Excimer Laser Processing and Laser-Lift-Off of High Brightness

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


Key Market Drivers in Microelectronics Industries

Flexible Displays

Slim & Lightweight

Advanced Chip Packaging

3D Integration

HB-LEDs

Vertical LEDs

Temporary Bonding and Debonding


Flexible Display Market (E-Readers, Mobile LCDs, OLEDs)

Source: Display Bank, 'Trend of Flexible Display

Technologies and Market Outlook (2008~2020)' Report


Trend to 3D Stacking in Advanced Packaging

2010 2011 2012 2013 2014

Source: ITRI


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


• 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)


Laser Lift-Off Debonding of Adjacent Layers

Fast

Contactless

Ambient Atmosphere

Re-Use of Material

No Wet Chemistry

No Mechanical Stress


OUTLINE

Motivation




Summary


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


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


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)


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


OUTLINE

Motivation




Summary


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


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)


LLO - Laser Lift-Off - HB LED, GaN

Superior Reliability & Performance August 2009 P. 19 Superior Reliability & Performance P. 19 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


Lift-Off via Photochemical Decomposition of GaN

Single Shot Process

Wavelength: 248nm

Fluence: ~800mJ/cm2

Single pulse ablation rate

Top view through sapphire


Sapphire LLO Removal - Processing Strategies

Square Field Maeandering Line Beam Scanning

Source: Fraunhofer IAF, Freiburg


Surface Analysis after LLO by White Light Interferometry

~50nm deep trenches in overlap region ~20nm deep trenches in overlap region

Source: Fraunhofer IAF, Freiburg


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


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


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


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


10/10/2012

Thank You for your Attention!

[email protected]

Excimer Laser Processing and Laser-Lift-Off of High Brightness

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