Abstract

The recent discovery of microscopic particles in plasmas used for etching, deposition, and sputtering has generated much scientific and technological interest. Key issues involve the formation, transport, and control of particles in plasmas. In some cases, the plasma glow is the single greatest contributor to surface contamination during the processing. Tool/process contamination may far exceed the level of surface contamination contributed by the exterior cleanroom. Laser light scattering studies have shown that suspension of particles is ubiquitous in all plasma processes. This result has been confirmed in both laboratory and manufacturing tools. Studies have also shown that suspended particles are negatively charged and are influenced by strong and weak electrical field effects in the plasma. One result of this is particle trapping, the electrostatic suspension and confinement of a charged particle in a slightly perturbed region of the discharge. The presence of a silicon wafer on an electrode, a common configuration used in plasma processing, creates significant particle traps along the edges and center of the wafer. This exacerbates the effect of plasma contamination by collecting and maintaining particles about sensitive wafer surfaces. It also provides increased residence time in the plasma for particle growth. Often, the result is a high particle count around the edges of wafers or other trapping regions in the plasma tool. Frequently, these findings are inappropriately attributed to faulty handling or storage of wafers and the contribution of the tool is overlooked. Controlling plasma contamination will be an important aspect of future equipment and process design and of high technology leadership.

© 1991 Optical Society of America