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Claudio Truzzi, Ph.D. Alchimer

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1 Claudio Truzzi, Ph.D. Alchimer
Integration of Electrografted Layers for the Metallization of Deep TSVs Claudio Truzzi, Ph.D. Alchimer International Wafer-Level Packaging Conference, October 11-14, 2010

2 Introduction: The Drivers for TSVs
Outline Introduction: The Drivers for TSVs Limitations of Traditional Dry-Process Approaches Electrografting Nanotechnology for TSV Applications Isolation/Barrier/Fill Isolation and Barrier Film Properties New Generation TSV Cu Fill Cost of Ownership 300-mm Wafer Wet-Process TSV Metallization - Existing Infrastructure Conclusion

3 Main 3D-IC Driver Mobile systems vendors need TSV interconnects to support the bandwidth needed for new data services, which include point-to-point video, a market set to accelerate over the next five years High-definition video encoding requires about 12.8 GB/s of bandwidth between the processor and DRAM memory The only way to do that in a mobile system is with TSV-connected logic-memory solution, such as an ARM-based processor stacked with 400 MHz DDR3 memory chips Source:, June 26, 2010

4 TSV Area Penalty as a function of AR
What Type of TSV? TSV Area Penalty as a function of AR The most strategic question from the design perspective is about aspect ratio The ability to decrease TSV diameter without affecting wafer thickness has huge implications for how much die space is available for working circuitry, and for the overall cost impact of TSV adoption At any given wafer thickness, 3DIC designers need TSVs that can be scaled down Assumptions die 10 x 10 mm # TSVs 10000 TSV depth 50 µm Total Wafer Cost 6359 USD 12µm 10µm µm µm µm Nominal TSV Diameter If AR < 10:1 then: area penalty > 1% cost >100 USD/wafer

5 Current TSV Solutions Based on Dry Process + ECD
Process Step Isolation Barrier Cu Seed Cu Fill Deposition Methods and Related Issues CVD High Temp>400C Not compatible with memory applications Smooth walls needed -> low etch rate Therm-Oxide Very high temp iPVD/CVD Discontinuous Film AR<10 Inefficient plasma cleaning for AR>5 ALD High Temp>400 C Extremely low UPH High Resistance (i)PVD Poor step coverage AR<10 Discontinuous film Large overburden: thick film on wafer flat to have thin layer on TSV bottom ECD AR<10 Low UPH Size>5µm Strongly acidic Many additives Expensive membrane cells

6 Dry-Process 300-mm TSV wafer CoO is too high
1. TSV Manufacturing 3. Backside RDL Litho Backside Insulation Deposition Soft or Hard Mask Backside Barrier layer Deposition Etch/Drill Via (DRIE) Cu Seed Deposition Post-Etch Clean Insulation Layer Deposition 4. Bumping Barrier Layer Deposition Solder Plate Seed Deposition PR Strip Cu-TSV Fill UBM etch CMP 5. Bonding Post CMP Clean Wafer Dicing 2. Wafer Thinning Die to Wafer Pick&Place Carrier Bonding Thermal Cure/attach Thinning Stacked Wafer Dicing Sequential Thinning/stress Relief Minimum CapEx (1 tool/step): 70 MUSD Equip. Depr. 10 kw/m: 120 USD/wafer Assumptions Reference Consumables Maintenance 3% of tool price Yole Hookup costs 10% of tool price Sematech Utilities Operator shifts 3 Overhead Footprint ratio 2.5 Total 10 kw/m: 253 USD/wafer

7 The Way Forward: Scalable Wet-Process TSVs
Current wet processing can easily deliver AR>20 at a significantly reduced cost: Wet Isolation: Polymer-based Wet Barrier: NiB-based Cu Fill: directly plated on barrier Wet Process Properties: Highly conformal Strong Adhesion High Step Coverage Film properties match or exceed those of dry-processed films Strong Adhesion High AR Highly Conformal High Step Coverage

