Peculiarities of Ion and Neutral Transport in Plasma Etch Applications

The continuous shrinkage of critical dimensions, introduction of new materials, and increase of integration complexity in semiconductor technology imposes stringent requirements to plasma processing techniques. The full utilization of existing process techniques and the development of new ones is impossible without a detailed understanding of the transport of charged and electrically neutral species within small etch features on a nanometer scale. At the same time, control over the transport of reactive ions and neutrals for surface interaction remains a vexing challenge in the industry and requires novel methods for further process improvement.

This presentation reviews a few important aspects of ionic and neutral species transport through microscopic dimension features in technological plasmas. We focus on methods for effective control over the key process parameters, including the ion and radical fluxes, ion energy, and ion angular distribution and consider advanced manipulation techniques for effective delivery of the reactive species to the targeted areas. Additionally, we describe various experimental methods to characterize ion and neutral transport and charge effects through the features with conductive and insulating sidewalls. Ion and neutral transport characteristics are monitored using commercially available and custom-made via structures, which are attached to the front of the sampling orifice of a mass spectrometer and a very sensitive electrostatic probe. Applying accelerating voltages of different tailored waveforms and frequencies to the structures enables a comprehensive charge effect study for conductive and insulating sidewalls. The relative radical densities for diatomic gas plasmas can be derived from the ionized mass intensity counts at electron energies below the dissociative ionization thresholds. The transport of atomic radicals (O* and N* in this study) is characterized by measuring their fluxes at the sample exit as a function of the aspect ratio.