MODEL FOR BEAM-INDUCED DEPOSITION OF THIN METALLIC-FILMS

Recent advances in focused ion beam (FIB) technology have expanded the applications of beam-induced deposition (BID) of thin metallic films in microcircuit fabrication. This paper provides a model for the BID process by examining the effects on film growth and morphology of various deposition parameters including the incident ion flux, adsorbate coverage of the substrate and residue, residue sputtering, and energy deposition by incident ions. Residue nucleation is examined, and a significant difference between adsorbate coverage of the substrate and residue is found to introduce large thickness variations in the film. Adsorbate depletion which is caused by an increase in the ion beam current density or target temperature results in a larger energy deposition per residue molecule and is proposed as a mechanism for enhancement of the metallic purity and electrical conductivity of the residue. By investigating the film growth rate during periodic ion bombardment characteristic of focused ion beams, the model demonstrates that the maximum film growth rate is obtained by maximizing the scanning frequency. The model is found to quantitatively agree with published experimental results.