Improved Relative Sputtering Rate
As described in Pt 1, the relative sputtering rate for a material composed of different elements is given approximately by(1)
where ci is the mass fraction of element i and qi is relative sputtering rate of the pure material.
However, when values calculated with this equation are compared with experiment, the calculated values are often more extreme (ie too dominated by the slower sputtering species) than measured values.
The equation assumes that each species behaves independently, and the discrepancy with experiment suggests that this is not entirely valid. A simple way to include some form of general interaction is to use an equation of the form
where d is a fitted parameter. When d = 0, the original equation is obtained. The following graph shows how the relative sputtering rate might vary in a binary alloy of elements a and b for different values of d, from -0.3 to 0.6, as a function of the content of a, where the relative sputtering rate of a is 7.06 (Zn) and b is 0.36 (Al).
The following graph shows experimental results(2,3) for Zn-Fe with d = 0 and 0.6.
(1) R Payling, in R Payling, D G Jones and A Bengtson (Eds), Glow Discharge Optical Emission Spectrometry, John Wiley, Chichester (1997), pp 260, 267.
(2) S Miyake, M Koda and T Yoshii, Nippon Steel Eng. Rept. 65, 51 (1992).
(3) Y Matsumoto, N Fujino and S Tsuchiya, Transactions ISIJ 27, 891 (1987).
First published on the web: 19 June 2000.
Author: Richard Payling