Reliability of Ultra-fine Line Multi-Redistribution Layers

Enabled by Excimer Laser Dual Damascene Process for

Wafer and Panel Level Packaging

Dr. Habib Hichri Applications Engineering Director

SUSS MicroTec Photonic Systems, Inc.

Corona, CA 92880, USA

CONTRIBUTORS TO THIS PRESENTATION

• SANJAY MALIK & OGNIAN DIMOV: FujiFilm

Electronic Materials U.S.A., Inc., North Kingstown, RI,

USA

• Dr. RICHARD HOLLMAN: TEL NEXX, Inc., Billerica,

MA, USA

• MARKUS ARENDT: Süss Microtec Photonic Systems

Inc., Corona, USA

Outline

Advanced Packaging Requirements

Dual Damascene Process for planar multilayer RDL

1

2

3

Excimer Laser Ablation Patterning ii

Enabling Technologies: 3

Results and Reliability Data 4

Conclusion 6

PVD and ECD for Cu Metallization iii

Advanced Polyimide Dielectric Material i

ADVANCED PACKAGING

REQUIREMENTS

REDISTRIBUTION LAYERS FOR ADVANCED PACKAGING

ARCHITECTURES

Application:

WLCSP: 200/300mm (RDL, Integrated Passive

Devices)

Fan out WLP: >300mm (eWLB,RCP,other)

Embedded IC: >300mm (FCBGA, FCCSP)

• Critical Aspects of RDL

– Small pitch: 2mm L/S or smaller

– Multiple layers

– Transferable to panel substrates

5

• Technical challenges

– Planarization to stay within DOF for

exposure tools

– Thermal/mechanical stability of dielectric

material

– Efficient removal of Cu overburden and

seed layer without damaging plated

metal

– Stability of deposited metal

– Process flow without CMP for panels

DUAL DAMASCENE PROCESS

FOR PLANAR MULTILAYER

RDL

DUAL DAMASCENE PROCESS FLOW

7

CRITICAL ADVANTAGES OF PROCESS

• Excimer laser ablation patterning does not require

photosensitive materials

– Wider choice of dielectric materials

– Polyimide can be chosen for mechanical and thermal

stability

• Ablation patterning is performed after cure

• Significant reduction in lithography-related steps

– No photoresist application, develop or strip required

• Planarization accomplished by preferential metal fill

– Overburden and seed layer can be removed without CMP

8

ELIMINATE MORE THAN 50% OF PROCESS STEPS

9

• RDL Via and Trench by Standard

Photolithography

• Polyimide Apply( Photo imageable)

• Bake

• Expose RDL Via

• Develop

• Descum

• Cure

• Seed Layer apply

• Resist coat

• Pre expose bake

• Expose RDL trace

• Post Expose bake

• Develop resist

• Descum

• Cu plate RDL

• Resist strip

• Etch seed layer

• Apply dielectric

• Bake (Polyimide Cure)

• Descum

RDL Via and Trench by Excimer Laser Ablation

Polyimide Apply (thickness for both Via and

Trench). Can be cheap using non-photo material

Bake

Ablate both RDL Trench and Via

Clean/desmear

Seed layer apply

Cu plate via and trench

Planarization

Seed Layer Removal (Excimer)

Post SLR cleaning

Comparison between photolitho process and laser direct etching

Significant cost reduction

Eliminate ~10 process steps

Eliminate equipment required

for deleted process steps

Eliminate operator overhead

Eliminate yield contributing

steps

ENABLING TECHNOLOGIES

An Ideal Dielectric material

Material format – dry film or slit coatable for ease of application

Thermal/Cure Properties Thermal cure <180˚C

Thermally stable to withstand reflow cycles

Pre-cyclized low thermal shrinkage

Low residual stress

Tunable CTE and elongation properties

Capable of forming high resolution patterns

Compatible with typical copper deposition methods

Minimize warpage

Highlights of Fujifilm’s Material

Pre-imidized Low thermal shrinkage ~5% during thermal bake step

Low temperature processing Post development bake (170˚C)

Thermally stable (2% weight loss @ 314

˚C)

Support dry film lamination for ease of

application

Low residual stress (~11 MPa)

Tunable CTE and elongation properties

Capable of forming high resolution

patterns even in filled system

CTE, (50 – 150˚C)

28 (filled system) ~ 56

(unfilled system) ppm/˚C

Modulus 3.3 GPa

Poisson’s ratio 0.31

Elongation-to-break 60%

Tg (DMA by storage

modulus) 247˚C

Thermal stability 2% weight loss: 315˚C

5% weight loss: 390˚C

Moisture uptake

(80%RH/80˚C) 0.97%

Dielectric constant/Dielectric

loss (1-20 GHz) 3.2/ 0.015

Peel strength

1.3KgF/cm (Before

HAST)

0.6KgF/cm (after 500

hours HAST)

Courtesy of Fujifilm

No CD or profile change after bake 100 to 250°C

Thermal Stability of Patterned Film

No Bake 100°C 250°C 175°C 150°C

0.0

1.0

2.0

3.0

4.0

5.0

6.0

100 125 150 175 200 225 250

CD

(µm

)

Post Bake T °C

CD Before bake

CD After bake

5mm

5mm

Courtesy of Fujifilm US

Courtesy of Fujifilm

• Laser ablation is the process of

removing material (subtractive process)

from a solid surface by irradiating it with

a laser beam.

