Avatrel® Stress Buffer Coatings: Low Stress Passivation and Redistribution Applications

May 6, 2004Symposium on Polymers for Microelectronics

Ed Elce, Chris Apanius, Jeff Krotine, Jim Sperk, Andrew Bell, Rob Shick*

Sue Bidstrup-Allen, Paul Kohl

Takashi Hirano, Junya Kusunoki, Toshiro Takeda

Outline

§ Motivation– Simple Coatings– FEM Verification of Concept

• Modulus vs. CTE

§ Avatrel– Properties– Processing

§ Materials Integration and Reliability – Flip Chip Packages– Thermal Cycling– Pressure Cooker Test

§ New Generations§ Summary

Low Stress Motivation

§ Die are getting larger and more fragile (low k)

§ Reduction of Stress is important to maintain reliability

§ Reduce material shrinkage§ Reduce thermal stress

– Reduce Modulus, E(T) and/or CTE, α(T)

E (T) x E (T) x ∆∆αα (T) dT(T) dTss = = ∫Thermal Stress (Simple View):

Wafer Warpage with Simple Coatings

Wafer: 8 inch Si WaferThickness: 625 µmMeasuring span: 100 mm

Wafer Stress with Simple Coatings

A More Detailed View UsingFinite Element Modeling

The distortion element of 4 nodal point (#11)Nodal point : 9007

Element : 8649

Thermal stress analysis from 125 to –55degC

5 µm Mesh cut

Magnification

x

y

o

Chip

Underfill ( SB: CRP-4152R5)

BT substrate

Bump

Buffer Material(Avatrel and PBO)

ppm/ºCkgf/mm2ºCUnit

40

300

-40ºC: 212025ºC: 162080ºC: 1320125ºC: 1120

x, z: 1990y: 870

E1: 820E2: 3.1

16800

Modulus

0.30150200Avatrel

10 µm thick

0.3050330PBO (CRC)

10 µm thick

0.3529.2-Bump

0.39x, z: 17.6y: 64.1

-BT substrate

0.30α1: 32

α2: 10280Underfill

0.343.0-Chip

Poisson’s ratioCTETgItem

Material Properties

FEM Findings…

0

5

10

15

20

25

HorizontalStress

VerticalStress

ShearStress

No CoatingPBOAvatrelSt

ress

(M

Pa)

(Stress is 5 µm inside chip surface)

Reducing Modulus has a greater impact than reducing CTE

SixNy Passivation

Redistribution

Buffer CoatingBuffer Coating

Pb/Sn Solder

Wafer Level Packaging

Synergies Between Two Chemistries

Polynorbornene§ Low Dielectric Constant § Low Moisture Absorption§ Isotropic Properties§ High Tg From Backbone§ Transparency § Alkyl – Tune Modulus/Stress

Epoxy§ Adhesion§ Photosensitive§ Accepted Chemistry

Epoxy

Alkyl

Typical Properties§ ElectricalØ Dielectric Constant

2.50 @ 1 MHz

Ø Dissipation Factor0.009 @ 1 MHz

§ Thermo-MechanicalØ Tg = 220oC (TMA)Ø Modulus, 0.5 GPaØ ETB, 20%Ø Stress, 0-5 MPa

§ MoistureØ 0.14% (100% RH, 24 hrs, RT)

§ PhotodefinitionØ Negative Tone, Solvent DevelopØ Up to 50 µm thickØ 1:1 Aspect RatioØ 250-500 mJ/cm2

§ AdhesionØ Pressure Cooker (196 hours) on Si,

SiON, SixNy, SiO2, PI, Al & Cu No delamination and passes tape test

§ Top Layer MetalØ Cr/Cu & Ti/Cu

90º Peel = 4 lb/in

§ JEDEC Solder Reflow*

Ø Level 2A – PASS(60ºC/60% RH, 120 hours, 260ºC reflow 3x)

Ø Level 3 – PASS(30ºC/60% RH, 192 hours, 260ºC reflow 3x)

* 8 µm on 0.32 mm SiN wafer, 160ºC cure, SB-epoxy molding compound, 208 L QFP with Cu L/F, scanning acoustic microscope inspection

