Ion-bombardment-enhanced plasma etching of tungsten with NF3/O2

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Abstract
Ions and neutrals sampled from a NF3/O2 etching plasma were observed by a quadrupole mass spectrometer and cylindrical mirror ion energy analyzer to investigate ion-bombardment-enhanced etching of tungsten. Dc biasing of a 13.56 MHz, 2.7 Pa, 1.24 W/cm2 , 3/1 NF3/O2 glow discharge raised the average ion energy bombarding the grounded electrode from 35 to 172 eV concurrent with an increase in the ion current by a factor of 3. Total conversion of NF3 to N2 and F2 occurred under these conditions yielding a typical etch rate of polycrystalline tungsten of 150 nm/min. The primary ion observed was WF+5. The WF6 etch product concentration was independent of ion energy, but correlated strongly with ion current. The results support a damage-induced chemical reaction as the enhancement mechanism.

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