Extraction and Transport of Positive and Negative Ions in Plasma Etch Applications

A fundamental understanding of ion transport in plasma processes is paramount to enabling better etch performance and developing novel solutions to complex processes. There is a very limited number of studies on the interaction of the positive ionic species inside narrow etch features. Similarly, there are almost no experimental studies on negative ions. In this work, we characterized the extraction and transport of positive and negative ionic species from a pulsed O2/Ar ICP discharge through custom fabricated dielectric coated Si vias with aspect ratios of >10:1. Deep into the afterglow, time-resolved electrostatic probe and mass spectrometer measurements showed that the charged species only consisted of positive and negative ions. The substrate was located in front of the time and energy resolved mass spectrometer and biased by square wave pulses of different polarity to accelerate negative or positive ions toward the surface. The ion flux of both charged species was proportional to the applied bias voltage amplitude as expected. Despite the large presence of negative ions in the earlier afterglow, their transport through the biased vias was very limited during that time period, which we attribute to the via sidewall charging by mobile electrons.