Application of EOlite Flexible Pulse Technology. Matt Rekow Yun Zhou Nicolas Falletto

Transcription

1 Application of EOlite Flexible Pulse Technology Matt Rekow Yun Zhou Nicolas Falletto 1

2 Topics Company Background What is a Flexible Pulse Laser? Why Tailored or Flexible Pulse? Application of Flexible Pulse lasers Thin Films c-silicon Bulk Materials Printed Circuit Board Laminate Materials Summary and Conclusions 2

3 Who We Are. PyroFlex Flexible Pulse Fiber Laser Technology 25 Watt nm Laser Micro Processing Systems Semiconductor Micromachining MLCC inspection FLEX PCB via drilling Marking Photonic Crystal Fiber Laser Technology 100 Watt 1030 nm 30 Watt 515 nm 14 Watt 343 nm 3

4 ESI Corporate Portland, OR Engineering Centers Bordeaux & Montreal Applications Center Sunnyvale, CA Manufacturing Beijing EOlite 60 people world wide ESI 600 people world wide

5 Peak Power (normalized) What is a Flexible Pulse Laser? Traditional Q-Switched Laser Pulse parameters determined by design Volume of gain medium Performance of Q-switch Pump source Power Flexible Pulse Fiber Laser Flexible pulse technology decouples pulse parameters from laser design Pulse duration selectable Repetition rate arbitrary Pulse energy selectable Pulse shape customizable. 1.0 Flexible Pulse Arbitrary Shape Arbitrary Duration Limited PRF Flexible Shape Adjustable Duration Unlimited PRF Time, ns

6 The Tailored Pulse Laser: PyroFlex TM Basic Architecture Seed Circulator YDFA Isolator YDFA Modulator YDFA FBG M PyroFlex TM 25 The temporal pulse shape of the optical pulse is controlled by the shape of the electrical waveform applied to the Modulator

7 Why is Pulse Shape and Flexibility Important? Any laser process has Excess peak power: = Damage A peak power threshold A total energy requirement Peak Power Process Threshold Process Window Wasted energy = (HAZ) Most processes also have A peak power limit A total energy limit Some processes also have Minimum, maximum and optimal pulse durations Thresholds that change as the interaction unfolds Time The tailored pulse laser designs in the flexibility to simultaneously meet all these requirements where traditional lasers can not

8 Applications THIN FILM PHOTOVOLTAIC DEVICES 8

9 Applications: Thin Film Solar Panels: Monolithic Integration Panel is divided into multiple cells, connected in series: Series connection is accomplished with three scribing steps and three deposition steps 3 patterning steps (P1, P2, P3) Laser or mechanical scribe Full length of active area Individual cells P3 P1 P2 Graphic: Hahn-Meitner Institut Berlin

10 CIGS P2 Process Optimization Utilizing Pulse Duration Tuning - Remove CIGS from Mo Cleanly with no CIGS melting 1 ns 2 ns 4 ns 6 ns 10 ns 15 ns 25 J 20 J Molybdenum CIGS 15 J 12.5 J 55 m 10 J 7.5 J 10

11 Example : CIGS Solar Cells Cu-In-Ga-Se Heat sensitive difficult process CIGS Brittle Fracture Process Very specific, patented, process window Minimum total energy Laser pulse must be shaped to fit Process Fails ns Q-switched pulse can not fit Short ns or ps pulse can not fit 11

12 Real World CIGS Processing Example Q-switched pulses Tail is too long ps or short ns pulses Pulse is too short Peak power too high PyroFlex shaped pulses Just right Time Domain Tailored-Pulse Laser Enables Scribing of CIGS Solar Modules, M. Rekow, et al. PV World, May 2011

