Low temperature growth kinetics of high Ge content SiGe in reduced pressure-chemical vapor deposition

We have studied the low temperature growth kinetics of high Ge content (27–74%) SiGe in reduced pressure-chemical vapor deposition. For this, we have grown at 600 °C, 20 Torr step-graded structures on top of polished SiGe virtual substrates. The individual SiGe layer thickness (and thus the associated growth rate) and Ge content has been determined thanks to cross-sectional scanning electron microscopy and X-ray diffraction, respectively. Adding GeH4 to SiH2Cl2 leads as expected to a monotonous increase of the Ge concentration. The behavior of the SiGe growth rate is somewhat different: it increases linearly for Ge contents in-between 27% and 57%, saturates around 60% of Ge and decreases for higher Ge contents. Injecting HCl (in order to be fully selective versus Si3N4 on patterned wafers) leads at 600 °C to a sharp Ge content increase together with a severe SiGe growth rate decrease (for given SiH2Cl2 and GeH4 mass flows), which we have quantified. We have combined those 600 °C data points with other data acquired in the past. This way, we benefit from a clear picture of the SiGe growth kinetics at 20 Torr with a chlorinated chemistry in the 550–950 °C temperature range. Differences in Ge incorporation kinetics (explained by differences in gaseous precursor decomposition pathways) have been evidenced as the growth temperature increases. They are associated to changes in SiGe growth rate versus temperature behavior (shift from a low temperature, H desorption from the surface-limited regime to a high temperature, gaseous precursors diffusion-limited regime).