Microelectronic Engineering

Impact of surface preparation for n-type Si:P and p-type SiGe:B semiconductors on low resistance silicide contacts

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In our study, we evaluate effective silicon and germanium oxide reduction by two surface treatments to achieve low contact resistivity at the semiconductor/metal interface. These chemistries, one alkaline and the other an acidic fluorine-based treatment, were utilized on epitaxial n-type Si:P and p-type Si1 − xGex:B (x = 0.47) substrates to isolate any unique effects that may be present on doped, n-type and p-type semiconductor surfaces. To mimic plasma damage and surface conditions in an integrated process flow for actual logic devices, X-ray photoemission spectroscopy (XPS) characterization was performed on simplified blanket films after NF3-based gas cluster ion beam (GCIB) exposure and subsequent aqueous treatments. Si:P and SiGe:B surfaces both demonstrated an increase in SiO2 concentration after GCIB exposure, with SiGe:B surfaces showing a preferential SiO2 surface oxidation. Subsequent acidic treatment showed reduction in SiO2 concentration on both epitaxial surfaces, with the alkaline (basic) treatment showing little change in surface composition. Electrical characterization on simplified contact structures showed a benefit in contact resistivity of 15–23% in Si:P and 10–13% in SiGe:B for the chemistries evaluated.