13 Modules Made with the Patented PyroFlex CIGS Process P1, P2 & P3 at 200X and 500X ~125 um ~50 um

14 CdTe 14

15 CdTe: Fast Process Exploration with PyroFlex P2/P3 2ns 5ns P1 10ns 20ns 120uJ 100uJ 80uJ 60uJ 40uJ 20uJ 10uJ

16 CdTe: P2 and P3 with Advanced TCO Materials Long Pulse Duration Short Pulse Duration Some advanced TCO materials are not as forgiving for laser processing as SnO2:F Color change indicates detrimental chemical change in TCO Optimized pulse duration preserves material chemistry and electrical properties

17 P1 : Temporal Distribution of Energy Within a Pulse has a Profound Impact on Scribe Morphology 10 ns Square Pulse 10ns Double Pulse

18 CdTe SnO 2 :F Scribing TEC10 Glass For CdTe Solar Cells Low Emissivity glass Highly reflective in the mid and far IR Architectural Glass Also a great substrate for solar cells and electronics Produced on a large scale One surface is conductive ~10 Ohm/square beam SnO 2 :F ~300 nm SiO 2 ~20 nm Intrinsic SnO 2 ~30 nm Soda Lime Glass ~ 3mm

19 SnO 2 :F : Film Side Ablation, Constant Pulse Energy, Variable Duration 2ns 4ns 6ns 8ns 10ns 12ns 14ns 16ns 18ns 22ns Pit Depth Depends on Pulse Duration Pit Bottoms are Flat in Spite of Gaussian Beam Profile Process is not driven by peak power but rather energy Density Hypothesis - Laser Driven Surface Chemistry

20 Depth of Cut (nm) SnO 2 :F - Effect of pulse duration at a fixed energy Etch Rate at Constant Pulse Energy Etch rate is directly proportional to pulse duration Change in slope appears represents transition from SnO2:F layer to SiO2 layer Pulse duration is the key parameter Pulse Duration (ns) Glass Damage SnO 2 :F SiO 2 Interface

21 Etch Depth (nm) Laser Peak Pulse Power (% of Maximum) SnO 2 :F - Avoiding Damage to SiO2 layer -Minimize Energy Input Initial Peak Power Determines spot size only Pulse tail duration Determines etch depth Chair shaped pulse Almost no energy is required to keep the process going. Only 3% of peak Laser Pulse Shape Chair Pulse Etch Rate vs Tail Duration 120% 100% 80% 60% Etch Depth Laser Pulse 40% 20% Tail Duration (ns) 0%

22 CdTe P1 Chair Pulse: Video 22

23 SnO 2 :F : Selective and Precise Film Removal Precise depth control + flat pit bottom + regular surface microstructure = colorful glass marking Color controlled by pulse duration 23

24 SnO 2 :F Color Marking 24

25 ZnO a-silicon P1 25

26 ZnO on Glass Pulse Duration Study 5ns removed 90% of material 50ns removed 95% of material 100ns and above crack glass and TCO layer even at low energy

27 ZnO on Glass Material Properties and Ablation Model T melt =1975 Celcius T decomposition ~1975 Celcius Zn vapor + O 2 Material Melts ~ 5 10 ns Decomposition and physical ablation After 10ns, hold material at constant temp so decomposition can proceed to completion Chair Shaped Pulse Lower fluence at edges results in white residue Energy beyond 50 ns clears residue but results in TCO and glass cracking

28 Target Temp Rise (K) Laser Peak Power (arb units) Target Temp Rise (K) Laser Peak Power (arb units) ZnO on Glass Simplistic Thermal Model Square Pulse: Continual Temperature Increase Chair Pulse: Constant Temperature Maintained. Al t 2 c Al Al Temperature Evolution At Target Spot Temperature Evolution At Target Spot Time (ns) Target Area Temp erature Laser Pulse Time (ns) Target Area Temp erature Laser Pulse

