An alternative approach to backside via reveal (BVR) for a via-middle through-Silicon via (TSV) flow

An alternative scheme has been developed to combine three major backside via reveal (BVR) processes, including (a) wafer polishing, (b) Si recess etching, and (c) wet clean, into an integrated wet etch process to replace the high cost chemical-mechanical planarization (CMP) and dry etching steps. The process combines two steps on a single-wafer platform: (1) bulk Si etching chemistry with high etch rate (>10 μm/min.) to replace the CMP or polishing and (2) selective Si etching chemistry (Si: SiO₂ ~ 1800:1) to replace the Si recess dry etching step. Using this process, Si thickness uniformity can be significantly improved (for 20 μm Si removal), resulting in a lower variation in step height of through-Si via (TSV) protrusion across a 300 mm wafer. The overall cost is significantly lower than CMP plus dry etching. After the integrated wet etching process, passivation layers of low-temperature silicon nitride and oxide were deposited on the backside, followed by CMP to planarize the wafer and expose the Cu nails. The film adhesion is very good without showing any film delamination or peeling. This new integration scheme is robust with a wide process margin and provides cost savings over the conventional BVR flow.