Atomic layer doping of SiGe

Abstract

We demonstrate atomic layer processing for P and B doping and for SiGe:C epitaxy using LP(RT)CVD between room temperature and 400°C. In the case of P doping, the process is self-limiting. P doses below one monolayer were deposited by separating adsorption of PH 3 and deposition of SiGe. Below 400 °C the dominant process is dissociative adsorption of PH 3 with an activation energy of 0.3 eV. At higher temperatures, desorption of P decreases the incorporated P concentration. The P dose incorporated into SiGe may be controlled by the partial pressures of phosphine and hydrogen. For B atomic layer doping, we find no self-limitation of diborane adsorption. At low diborane partial pressures it is possible to prepare B peaks with a concentration below one monolayer. In this case the doping is dominated by the dissociative adsorption of diborane at Si and Ge surface sites. Using high partial pressures of diborane, several monolayers of B can be deposited. The diborane is adsorbed at B occupied surface sites. The SiGe:C atomic layer epitaxy was found to be controlled by the dissociative adsorption of methylsilane at temperatures below 400°C. At these temperatures the process is self-limiting. An effective activation energy of (0.36±0.4) eV was determined for the dissociative adsorption of methylsilane.