Effect of HCl on the SiGe growth kinetics in reduced pressure—chemical vapor deposition

Abstract

Abstract We have studied the growth kinetics of Si and SiGe using a dichlorosilane+germane+hydrochloric acid chemistry. Adding HCl to SiH 2 Cl 2 leads to a slight decrease of the Si growth rate at high temperature (same activation energies E a =4 kcal mol −1 with or without HCl, however). A more consequent drop occurs in the low-temperature region, where the Si growth rate is limited by the desorption of the Cl atoms (instead of the H atoms) from the growing surface ( E a =87 ⇔ 48 kcal mol −1 ). Adding HCl leads at 750°C to a significant increase in the germanium content x of SiGe layers. Adopting a x 2 /(1− x )= n ( F (GeH 4 )/ F (SiH 2 Cl 2 )) dependence of x on the F (GeH 4 )/ F (SiH 2 Cl 2 ) mass flow ratio, this translates into a n value linearly increasing with the HCl mass flow from n =0.58 (no HCl) to n =1.08 ( F (HCl)/ F (H 2 )=0.0104). The SiGe growth rate increases strongly with an increasing GeH 4 flow, with no influence of the actual SiH 2 Cl 2 flow. This is attributed to an increased hydrogen desorption caused by the presence of Ge atoms on the growing surface that frees nucleation sites for the incoming Ge and Si atoms. Adding HCl leads to a strong, linear decrease of the SiGe growth rate with the HCl mass flow.