Very low temperature epitaxy of Ge and Ge rich SiGe alloys with Ge2H6 in a Reduced Pressure – Chemical Vapour Deposition tool

• Reduced Pressure Chemical Vapour Deposition of pure Ge and GeSi alloys.
• 5 to 40 times higher Ge growth rates at T<400 °C with digermane than with germane.
• Linear decrease of the Ge growth rate from digermane as the pressure increases.
• Dichlorosilane instead of disilane yields higher Ge content GeSi at 475 °C, 100 Torr.
• GeSi growth rate increase with the Si2H6 mass-flow (stable with SiH2Cl2).

We have studied the very low temperature epitaxy of pure Ge and of Ge-rich SiGe alloys in a 200 mm industrial reduced pressure chemical vapour deposition tool. We have, first of all, benchmarked germane (GeH4) and digermane (Ge2H6) for the growth of pure Ge. Used Ge2H6 instead of GeH4 enabled us to dramatically increase the Ge growth rate at temperatures 425 °C and lower (5.6 nm min−1 compared to 0.14 nm min−1 at 350 °C with a Ge2H6 mass-flow one fourth that of GeH4). We have also evaluated at 400 °C, 100 Torr, the impact of the GeH4 or Ge2H6 mass-flow on the Ge growth rate. For a given Ge atomic flow, the higher surface reactivity of digermane yielded roughly five times higher growth rates than with germane. We have then combined digermane with disilane (Si2H6) or dichlorosilane (SiH2Cl2) in order to study the GeSi growth kinetics at 475 °C, 100 Torr. While the SiH2Cl2 mass-flow did not have any clear influence on the GeSi growth rate (with a 14 nm min−1 mean value, then), a Si2H6 mass-flow increase resulted in a slight GeSi growth rate increase (from 11 nm min−1 up to 14 nm min−1). Significantly higher Ge concentrations were otherwise accessed with dichlorosilane than with disilane, in the 77–82% range compared to the 39–53% range, respectively.