Deposition of Silicon by Electron Irradiation of Tetramethylsilane

The deposition of thin silicon films by the electron beam dissociation of adsorbed tetramethylsilane has been investigated. Growth rate was studied as a function of P the vapor pressure of tetramethylsilane, T the substrate temperature, and J the current density. It was found that there is a region where the value of the growth rate can be calculated from the expression r=KPJ expa/T, where K and a are constants. Assuming a model in which a=Q/R and K=cσ, where R is the gas constant and c is a calculable constant, Q, the heat of adsorption, was found to be 11.6 kcal/mole and σ, the collision cross section, was determined to have the unexpectedly high value of 3.86×103 Å2 for 300-V electrons. Electron diffraction and transmission electron microscopy showed the as-deposited films to be amorphous. The resistivity of these films varied with thickness and showed a minimum value of approximately 5×104Ω·cm when the film thickness was between 1000 and 1500 Å. Thinner films were less conductive because the high amount of stress in the film increased scattering. Thicker films were less conductive because the impurity content of the films increased with film thickness. Heat treating at 800°C produced extensive grain growth and resistivities dropped by a factor of 103. Annealing at 300°C for a few hours decreased the resistivity by about a factor of two although no grain growth occurred at this temperature.