Optical diagnostic of LiNbO3 etching in NF3/Ar ICP plasma: Part I

Abstract

Optical emission spectroscopy is informative and nondisturbing technique for diagnostics of various plasmas used for material treatment. In this work the distinctive features of emission spectra of NF3/Ar plasmas of various compositions formed during the plasma chemical etching of lithium niobate were studied. It was found that the wavelength region (220–290 nm) is of a particular interest for LiNbO3 etching control because it can be used to determine "endpoint" in multistep processes with sequencing of plasma etching and wet cleaning for LiF barrier layer removal. The influence of RF Inductively Coupled Plasma (ICP) power, total pressure, bias voltage, NF3 flow rate, and temperature of the susceptor was studied for five different ratios of NF3/Ar flow rates: NF3 (1.5 sccm)/Ar(9.2 sccm), NF3(7.0 sccm)/Ar(4.9 sccm), NF3(7.8 sccm)/Ar(10.8 sccm), NF3 (9.4 sccm)/Ar(3.3 sccm), NF3(11.7 sccm)/Ar(5.4 sccm). It has been shown that a decrease in total pressure and an increase in ICP power lead to an increase in the relative intensities of both argon and fluorine lines. At the same time the variations of bias voltage and susceptor temperature did not have a significant impact on spectral lines intensity of Ar and F. Optical actinometry technique was used to determine concentration of atomic fluorine in NF3/Ar plasmas at various process conditions to demonstrate a correlation between etching rate of LiNbO3 and fluorine atoms concentration.