In 1972, Paul Boumans introduced the following equation for the sputtering rate, q, in GD-OES(1)
where q is in mass/s, CQ is a sputtering constant which may vary with the plasma gas species but not with current, potential or pressure in the source, ig is the current, Ug the voltage and U0 a turn-on voltage, typically 300 V in DC operation.
In 1994, Payling suggested a modification to this equation when he found sputtering rates were not quite linear with voltage(2)
where N = 0.74. With the modified equation, U0 is typically about 400 V in DC operation, so that when the two equations are plotted together they appear very similar. As a result many continue to use the original Boumans' equation.
Blue points are original equation, red points are the modified equation
The sputtering rate can also be expressed as
where Pg is the power and P0 is a constant. Since P0 is generally quite small, perhaps 2-3 W, the sputtering rate is nearly proportional to power. But also depends on the carrier gas pressure in the discharge source.
- P W J M Boumans, Anal. Chem. 44, 1219 (1972).
- R Payling, Surf. Interface Anal. 21, 791 (1994).
First published on the web: 15 May 2000.
Authors: Richard Payling & Thomas Nelis