Section 4 Diffusion part 2 Jaeger Chapter 4 EE143 Ali Javey Example High Concentration Arsenic diffusion profile becomes box like EE143 Ali Javey Summary of High Concentration Diffusion If doping conc ni Use constant diffusivity solutions profile is erfc or half gaussian If doping conc ni Solution requires numerical techniques EE143 Ali Javey Transient Enhanced Diffusion TED Dopant Implantation C x no annealing Si substrate 900oC several minutes After excess point defects recombine slower diffusion Implantation induced excess point defects Implantation creates large number of excess Si interstitials and vacancies 1000X than thermal process After several seconds of annealing the excess point defects recombine x 900oC several sec TED Extremely rapid diffusion due to excess point defects EE143 Ali Javey Diffusion p n Junction Formation x j Metallurgical Junction Depth P n junction occurs at the point x j where the net impurity concentration is zero i e p type doping cancels out n type doping Gaussian Profile N x j 2 Dt ln 0 NB N Error Function profile x j 2 Dt erfc 1 0 NB EE143 Ali Javey Sheet Resistance A W t L R t W RS t L R S W Sheet Resistance Ohms per Square EE143 Ali Javey Resistivity vs Doping q n n p p 1 1 n type q n N D N A 1 p type q p N A N D 1 EE143 Ali Javey Resistivity Measurement Four Point Probe V 2 s m for t s I t V m for s t ln 2 I V V RS 4 53 square t ln 2 I I Four Terminal Resistance Measurement EE143 Ali Javey Impurity Profiling Secondary Ion Mass Spectroscopy SIMS EE143 Ali Javey Self limiting approach for doping of nanostructures H H H H Si 120 C SiO2 capping 2 5 hrs RTA and SiO2 etch Ultra Shallow Doped Si Strategy 1 Boron monolayer formation on Si 2 Capping with SiO2 cap 3 RTA to diffuse the B atoms Chemistry is important for nano devices Monolayer Doping of Nanomaterials B doping 10 10 20 10 19 Baseline 18 10 10 17 5 b 950oC 1000o C1050 oC c 10 4 10 20 40 Depth nm 60 900oC 950oC 1000o C 21 10 19 10 17 10 0 3 20 40 60 80 Depth nm 3 10 0 4 3 950oC 1000o C P atoms cm 10 a R s 10 21 R s 3 B atoms cm 10 P doping 0 200 400 Annealing Time s 2 0 200 400 Annealing Time s 1 Various doping profiles can be readily achieved by tuning the RTA condition 2 Doping efficiency of 30 for B and 90 for P
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