SUPPRESSION OF OXIDATION-ENHANCED BORON-DIFFUSION IN SILICON BY CARBON IMPLANTATION AND CHARACTERIZATION OF MOSFETS WITH CARBON-IMPLANTED CHANNELS

In NMOS transistors with boron-doped channels, Oxidation-Enhanced Diff usion (OED) is a key contributor to boron profile broadening, Starting with the arguments presented in several recent reports on tile role o f carbon in silicon as a sink for self-interstitials, we have explored the feasibility of using carbon in the Metal Oxide Silicon Field Effe ct Transistor (MOSFET) active region to retard boron diffusion during gate oxidation. A highly effective suppression of OED of boron was obs erved providing more than an order of magnitude reduction in boron dif fusivity, MOSFET's with carbon-and boron-implanted channels have been fabricated to evaluate the impact of carbon on the electrical properti es of Si, Boron diffusion, activation, and critical electrical paramet ers including subthreshold swing, threshold voltage, off-state leakage current, and channel mobility have been evaluated as a function of th e carbon dose, While our results show that carbon can effectively supp ress boron diffusion during gate oxidation, carbon can also lead to po or boron activation and degradation in MOSFET performance when carbon dose levels above a threshold of similar to 10(14) cm(-2) are utilized , Our results, however, indicate considerable improvement in boron act ivation with increases in the thermal budget, We show that if carbon i mplantation damage is annealed out prior to boron implantation, not on ly is boron activation improved, but carbon continues to serve as a si nk for self-interstitials, thereby effectively suppressing OED.