EE143 – Ali JaveySection 4: Diffusionpart 2Jaeger Chapter 4EE143 – Ali JaveyExample : High Concentration Arsenic diffusion profile becomes “box-like”EE143 – Ali JaveyIf doping conc < ni:Use constant diffusivity solutions(profile is erfc or half-gaussian)If doping conc > ni:Solution requires numerical techniquesSummary of High-Concentration DiffusionEE143 – Ali JaveyTransient Enhanced Diffusion (TED)Dopant ImplantationSisubstrateImplantationinduced excesspoint defectsxC(x)no annealing900oC, several sec (TED)Extremely rapid diffusion due to excess point defectsImplantation createslarge number of excess Siinterstitials and vacancies.(1000X than thermal process).After several seconds of annealing, the excess point defects recombine.900oC, several minutes(After excess point defects recombine. slower diffusion)EE143 – Ali JaveyDiffusion: p-n Junction Formation⎟⎟⎠⎞⎜⎜⎝⎛=⎟⎟⎠⎞⎜⎜⎝⎛==B01-B0NNerfc 2 :profileFunction Error NNln 2 :ProfileGaussian doping) type-nout cancels doping type-p e. (i. zero ision concentrat impuritynet the wherepoint at the occursjunction n -PDepthJunction calMetallurgiDtxDtxxxjjjjEE143 – Ali JaveySheet ResistanceSquare]per [Ohms ResistanceSheet =tRWLRWLtRtWASSρρ=⎟⎠⎞⎜⎝⎛=⎟⎠⎞⎜⎝⎛⎟⎠⎞⎜⎝⎛=•=EE143 – Ali JaveyResistivity vs. Dopingρ=σ−1= qμnn +μpp()[]−1n − type : ρ≅ qμnND− NA()[]−1p − type : ρ≅ qμpNA− ND()[]−1EE143 – Ali JaveyResistivity Measurement: Four-Point ProbetMeasuremen ResistanceTerminalFour /square][ 53.42lnt>> sfor m]-[ 2lns>>for t m]-[ 2Ω≅==Ω=Ω=IVIVtRIVtIVsSπρπρπρEE143 – Ali JaveyImpurity ProfilingSecondary Ion Mass Spectroscopy (SIMS)SiO2 capping RTA and SiO2 etch Ultra Shallow Doped SiSi H H H H 120 ºC 2.5 hrs Self-limiting approach for doping of nanostructuresStrategy:1. Boron monolayer formation on Si2. Capping with SiO2 cap3. RTA to diffuse the B atomsChemistry is important for nano devices!1. Various doping profiles can be readily achieved by tuning the RTA condition.2. Doping efficiency of ~30% for B and ~90% for P.Monolayer Doping of Nanomaterials10171018101910201021[B] (atoms/cm3) 6040200Depth (nm)Baselinea950oC1000oC103104105Rs (Ω/ ) 4002000Annealing Time (s)950oC1000oC1050oCb102103104Rs (Ω/ ) 4002000Annealing Time (s)1017 1019 1021[P] (atoms/cm3) 806040200Depth (nm)900oC 950oC 1000oCcB dopingP
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