抄録
This article reviews recent work concerning the surface production and loss mechanisms of CFx radicals and their role in polymer deposition processes occurring in radio-frequency plasmas in fluorocarbon gases used for the selective etching of SiO2 layers in microelectronic device fabrication. In capacitively-coupled plasmas, CFx radicals are often produced predominantly at the powered electrode surface. In fluorine-rich plasmas the instantaneous back-scattering of neutralised, fragmented incident CFx+ ions is the dominant mechanism. Simultaneously, the radicals are destroyed by recombination at the various surfaces of the reactor. This process is most efficient when the fluorine atom concentration is high, and probably leads to the re-creation of volatile CF4. Therefore, the different reactor surfaces can behave either as net sources or sinks for the radicals. When the fluorine concentration is low, another surface production mechanism dominates the production of CF2, and involves a long-lived surface intermediate. This mechanism is linked to the formation of a polymer layer at the surface via heavy neutrals and ions formed in the gas phase by concatenation reactions of CF2 radicals. Finally, the results obtained in higher density (inductively-coupled, electron cyclotron resonance and helicon) sources is compared to the results in capacitively-coupled sources. In this case, similar surface production and loss mechanisms occur, but the relative importance is changed due to the higher degree of fragmentation, the higher ion fluxes and the lower gas pressure.
