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

In semiconductor production, the wafers should be processed in different chambers which are readily available, rather than waiting for the right chamber. To avoid these time delays, and the associated cost, chamber matching is generally carried out. This study examines the impact of varying the concentrations of oxygen/fluorine and the operating pressure in an SF6–O2 plasma in two capacitively coupled plasma etch chambers with different geometries. Silicon wafers were used to investigate the anisotropic nature of the 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%. The results showed that in both chambers the atomic concentrations of fluorine increased rapidly when the percentage of oxygen in the SF6 plasma was increased to 20%, and decreased with further addition of oxygen at 10 mTorr/200 W. However, the peak of fluorine density occurred at a higher oxygen percentage (>20%) when the operating pressure was increased to 600 mTorr. Scanning electron microscopy showed an etch feature with a minimal lateral depth at various oxygen concentrations in both chambers. A qualitative theoretical analysis of the ion energy distribution and its correlation with the etch rate and the density of F in SF6–O2 plasma is also presented. In conclusion, chamber matching can be achieved through the experimental investigations carried out in this study, focusing on chamber geometry, fluorine/oxygen concentrations and operating pressure to achieve optimal etch rates and profile