Study of Nitrogen Effect on the Boron Diffusion during Heat Treatment in Polycrystalline Silicon/Nitrogen-Doped Silicon Thin Films

Abstract

The present paper studies the boron (B) diffusion in nitrogen (N) doped amorphous silicon (a-Si) layer in original bi-layer B-doped polycrystalline silicon (poly-Si)/in-situ N-doped Si layers (NIDOS) thin films deposited by low pressure chemical vapor deposition (LPCVD) technique. The B diffusion in the NIDOS layer was investigated by secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR) analysis. A new extended diffusion model is proposed to fit the SIMS profile of the bi-layer films. This model introduces new terms which take into account the effect of N concentration on the complex diffusion phenomena of B atoms in bi-layer films. SIMS results show that B diffusion does not exceed one third of NIDOS layer thickness after annealing. The reduction of the B diffusion in the NIDOS layer is due to the formation of complex B–N as shown by infrared absorption measurements. Electrical measurements using four-probe and Hall effect techniques show the good conductivity of the B-doped poly-Si layer after annealing treatment.

Complex boron redistribution kinetics in strongly doped polycrystalline‐silicon/nitrogen‐doped‐silicon thin bi‐layers

“…Figure 1 shows superposition of experimental SIMS profiles obtained before and after annealing at 600 °C and 700 °C, for various annealing times. The SIMS data have been initially reported in reference 8. All the SIMS profiles show a concentration peak appearance, in the NiDoS region, near the bi‐layers interface, which indicates important B transfer from the poly‐Si layer and the trapping at NiDoS layer.…”

“…Two related processes limit the realization of this goal: (i) the enhanced redistribution of the B during the thermal dopant‐activation annealing, which causes B penetration through thin oxides from the p + poly‐Si gate into the underlying layers 3, and (ii) the formation of electrically inactive B clusters and B precipitates 4,5, which decreases the dopant activation rate. The use of low‐energy doping methods, co‐doping techniques, low thermal annealing temperatures, short annealing times, amorphous‐silicon layers, and thin Nitrogen‐Doped‐Silicon (NiDoS) layers have been practiced to avoid the doping depletion of p + polysilicon gate at the oxide interface 6–8. Currently, significant research efforts are focused on improving the B activation and reducing fast B diffusion behaviour; problem common to all the practiced methods and technics.…”

“…Currently, significant research efforts are focused on improving the B activation and reducing fast B diffusion behaviour; problem common to all the practiced methods and technics. In particular, recent studies have revealed that in‐situ NiDoS layers are efficient B redistribution barriers 7,8. However, several physical phenomena have so far not been modeled sufficiently.…”