Growth kinetics and boron doping of very high Ge content SiGe for source/drain engineering

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

“…associated to our intrinsic Si 0.65 Ge 0.35 or Si 0.65 Ge 0.35 :B layers are independent of the diborane mass-flow, with 0.22 and 2.0 nm mean values (in agreement with Ref. [25] conclusions).…”

“…The F(HCl)/F(H 2 ) MFR adopted here (0.00258) was roughly two times higher than in Refs. [24] and [25], in order to achieve full selectivity in 3D MOSFETs (where low temperature SiN sidewall spacers might be used). SiGe:B (SiGe:P) layer thicknesses were in between 23 and 33 nm (17 and 25 nm), i.e.…”

“…A major increase in the SiGe:B growth rate occurs as diborane is sent in larger and larger amounts on the growing surface (from 2.3 up to 5.9 nm min À 1 for monocrystalline layers), in full agreement with Refs. [24] and [25] findings. This is explained by an enhanced H desorption when B atoms are present on the surface (freeing surface sites for the adsorption of Si or Ge gaseous precursors).…”

“…A similar transition from monocrystalline to polycrystalline has been found in the past for Si 0.8 Ge 0.2 :B layers grown at 700 1C [24] or for Si 1 À x Ge x :B (x ¼30%, 40% or 50%) layers grown in between 600 and 650 1C [25] on blanket Si(0 0 1), albeit with less chlorinated chemistries. The F(B 2 H 6 )/[F(SiH 2 Cl 2 )þ F(GeH 4 )] MFR threshold for such a transition seems however to decrease as the growth temperature increases (and concurrently the Ge concentration increases): close to 0.003 at 700 1C for 20% of Ge [24]3some-where in the 0.003-0.008 range at 600-650 1C for 30-50% of Ge [25] and somewhere in the 0.004-0.009 range at 650 1C for 35% of Ge (current study).…”

“…Temperatures should indeed not be over 650 1C, in order to keep the salicide of the bottom MOSFETs electrically stable [22]. One has then to resort to SiGe in order to have meaningful growth rates at temperatures inferior or equal to 650 1C with a heavily chlorinated chemistry [22,24,25]. Beside thermal budget constraints, low growth temperatures are also strongly advised in order to avoid any elastic relaxation of the compressive strain stored in rather high Ge concentration SiGe layers through the formation of surface undulations [26].…”