Arsenic Plasma Doping in Si Characterized by High Resolution Medium Energy Ion Scattering Depth Profile Analysis

In the plasma doping (PLAD) process studied, Si(100) wafers were exposed to an As containing plasma and pulse biased to between 4 and 10 kV to ion fluences of 1x10¹⁶ cm^-2. Medium energy ion scattering (MEIS) analysis was applied after i) the PLAD implant, ii) two types of wet chemical clean and iii) spike annealing to 1000°C, to determine quantitative depth profiles of As, Si and O and retained As dose at each stage. Following PLAD at a 7 kV bias, MEIS showed the formation of an intermixed Si/As layer which decayed almost linearly from a ~40% As fraction directly under a 1.2 nm thick surface oxide to near-zero over a depth of ~17 nm. A non-oxidizing wet clean is shown to etch away 7 nm of the mixed layer, stopping at a Si concentration of 4x10²² cm³ and remove around 80% of the implanted As. Concentration depth profiles of As visible to the beam in both random and aligned lattice directions, yielded the substitutional As profile and retained As dose of 8x10¹⁴ cm^-2. This dose is shown to be strongly bias voltage (implant energy) dependent, giving a ~10-fold increase going from 4 to 10 kV. The application of an industry standard SPM wet clean on the other hand, produced a 13.5 nm thick surface oxide overlaying the retained As implant and, after annealing a substitutional As depth profile with a concentration of 1x10²¹ cm^-3 over a depth greater than 10 nm. This gives a substitutional As dose of 1.35x10¹⁵ cm^-2 which represents a 70 % increase on that measured after a non-oxydizing chemical wet clean.