29 ZnO on Glass: Pulse Shape Comparison: Constant Pulse Energy Q-Switched Pulse Square Pulse Shaped Pulse 44µm 54µm 54µm Glass Cracks TCO Cracks Smaller Ablation Region ZnO Residue No Glass Cracks Few TCO Cracks Reduced ZnO Residue No Glass Cracks No TCO Cracks Little ZnO Residue

30 Applications CRYSTALLINE SILICON PHOTOVOLTAIC DEVICES 30

31 c-silicon : Laser Fired Contacts Challenge: Diffuse some of the Al into the Silicon Reduce the contact resistance Aluminum Silicon Substrate

32 c-silicon: Laser Fired Contacts Pulse Duration Study: Fixed Peak Intensity, Variable Duration and Energy 75ns 236uJ 100ns 282uJ 250ns 125ns 325uJ 150ns 390uJ 200ns 466uJ 250ns 550uJ Best Result: 250 ns Aluminum de-wets and leaves the reaction zone before the alloy can form

33 Opening Area c-silicon: Laser Fired Contacts Quench Rate Study Probing the process dynamics with the Flexible Pulse Laser Delay = 0ns 150ns 200ns 275ns infinity At what finite delay does the infinity pulse Match the curve? Cooling time is on the order of 500ns LFC Quench Rate Delay Between First and Second Pulse (ns)

34 Passivated Emitter Rear Contact PERC Passivated Emitter Rear Locally diffused PERL PERC/PERL SOLAR CELLS 34

35 Silicon PV Laser Processing PERL Cell PERC/PERL cell Back surface dielectric layer is added for Surface recombination reduction Improved light reflectivity Absolute cell efficiency may be improved by as much as 2% Laser perforates passivation layer to allow electrical contact. Damage to Si substrate must be minimized 35

36 Depth of Ablation Pit (nm) Depth of Ablation Pit (nm) c-silicon Pulse Duration and Wafer Penetration at 532 nm Pulse Duration and Depth Pulse Energy and Depth Impact of Pulse Duration on Pit Depth at 80% of Maximum Pulse Energy Impact of Pulse Energy on Pit Depth for a 2ns 532 nm Laser Pulse Pit Depth Data Absorption Depth Expected Behavior: Optical absorption depth should limit minimum pit depth and therefor define the optimal pulse duration Pulse Duration (ns) Pulse Energy (µj) Pulse duration is more important than pulse energy 36

37 Dielectric Removal: Gaussian Beam Results 1 ns 2 ns 5 ns 20 ns 12 uj 12 uj 12 uj 12 uj 20 um 290 nm Penetration is minimal at 1 ns but material is forced into a ~1 um high ridge at the edge of the ablation spot. 37

38 Ridge Elimination With Spatial Beam Shaping Top hat beam shaping was implemented utilizing a 100 mm focal length refractive-diffractive beam shaping optic. Schematic below depicts basic set up Diffractive Flat Top Beam Shaper 100 mm fl 200 mm fl lens Top Hat Image Plane 37.5 um diameter Target Wafer 200 mm Top Hat Image Plane 75 um diameter arbitrary 100 mm Telecentric F- Scan lens 38

39 Dielectric Removal: Flat Top Beam Results 1 ns 2 ns 4 ns 8 ns 17 uj Flat Top Beam Result 18 uj 18 uj 18 uj Gaussian Beam Result Ridge height is not measurable compared to surface texture with beam shaping and short pulse duration 39

40 Dielectric Removal: Flat Top Beam Results (SEM) 1ns, 16 uj 2ns, 25 uj 4ns, 25 uj 8ns, 25 uj 37.5 um Unablated Area Ablated Area Short pulse duration and flattop beam shaping remove the dielectric layer with practically no dmage to underlying Si substrate

41 Emitter Wrap Through EWT 41

42 EWT: Silicon PV Laser Processing Advantages of EWT Cell Architecture Shading by metal collection grids and bus bars is eliminated. Reduced carrier diffusion length Requirements Up to 20,000 holes must be drilled on 1 mm pitch in 200 um thick wafers Takt time requirement is about 1 second Hole diameter must be large enough for effective damage removal etch 42

