Octadecaborane implant technology for 72nm node stack DRAM p+ poly gate doping process

Octadecaborane (B₁₈H₂₂) implant technology was evaluated for p+ poly gate doping process in a 72 nm node stack DRAM device. The evaluation criteria were to improve the productivity of the process, which was initially built with conventional atomic boron implantation (¹¹B), while maintaining process equivalency. Before implanting into device wafers, process matching to conventional boron implant was done using both crystalline silicon and poly-silicon on Si wafers. For the crystalline silicon wafers, the Rs of blanket B₁₈H_x ⁺ implants were compared to that of atomic boron. For the poly-Si silicon wafers, SIMS dopant profiles were compared. For the device wafers, boron penetration, gate depletion, and final yield were compared. In addition, B₁₈H₂₂ implant splits of various energies and doses have been studied for their sensitivities to the electrical performance of the p-MOSFET in the 72 nm node stack DRAM devices. In this study, we have demonstrated that B₁₈H₂₂ can provide up to 5X wafer throughput advantage over conventional atomic boron process due to much higher effective beam currents. Besides the significant productivity improvement, B₁₈H₂₂ implant device characteristics were well matched to the baseline atomic boron process. Additionally, negative impact on post implant ashing and cleaning processes was not observed for the B₁₈H₂₂ process.