Arsenic gas-phase doping of polysilicon

Abstract

Polysilicon layers have been doped with high uniform concentrations of arsenic in short processing times using gas‐phase doping. The polysilicon layers were doped at total system pressures from 1 to 760 Torr with arsine or tertiarybutylarsine (TBA) as gas‐phase dopant sources. An arsenic concentration as high as ≳4×1020 atm/cm3 in 100 nm polysilicon layers was measured after a 60 s diffusion in 2.4% arsine in He at 1000 °C at 760 Torr. Using tertiarybutylarsine (TBA) at 3 Torr, a sheet resistance of 2.5 kΩ/⧠ was measured in a 100 nm polysilicon layer after 12 min at 900 °C. Doping at temperatures as low as 770 °C also gave high arsenic concentrations. Finally, a 6 μm deep DRAM trench capacitor was uniformly doped with arsenic to a concentration of 8×1019 atm/cm3 using gas‐phase doping and a two‐step polysilicon deposition process.