PHOSPHORUS DOPING USING ELECTRON-CYCLOTRON-RESONANCE PLASMA FOR LARGE-AREA POLYCRYSTALLINE SILICON THIN-FILM TRANSISTORS

We have investigated phosphorus doping using an electron cyclotron res onance (ECR) plasma, for application to the poly-Si driving circuits o f liquid crystal displays or image sensors. The PH3/He was ionized and accelerated to poly-Si and c-Si substrates with a self bias of -220 V . The P concentration, as detected by secondary ion mass spectroscopy (SIMS), is similar to 5 x 10(21) cm(-3) at the surface, which decayed to similar to 10(17) cm(-3) within 50-100 nm depth. The surface is fou nd to be etched during doping. The etching is restored by adding a sma ll amount of SiH4 and the sheet resistance R(5) decreases. The optimiz ed as-irradiated R(5) is similar to 1 x 10(5) Omega/rectangle and 1.7 x 10(2) Omega/rectangle for poly-Si and (110) c-Si, respectively. The dependence of R(5) on the substrates and the anomalous diffusion const ants derived from SIMS are also discussed.