KINETICS OF ION-BEAM NITRIDATION (IBN) OF SI AND OF MBE-GROWN GE AND SIXGE1-X ALLOYS - THE ROLE OF ION ENERGY, ION DOSE AND SUBSTRATE-TEMPERATURE

The growth of thin nitride films of Si, MBE-grown Ge and SixGe1-x alloys on Si by low energy ion beam nitridation (IBN) has been investigated both theoretically and experimentally. This paper focuses on the modeling of the kinetics of IBN thin film growth. The model is based on our recent experimental results and includes the present understanding of atomic collisions at low energy and the thermal diffusivity and chemical reactivity of point defects generated by IBN. Three variables relevant to ion beam nitridation (IBN), ion energy, ion dose, and substrate temperature, are studied for their effect on the growth of nitride films and their resulting properties. These variables are shown to constitute attractive processing parameters to control nitride properties in a way that cannot be achieved thermally. The proposed model takes into account the range and range straggling of the ions, physical sputtering, desorption, chemical reaction and enhanced mobility of point defects created in the collision cascade. Based on this model, the film thickness and stoichiometry at any stage of IBN can be computed using finite differences calculation methods. Analytical expressions can also be derived for the two limiting cases of "low dose" or initial stage, and "high dose" which corresponds to growth saturation at steady state. Such modeling is shown to be useful in determining the chemical processes which govern the reactive growth of IBN nitride thin films. IBN is shown for instance to be a reaction of order greater than one. Diffusivity and reactivity are found to be competitive during IBN, quite the opposite of ion beam oxidation (IBO), where reactivity dominates over diffusivity.