Polarity asymmetry of polyoxide grown on phosphorus in situ doped polysilicon

Abstract

We show that polyoxides grown on phosphorus in situ doped polysilicon have larger polarity asymmetry than that on the POCl3-doped polysilicon. It may be not only the surface roughness between the polysilicon/polyoxide interfaces, but also the phosphorus distribution in the interfaces. For the phosphorus in situ doped poly film, the phosphorus piled up at the poly-1/polyoxide interface should result from the out-diffusion of the poly-1 doping during the tetraethyl orthosilicate oxide deposition process. However, the phosphorus concentration near the polyoxide/top poly-2 interface was lower than the bulk concentration of the polysilicon film, which may result from insufficient phosphorus concentration near the polyoxide/top poly-2 interface without subsequent annealing and dopant activation. Therefore, this may affect the polarity asymmetry of the electrical characteristics for the phosphorus in situ doped samples. Especially, the thermal polyoxide had the largest polarity asymmetry due to very high phosphorus concentration piled up in the bottom poly-1/polyoxide interface. We also show that the top poly-2 doping process affects the phosphorus distribution in the polysilicon/polyoxide interfaces, and further, affects the polyoxide performance.