Wafer to Wafer Hybrid Bonding for DRAM Applications

This study proves the applicability of wafer to wafer hybrid bonding to commercialized DRAM products for the first time. A metal interconnection process for bonding Cu pad was carried out on the already fabricated DRAM wafer and another bare Si wafer. Two wafers were stacked with wafer to wafer hybrid bonding process. Afterwards, TSV last process with BEOL Metallization was carried out. After applying the optimized bonding process conditions with CMP flatness, Cu dishing control, bonding voids free was confirmed. The stable connectivity of bonding could be confirmed through the daisy chain pattern with 100% pass rate. Finally same wafer yields with current DRAM product can be obtained. Cell characteristics have changed as the hydrogen passivation effect due to the hybrid bonding process and subsequent metal processes has changed. Through thermal budget control, the same cell characteristics could be obtained as existing DRAM.