Optical emission spectroscopy as a method for evaluating the change in Si etching structures profile in ICP SF6/C4F8 plasma: Microstructures

In this work, a method for in situ diagnostics of the etching profile of silicon structures (etching window sizes 15–400 μm) using optical emission spectroscopy was proposed. To determine the relationship between the etching profile and plasma parameters, the influence of technological parameters on the etching characteristics (vertical and lateral etching rate, selectivity in relation to photoresist, and sidewall angle) was studied. As a general parameter, which reflects the changes in plasma characteristics depending on the selected technological parameters, the parameter X (C/F ratio in SF6/C4F8 plasma) was introduced. Based on the results obtained, a general pattern between the lateral etching rate, sidewall angle, and optical emission spectra was identified. Thus, ranges of X values, at which the lateral etching rate does not exceed 5 nm/min for 15–30 μm structures and 15 nm/min for 100 μm structures, were estimated: 0.38 ≤ X ≤ 0.77 and 0.28 ≤ X ≤ 0.46, respectively. For 250–400 μm structures, ranges of X values, at which the sidewall angle is acute, straight, and obtuse, were determined: 0.16 ≤ X < 0.29, 0.29 ≤ X ≤ 0.41, 0.41 < X ≤ 0.75, respectively.