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Product Briefing Outline: Alchimer S.A. has introduced the ‘eG ViaCoat,’ an electrochemical coating processes, for the metallization of high aspect ratio through-silicon vias (TSVs) used in advanced 3D packaging applications. eG ViaCoat enables conformal, thin, uniform and adherent copper seed layers, even on resistive barriers. It is claimed to reduce processing costs over conventional dry vacuum processes. For example, for 10:1 aspect ratio TSVs, the CoO of eG ViaCoat is claimed to be 75% less than that of a traditional PVD (physical vapor deposition) process.

Problem: A conventional PVD tool without expensive re-sputtering capability cannot reliably coat scalloped TSVs with aspect ratios above 3:1. ALD and CVD techniques are expensive and slow. The challenge is even more acute for filling Bosch etched TSVs as they have scalloped walls that make it difficult for a line-of-sight process like PVD to deposit a continuous and conformal film on the sidewalls. Electroplating of copper on a discontinuous copper seed film along the TSV sidewalls results in poor copper fill of the TSV with undesirable voids. Therefore, for the copper barrier and seed films it is essential that they be continuous and preferably conformal along the entire inside surface of a TSV. A conventional PVD tool without expensive re-sputtering capability runs out of steam when filling high aspect ratio scalloped TSVs. ALD technique for copper barrier deposition is expensive and slow while ALD deposition of copper seed currently does not commercially exist.

Solution: Electrografting is a new technology based on electrochemical process. It uses water-based formulation for direct plating on barrier material, which makes it easy to implement on standard plating equipment. A major advantage of electrografting over electroplating is that it does not suffer from Ohmic drop. thus giving excellent across wafer uniformity. The technique is shown to produce highly conformal copper seed layers even in very high aspect ratio vias. eG ViaCoat is specifically formulated for the deposition of copper seed layers during TSV metallization. It is an aqueous copper electrolyte solution that enables the deposition of ultra thin, homogeneous, uniform, adherent and conformal copper seed layers. Reliable metallization of TSVs with aspect ratios of 13:1 is now possible. A major advantage of electrografting over electroplating is that it does not suffer from Ohmic drop, giving excellent across wafer uniformity. Low-resistivity copper seed layers in the 50- to 500-nanometer range can be deposited on various barrier materials with very high adhesion. Continuous coverage of high aspect ratio (> 10:1) TSVs is achieved, enabling subsequent void-free copper filling of vias.

Applications: It is compatible with standard barrier materials, including, but not limited to, PVD, CVD and ALD deposited Ta, TaN, Ti, TiN, WN, Ru and bi-layers. eG ViaCoat is suitable for all applications requiring Cu metallization of TSVs: high-density vias for 3D-ICs such as stacking of memories, medium and low-density vias for image sensors, heterogeneous components integration and System-in-Package applications.

Platform: eG ViaCoat is a ready-to-use mild acidic ultra-pure aqueous copper-based electrolyte solution. This wet copper seeding technology can be implemented onto industry-standard copper electroplating equipments and provides cost-effectiveness compared to high-cost vapor phase deposition techniques. It is fully compatible with commercial copper electroplating blend waste stream.

Availability: July 2008 onwards.