Physicochemical characterizations of polysilicon thin multilayer films have been studied after annealing. In-situ heavily boron-doped polysilicon (poly=Si) and nitrogen-doped silicon (NIDOS) films were deposited by low-pressure chemical vapor deposition (LPCVD) onto an oxidized monocrystalline silicon substrate. Secondary ion mass spectrometry (SIMS) profiles showed a boron diffusion reduction in the NIDOS layer. In addition, Fourier transform infrared spectroscopy (FTIR) analysis clearly showed an evolution of the absorption picks related to the nitrogen atom in the complex form leading to boron atom activation in the films. Therefore, this multilayer structure can be largely used for metal-oxide-semiconductor (MOS) devices.
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.
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