Plasma characterization in sputtering processes using the Langmuir probe technique

The Langmuir probe technique, which has long been used in the field of plasma physics, can be a very powerful tool in characterizing the sputtering process. In this context, theoretical formalism, design requirements and the experimental procedures necessary for the application of this technique to both r.f. and d.c. sputtering are presented. It is shown that the plasma parameters can be determined in a simple way only if the probe operation is in the orbital motion limited regime. This condition is fulfilled for a cylindrical probe when the ratio of the probe radius to the Debye length of the plasma is less than 3. In the case of r.f. discharges erroneous data are obtained if a large r.f. current is flowing to the probe. This current can be blocked by a suitable LC circuit. Using the Langmuir probe technique the variations in the plasma parameters in d.c./r.f. sputtering discharges as a function of target voltage/power and argon pressure are determined. (Auth.)