thermal laser separation tls wafer-dicing der zukunft · thermal laser separation – tls...

IISB-Jahrestagung 20.11.2015 TLS-Dicing © Fraunhofer IISB

IISB-Jahrestagung 20.11.2015

Dirk Lewke

Thermal Laser Separation – TLS Wafer-Dicing der Zukunft


Agenda

- State of the art dicing technology in semiconductor industry

- Principle of Thermal Laser Separation

- Exemplary applications

- TLS for Silicon dicing

- TLS for SiC dicing


Principle:

fast rotating dicing blade is guided along the dicing street and separates the chips out of the wafer.

abrasive process (material loss)

water cooling is necessary

State of the art dicing techniques Mechanical blade dicing

Source: Disco

Source: Dohnke, et al.: Comparison of different novel chip separation methods for 4H-SiC; ECSCRM 2014


1. Step – Crack initiation

With a diamond tip or a short pulsed

ablation laser

Realization of a predetermined cleaving

point

2. Step – Cleaving

Laser-based heating, subsequent water

spray cooling

Mechanical stress field capable of

guiding a crack along a line to be

cleaved

Crack guiding with thermally induced mechanical stress

Crack

initiation

Thermal Laser Separation – TLS

Principle


Thermal Laser Separation – TLS

Properties and Benefits

Kerf free crack guiding

More chips per wafer possible

High edge quality

No chipping, no micro cracks

High bending strength

No delamination of backside metal

No tool wear

Low CoO

High feed rate

Typical 200 - 300 mm/s

Works for different materials

Si, mc-Si, SiC and Ge with one tool configuration

No frontside chipping No backside

chipping

BSM


TLS – a joint development with equipment supplier

More than 10 years cooperation between IISB and TLS equipment supplier

Expertise of Fraunhofer IISB:

Semiconductor manufacturing and its requirements (processes, equipment, standards, …)

Development, evaluation and optimization of equipment

Comprehensive metrology and analytic equipment

Clean room environment


TLS – a joint development with equipment supplier

More than 10 years cooperation between IISB and TLS equipment supplier

Current Activ ities at IISB – R&D and Customer Applications

Joint development of TLS technology with equipment supplier

TLS customer applications, e.g., microelectronics, power electronics, PV

Resizing/Downsizing of Si wafers, e.g., 450 mm → 300 mm

Materials under investigation: S i, S iC, mc-Si, Ge


Agenda







TLS for Silicon dicing Cutting through an active pn-junction 1/2

Conversion of AC current to DC current in automotive alternators

Important specifications:

Clearly defined break through voltage UB

Low leakage current IR

Leakage current edge quality

U (V)

I (A)

IR

UB

Schematic diode characteristic

metal

p+

n

metal

tape

Schematic cross section

Source: 24th Annual SEMI Advanced Semiconductor Conference

(ASMC 2013) May 14-16, 2013 Saratoga Springs, NY


Source: 24th Annual SEMI Advanced Semiconductor Conference

(ASMC 2013) May 14-16, 2013 Saratoga Springs, NY

TLS for Silicon dicing Cutting through an active pn-junction 2/2

Dicing blade

TLS crack

no side

wall damage

Side wall

damage


Agenda







TLS for SiC dicing Motivation

Due to the hardness of SiC – 9.2 on Mohs scale – dicing SiC is a “hard job”

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10

Hardness (Mohs)


TLS for SiC dicing

State-of-the-art SiC dicing technology

Challenges:

Edge quality critical

Chipping

Ridges and micro cracks at side

walls

Delamination of back side metal

Heavy tool wear

Costs due to tool changes

Risk of uncontrolled blade breakage

Low feed rate

2-10 mm/s

Mechanical blade dicing is not feasible for SiC volume production

250 µm

Chipping

Delamination of

backside metal

Ridges


Imide

Source Gate

Metal structures

Kerf

aft

er

tap

e e

xpansio

n

TLS for SiC dicing Overview of a TLS result

TLS-diced 100 mm SiC JFET wafer - 170 µm thickness - Backside metallization - PCM structures inside dicing street - Imide coating near dicing street - Kerf visible due to tape expansion


Assembly of TLS diced SiC diodes

TLS wafer dicing

Erlangen

Malaysia packaging

Germany

electrical characterization


Backend assembly yield

All values in spec according data sheet

I-V characteristics (@RT)

x Typical value at 1200V: 9µA

TLS for SiC dicing Electrical characterization


Imide Metal

structures inside

dicing street

100 µm

Modified zone due to laser

ablation for scribing

Smooth side walls without

any scratches or micro

cracks

Smooth cut of back side

metal no chipping and

no delamination

TLS for SiC dicing Edge quality – overview


no damage found at the cleaved surface

SEM image

TLS cut

TEM image TEM image – focus on fracture mark

TLS for SiC dicing Edge quality – TEM analysis


SEM image of a SiC chip diced with laser ablation

TEM analysis of a SiC chip side wall diced with laser ablation

Source: Dohnke, et al.: Comparison of different novel chip separation methods for 4H-SiC; ECSCRM 2014

TLS for SiC dicing Edge quality – comparison with ablation laser


Wafer: • 150 mm SiC • Back side metal • 160 µm thickness • 1 mm die edge length • PCM in street • 70 µm street width

Considered: • Consumables (saw blades) • Invest/depreciation for tool • Footprint

Process speed: • TLS: 200 mm/s • Mechanical blade dicing: 7 mm/s

TLS-Dicing™: 3.00 €

Mechanical blade dicing: 37.00 €

Blade dicer: 150 min per wafer microDICE™: 17 min per wafer

TLS for SiC dicing Cost calculations – Comparison with state-of-the-art


Summery and outlook

Summery

- TLS is a kerf free laser based dicing technology which is based on crack guiding using thermally induced mechanical stress.

- TLS has major benefits compared with state-of-the-art regarding:

- Edge quality

- Throughput

- Costs

- TLS works for different materials with same machine configuration

Outlook

- Improve the reliability and shift technological limits of the TLS process

- Investigate TLS for other materials like GaN

- Bring the TLS technology to industrial application


Thank you for your attention !

Contact:

Dirk Lewke

Fraunhofer IISB

[email protected]

Tel.: +49 9131 761-155

thermal laser separation tls wafer-dicing der zukunft · thermal laser separation – tls...

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