Quantitative modelling of nucleation kinetics in experiments for poly-Si growth on SiO2 by hot wire chemical vapor deposition
Abstract We apply a rate-equation pair binding model of nucleation kinetics to the nucleation of Si islands grown by hot wire chemical vapor deposition on SiO 2 substrates. The grain size of poly-Si films increases with H 2 dilution, which is attributed to atomic H etching of Si monomers rather than stable Si clusters during the early stages of nucleation. The nucleation density increases sublinearly with time at low coverage, implying a fast nucleation rate until a critical density is reached, after which grain growth begins. The nucleation density decreases with increasing H 2 dilution (H 2 :SiH 4 ) due to etching, and with increasing temperature, due to enhanced Si monomer diffusivity on SiO 2 . From temperature-dependent measurements, we estimate the activation energy for surface diffusion of Si monomers on SiO 2 to be 0.47±0.09 eV. Simulations of the temperature-dependent supercritical cluster density lead to an estimated activation energy of 0.42±0.01 eV and an estimated surface diffusion coefficient prefactor of 0.1±0.03 cm 2 /s.
Formation of polysilicon films by catalytic chemical vapor deposition (cat-CVD) method
Silicon films are deposited by a new plasma-free and low-temperature deposition technique, the catalytic chemical vapor deposition (cat-CVD) method, in which deposition gases are decomposed by reactions with a heated catalyzer placed near substrates. It is found that polysilicon films of a grain size of around 0.1 µm can be easily obtained at substrate temperatures lower than 450°C by this cat-CVD method when gas pressure Pg is below a certain critical value, although films are amorphous even for substrate temperatures higher than 450°C when Pg is larger than such a critical gas pressure.
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.