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Excimer Laser Processing and Laser-Lift-Off
of High Brightness LEDs
Rainer Paetzel
Coherent GmbH, Germany
SEMICON EUROPE 2012, TechArena 2 11th of October 2012
Superior Reliability & Performance P. 2 Semicon Europe 2012
OUTLINE
Motivation
UV-Excimer Laser Capabilities for LLO
Excimer Laser Lift-Off Processing for
HB LED Manufacturing
Summary
Superior Reliability & Performance P. 3 Semicon Europe 2012
Key Market Drivers in Microelectronics Industries
Flexible Displays
Slim & Lightweight
Advanced Chip Packaging
3D Integration
HB-LEDs
Vertical LEDs
Temporary Bonding and Debonding
Superior Reliability & Performance P. 4 Semicon Europe 2012
Flexible Display Market (E-Readers, Mobile LCDs, OLEDs)
Source: Display Bank, 'Trend of Flexible Display
Technologies and Market Outlook (2008~2020)' Report
Superior Reliability & Performance P. 5 Semicon Europe 2012
Trend to 3D Stacking in Advanced Packaging
2010 2011 2012 2013 2014
Source: ITRI
Superior Reliability & Performance P. 6 Semicon Europe 2012
Trend to Silicon Wafer Thinning and Temporary Bonding
Thinned Si wafer (30µm) Thin wafers below 100µm become flexible
Bonding to rigid carrier wafer
Debonding after processing
Source: Süss
Source: Yole Développement
Superior Reliability & Performance P. 7 Semicon Europe 2012
• General lighting will be the “next wave”
• Many countries have 20-50% SSL policies. The 2013-2014 period will be used
to achieve these 2015 phase-out targets
• LED makers must react rapidly, targeting the lighting market with HB-LEDs
10/10/2012
HB-LED Market (Large Display Backlights, General Lighting)
Superior Reliability & Performance P. 8 Semicon Europe 2012
Laser Lift-Off Debonding of Adjacent Layers
Fast
Contactless
Ambient Atmosphere
Re-Use of Material
No Wet Chemistry
No Mechanical Stress
Superior Reliability & Performance P. 9 Semicon Europe 2012
OUTLINE
Motivation
UV-Excimer Laser Capabilities for LLO
Excimer Laser Lift-Off Processing for
HB LED Manufacturing
Summary
Superior Reliability & Performance P. 10 Semicon Europe 2012
Coherent Excimer Laser – Overview
Repetition Rate (0-2000Hz)
Pu
lse
Energ
y (
0-2
00
0m
J)
IndyStar
ExciStar XS
LAMBDASX
COMPexPro
LEAP
LPXpro
VYPER
Xantos XS
EX
CIM
ER
Excimer cover the largest range of wavelength, pulse
energy and average power in the UV spectrum
Superior Reliability & Performance P. 11 Semicon Europe 2012
Short wavelength = high photon energy • directly absorbed by molecular bonds in many materials
• directly break atomic bonds without bulk heating.
Short wavelength = high spatial resolution. • Minimum Feature Size (MFS) only limited by diffraction.
