Electrical properties after thermal oxidation, of B-LPCVD polysilicon films

In this paper, we present the electrical properties evolution, following a dry thermal oxidation, of LPCVD polycrystalline silicon layers. The polysilicon thin films deposited on monosilicon substrates, at different temperatures (T_d = 520 to 605degC), are highly in situ boron doped (2times10²⁰ cm^-3). The thermal oxidation treatment was carried out under dry oxygen atmosphere at the temperatures T_ox = 840, 945 and 1050degC. SIMS Profiles, as well as the resistivity measures, show clearly that this treatment largely influences the electric behaviour of polycrystalline silicon films. It results from the deduced values of the diffusion coefficients, that diffusivity D_GB, in the grain boundaries, are higher than those in the grains, when the temperature is lower than 1000degC. While for T_ox = 1050degC, this tendency is reversed. Furthermore, the activation energy of D_GB is lower than D_G one. We consider that the precipitation of the doping agent in the grain boundaries is one of the principal causes of these remarkable results when compared with slightly doped polysilicon. The results rising from behaviour, with respect to electrical conduction, reveal that the films present overall a resistivity reduction in consequence of oxidation. This is correlated with an improvement of the films crystallinity.