Low temperature treatments to control the Si-interface properties become more and more relevant to the broad Si-based electronics and photonics technology when the back-end-of-line processing is developed and the integration of hybrid materials on the Si platform increases. In this work we have investigated effects of NH₃ nitridation of three different Si surfaces in ultrahigh-vacuum (UHV) chamber at 400 ^°C: (i) nitridation of well-defined Si(100) (2 × 1)+(1 × 2) cleaned by the high-temperature flash heating, (ii) nitridation of the Radio Corporation of America (RCA)-cleaned H-terminated Si(100) with the final HF dip, and (iii) nitridation of the RCA-treated (without the final HF dip) Si(100) which includes so-called wet-chemical oxide of SiO₂. X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy/spectroscopy measurements show that nitrogen incorporates into subsurface layers of clean Si and into the SiO₂ chemical-oxide layer, when the materials are exposed to NH₃ background in UHV chamber without a plasma source at 400 ^°C or even at room temperature. XPS results indicate that the nitridation does not remove oxygen from the SiO₂ chemical oxide. The nitridation of SiO₂ is also found to increase the density of electron levels at 3 to 4 eV above the Fermi level. Electrical measurements of atomic-layer deposited HfO₂/Si(100) capacitors with and without the nitridation support that the method has potential to decrease amount of interface defects and to control interface properties.

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