Electron cyclotron resonance plasma etching of photoresist at cryogenic temperatures

An electron cyclotron resonance oxygen plasma discharge was used to anisotropically etch photoresist at a low substrate temperature (−100 °C). The results of using a lower temperature are seen in a reduction in lateral etch rate, with concomitant improvement in anisotropy. Langmuir probe and flux analysis at the substrate with a quadropole mass spectrometer was used to characterize the plasma stream as a function of the operating conditions. The plasma stream flux was composed of approximately 10 times as many reactive oxygen neutrals as O2+ ions. Etch rate was found to be strongly affected by the ion power density impinging on the substrate. Four mechanisms were identified that may contribute to lateral etching. Lateral etching was observed to decrease by the combined application of rf substrate bias and low substrate temperature.