Atomic layer doping of SiGe – fundamentals and device applications

Abstract

The paper reviews results of atomic layer processing for P and B doping of SiGe and for SiGe:C epitaxy using LP(RT)CVD. Atomic layer processing for the base doping of SiGe:C heterojunction bipolar transistors (HBTs) is demonstrated for the first time. P atomic layer doping is self-limiting. The process is controlled by the dissociative adsorption of PH3 with an activation energy of 0.3 eV. We find no self-limitation of diborane adsorption for B atomic layer doping. At low diborane partial pressures, the doping is dominated by the dissociative adsorption of diborane at Si and Ge surface sites. B doses below 1 ML can be deposited. At high partial pressures of diborane the diborane is adsorbed at B occupied surface sites, resulting in several monolayer equivalents of B. The SiGe:C atomic layer epitaxy is found to be controlled by the dissociative adsorption of methylsilane with an activation energy of 0.36 eV. Transit frequencies of about 45 GHz have been obtained for B atomic layer doped SiGe:C HBTs. The HBT results demonstrate the capability of atomic layer processing for doping of advanced devices with critical requirements for dose and location control.