Unique Feature of UV Lasers
NAkMFS
1
Cold Ablation
Smallest Feature
k1 – process factor – Wavelength NA – Numerical Aperture
Excimer
3rd w 2nd w
pulsed-
ND:YAG
qs-
ND:YAG
CO2
Superior Reliability & Performance P. 12 Semicon Europe 2012
High Energy / High Power High Productivity
Projection Imaging
Line Beam Generation
Advantages:
Pattern placement accuracy,
and consistency ( submicron)
High patterning precision
High Energy Large shot area
High Power High throughput
Advantages:
Large area covered in one scan
High Energy Longer Line (i.e. 6”, 12”)
High Power High throughput
NAkMFS
1
P. 13 Semicon Europe 2012
Homogenized Rectangular Processing Beam
Raw Beam
Homogenized beam in mask plane
e.g. 4 x 5 mm
Homogeneity: ~1 % (rms). Raw beam at laser exit
30mm x 12mm (LEAP)
P. 14 Semicon Europe 2012
Homogenized Line Beam
Raw Beam Raw beam at laser exit
30mm x 12mm (LEAP)
Line length:
150mm,
Uniformity: 0.8%, rms
Line width:
0.4 mm,
Uniformity: 1.5%, rms
Superior Reliability & Performance P. 15 Semicon Europe 2012
OUTLINE
Motivation
UV-Excimer Laser Capabilities for LLO
Excimer Laser Lift-Off Processing for
HB LED Manufacturing
Summary
Superior Reliability & Performance P. 16 Semicon Europe 2012
Trend in HB-LED: Larger Sapphire Substrate Diameter
Forecast of monthly capacity of sapphire ingot by manufacturer
Source: Sino-report LED Research Center, May 2012
Source: Yole developpement
Superior Reliability & Performance P. 17 Semicon Europe 2012
Vertical LED Designs - Scalable in Current and Size
Tran, J Cryst. Growth 298, 2007
Vertical HB-LED Chip
Horizonal HB-LED Chip
Horizontal flow (current crowding)
Vertical current flow (scalable)
Superior Reliability & Performance P. 18 Semicon Europe 2012
LLO - Laser Lift-Off - HB LED, GaN
Superior Reliability & Performance August 2009 P. 19 Superior Reliability & Performance P. 19 Semicon Europe 2012
Superior Reliability & Performance P. 20 Semicon Europe 2012
248nm Wavelength strongly absorbed at GaN Interface
248n
m
248nm, 5eV
3.3eV 9.9eV
Energy of 248nm photons (5eV) is between band
gaps of sapphire (9.9 eV) and GaN (3.3 eV).
248nm laser light transmitted by sapphire and
strongly absorbed by GaN buffer layer.
Epitaxial structure of GaN/Sapphire-Epiwafer
Superior Reliability & Performance P. 21 Semicon Europe 2012
Lift-Off via Photochemical Decomposition of GaN
Single Shot Process
Wavelength: 248nm
Fluence: ~800mJ/cm2
Single pulse ablation rate
Top view through sapphire
Superior Reliability & Performance P. 22 Semicon Europe 2012
Sapphire LLO Removal - Processing Strategies
Square Field Maeandering Line Beam Scanning
Source: Fraunhofer IAF, Freiburg
Superior Reliability & Performance P. 23 Semicon Europe 2012
Surface Analysis after LLO by White Light Interferometry
~50nm deep trenches in overlap region ~20nm deep trenches in overlap region
Source: Fraunhofer IAF, Freiburg
Superior Reliability & Performance P. 24 Semicon Europe 2012
Excimer – LLO for LED; typ. Layout
Laser LPXPro 210 248nm, 500mJ, 100Hz
Beam Uniformity 5%, 2
Homogenized Field (@ mask) 20 x 20 mm
Field Size @ Substrate 3.5 X 3.5 mm
Energy Density max. 1600 mJ/cm^2
Resolution 30 µm L/S
Working Distance 80 mm
Laser Class 4 i.e. one pulse
covers 12 dies
Superior Reliability & Performance P. 25 Semicon Europe 2012
GaN-Sapphire 6“-Wafer LLO – Processing Metrics
Laser Parameters and 6“-Wafer Throughput
Field Geometry Square Beam Line Beam
Field Size 5mm x 5mm 150mm x 0.25mm
Pulses/Wafer 800 pulses 600 pulses
Repetition Rate 20Hz 15Hz
Throughput 60 wafers/hr 60 wafers/hr
COMPexPro, 248nm
E=700mJ, 1-50Hz ED=800mJ/cm2
A=5mm x 5mm
ED=800mJ/cm2
A=150mm x 0.25mm
1
2
3
Superior Reliability & Performance P. 26 Semicon Europe 2012
Excimer Laser – Process Metrics
• LLO by Excimer is a very efficient process – one shot per area
• High troughput is reached, even at low laser power
• Higher power readily available
• Long maintenance intervals are achieved in this application
High Uptime
• Mainetance Intervals
• Fully automated operation, automated gas control
• Optical maintenance interval (calibrate) 500 k Wafer
• Service interval for the laser tube 2 M Wafer
Superior Reliability & Performance P. 27 Semicon Europe 2012
Summary of
Advantages of Laser Lift Off by Excimer
High Pulse Energy
Large field size, Long line beam
UV Wavelength – 193nm, 248nm, 308nm
Matching the interface (GaN)
High Energy Stability (0.5% rms)
Short pulse (ns) for minimized heat effect
Established process
HB LED, Flexible Display, and Wafer