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 900oC, several minutes (After excess point defects recombine. slower diffusion) Si substrate 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 EE143 – Ali Javey
Sheet Resistance EE143 – Ali Javey
Resistivity vs. Doping EE143 – Ali Javey
Irvin’s Curves p-type erfc n-type erfc p-type half-gaussian n-type half-gaussian Explicit relationship between: N (surface concentration) , o x (junction depth), j N (background concentration), B R (sheet resistance), S EE143 – Ali Javey
Motivation to generate the Irvin’s Curves Allows us to calculate doping parameters if we know 3 out of 4 of the parameters on the previous page Approach 1) The dopant profile can be uniquely determined if one knows the concentration values at two depth positions. 2) We will use the concentration values No at x=0 and NB at x=xj to determine the profile C(x). (i.e., we can determine the Dt value) 3) Once the profile C(x) is known, the sheet resistance RS can be integrated numerically from: 4) Irvin’s Curves are plots of No versus ( Rs xj ) for various NB. EE143 – Ali Javey
Resistivity Measurement: Four-Point Probe EE143 – Ali Javey
Impurity Profiling: Spreading Resistance Region of Interest is Angle-Lapped Two-Point Probe Resistance Measurements vs. Depth Profile Extracted EE143 – Ali Javey
Impurity Profiling Secondary Ion Mass Spectroscopy (SIMS) EE143 – Ali Javey