SiGe growth kinetics and doping in reduced pressure-chemical vapor deposition

Abstract

Using a reduced pressure-chemical vapor deposition cluster tool, we have studied the growth kinetics of Si and SiGe and the n-type and p-type doping of Si with both silane and dichlorosilane chemistries. As far as Si is concerned, a conventional behavior is found for both gases, i.e. a low-temperature region where the Si growth rate is limited by the desorption of the H atoms from the growing surface (activation energy equal to 47 kcal/mol), and a high-temperature region, where the Si growth rate is mainly piloted by the incoming flow of SiH 4 or SiH 2Cl 2 (activation energy of 4 kcal/mol). The incorporation of B in Si is linear with the B 2H 6 flow (p-type doping of Si), achievable with an overall 9×10 16–4×10 19 cm −3 B ions concentration range. There is a sub-linear dependency of the P incorporation into Si with the PH 3 flow (n-type doping of Si). A 2×10 16–9×10 18 cm −3 P ions concentration range can be reached with both silicon gas sources. The growth rate of boron-doped Si is virtually unaffected by increasing B 2H 6 flow. Meanwhile, the growth rate of phosphorous-doped Si steadily drops when the PH 3 flow is increased. As far as the SiH 4+GeH 4 chemistry is concerned, the Ge concentration x in the SiGe film obeys at 650°C the following law as a function of the F(GeH 4)/F(SiH 4) mass flow ratio: x/(1− x)=2.7(F(GeH 4)/F(SiH 4)). For the SiH 2Cl 2+GeH 4 chemistry, x is linked at 750°C to the F(GeH 4)/F(SiH 2Cl 2) mass flow ratio through the following relationship: x 2/(1− x)=0.55(F(GeH 4)/F(SiH 2Cl 2)). The SiGe growth rate increases strongly with an increasing GeH 4 flow, with no apparent influence of the actual SiH 4 or SiH 2Cl 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.