Measurement of relative sticking coefficient of nitrogen on Al/Ti in a magnetron sputtering system

Abstract

A mathematical model was simulated to predict the composition of the metallic constituents of the coatings deposited by sputtering using two metals composite target in the presence of a reactive gas atmosphere. In the development of model, value of relative sticking coefficient of reactive gas on the metallic surfaces assumes significance. Very little literature is available on the sticking coefficient of reactive gases on the metallic surfaces. In the available literature the value of sticking coefficient of reactive gases on metallic surfaces in the plasma environment has most often been assumed to be unity. Experimental data is not available at all. Therefore, the relative sticking coefficient of nitrogen for the two metals - titanium and aluminium - has been generated experimentally. The samples were polished, chemically cleaned and mounted on to the target to replicate the actual sputtering condition. These were cleaned in-situ by ion cleaning too. The coupons were then treated in nitrogen and argon plasma. X-ray photo electron spectroscopy (XPS) was utilized to analyze the treated samples. The sticking coefficient values have been generated by treating the coupons for fixed duration at different partial pressures of nitrogen as well as for different duration at fixed partial pressure of nitrogen. The sticking coefficient was found to vary from 0.423 to 0.368 when the treatment time was varied from 1 min to 30 min. The value was found to vary from 0.374 to 0.420 when the N2 flow in the plasma was increased from 5% to 40%.