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|Highly Ionized Sputtering for TSV-Lining|
|Keywords: Highly Ionized Sputtering , through silicon via, high aspect ratio|
|The barrier and seed layers for electroplating of copper play a critical role in the realization of through silicon vias (TSV) in 3D IC packaging. Physical vapour deposition (PVD) is still the preferred method, but with challenging demands of high aspect ratios (AR) of 10:1 or more, oftentimes rough sidewalls and low costs. Alpha-Tantalum is the preferred diffusion barrier and provides a good adhesion and wetting layer for copper. A new method called Highly Ionized Sputtering (HIS) has been developed using power pulses of 50 to 200 μsec length with a low duty cycle but very high current of several hundred Amps. The high pulse current generates a very high ionization of the sputtered material giving - with a proper bias voltage - a high directionality of metal ions and providing very dense films as needed for the diffusion barrier. HIS uses regular sputter equipment, flat targets and works at a low target substrate distance thus providing excellent transfer factors of the ionized PVD process and a low cost of ownership. HIS processes and hardware have been developed for TaN, Ta, Ti and Cu on the Oerlikon PVD cluster tools for 200mm as well as for 300mm wafers with competitive deposition rates, good uniformities and low stress. The applicability has been tested in TSVs with different sidewall qualities and supported by simulations.|
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