In-situ HCl etching and selective epitaxial growth of Boron-doped Ge for the formation of recessed and raised sources and drains

摘要

The aim being the integration of either recessed or raised Ge: B Sources and Drains (S/Ds), we have studied the growth kinetics and the in-situ boron-doping of Ge in Reduced Pressure -Chemical Vapour Deposition. The Ge growth rate at 400°C, 60 Torr on blanket Si(001) is lower when adding HCl to GeH{sub}4. The B atoms concentration increases linearly with the F(B{sub}2H{sub}6)/F(GeH{sub}4) mass-flow ratio (maximum: 3.5 × 10{sup}19 cm{sup}(-3)). 20% to 40% of (almost all) the B atoms are electrically active in Ge: B layers grown at 400°C (subsequently annealed at 750°C under H{sub}2 for 10 minutes). The macroscopic degree of strain relaxation R of as-grown Ge layers increases slowly from 92% up to 100% as the Ge layer thickness increases. We have also studied the kinetics of the in-situ HCl etching at 20 Torr of recess in the Si active regions of patterned wafers. A transition from a Low Temperature, Cl desorption-limited regime (T ≤ 865°C) to a High Temperature, HCl supply-limited regime (T ≥ 895°C) has been evidenced. Almost none (significant) etch rate increases when switching from blanket to patterned wafers are associated to the LT (the HT) regime. A factor of 2 increase in the Ge: B growth rate has been observed when growing Ge: B layers in the S/D regions of patterned wafers with Si{sub}3N{sub}4 dummy gates. A full selectivity versus SiO{sub}2 and Si{sub}3N{sub}4 has been achieved, with a smooth resulting surface whatever the integration scheme (i.e. recessed versus raised). Finally, the presence of a regular array of pure edge misfit dislocations 10 nm apart together with a large number of {111} stacking faults has been shown in 20 nm thick Ge: B recessed S/Ds.