43 EWT: Pulse Duration Impact on Drilling Rates Longer pulse duration Better drilling efficiency. Increased PRF Improved drilling efficiency until energy crosses minimum threshold. Energy in excess of what is required to heat, vaporize and eject material does not contribute to the drilling speed. =>Available pulse energy and spot size determines optimal pulse duration 43

44 EWT: Pulse Shaping Improves High Speed Through Silicon Via (TSV) Drilling 5,000 holes per second 12,000 holes per second 20 Watt average power, 1064 nm 200 um thick Si wafers 44

45 EWT: Post Drilling Etch 30 seconds in ESI proprietary etchant 5000 hps laser process 88 um exit, 99 um entrance 10% taper m holes are sufficient for 100% yield on etch process 45

46 Conclusions Flexible and Tailored laser pulse shapes have: Enabled optimization of dielectric removal for PERC/PERL solar cells Enabled record setting drilling rates in Silicon for EWT applications Enabled a novel SnO 2 :F removal process that allows rapid and precise material removal in a way not before possible

47 PCB/FLEX PROCESSING WITH THE PYROFLEX NM

48 Connector Edge Cutting Challenge Cut through the Polyimide and the Cu without excess heat effect on the PI and minimal burr on the Cu. ~25 um Cu ~25 um PI/Adhesive/PI Cut 48

49 Flex Connector Cutting Strategy Cut through the PI utilizing short pulses with minimal effect on Cu C u Cut through the Cu utilizing 100 ns pulses Minimal effect on the PI Cut through the remaining PI with 2 ns pulses Optional clean with low energy short pulses. Remove debris and oxidation from cutting process 49

50 Connector Edge Cutting Results Optical image of cut and cleaned flex connector. Cleaned Regions 50

51 Connector Edge Cutting Results Cleaned Regions Laser cleaning process applied to two cut traces compared with an un cut trace. Oxidation and contamination are effectively removed with the laser cleaning process 51

52 Blind Via Drilling in Flex Circuit Materials Drill 52

53 Flex Via Drilling Pulse Duration Impact on Cu Removal (532 nm) Parameters 33 uj - Fixed 50 um Diameter 2ns 5ns 10ns 25ns 50ns 75ns 100ns 150ns 200ns High pulse energy is not required to rapidly remove the Cu, the key is longer pulse duration 53

54 Total Energy uj Flex Via Drilling Pulse Duration and PI Removal Shorter pulse durations are more effective at removing the PI layer. Have relatively small impact on the Cu layer below. Energy Required to Open a 50 um Via in PI Material Pulse Duration (ns) 54

55 Blind Via Drilling Cu/PI/Cu 12/25/12 Single 100 ns pass opens the Cu layer 4ns passes removes PI with minimal impact on underlying Cu. 1ns low energy pulses clean the surface of debris 55

56 MACHINING BULK MATERIALS 56

57 Silicon Processing: Impact of pre-pulsing Applications Thin wafer dicing Short pulse required 1064 nm Penetration depth is high Larger melt volume High pulse energy required for efficient material removal Pre-pulse raises temperature ahead of primary machining pulse Improved efficiency Silicon T=25C Silicon T>>25C 57

58 Silicon: Impact of Pre-pulsing Pre-Pulsing delivers marked increase in cutting rate. Morphology remains similar to 2 ns pulses.

59 Ceramic Cutting: 1064 nm Corner SEM Edge Double Pulse Increase Machining rate by 50% compared to single pulse process 59

60 Summary PyroFlex Arbitrary Pulse Shaping Enables: Detailed study of laser pulse - material interaction. Precise process optimization not possible with other lasers. Novel thin film removal processes for solar and other applications. On the fly pulse parameter switching for processing multilayer composite PCB materials. Novel surface and bulk materials processing for c-si PV applications 60

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