In situ diagnostics of the Si etching structures profile in ICP SF6/C4F8 plasma: Macrostructures

In this work, we studied the influence of technological parameters of plasma chemical etching of silicon on silicon etching rate, photoresist etching rate, etching selectivity of silicon in relation to a photoresist, and sidewall angle of etched structures. It was found that the silicon etching rate increases with raising percentage of SF6 in the gas mixture (25%-50%), pressure (1-2.5 Pa), high-frequency (HF) power (1000-2000 W), and bias voltage module (15-75 V) and decreases with a raising total flow rate of the gas mixture (5-35 SCCM) due to the increasing passivation efficiency of the sample surface. The etching selectivity increases with a raising percentage of SF6 and pressure and decreases with the raising total gas flow rate, HF power, and bias voltage module due to different influences of technological parameters on the photoresist etching rate. In addition, based on the obtained results, a common regularity between the sidewall angle and the optical emission spectra was revealed. The method of in situ diagnostics was proposed, namely, controlling the sidewall angle by a ratio of emission intensities of a carbon line (517.1 nm) to a fluorine line (685.8 and 703.9 nm) designated as parameter X. It was found that the sidewall angle of etched structures takes certain values depending on the value of the X parameter. The ranges of X values at which the sidewall angle is acute, right, and obtuse were estimated. So, at values of X from approximate to 0.15 to approximate to 0.35, an acute angle (from 81 degrees +/- 0.5 degrees to 89 degrees +/- 0.5 degrees) is obtained; at X from approximate to 0.35 to approximate to 0.42, a right angle is obtained (90 degrees +/- 0.5 degrees); and at X from approximate to 0.42 to approximate to 0.75, the values of the sidewall angle are in the range from 91 degrees +/- 0.5 degrees to 94 degrees +/- 0.5 degrees, no matter which technological parameters were set. Experiments were conducted for etching windows with linear dimensions from 0.5 x 20 to 2 x 20 mm.

Automated summary

In this work, the influence of various technological parameters on plasma chemical etching of silicon was investigated. It was found that the silicon etching rate, etching selectivity, and sidewall angle of etched structures are all affected by the percentage of SF6, pressure, total flow rate, high-frequency power, and bias voltage. The study also revealed a correlation between the sidewall angle and the optical emission spectra. A method of in situ diagnostics using the emission intensities of specific lines was proposed to control the sidewall angle. The experiments were conducted on windows with different linear dimensions.