Particle contamination characterization in a helicon plasma etching tool

Abstract

There is much current interest regarding the formation, transport, charging, and behavior of particulate contamination in high density plasma tools, as these tools are generally regarded as the future of plasma processing for the semiconductor industry due to the need to obtain greater anisotropy and faster process rates concurrently with reduced surface damage. Because of the low pressures in which these tools typically operate (<5 mTorr), the likelihood of homogeneous nucleation processes leading to particle contamination problems is low. Similarly, the effect of ion drag is also expected to be greater, possibly leading to reduced particle trapping effects. Yet, few laser light scatter studies have been performed in high density plasma tools. This study is the first in situ characterization of particle contamination in a plasma etching tool using a helicon source. It was performed during normal process conditions for poly-Si etching and also under intentionally altered process conditions designed to produce particles. The effect of a bipolar, electrostatic chuck on wafer particle deposition was also investigated. Results showed that under normal process conditions, few particles were deposited onto the wafer; those that were observed were attributed to thermal stress effects resulting in flaking of deposition films, probably on the quartz bell jar of the source. Results also suggest that the electrostatic chuck increased particle deposition when the clamping voltage was applied. No trapping was observed over the wafer or near the source. However, some trapped particles were observed below the wafer platform. These particles showed unusual motion, but probably have minimal effect on wafer contamination. The issues pertaining to particle contamination formation and transport in this high density plasma tool are discussed.