process and equipment enhancements for c2w …€¦ · process and equipment enhancements for c2w...
TRANSCRIPT
PROCESS AND EQUIPMENT
ENHANCEMENTS FOR C2W BONDING
IN A 3D INTEGRATION SCHEME
Keith A. Cooper, Michael D. Stead SET- North America Daniel Pascual, Sematech Gilbert Lecarpentier, Jean-Stephane Mottet SET SAS
Outline
Introduction and Statement of Challenges Hybrid Bonding with Collapsible Polymer Particulate Improvement Study Removal of Oxides prior to Bonding Conclusions and Further Work
3D Definitions
3D-Packaging: Traditional packaging interconnect technologies, including package stacking, wire bonding
3D-WLP: Wafer-level packaging, where interconnects processed post-IC passivation
3D-IC: IC technology, where 3D interconnects processed at the local level*
* Adapted from Huyghebaert, Soussan, et al. IMEC. ECTC 2010
Via “middle” Cu process
1. TSV litho (I-line)
2. TSV etch, strip & clean
3. O3-TEOS liner
5. Cu electro- plating/anneal
6. Cu/barrier/ liner CMP
Start: After W CMP
After TSV: BEOL or
passivation + sintering
W-via or contact plug
4. Ta/Cu Cu seed
Adapted from Huy-ghebaert, Soussan, et al. IMEC. ECTC 2010
Attractions of Cu TSV Fill
Familiarity of Processing Mechanical Strength Electrical Integrity Scalability of Copper Cost
Die-to-Wafer (D2W) Bonding
DIE-TO-WAFER Lower Throughput Single Chip Placement Long Bond Processes High Yield Known Good Die Good Overlay Flexibility Component and wafer sizes Different Technologies
Heterogeneity!
Challenges with Cu–Cu bonding
Bond requires high temp, long process Flat, particle-free surfaces Oxides
Cu oxidizes at STP, oxidizes rapidly at elevated temperatures
Metal oxides inhibit mechanical and electrical integrity
Outline
Introduction and Statement of Challenges Hybrid Bonding with Collapsible Polymer Particle Improvement Study Removal of Oxides prior to Bonding Conclusions and Further Work
Collective Hybrid Bonding
Cost-effective processing by segmentation of 3D assembly into D2W + Collective Bonding
Combines: High Yield and flexibility of D2W High Speed and efficiency of parallel process
Landing wafer
Wafer-level bonding tool
Landing wafer
TSV-die
Pick-and-place tool
Patterned
dielectric
glue
Landing wafer
Wafer-level bonding tool
Landing wafer
Wafer-level bonding tool
Landing wafer
TSV-die
Pick-and-place tool
Patterned
dielectric
glue
Landing wafer
TSV-die
Pick-and-place tool
Patterned
dielectric
glue
Die pick and place Collective bonding
In-Situ vs. Collective Bonding
Temperature Profile
Sequential D2W bonding High Accuracy capability,
controlled by the bonder Time consuming Landing wafer sees several
bonding T-cycles
Temp.
Met
al b
ondi
ng
Die
1
time
Met
al b
ondi
ng
Die
2
Met
al b
ondi
ng
Die
n
Temp.
Bon
ding
, po
lym
er
cure
Collective bonding @ wafer level
LT
Pick
& p
lace
: die
1
Poly
mer
Ref
low
time
die
2
die
n
Wafer population @ wafer level
Collective D2W bonding Higher throughput Landing wafer sees only one
temperature cycle Accuracy depends upon
several process steps
2-Step Cu-Cu Direct Bond*
Advantages Low temp and force
attachment process Strong initial bond
maintains alignment for collective bond step
Challenges Very planar, clean,
smooth surfaces Long diffusion process Very clean bonding
environment
Bond evolution with annealing
Direct Metallic Bond after annealing (2h @ 400C)
Triple junctions at equilibrium T-Shape Triple junctions
Diffusion cones
*Source: CNRS-CEMES and CEA-LETI
1. TSV wafer with bond and probe pads 2. Spin coat thin layer of sacrificial adhesive 3. Tack dice individually using die bonder tool 4. Apply heat/force to decompose the adhesive and bond all dice in
parallel using wafer bonding tool
1. 2.
3. 4.
