Non-Sinusoidal-Waveform for High Aspect Ratio Etching

As semiconductor devices become more highly integrated, the plasma etching is challenged to increase aspect ratio in the various semiconductors. The plasma characteristics required to improve the etching rate and profile are to maximize the physical etching by injecting ions with the desired energy accelerated by the voltage applied to the plasma sheath at a high density as close to the vertical as possible onto the substrate. At this time, electrons have a relatively wide angular distribution compared to ions, so ions accumulate on the bottom and side walls, and electrons accumulate on the top which ultimately slows down the etching rate and causes distortion in the profile. 

To solve this problem, several methods were introduced to apply pulsing or multiple frequencies so that the more accelerated ions can reach the bottom by breaking through the electric field created by the accumulated ions and electrons on the substrate, but since it does not solve the fundamental problem of ions and electrons accumulation. Non-sinusoidal-waveform is the most efficient method among the methods announced so far. It can control the energy and angular distributions of ions and electrons by shaping the bias voltage. 

In this content, the analysis of output waveform for monitoring the plasma characteristics, and the design consideration of voltage waveform are introduced.