Low temperature boron and phosphorous doped SiGe for recessed and raised sources and drains

Abstract We have first of all studied the growth kinetics of boron and phosphorous doped, 20–30 nm thick Si 0.65 Ge 0.35 layers, the aim being their integration in recessed and raised sources and drains. Those layers have been grown at low pressure (20 Torr) and low temperature (650 °C) with a heavily chlorinated chemistry (in order to be selective versus SiO 2 (isolation) and Si 3 N 4 (sidewall spacers)). We have quantified the impact of the diborane and phosphine flow on (i) the SiGe crystalline quality and strain state, (ii) the amount of boron or phosphorous atoms incorporated in it and (iii) the SiGe:B or SiGe:P growth kinetics. As the diborane flow increases, the SiGe:B growth rate definitely increases, while the real Ge concentration (from Time-Of-Flight Secondary Ions Mass Spectrometry) is more or less steady. B atoms, being much smaller than Si or Ge, partially compensate the compressive strain in the SiGe:B layers, leading to a decrease in the apparent Ge concentration (from X-ray diffraction). Opposite trends are observed for SiGe:P. There is indeed a definite decrease in the SiGe:P growth rate together with a definite increase in both the apparent and real Ge concentration as the phosphine flow increases. The Boron atomic concentration increases linearly with the diborane flow, with however a practical limit around 3.5×10 20  cm −3 in order to stay monocrystalline. Meanwhile, the phosphorous atomic concentration saturates quite rapidly at values close to 8–9×10 19  cm −3 as the phosphine flow increases (most likely due to surface segregation). In the second part we have highlighted some of the difficulties encountered when trying to selectively grow intrinsic SiGe raised S/Ds at 650 °C on patterned, extra-thin Silicon-On-Insulator wafers and some of the solutions identified in order to obtain 2D thick films. Amongst those, we can mention the 750 °C deposition of a thin Si buffer or the in-situ high HCl partial pressure etch at 650 °C of a few nm of Si prior to SiGe Selective Epitaxial Growth (SEG), the drastic reduction of the incoming HCl flow during SiGe SEG, etc.