Schottky barrier height modulation by ultra-shallow low-dose dopant diffusion

Arsenic deposited as a monolayer of pure As on silicon by chemical-vapour-deposition (CVD) epitaxy and capped by an oxide layer has been investigated for the first time as a dopant diffusion source when using anneal temperatures below 900 degC. Schottky diodes of Al to n-and p-type Si with and without such an As-doped surface layer were fabricated. The I-V diode characteristics show that a very small but significant amount of As diffuses into the Si already at 700 degC and that this amount increases with increasing temperature. Thus, when going from 700 degC to 900 degC, on p-type wafers a transition from a low-barrier Schottky diode to an n⁺p junction diode is seen while on n-type wafers the initially high Schottky barrier is lowered until an n⁺n ohmic contact is formed. Moreover, sheet resistance measurements and SIMS of capped As-doped layers where performed showing that diffusion depths below 5 nm are achieved