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

We have studied the growth kinetics of Si and SiGe using a dichlorosilane + germane + hydrochloric acid chemistry. Adding HCl to SiH2Cl2 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 HCI leads at 750degreesC to a significant increase in the germanium content x of SiGe layers. Adopting a x(2)/(1 - x) = n(F(GeH4)/F(SiH2Cl2)) dependence of x on the F(GeH4)/F(SiH2Cl2) 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(HCI)/ F(H-2) = 0.0104). The SiGe growth rate increases strongly with an increasing GeH4 flow, with no influence of the actual SiH2Cl2 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 HCI leads to a strong, linear decrease of the SiGe growth rate with the HCl mass flow. (C) 2002 Elsevier Science B.V. All rights reserved.