Synchrotron X-Ray Topography for Laser-Drilled

ViasKevin Wang, March 9, 2009

Through Silicon Via

Via connecting one side of silicon wafer to another

Reduce connection length

Drilling options Mechanical Deep Reactive Ion Etching (DRIE) Laser pulses

DRIE Vias, Source: Albany Nanotech

Paper

Laser Drilled Through Silicon Vias: Crystal Defect Analysis by Synchrotron X-ray Topography Landgraf, R., Rieske, R., Danielewsky, A., Wolter, K. Technische Universtät Dresden, Germany

Synchrotron Source: ANKA (Karlsruhe, Germany) 2.5 GeV,current 80-180 mA: white radiation 2Å

Presented at: 2nd Electronics System-Integration Technology

Conference, Greenwich, UK (2009-09-01)

DRIE vs. Laser Drilling

DRIE Vias, Source: Lam Research

Laser Via, Source: Landgraf

Sidewall Scalloping, Source: Aviza Technology

Laser Via Fabrication

525μm thick Si wafer (100) 4in. (100mm)

Target via diam: 50 μm

Laser Drilling Methods

Single Pulse

Trepanning (cut an annulus)

Percussion (high power pulsing)

Conventional drilling patterns, Source: Verhoeven, K.

X-ray Diffraction Setup

Section Transmission (15μm slit), Lang Method

Results – Strain Imaging

ns laser: 540 μm strain zone

ps laser: 290 μm strain zone

Trend with Laser Pulse Width

Strain affected region: Distance from via edge to

strain edge

fs laser: 220 μm strain zone

Conclusion

Transmission topography by synchrotron source successfully imaged strain near vias, nondestructively

Strain affected zone decreased with pulse width Electron-phonon relaxation time in Si, 400fs

Femtosecond lasers should be considered for commercial production Depth remains to be improved

Motivation: Multi-Chip Packages

Wirebonding Longer paths Failure due to fatigue,

bond lifting

Flipchip bumps Reduce path length Still require redistribution layer (RDL) Thermal cycling failure

Flipchip Die, Source: IMEC

Wirebonded Die, Source: Aspen Tech.