N-Channel Mos Transistors below 0.5 μm with Ultra-Shallow Channels formed by Low Temperature Selective Silicon Epitaxy

Abstract

AbstractIn this paper, we present an application of ultra high Vacuum Rapid Thermal Chemical Vapor Deposition (UHV-RTCVD) to MOSFET channel engineering. MOSFETs were fabricated on ultra-thin (200 Å), moderately doped (l×1017 - 6×1018 cm−3) p-type epitaxial layers selectively grown in active areas defined by standard LOCOS isolation. The selective epitaxy was achieved using a novel Si2H6Cl2/B2H6 process at 800°C and at a total pressure under 30 mtorr. Low thermal budget processing techniques were emphasized to minimize spread in the channel doping profile. Threshold voltages below 0.6 V were obtained. Transistors with effective channel lengths of 0.45 μm exhibit subthreshold slopes from 78 to 92 mV/decade determined by the epitaxial channel doping density. We have found that by using ultra-thin channels, expected transconductance degradation at high channel doping densities can be minimized. Furthermore, ultra-thin channels help reduce the sensitivity of the threshold voltage on substrate bias. The results show that low temperature selective silicon epitaxy can be used to form ultra-shallow channel doping profiles that can enhance the performance of MOSFETs in the deep submicron regime.