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 °C. 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 °C and that this amount increases with increasing temperature. Thus, when going from 700 °C to 900 °C, 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.