Bonding Plate
Heat + Force
N2 Environment
Tack/Collective Bond Overview
Die Tacking Results
Tack dice onto wafer Align each die to bond site on 300 mm wafer Place die onto wafer and apply force at
low temperature (~135 C) Repeat tack process to populate wafer 2.5 μm average placement accuracy
observed Source: Sematech
Alignment Shift From
Collective Bonding
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
-11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
• Optimized Tooling and Process • Alignment improved to 2 μm (average = 0.8 um) • No damage to tooling
Misalignment vector map 300 mm wafer 1unit = 1μm
FIB-SEM Sectional Image
• Diffusion of Cu across bonding interface
Particles at Cu-Cu interface were major source of yield loss
Outline
Introduction and Statement of Challenges Hybrid Bonding with Collapsible Polymer Particle Improvement Study Removal of Oxides prior to Bonding Conclusions and Further Work
Schematic of Cu-Cu Bonding
Areas of Particulate Contributors
Particle Reductions
Performed in the framework of PROCEED project funded by French authorities and by European authorities (FEDER). PROCEED partners are: ALES, CEA LETI, STMicroelectronics, CNRS-CEMES and SET.
Sample Modifications
TEFLON Cable
channels
Particle collection
Stages and guides of low-particulate materials
Teflon Cable channels Enclosures around specific
assemblies to exhaust any particles generated locally
After Particulate Improvements
Particle counts reduced by 2-3 orders of magnitude
Alignment improved to ± 1μm Tight distribution of daisy chain contact
resistance
Outline
Introduction and Statement of Challenges Hybrid Bonding with Collapsible Polymer Particle Improvement Study Removal of Oxides Conclusions and Further Work
Requirements of
Oxide Removal Process Rapid and effective Inert to surrounding materials Minimal or no residue EHS Compliant Long-lasting Low-cost
Historical Methods of
Reducing Oxides Wet acid dips, e.g. HCl, citric acid Liquid or paste fluxes Vacuum plasma treatments
In-situ Removal of oxides
Description Schematic of In-situ reduction
Reduction Chamber Hardware
2 versions – D2D and D2W Photos of micro-chamber D2D version:
View of Chuck View of Bonding Arm
Proposal:
Novel Ex-situ Removal of Oxides Dry process at atmospheric ambient Non-toxic, non-corrosive chemistry Rapid turnaround (< 1 minute) Reduces oxide from metal surfaces and
passivates surface against re-oxidation
Ellipsometry
Change in polarization defined by Δ = phase change of reflected light Δ indicates morphology or composition
Ellipsometry of In
SETNA/SET Proprietary
► Ellipsometry confirms oxide removal
Results with Indium Bumps
Untreated Indium No adhesion Bumps were coined
Treated Indium Good adhesion Good “taffy pull”
Process Validated for Indium
Validated for: Indium-to-Indium Indium-to-metal contact pads
Room temp bonding process Strong bump-to-bump adhesion Perfect tensile rupture with pull test Demonstrated for Indium-to-Nickel Demonstrated for Indium-to-Titanium
SETNA/SET Proprietary
Process Validated for In alloys
Validated for Indium alloy-to-metal contact pads Room temp and elevated temp bonding Strong bump-to-pad adhesion MP > In, depending on composition Demonstrated for In alloy to Ni or Ti Projected to work on Sn and Ag solders
Protection from Re-oxidation
SETNA/SET Proprietary
Passivated Indium surface remains stable after 50 hours
Application-Specific Metallurgy
Indium* Indium alloys* Titanium* Nickel* Copper** Silver ** Tin** Aluminum** SnAg**
Surface prep process shows promise for a broad range of metals and alloys:
*Demonstrated with bonding tests
**Ellipsometry results are promising, no bonding tests yet
Summary
3D-IC Integration opportunity is expanding, good process flow options
Technical hurdles addressed: Throughput – Hybrid Polymer Bonding Yield – Particulate Reduction Materials – Oxide Removal Options
Areas for further study
Further Work foreseen: Characterization of ex-situ oxide reduction
process Further exploration of Collective Hybrid
Bonding
Thanks for your attention
For further info, please contact: [email protected] [email protected] +33 4 50 35 83 92
www.set-sas.fr