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Optical loss in silicon microphotonic waveguides induced by metallic contamination
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Image of FIG. 1.
FIG. 1.

Illustration of the mechanism to which the optical loss is attributed. During RIE, sputtered metal atoms react with the silicon sidewall to form a dilute silicide. The silicide is difficult to remove and induces an optical loss that is comparable to loss induced by a metal. The metal hard mask was thoroughly stripped before optical characterization.

Image of FIG. 2.
FIG. 2.

Scanning electron micrograph of the high-loss waveguide with the largest sidewall roughness observed in this study. This order of roughness is not sufficient to account for the observed loss. The waveguide was fabricated with a Co hard mask. The roughness on the top surface of the thick under-cladding is due to thin lift-off imperfections partially masking the waveguide surroundings during RIE until they were sputtered away.

Image of FIG. 3.
FIG. 3.

STEM-EDS analysis of a Si waveguide etched in proximity of Pd and thoroughly cleaned with wet chemical processing. (a) Cross-sectional micrograph indicating where the EDS spectra were acquired. (b) EDS spectrum acquired from the waveguide sidewall showing no detectable Pd. [(c)–(e)] EDS spectra acquired from the waveguide sidewall showing, in average, about 5% atomic concentration of Pd in Si. The distribution of Pd along the waveguide sidewall is consistent with sputtering from the top metal mask.


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Table I.

Transparency of waveguides etched with various metal hard masks.


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Scitation: Optical loss in silicon microphotonic waveguides induced by metallic contamination