Mass-analyzed CF_(x)~(+) (x=1,2,3) ion beam study on selectivity of SiO_(2)-to-SiN etching and a-C:F film deposition

摘要

To clarify the origins of high selectivity in SiO_(2)-to-SiN etching in fluorocarbon gas plasma, mass-analyzed CF_(x)~(+) (x=1,2,3) ions with a definite kinetic energy of 250-2000 eV were irradiated on SiN and SiO_(2) surfaces. Selectivity in SiO_(2)-to-SiN etching varies greatly for different CF_(x)~(+) ions. For CF_(3)~(+) ions, the etch yield of SiN is almost the same as that of SiO_(2), causing poor selectivity. For CF~(+) ions, on the other hand, the etch yield of SiN is much smaller than that of SiO_(2). An amorphous fluorinated carbon (a-C:F) film grows without any neutral radicals on the SiN surface at energies below 1250 eV and on the SiO_(2) surface at energies below 500 eV due to CF~(+) ion irradiation. The difference in threshold energy of a-C:F film deposition causes high selectivity in SiO_(2)-to-SiN etching. Slight etching of substrate films first takes place at the initial stage of deposition, then etching stops, and a homogeneous a-C:F film is grown. Accumulated carbons during the initial etching reaction modify the surface reaction layer, which causes drastic changes in reactions such as etching to "etch stop" and a-C:F film growth.