Synchrotron X-Ray Topography for Laser- Drilled Vias Kevin 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 mA: white radiation 2Å  Presented at:  2 nd Electronics System-Integration Technology Conference, Greenwich, UK ( )

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.