 nm CW 532 nm

psec UV

fsec Green, NIR

20W, 40 W+

fsec NIR

psec 532 nm

quasi-CW UV

Diode Pumped Solid State Laser Systems

10

Classes of materials processing laser

• Power– High power – several kilowatts– CW or long pulse width (ms to µs)– Multi-mode– Metal welding, cutting, cladding, etc.– Brute force application

• High finesse– Lower power but high peak power– Short pulse width (ns to fs)– TEM00 single mode– Precision micromachining – small spot size– High pulse to pulse stability and spatial stability– Customized beam characteristics – wavelength, pulse

width, repetition rate, pulse energy, etc.

11

World market for DPSS laser

• Source: Optoelectronics Report (January 1, 2005)

• 2004 total sales $270 million (48% gain over 2003) and 2005 estimates $300 million

• DPSS for materials processing $115 million in 2004 and estimated $123 million in 2005

• Most DPSS lasers TEM00 single mode

12

Requirements for industrial DPSS laser

• Hands-off, reliable 24/7 operation– Rugged and sealed housing– No laser alignment adjustment needed

• Long lifetime– Long lifetime diode– Long lifetime harmonic crystal

• Good serviceability– Interchangeable diode module

• Affordable– Low cost of ownership

13

Commercial DPSS laser for precision materials processing

• Q-switched laser– Based on Nd:YAG, Nd:YVO4, and Nd:YLF– Pulse width in ns range– High pulse energy, very rugged, and different wavelengths– Widely used in micromachining and marking

• Mode-locked (ultrafast) laser– ps high repetition rate oscillator and amplifier based on

Nd:YVO4– fs oscillator and amplifier based on Ti:sapphire and

Yb:KGW– Extremely high peak power amplifier

• CW laser– High power fiber laser– CW green laser

14

Power of industrial single mode Q-switched DPSS laser

> 35 W at 1064 nm, > 20 W at 532 nm, > 10 W at 355 nm, and > 3 W at 266 nm

15

Short-pulse, high-power Q-switched DPSS laser

0 20 40 60 80 1000

5

10

15

20

266 nm

355 nm

532 nm

1064 nm

Out

put P

ower

[W]

Repetition Rate [kHz]0 20 40 60 80 100

0

5

10

15

20

266 nm

355 nm

532 nm

1064 nm

Puls

e W

idth

[ns]

Repetition Rate [kHz]

HIPPO = High Intensity Peak Power Oscillator

16

Applications of Q-switched lasers

Wavelength [nm]

Power[W]

Pulse width [ns]

Repetitionrate [kHz]

Main application

13201064

> 1> 35

5 – 205 – 100

10 – 201 – 400

• memory repair• marking, diamond cutting,

resistor trimming, solar cell scribing, disk texturing, memory repair

355 > 10 5 – 100 1 – 300 • via drilling, glass marking, stereolithography, semiconductor dicing, dielectric scribing, memory repair

532 > 20 5 – 100 1 – 300 • wafer marking, PCB structuring, Cu drilling/cutting, TFT annealing, laser pumping

266 > 3 5 – 30 15 – 300 • compound semiconductor scribing, glass marking, inspection

17

Applications of mode-locked lasers

Wavelength[nm]

Power[W]

Pulse width

Repetition rate Main application

1048

800

>3

> 2

500 fs

110 fs

1 – 7 kHz

1 – 5 kHz

• high precision materials processing

• photomask repair, fuel injector nozzle drilling, stent cutting

800 > 2 100 fs 80 – 100 MHz • multiphoton imaging, thin film metrology, laser pumping

532 > 1 12 ps 80 – 100 MHz • laser pumping, surface scribing

355 > 4 12 ps 80 – 100 MHz • PCB direct imaging, inspection, printing, FBG writing, dielectric scribing, polymer film cutting

18

Applications of CW lasers

Wavelength[nm]

Power[W]

Pulse width Repetition rate

Main application

1090*(*typical fiber laser)1064

> 100

> 15

N/A

0.1 – 100 µs

N/A

5 – 40 MHz

• printing, marking, cutting, welding, bending

• printing, spectroscopy

532 > 10 N/A N/A • wafer inspection, image recording, TFT annealing, fingerprinting detection, laser pumping

266 > 0.5 N/A N/A • wafer inspection, FBG writing, DVD disk mastering

19

Major markets for materials processing using single mode DPSS lasers

• Industrial manufacturing– Stereolithography– Precision marking– Plastic welding– Diamond processing

• Microelectronics manufacturing– Silicon dicing/scribing– Compound semiconductor scribing– Dielectric scribing– Laser direct imaging and structuring– Resistor trimming– Memory repair– Wafer marking– Disk texturing– Via drilling

20

Plastic Welding

Flat Panel Display Titling

Memory Repair

Resistor Trimming

Read/Write Head Bending

Keyboard Marking

Disk Texturing

Flat Panel Annealing

21

Hard Disk Texturing

22

Landing Zone

23

Hard disk texturing

Bump height: 5 nmExtremely low noise required

Q-switched, 1064 nm, 4 W, 200 kHz, 80 ns

24

25

PCB structuring

Q-switched, 532 nm, 9 W, 20 kHz, 35 ns

25 µm wide line (Cu ablated by laser) with 50 µm pitch

Courtesy of Siemens Dematic, Germany

26

Hole drilling

• Percussion drilling– Smaller holes (size comparable to focal spot

diameter)– Beam characteristics controls hole quality

• Trepanning drilling– Larger holes (size larger than focal spot diameter)– Accuracy of rotation determines the precision of

hole diameter

27

Trepanning drilling of blind via in multi-layer PCB

Q-switched, 355 nmTop copper:18 µm thick

Dielectric:60 µm thick

Bottom copper:18 µm thick

Via diameter: 100 µm

Copper plated after drilling

Courtesy of Exitech, UK

28

Thick film resistor trimming

Q-switched, 1064 nm, 6 W, 10 kHz, 70 ns

“L-cut”

