Paper EM-FrM3
Suppression of Ge-N Bonding at Ge-HfO₂ and Ge-TiO₂ Interfaces: Deposition on Nitrided Ge Surfaces, and Post-Deposition Annealing at 800°C

Friday, October 19, 2007, 8:40 am, Room 612

Differences in length scales for nano-scale order in thin film nano-crystalline HfO₂ and TiO₂ deposited on i) remote plasma-nitrided Ge(100) substrates, and ii) Si(100) substrates with ultra-thin (~0.8 nm) SiON interfacial layers are addressed. Near edge X-ray absorption spectroscopy (NEXAS) is used to determine nano-scale order through the presence or absence Jahn-Teller (J-T) distortion removal of band-edge d-state degeneracies. These studies identify a new and novel application for NEXAS based on the resonant character of the respective N K₁ and O K₁ edge absorptions; these absorptions, respectively, provide a novel way to probe correlated changes in buried interfaces and nano-scale order for as-deposited and 800°C Ar annealed HfO₂and TiO₂ thin films. After an 800°C anneal, N K₁ edge spectra indicate an essentially complete elimination of interfacial GeN interfacial bonding on the Ge substrates, but no changes in SiON interfacial layer bonding on Si substrates. As-deposited films 2 nm, 4 nm and 6 nm thick on Ge and Si with interfacial transition regions do not display J-T splittings. This has been attributed to kinetically hindered nano-crystalline grain dimensions smaller than 2 nm. In contrast, after annealing, HfO₂ and TiO₂ films on Ge display spectroscopic evidence for J-T splittings, independent of film thickness. Annealed films on SiON interfaces display J-T splittings, but only for film thickness >3 nm in which grain size is not dimensionally constrained. The spectral signature of the J-T splittings for HfO₂ films on Ge is qualitatively different than for HfO₂ films SiON interfaces on Si. This is attributed to the TM oxide bonding directly to a Ge surface devoid of interfacial GeN serving as a template for mosaic in-plane controlled HfO₂ and TiO₂ grain growth to >3.5 nm. This grain size is sufficient to promote observable J-T spittings in O K₁ spectra. Equally significant, and consistent with the mosaic template description, the half-width-half-maximum of the O K₁ edge for annealed TiO₂ films is smaller for Ge substrates, 0.5 eV as compared with 0.6-0.7 eV for SiON interfaces on Si.