8 Wet Isolation and Barrier Films
13x133 µm 11:1 AR 9x120 µm 15:1 AR 5x75 µm 18:1 AR 4x72 µm Isolation = 160 nm Barrier = 71 nm Isolation = 130 nm Barrier = 65 nm Isolation = 110 nm Barrier = 48 nm Step coverage : Isolation : 68 % Barrier : 67 %

9 Wet Isolation - Film properties
CTE falls well within accepted range Wet Isolation electrical properties match or exceed those of Si02 Elasticity Modulus and stress values enable the Wet Isolation to play a stress buffer role between Si and Cu Parameter Value Unit Notes CTE 30 ppm/ºC Dielectric constant 3 SiO2 = 4.2 Breakdown Voltage 28 MV/cm SiO2 = 10 Capacitance Density 0.13 fF/µm2 Leakage current 15 nA/cm2 SiO2 = 10-20 Surface Finish 1.6 nm SiO2 = 2nm Substrate compatibility < 200 Silicon substrate resistivity Young Modulus 3.4 GPa SiO2 = 107 Stress 10 MPa SiO2 = 100

10 Wet NiB Barrier - Film properties
Resistivity is much lower than industry reference Barrier properties are equivalent to TiN Cu diffusion rates equivalent to TaN/Ta Hardness value is half that of TiN This is indicative of a less brittle material Parameter Value Unit Notes Resistivity 25 µ TiN = Rs uniformity 5 % Barrier property Equivalent to TiN after 400 ºC 2 hours Cu penetration after 2 hrs 400°C 42 % barrier thickness TaN/Ta = 54% Hardness 14.3 GPa TiN = 25 Stress 200 MPa TaN = 1500 Ta = 350

11 High purity Cu fill for narrow, high AR TSVs
Small-diameter high-AR plating capability High-purity chemistry Direct plating on Barrier No chemical degradation of underlying layer No need for “hot entry” Seamless integration of complete wet-process TSV Metallization module Cu-fill TSV 2.5X25µm

12 Contaminants in copper bulk deposited with new fill vs
Contaminants in copper bulk deposited with new fill vs. Baseline ECD chemistry Anneal 250°C Cu bulk Baseline New fill Cl S C S C Cl C: 10X less for new fill chemistry Cl: 100X less for new fill chemistry S: comparable values

13 Grain size post anneal 400°C under forming gas
Commercially Available New fill Chemistry Much higher grain size uniformity Higher grain mean value

14 Wet Process TSV- Reliability
Successfully passed industry standard reliability tests Wet-Processed TSVs after 1000 temp cycles Moisture Sensitivity Levels (IPC/JEDEC J-STD-20 Level 1) Pass  High Temperature Storage (Mil Std 883 Method 1008 Condition C) Temperature cycle (Mil Std 883 Method 1010 Condition B, 1000 cycles) Pass Thermal shock (Mil Std 883 Method 1011 Condition B) Solder Heat Resistance (JEDEC J-STD-020)

15 Cost of Ownership Model
via size: 3x30 μ, AR=10 NEW equipment for etching, deposition (dry, wet), filling Assumptions: 150 kwspy 300 mm wafer size 95% process yield License included 3 shifts per day Clean room class: 100 CR surface ratio: 2,5 Equipment Depreciation time: 5 years Maintenance : 3% CR fully depreciated VIA DIMENSIONS (µm) ETCH + ISOLATION, BARRIER, SEED + FILLING + CMP (1) ISOLATION, BARRIER, SEED (2) 3 x 30 Dry $89 $43 $52 eG $18 eG insensitivity to scalloping allows for up to 40µm/min etch rate, contributing to CoO reduction Average savings with Electrografting: 60% Source: Yole Développement

16 Wet-Process TSV Metallization - 300-mm Wafer Existing Infrastructure
100m2 class 10K clean room SEMI complaint consumables and waste treatment TOOLS Manual wet benches ECD cell SRDs

17 Wet-Process TSV Metallization - Results
Liner Barrier Liner and barrier on Si/SiO2 stack Full stack non-uniformity < 10% Seed

18 Conclusion Expensive dry-process tools developed for dual damascene applications are not at home in the TSV world Integrated, streamlined wet-process solutions are available today delivering higher performance at a significantly reduced cost

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