X-ray photoemission spectroscopy characterization of silicon surfaces after CF4/H2magnetron ion etching: Comparisons to reactive ion etching
Abstract
Silicon surfaces subjected to CF4/H2magnetron ion etching (MIE) have been characterized by x-ray photoemission spectroscopy. Low-power-density (0.274 W/cm2) 25-mTorr MIE plasmas cause fluorocarbon films on Si which are characterized by C-CFx, CF, CF2, and CF3groups. Graphitic carbon and silicon carbon type bonding can also be observed at the film/silicon interface. Thicker films are formed in hydrogen-rich CF4/H2etching gas mixtures. Carbonaceous films with significant chemical differences are produced under high-power/low-pressure MIE operating conditions (1 W/cm2 at 4 mTorr). These films are characterized primarily by C-C/C-H type carbon and a very low intensity of highly fluorinated carbon groups. The carbon/fluorine ratio is 0.8 for the films formed in a pure CF4magnetron discharge at a power density of 0.27 W/ cm2, similar to that of films formed in a conventional reactive ion etch plasma, whereas it is 2.2 for the films formed at a power density of 1 W/cm2. The carbonaceous film formed during high-power MIE does not have a dominant role in determining the silicon etching behavior in contrast to fluorocarbon films formed under low-power MIE conditions which suppress the Si etch rate. This explains the lack of SiO2/Si etch selectivity observed under high-power MIE conditions using CF4/H2in contrast to low-power magnetron ion etching where SiO2/Si etch selectivity is achieved. The formation of carbon-rich film in high-power MIE can qualitatively be explained by a large flux of highly dissociated CF4derived plasma species to the silicon surface under high-power magnetron ion etching conditions and a Si substrate temperature difference of more than 100°C between high-power MIE (>200°C) and low-power MIE (near 100 °C or less) processing. © 1988, American Vacuum Society. All rights reserved.