reliability of ultra-fine line multi-redistribution layers...
TRANSCRIPT
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