Processing

1. Plasma Pre-Treatment (O2:Ar) at 300 mTorr and 300 Watts for 30 seconds

2. Dehydration bake before coating is optional § 4 minutes at 250ºC is effective

3. Spin Coat Avatrel on wafer with a spread spin of 800 rpm for 8 seconds and Final Spin for 30 seconds to obtain final film thickness

4. Soft Bake at 120°C for 5 minutes5. I-Line UV Exposure with Adjusted Depth of Focus6. Post Exposure Bake at 100°C for 4 minutes7. Spray Develop for 30 seconds with limonene, Rinse with IPA for

10 seconds 5 second overlap and Spin Dry8. Cure at 160°C for 60 minutes

Typical process, but low T final cure

Formulation & Process Optimization: Overlapping process space for Al and Silicon Nitride

100

89

78

67

56

44

33

22

11

DepthOf

Focus(% Film

Thickness)

9008508007507006506005505004504003503002502001501005010 um

Via

365nm UV Exposure Dose (mJ/cm2)

Peeling on Al Good on Al Good on PE SiN Good on both

Imaging of 2195P

Imaging of Avatrel, 50 µm

Test Package

100 µm Vias150 µm Dicing

Lanes

Avatrel® PD Dielectric Polymer

Avatrel® PD Dielectric Polymer

Silicon Oxynitride

Silicon

Al

Imaging of Avatrel, 10 µmPrebake: 120ºC/5minExposure dose: 400mJ/cm2

PEB: 100ºC/4min

Bird’s-eye View Cross section

Magnification : x2000Magnification : x400

Curing: 160ºC/60min in N2Observation pattern: 40um via hole

Afterdeveloping

After curing

10 micron film

Reliability Testing of Avatrel

§ Sample Preparation– Silicon wafer coated with Avatrel or Non-photosensitive Polyimide, 5 µm thick– Substrate: FR5 with solder resist– Underfill: standard grade (CRP-4152R5) or new, low stress grade (CRP-X4498)– Post-cure 150ºC, 120 minutes

§ Treatment– JEDEC Level III

• Baking: 150ºC / 24 hours• Humidity: 30ºC / 60%RH / 192 hours• Reflow: 240ºC IR reflow 3 times

§ Reliability Testing– Thermal Cycling (T/C): 125ºC/30min ßà -55ºC/30 min (no interval), 200

cycles– Pressure Cooker Test (PCT): 125ºC/100%RH/2.3 atm, 96 hours

§ Evaluation by Scanning Acoustic Microscopy

Reliability Testing of Avatrel 2195P

100% Fail100% PassPCT

100% Pass100% PassT/C TestLow Modulus & Low Moisture Underfill(CRP-X4498)

100% Pass100% PassPCT

100% Pass100% PassT/C TestConventional Underfill(CRP-4152R5)

Non-photo PIAvatrel

Avatrel is compatible with standard and new, high reliability underfill materials

Major Factors Affecting Reliability

0

10

20

30

40

50

60

70

80

90

100

Modulus CTE Cure Temp Shrinkage Moisture

PIPBOAvatrel

2.8

GP

a

2.8

GP

a0.

5 G

Pa

150

-19

0 p

pm

/C

43 p

pm

50 p

pm

340º

C

340º

C16

0ºC

40%

40%

3%

1.5%

0.3%

0.14

% M

axim

um V

alue

Avatrel Development Activities

§ Sloped Sidewalls to facilitate conformal metalization and bumping processes§ Increased elongation and higher strength

versions under evaluation§ Aqueous Base developable versions are

underway

GT – “Polymer Pillars” Highly Compliant, Low Stress Approach

Polymer pillar

Metal interconnect

WG ElevatorPolymer WG

Mirror

Optical I/O Interconnection Electrical I/O Interconnection

Substrate

Chip

Solder

Single I/O structure functioning as both an electrical and optical interconnection

Grating Coupler

Avatrel Pillars…

63 x 325 µm

Avatrel Summary

§ Low Stress Materials focusing on stress buffer layers and redistribution

§ Early results indicate significantly improved reliability is possible§ 160°C final cure temperature is compatible with back end wafer

processing and post bump process steps§ Exceptionally low cure shrinkage§ Very good mechanical properties§ Very good photo definition in 5 to 50 µm thick films§ Good adhesion to all substrates§ Very low moisture absorption§ Highly tailorable – new versions are in development