Hydrogen in hydrofluorocarbon plasmas plays an important role in silicon nitride (Si 3 N 4 ) reactive ion etching. This study focuses on the elementary reactions of energetic CHF þ 2 and CH 2 F þ ions with Si 3 N 4 surfaces. In the experiments, Si 3 N 4 surfaces were irradiated by monoenergetic (500-1500 eV) beams of CHF þ 2 and CH 2 F þ ions as well as hydrogen-free CF þ 2 and CF þ ions generated by a massselected ion beam system and their etching yields and surface properties were examined. It has been found that, when etching takes place, the etching rates of Si 3 N 4 by hydrofluorocarbon ions, i.e., CHF þ 2 and CH 2 F þ , are higher than those by the corresponding fluorocarbon ions, i.e., CF þ 2 and CF þ , respectively. When carbon film deposition takes place, it has been found that hydrogen of incident hydrofluorocarbon ions tends to scavenge fluorine of the deposited film, reducing its fluorine content.
In this review, we discuss the progress of emerging dry processes for nanoscale fabrication of high-aspect-ratio features, including emerging design technology for manufacturability. Experts in the fields of plasma processing have contributed to addressing the increasingly challenging demands of nanoscale deposition and etching technologies for high-aspect-ratio features. The discussion of our atomic-scale understanding of physicochemical reactions involving ion bombardment and neutral transport presents the major challenges shared across the plasma science and technology community. Focus is placed on advances in fabrication technology that control surface reactions on three-dimensional features, as well as state-of-the-art techniques used in semiconductor manufacturing with a brief summary of future challenges.
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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