Constraints on particle growth in plasmas

Many electrical discharges of technical interest are run in gases or gas mixtures that are strongly electronegative. Attachment will often be an important electron loss process. Even in discharges in gases that are only slightly electronegative, the ambipolar fields will tend to trap the negative ions and the negative ion concentrations are especially important in the plane-parallel electrode of reactor, where the electrodes maintain a cycle. The negative ion density is eventually limited by electro impact detachment (ionization) of the negative ions, and by ion-ion recombination. Particulate contamination in etching and deposition plasmas is a serious problem accounting for up to 50% of the wafer rejections. Macroscopic particles (0.01-10 microns in diameter) also will be trapped and will act like very low mobility negative ions in their transport properties and also as volume distributed surface recombination sinks for ions, electrons and radicals. Estimates are made of the various effects caused by such particles in processing plasmas