29

30

Industrial Marking

31

Marking

• Black carbonization• Color change• Shallow groove by ablation• Surface modification by melting• Controlled micro-cracking• Combination of various mechanisms

32

Back side marking on silicon dies

Q-switched, 532 nm, 3 W, 10 kHz, 25 ns

33

34

Scribing indium tin oxide (ITO) coating on flat panel display (FPD) substrate

Q-switched, 532 nm, 9 W, 20 kHz, 35 ns

Left: Beam focusedLine width 30 µm

Right: Beam de-focusedLine width 100 µm

Maskless pattern generation

35

Intra-glass markingQ-switched, 355 nm, 4 W, 20 kHz, 35 ns

Soda lime glass thickness: 0.7 mm

Line width: 20 µm

36

Intra whiskey marking

Q-switched, 355 nm, 4 W, 20 kHz, 35 ns

37

Spectra-Physics quick response time

38

Cutting and scribing

• Fusion cutting (Inert gas cutting)– Inert gas for melt ejection and shielding– Cut edge free of oxides– All metals, some polymers, and some ceramics

• Oxidation cutting (Oxygen cutting)– Oxygen reaction providing additional heat input– Higher cutting speed but cut edge oxidized– Mainly mild and low alloyed steels

• Vaporization cutting (Ablation)– Molten state minimized by short pulses and high peak power

density– Very precise and complex cut in thin work pieces– Polymers, semiconductors, ceramics, thin films, etc. – Suitable for surface cutting/scribing

39

Silicon micromachining

• Scribing/dicing solar cell• Dicing thin silicon wafer• Drilling, slotting, and drilling in thick (standard)

silicon wafer• Dicing released MEMS device

Subrahmanyan, Photonics West 2003

40

Cutting slot in silicon wafer

Q-switched, 532 nm, 11 W, 50 kHz, 13 ns

Slot width: 200 µm

Courtesy of Exitech, UK

41

Cutting complex shapes in silicon wafers

Q-switched, 355 nm, 5 W, 50 kHz, 12 ns

Wafer thickness: 625 µm

42

Low-K dielectric scribingSubrahmanyan, Photonics West 2003

43

Scribing sapphire wafer

Q-switched, 266 nm, 2 W, 50 kHz, 11 ns

Cutting speed: 30 mm/s Cut width: 5 µm

Courtesy of JPSA

44

Scribing GaAs wafer

Q-switched, 266 nm, 2 W, 50 kHz, 11 nsWafer thickness: 200 µm Scribe depth: 30 µm Cut width: 5 µm

Stretching on tape after scribing

Courtesy of JPSA

45

Cutting polyimide filmMode locked Q-switched 4 W, 355 nm, 10 ps, 80 MHz 4 W, 355 nm, 35 ns, 30 kHz600 mm/s 80 mm/s

Film thickness: 50 µm

46

Scribing micro-grooves on titanium surface

Q-switched, 355 nm, 4 W, 20 kHz, 32 ns

To increase cell adhesion of biomedical implants

Groove height: 7 µm -comparable to mammalian cell size

47

Single mode fiber laser cutting of cardiovascular stent

50 W CW modulated

Courtesy of Guidant Corporation

48

– Rapid ionization and plasma formation

– No heating of surrounding material– Little or no redeposited material– Non wavelength dependent

multiphoton absorption– Sub-wavelength size features

– Slow melting and vaporization – Heating of surrounding material

(heat affected zone)– Redeposited molten material– Absorption strongly depends on

wavelength– Wavelength size features

Time [ps]10-2 10-1 100 101 102 103

Ultrafast Ablation Longer Pulse Ablation

Ultrafast vs. long pulse ablation

Time constant for heat dissipation from electron/plasma to the surrounding lattice in the order of a few picoseconds

49

Ultrafast laser drilling of fuel injector nozzle

Courtesy of Laserzentrum Hannover, Germany

50

Ultrafast laser cutting of cardiovascular stent

Courtesy of Laserzentrum Hannover, Germany

51

Ultrafast laser micromachining

Silicon

StainlessSteel

FusedSilica

Courtesy of Exitech, UK

52

Ultrafast photomask repair

Before Repair After Repair

Chromium-on-fused-silica photomask for deep UV microlithography – line width: 0.75 µm

R. Haight et. al., Laser Focus World 5/02

53

Ultrafast laser glass processing

Q-switched laser, 12 ns, 355 nm New directly diode pumped Yb:KGW laser, 500 fs, 1048 nm

54

Ultrafast laser precision trimming of MEMS device

Directly diode pumped Yb:KGW laser, 500 fs, 1048 nm

55

Outlook

• Optical based materials processing solutions continue to gain ground for a wider range of applications

• Laser sources continue to evolve– New architecture – direct diode pumped ultrafast laser, thin

disk laser, fiber laser– More wavelength choice– Higher power– Higher repetition rate– Shorter pulse width– Less complexity– Longer lifetime– Lower cost of ownership

56

Vision

To Be the Premier Global Resource for Customers Who Need to Make, Manage and/or Measure Light.