• The ablation of polymer is a photo

physical process: mixture of photo-

chemical and photo-thermal processes.

– The ratio of the two mechanisms is

function of irradiation wavelength,

fluence, and the polymer backbone

WHAT IS EXCIMER LASER ABLATION?

14

• Typical setup of an Excimer Laser stepper:

– Laser beam is made uniform and shaped through the optics train

– The laser beam hits the mask, and the resulting image is projected through a reduction

projection optics on the substrate

– The system operates like a normal stepper, with a laser source instead of a UV lamp

SCHEMATIC SETUP OF AN EXCIMER LASER STEPPER

15

• Excimer ablation allows us to control many things…

Side-wall Angle Control (WPR5100):

Higher fluence: Steeper wall-angle

Lower fluence: Shallow wall-angle

Wall angles to < 85º

Depth Control - by No. of Pulses:

Each pulse removes a certain amount of material

Etch-rate = material removed/pulse

With a known etch-rate – the number of pulses to

reach a desired depth can be predicted and controlled

Selective Material Removal:

Metal pads >1µm thick are a Stop Layer

EXCIMER ABLATION PROCESS CONTROL

~65º ~81º

16

Example:

Assume Typical Polyimide Etch-rate = ~0.30mm / pulse

Desired Depth for Trench & Pad Pattern = ~5mm

5mm Depth

Desired

Pulse Estimate Calculation:

5mm Depth / 0.30mm Etch-Rate = 16.667 = ~17 pulses

• In addition to the debris cell, post-laser ablation cleaning is needed.

• Depending on the ablated material, several options are available:

O2 plasma cleaning: Recommended

• Most common cleaning method

• Successful cleaning of wafer with PBO (HD8820)

Sacrificial layer for debris removal: • Successful removal process shown for

FCPi 2100 (Fuji Film) Sacrificial layer removed using high-pressure CO2 ionized water

Post Laser Ablation Cleaning

17

Post Ablation Post Cleaning

3D ASIP 2016 – December 13-15, 2016 – San Francisco, CA - USA

REQUIREMENTS FOR METALLIZATION IN DUAL

DAMASCENE PROCESS

• Seed layer adhesion to dielectric

–Adhesion layer and Cu seed deposited in same

chamber without breaking vacuum

• Preferential bottom-up fill for vias and traces

• Uniformity of deposition

• Minimal overburden: overburden and seed layer

can be removed by combination of de-plating

and wet etch

18

Test pattern results: overburden ~0.5mm

Before plating After plating

800X

Cross section SEM

2-layer structure:

via & trace, without CMP

Courtesy of TEL NEXX

RESULTS AND RELIABILITY

DATA

2/3um L/S in Polyimide

10um

Excimer Laser Patterning Capabilities of FCPi 2100

Courtesy of Fuji and TEL NEXX

Results after Thermal Shock: No delamination after 400 cycles

Fine Cu trenches (2/2 to 5/5 um) with long trace lengths

Thermal Shock Cycling – JEDEC JESD22

A106B and MIL-STD-883E

Courtesy of GIT- PRC

Results after Thermal Shock: No delamination after 400 cycles

Fine Cu trench (2/3 um L/S) with short trace lengths Courtesy of GIT- PRC

Reliability Summary and Next Steps

• Sample wafer showed excellent adhesion reliability of copper and

polymer interfaces with Liquid to Liquid Thermal Shock Cycling

• In one coupon, the sample was tested for three different structures

(daisy chain, fine trenches with long trace lengths and short trace

lengths). Three such coupons were tested and none showed any

delamination.

• Ongoing Reliability with Thermal Cycling in Air (After 100 cycles,

there was no delamination; 250 cycles data to be collected by next

week; Data to be put together after 250 cycles)

• Reliability with Liquid to Liquid Thermal Shock Cycling is continued

for 1000 cycles at GIT-PRC

CONCLUSION

DUAL DAMASCENE PROCESS OFFERS COST-

EFFECTIVE SOLUTION FOR MULTILAYER RDL

• Significant reduction in process steps and overall

cost of ownership

• Eliminating need for CMP enables transfer to panel

processing

• Ablation patterning of polyimide dielectric leads to

improved stability and feature control

• Planarization is an inherent feature of the process

26

• ACKNOWLEDGE AND THANK THE

FOLLOWING CONTRIBUTORS:

–Georgia Institute of Technology: PRC

–FUJIFILM Electronic Materials U.S.A.,

Inc.

–TEL NEXX, Inc.

27

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SUSS MicroTec Photonic Systems Inc.

220 Klug Circle

Corona, California 92880-5409

Suss.com

Embedded RDL Enabled by Excimer Laser Ablation – IMAPS Device Packaging Conference 2016

AFFECT OF ABLATION ON METAL PAD/UNDERLYING

METAL

3rd party confirmation of no

damage to Cu pads

Excimer ablation over Cu and Al pads:

3rd party tests have been performed showing no

damage to the underlying materials

Case study:

Si/SiOx/SiNx/TiTiN/AlCu(1.4um)/

dielectric(8.5um)

Over pulsed 40 and 50 with no damage to the low k

dielectrics

29

Appendix: Thermal Shock Cycling – JEDEC JESD22

A106B and MIL-STD-883E

Both standards are similar; however, MIL-STD specifically mentions a dwell time

of > 2 mins for thermal shock in perfluorocarbon fluid