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Boosting Ge-Epi P-Well Mobility & Crystal Quality with Si or Sn Implantation and Melt Annealing

Wednesday, 3 October 2018: 11:40
Universal 13 (Expo Center)
J. O. Borland (J.O.B. Technologies), A. Joshi (Active Layer Parametrics), B. Basol (ALP Inc), Y. J. Lee (National Nano Device Labs), T. Kuroi (Nissin), T. Tabata (LASSE-Screen), K. Huet (SCREEN-LASSE, Gennevilliers, France), G. Goodman, N. Khapochkina, and T. Buyuklimanli (EAG)
We investigated the effects of Sn, Si and C7 implantation into both P-well and N-well doped regions of Ge-epi on Si wafers after RTA and laser annealing, on crystal quality using XRD analysis and mobility using ALPro profiler of Active Layer Parametrics , which provides mobility and carrier concentration profiles at sub-nm resolution. SIMS analysis was also used for chemical depth analysis. XRD analysis shows improved Ge-epi crystallinity after >1.5J/cm2 laser melt annealing (liquid phase epitaxial regrowth). Since µ=1/ρqN where µ=mobility (cm2/volt-sec), ρ=resistivity (ohm-cm), q=charge of an electron and N=dopant concentration (cm3), if we assume qN=K a constant for these low dopant well regions then we can estimate change in mobility based on change in P-well or N-well resistance then compare to mobility measured by ALPro profiler. For the P-well cases doped with B=5keV at 1E13/cm2 dose for a retrograde P-well ~1E18/cm3 the Ge-epi Rs decreased to 1,600Ω/□ compared to Si at 3,400Ω/□ suggesting a hole mobility increase of 2.1x from 150cm2/V-s to 315cm2/V-s based on literature with actual measured Hall mobility of 465.2cm2/V-s, an increase of 3.1x. The 1.8J/cm2 laser melt anneal boosted P-well Hall mobility by 22% to 567cm2/V-s to a depth of 80nm and adding Sn implant improved mobility 91% to 889cm2/V-s and at a depth beyond 80nm mobility increases to 3,000cm2/V-sec. Si implant improved mobility by 43% to 667cm2/V-s to a depth of >100nm. For the N-well cases doped with P=40keV at 1E13/cm2 dose for a retrograde N-well ~1E18/cm3 the Ge-epi Rs increased to 2,000Ω/□ compared to Si at 1,600Ω/□ suggesting an electron mobility decrease of 0.8x to 216cm2/V-s rather than the expected increase of 3.3x from 270cm2/V-s for Si to 900cm2/V-s for Ge reported in the literature and expected N-well Rs of 485Ω/□. The actual Ge-epi N-well Hall mobility measured was 449cm2/V-s so only a 1.7x increase and nearly identical to the P-well mobility of 465cm2/V-s but the mobility drops off beyond a depth of 40nm. The 1.8J/cm2 laser melt anneal reduces N-well mobility to 191cm2/V-s but is uniform to a depth of 70nm. Adding Si implant had a slight decrease in mobility to 183cm2/V-s while Sn implant increases mobility to 280cm2/V-s uniformly to a depth >100nm. C7 (cluster-C) implant reduced N-well surface mobility to 50.3cm2/V-s to a depth of 30nm but then mobility increases 10x up to ~500cm2/V-s to a depth of 80nm and then drops to ~100cm2/V-s in the non-carbon N-well region as revealed by C-SIMS analysis to a depth of 110nm, therefore measuring mobility versus depth can be very critical in engineering surface and bulk mobility improvements based on chemical compositional changes in the Ge-epilayer. B-SIMS analysis shows retrograde P-well profile with 2E18/cm3 Rp at 50nm and Xj at 150nm also the Ge/Si epilayer interface. The laser melt flattens the B P-well profile to ~1E18/cm3 with a B pile-up at ~2E18/cm3 at the Ge/Si interface. C-SIMS analysis revealed only slight to no C diffusion even in the liquid Ge-melt phase while we observe 2-5% Si intermixing in the Ge-melt but no B nor P diffusion when C was present. Additional results for RTA anneals will be presented.