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

Octadecaborane (B
18
H
22
) implant technology was evaluated for p+ poly gate doping process in a 72nm node stack DRAM device. The evaluation criteria were to improve the productivity of the process, which was initially built with conventional atomic boron implantation (
¹¹
B), 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 R
s
of blanket B
18
H
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, B
18
H
22
implant splits of various energies and doses have been studied for their sensitivities to the electrical performance of the p-MOSFET in the 72nm node stack DRAM devices. In this study, we have demonstrated that B
18
H
22
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, B
18
H
22
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 B
18
H
22
process