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

We have studied, at 20 Torr, the high-temperature growth kinetics of SiGe using a dichlorosilane + germane + hydrochloric acid chemistry. Adding HCl leads at 850degreesC to a slight increase in the germanium content x of SiGe layers. Its dependence on the F(GeH4)/F(SiH2Cl1) mass flow ratio is well accounted for by a x/(1 - x) = m(F(GeH4)/F(SiH2Cl2) 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 GeH4 flow increases. This is attributed for low GeH4 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 GeH4 flows, we are at 850degreesC 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 850degreesC to a strong decrease of the SiGe growth rate. The influence of the growth temperature between 750 and 950degreesC on the SiGe growth kinetics can schematically be described as follows: (i) The Ge concentration decreases for given amounts of SiH2Cl2 and GeH4 as the growth temperature increases (at least for Ge contents less than or equal to 25 %), which is reflected by an m parameter value decreasing from 2.43 (800degreesC to 1.71 (950degreesC). (ii) The SiGe growth rate increases as the GeH4 and/or the growth temperature increases; for high GeH4 flows and/or high temperatures we are in a supply-limited regime, whereas for low GeH4 flows and/or low temperatures we are in a surface hydrogen-desorption-limited regime. Playing with the absolute values of the SiH2Cl2 and GeH4 flows (in order to have access to both low and high F(GeH4)/F(SiH2Cl2) + F(GeH4) 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 %. (C) 2004 Elsevier B.V. All rights reserved.