Influence of water background pressure on removal rates of SiO2, Si and photo resist in reactive ion beam etching

Abstract

Process stability and reproducibility are indispensable for the high-precision production of optical components using reactive ion beam etching. The influence of residual water on the etching mechanism of SiO${}_2$, Si and a photo resist has been investigated using the feed gas mixture of CHF${}_3$ and O${}_2$ with a radio-frequency broad beam ion source. Removal rates were determined for all materials at different water background pressures and etching yields were calculated using current density measurements of the ion beam. The composition of the reactive ion beam was investigated at three water background pressures using energy selective mass spectrometry. The composition of the near-surface was analyzed using two complementary techniques: time-of-flight mass spectrometry and X-ray photoelectron spectroscopy. A steady state oxygen-containing hydrocarbon and Si(OF) layer is found to form during reactive ion beam processing. A correlation is identified with the ion beam composition, whereby the composition and thickness of this layer is dependent on the water background pressure. Consequently, the etching yields and selectivities for the investigated materials are systematically altered. The technological consequences for reactive ion beam etching are discussed.