The study of the kinetics of thin-film lithium niobate reactive ion etching in a fluorine-containing plasma

Abstract

The present paper aims to investigate the kinetics of reactive ion etching (RIE) of thin-film lithium niobate (TFLN, X-cut) in a mixture of SF6/Ar with an ICP/CCP plasma without taking into account the real structure of TFLN. The paper provides a description of the RIE mechanism, including as of a topochemical reaction of TFLN etching with the formation of non-volatile etching products (LiF). Series of kinetic curves were plotted. To study the TFLN RIE kinetics, we used the methods of optical spectral reflectometry, X-ray energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). It is shown that the TFLN RIE rate is inversely proportional to the pressure during the process and drops by an order of magnitude as the pressure increases from 0.005 mbar to 0.1 mbar. This study is the first to reveal that at pressures below 0.08 mbar, the RIE rate reaches the maximum at a percentage of SF6 ≈ 5%. An explanation for the presence of an extremum at given percentage is proposed based on Langmuir adsorption kinetics theory. The linear dependences of the TFLN RIE rate on the powers at the ICP and CCP sources are shown. It is for the first time that the time dependences of RIE at different stages of the topochemical reaction are demonstrated. Differences in the LiF growth mechanisms on the TFLN surface are shown using XPS and EDS analysis. This study is the first to demonstrate the effect of plasma heating of TFLN on the transition between the induction period and the stage of etch rate growth during the topochemical reaction.