Mitigating the effects of surface charging during high aspect ratio plasma etching using voltage waveform tailoring

High aspect ratio (HAR) plasma etching of nanoscale features using halogen containing gas mixtures faces major challenges posed by shrinking features sizes, increased aspect ratio and less tolerance for feature distortion. Electrostatic charge effects and the resulting deflection of electrons and ions can be a major cause of feature distortion and etch rate reduction during the processing of non-conductive materials such as SiO_2. The use of non-sinusoidal voltage waveforms as a means of power coupling has become an area of interest due to its potential to control electric field and charged particle dynamics in the sheath region. In this work the influence of tailored voltage waveforms on the distributions of surface incident electrons and ions in a capacitively coupled CF₄ containing plasma, operated at 40 mTorr, was investigated using the Hybrid Plasma Equipment Model (HPEM). The applied waveform consists of 5 consecutive harmonics with a base frequency of 1 MHz and fixed relative amplitudes. Based on the energy and angularly resolved fluxes from the HPEM, a via etch through SiO₂ was simulated using the Monte Carlo Feature Profile Model (MCFPM).  The resulting features were evaluated with respect to surface charge distribution. feature deformation and etch rate.