Exploration of PLAD aluminum implants for work function adjustment

It is well known that aluminum ion implant can shift the flatband voltage (Vfb) in hafnium-oxide high-k/metal gate PMOS 3D devices [1, 2]. The current work focuses on using a high-throughput plasma doping tool for aluminum implantation into metal-oxide-semiconductor capacitor (MOSCAP) structures as a test of work-function adjustment in PMOS devices. Work was conducted in a modified Applied Materials VSE PLAD doping tool [3,4], using a 2MHz RF ICP source varying from 500W to 1,500W of power to create an approximately 1e11 cm^-3 density argon plasma. This is used both for sputtering aluminum off a biased target as well as for drive-in implant, the mechanism for which has been described previously [5]. Typical Ar⁺ dose varied from 1e15 to 1e17 ions/cm², and chamber argon pressure was changed from 5mT to 15mT. Optical emission data indicated the presence of aluminum in the spectrum at 309nm and 396nm. SIMS analysis on prime silicon wafers was employed to optimize the process for implant depth and retained dose. Metal oxide semiconductor capacitor (MOSCAP) structures demonstrated initial Vfb shifts of more than 400mV on the high-k metal gate (HKMG) structures. It is believed that the Ar/Al dose implanted was in excess of that required for the targeted Vfb shift, which led to oxide degradation. Future work will focus on maintaining Vfb shift by modulating the target bias and implant conditions, while reducing the accompanying increases in equivalent oxide thickness (EOT) and gate leakage current (Jg).