Experimental investigation of SF₆–O₂ plasma for advancement of the anisotropic Si etch process

This study examines the impact of varying the internal process parameters, such as the concentrations of oxygen and fluorine in a SF₆–O₂ plasma, in two capacitively coupled plasma etch chambers with different geometries. Silicon wafers were used to investigate the anisotropic nature of etch profiles. The oxygen and fluorine concentrations were measured via optical emission spectroscopy using the actinometry technique, which requires the electron energy distribution function to remain unchanged under the different plasma conditions employed in this work. A Langmuir probe was used to investigate the electron energy distribution function, where the chamber pressure, power, and process duration were kept constant and the oxygen concentration was varied from 0 to 60 vol. %. The results showed that in both the chambers, the atomic concentrations of oxygen and fluorine increased rapidly when the fraction of oxygen in the SF₆ plasma was increased to 20 vol. % and decreased with further addition of oxygen. Scanning electron microscopy showed an etch feature with a minimal lateral run-out at an O₂ concentration of 20 vol. % in both the chambers. The distribution of electron energy and the concentrations of oxygen and fluorine exhibited similar patterns as functions of the oxygen concentration in the SF₆ plasma in the two chambers, but the values were different because of the different chamber geometries, which also affected the silicon etch rate and lateral run-out.