ARSENIC GAS-PHASE DOPING OF POLYSILICON

Polysilicon layers have been doped with high uniform concentrations of arsenic in short processing times using gas-phase doping. The polysil icon layers were doped at total system pressures from 1 to 760 Torr wi th arsine or tertiarybutylarsine (TBA) as gas-phase dopant sources. An arsenic concentration as high as >4 X 10(20) atm/cm3 in 100 nm polysi licon layers was measured after a 60 s diffusion in 2.4% arsine in He at 1000-degrees-C at 760 Torr. Using tertiarybutylarsine (TBA) at 3 To rr, a sheet resistance of 2.5 kOMEGA/square was measured in a 100 nm p olysilicon layer after 12 min at 900-degrees-C. Doping at temperatures as low as 770-degrees-C also gave high arsenic concentrations. Finall y, a 6 mum deep DRAM trench capacitor was uniformly doped with arsenic to a concentration of 8 X 10(19) atm/cm3 using gas-phase doping and a two-step polysilicon deposition process.