Changes in the densities of fluorocarbon radicals and fluorine atoms in a size-scalable large-area compact permanent magnet electron cyclotron resonance etching plasma source employing C4F8 gas with CH4 addition have been investigated. Measurements using infrared laser absorption spectroscopy and actinometric optical emission spectroscopy show that, for a pure C4F8 plasma, the dominant species is CF2 radicals with a density of the order of 1013 cm−3, followed by fluorine atoms, CF3 and CF2 radicals which have a density an order of magnitude lower at 1012 cm−3. The densities of the different fluorocarbon radical species were found to display different dependencies on increasing CH4 gas addition. Hollow cathode absorption spectroscopy was used to estimate the carbon atom density for the first time, to the best of our knowledge, in an etching plasma. The carbon atom density in the plasma increases linearly with CH4 gas addition between 20 and 80%. Analysis of actual SiO2/Si etching revealed that the etch selectivity and carbon atom to fluorine atom ratio follows a similar trend indicating a direct correlation between the carbon atom density in the plasma and the etch selectivity.
Diagnostics of fluorocarbon radicals and fluorine (F) atom species in a size-scaleable large-area permanent magnet electron cyclotron resonance (ECR) etching plasma employing CF4 and C4F8 gases are carried out. Non-intrusive infrared laser diode absorption spectroscopy and actinometric measurement techniques are used in evaluating the performance of the permanent magnet ECR plasma source and in studying the kinetic processes associated with etching plasma chemistry. Successful measurements of the absolute CF and CF2 radical and F atom densities have been achieved. In particular for C4F8 plasma, enhanced CF and CF2 radical densities which afford higher selectivity in the etching of SiO2 on Si are discussed. At a pressure of 0.4 Pa and an input microwave power of 900 W the CF and CF2 radical and F atom densities in C4F8 plasma were 1.7×1013 cm-3, 6.0×1013 cm-3 and 1.5×1013 cm-3, respectively. These results are also discussed in comparison with results for a conventional electromagnet ECR plasma source.
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