In-situ Particulate Contamination Studies In Process Plasmas

Abstract

Laser light scattering measurements show that a variety of processing plasmas used during semiconductor fabrication produce significant amounts of in - situ particulate contamination. The particles are produced by chemical and /or mechanical means during plasma exposure. In etching plasmas, simultaneous measurement of particulates by laser light scattering and of plasma negative ions by two -photon laser -induced fluorescence indicates the particles are negatively charged and are electrostatically trapped at the sheath boundaries. Similar observations have been obtained in sputtering plasmas. Mechanisms for particle formation are suggested. In some cases, nucleation and growth from plasma negative ions and etch products is indicated. In other cases, stress -inducing processes may fracture thin films on chamber surfaces thereby injecting particles into the plasma. These particles become negatively charged by acquiring electrons from the plasma. In each case, the particles are suspended at the sheath boundaries and drop onto the wafer when the rf power is turned off, thereby contaminating critical product surfaces. The use of an inexpensive IIeNe laser for monitoring particle contamination levels during processing is discussed along with implications of this work for dry process equipment technology.