SiGe high-temperature growth kinetics in reduced pressure-chemical vapor deposition

Abstract

We have studied, at 20 Torr, the high-temperature growth kinetics of SiGe using a dichlorosilane+germane+hydrochloric acid chemistry. Adding HCl leads at 850 °C to a slight increase in the germanium content x of SiGe layers. Its dependence on the F(GeH 4)/F(SiH 2Cl 2) mass flow ratio is well accounted for by a x / ( 1 - x ) = m ( F ( GeH 4 ) / F ( SiH 2 Cl 2 ) relationship, with m increasing from 2.41 (no HCl) to 2.77 (F(HCl)/F(H 2)=0.00833). The SiGe growth rate increases slightly, and then stabilizes as the GeH 4 flow increases. This is attributed for low GeH 4 flows 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. For high GeH 4 flows, we are at 850 °C in a supply-limited regime, where the growth rate is limited by the amount of gaseous precursors on the growing surface. Adding some HCl leads at 850 °C to a strong decrease of the SiGe growth rate. The influence of the growth temperature between 750 and 950 °C on the SiGe growth kinetics can schematically be described as follows: (i) The Ge concentration decreases for given amounts of SiH 2Cl 2 and GeH 4 as the growth temperature increases (at least for Ge contents ⩽25%), which is reflected by an m parameter value decreasing from 2.43 (800 °C) to 1.71 (950 °C). (ii) The SiGe growth rate increases as the GeH 4 and/or the growth temperature increases; for high GeH 4 flows and/or high temperatures we are in a supply-limited regime, whereas for low GeH 4 flows and/or low temperatures we are in a surface hydrogen–desorption-limited regime. Playing with the absolute values of the SiH 2Cl 2 and GeH 4 flows (in order to have access to both low and high F(GeH 4)/F(SiH 2Cl 2)+F(GeH 4) mass flow ratios) and the growth temperature, we have been able to gain access to a very large Ge concentration range, between 2% and 50%.