In situ plasma contamination measurements by HeNe laser light scattering: A case study

Abstract

Using a simple, inexpensive HeNe laser and a video camera to measure light scattering intensity and location, particulate contamination in an Si02 sputtering process used in semiconductor manufacturing has been studied under actual process conditions in a class 10 cleanroom. Particulates were observed during all aspects of the sputtering process. It was seen that portions of the process which resulted in mechanical stress on the tool walls produced the greatest flux of particles inside the tool. However, the sputtering step was the major contributor to contamination in this chemically simple process, because of its long duration and the stress-inducing nature of the plasma. The contamination level in this plasma is estimated to exceed the cleanroom ambient by three orders of magnitude. As in other process plasmas, the particles were suspended at the sheath/plasma boundary. It is argued that a relatively weak electrostatic field is required for gravitational counterbalance of these highly charged particles. Finally, the use of “tool tapping” is described for studying the effect of mechanical stress on plasma contamination. This simple yet effective technique can dramatically reduce particulate contamination from tool walls. © 1990, American Vacuum Society. All rights reserved.