To clarify the origins of high selectivity in SiO2-to-SiN etching in fluorocarbon gas plasma, mass-analyzed CFx+ (x=1,2,3) ions with a definite kinetic energy of 250–2000eV were irradiated on SiN and SiO2 surfaces. Selectivity in SiO2-to-SiN etching varies greatly for different CFx+ ions. For CF3+ ions, the etch yield of SiN is almost the same as that of SiO2, causing poor selectivity. For CF+ ions, on the other hand, the etch yield of SiN is much smaller than that of SiO2. An amorphous fluorinated carbon (a-C:F) film grows without any neutral radicals on the SiN surface at energies below 1250eV and on the SiO2 surface at energies below 500eV due to CF+ ion irradiation. The difference in threshold energy of a-C:F film deposition causes high selectivity in SiO2-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.

Etching yields of SiO2 have been determined for F+, CFx+ (x=1,2,3) ion irradiation with energy ranging from 250 to 2000 eV using a mass-analyzed ion-beam apparatus that can irradiate a single species ion to sample surfaces under an ultrahigh vacuum condition. The etching yield of CFx+ (x=1,2,3) was enhanced by the chemical effects of the ions, and both carbon and fluorine atoms from the incident ions were significant reactants. For lower energies, the etching yield increased with increasing ion energy. Above 1000 eV, the etching yield was gradually saturated with increasing ion energy. In the low ion energy region, steady etching did not occur, and an amorphous fluorinated carbon (a-C:F) film was deposited on the SiO2 surface. The ion energy region in which a-C:F film deposition occurred decreased with increasing fluorine atoms in incident CFx+ (x=1,2,3) ions.

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We report a case of pancreatic melanotic schwannoma mimicking an epithelial cystic neoplasm of the pancreas. A 67-year-old Japanese woman underwent routine ultrasonography, which showed a large cystic mass in the head of the pancreas. Contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) showed an inhomogeneous, round cystic mass, which was encapsulated, in the head of the pancreas. We performed pyrolus-preserving pancreatoduodenectomy under the tentative diagnosis of a cystic neoplasm of the pancreas. The histopathologic diagnosis was benign melanotic schwannoma. The patient is now well after 43 months of follow-up. We describe the CT and MRI findings in detail, and review the literature on previously reported cases of pancreatic schwannoma.

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