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Product Briefing Outline: Alchimer S.A has launched its cost-saving ‘AquiVia’ deposition process. The AquiVia process is claimed to reduce overall cost of ownership for through-silicon via (TSV) metallization by up to 65 percent vs. conventional dry processes. Alchimer’s new process encompasses three distinct process steps required before the TSV can be filled with metal. It enables wet-process deposition of insulator, barrier and copper seed layers within high-aspect ratio TSVs, using Electrografting technology.

Problem: 3D chip stacking has been identified as the solution that can deliver increased functionality and performance while simultaneously reducing size, cost, and power consumption. A key enabling technology for 3D stacking is the filling of through silicon vias (TSV). These TSVs may have aspect ratios ranging anywhere from 5:1 to more than 20:1, so filling them with metal presents a unique challenge. 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 continuous and conformal films on the sidewalls, resulting in poor Cu fill of the TSVs with undesirable voids. Therefore, for the Cu barrier and seed films it is essential that they be continuous and conformal along the entire inside surface of a TSV. A conventional PVD tool without expensive re-sputtering capability is not capable of seeding high aspect ratio scalloped TSVs. ALD and CVD techniques, although conformal are prohibitively expensive, due to equipment and precursor costs.

Solution: AquiVia combines, for the first time, wet deposition processes for insulation, barrier, and seed layers in TSV metallization. The insulation liner is deposited by Electrografting, leading to strong covalent bonds between the insulator and the semiconductor surface. The resulting grafted polymer shows excellent insulator properties and very good thermal stability. An improved wet current-free deposition process then produces a conformal nickel-based barrier layer grafted directly to the insulator. The Cu seed is then deposited using Alchimer’s eG ViaCoat, creating an extremely adherent ultra-conformal layer. This results in highly conformal and uniform layers for TSVs with aspect ratios of 18:1 and beyond, even on the highly scalloped TSV etch profiles produced by the DRIE/Bosch process.

Applications: High-aspect ratio TSVs

Platform: AquiVia chemistries are ready-to-use aqueous solutions. Formulations and process recipes are fully compatible with standard electroplating tools, and the full wet-process TSV filling flow (isolation/barrier/seed and Cu fill) can now be implemented on a single electroplating tool, with only minor hardware modifications.

Availability: July 2009 onwards.