Large fluorocarbon ions can contribute to film growth during plasma etching of silicon

The preferential etching of SiO2 over Si in fluorocarbon plasmas occurs in part through the growth of a fluorocarbon layer. Large CxFy+,0 (x>1) ions and radicals have been observed in etching fluorocarbon plasmas, but their role in the etching processes has not been clearly identified. Here we use mass-selected 5-200 eV C3F5+ and C2F4+ ion beams to form nanometer thick fluorocarbon and SixCyFz films on H-Si(100). Monochromatic x-ray photoelectron spectroscopy (XPS) shows that the average elemental and chemical content of the deposited film is nearly independent of ion identity and kinetic energy. The chemical nature of the fluorocarbon film instead is controlled largely by surface chemical and diffusion processes. However, ion energy and structure do control the fluorocarbon film morphology. Atomic force microscopy shows that 200 eV C3F5+ ion impact forms large oblong pits in the Si substrate that are similar to30 nm deep and similar to200 nm across. No large pits are observed in the Si substrate for 25 eV C3F5+ bombardment. XPS depth profiles of the films depend strongly upon ion energy and structure where the spatial distribution of the F depth profile increases with incident ion energy for both C3F5+ and C2F4+. Higher F content is found deeper in the surface and the SixCyFz buried interface is thickest at higher ion energies. These results are discussed in terms of the role of large ions and radicals in etching fluorocarbon plasmas. (C) 2002 American Institute of Physics.