No abstract

Effects of interfaces and thermal annealing on the electrical performance of the SiO 2 /Si 3 N 4 /Al 2 O 3 ͑ONA͒ stacks in nonvolatile memory devices were investigated. The results demonstrated the principal role of Si 3 N 4 /Al 2 O 3 and Al 2 O 3 /metal-gate interfaces in controlling charge retention properties of memory cells. Memory devices that employ both electron and hole trappings were fabricated using a controlled oxidation of nitride surface prior to the Al 2 O 3 growth, a high-temperature annealing of the ONA stack in the N 2 +O 2 atmosphere, and a metal gate electrode having a high work function ͑Pt͒. These devices exhibited electrical performance superior to that of their existing SiO 2 /Si 3 N 4 / SiO 2 analogs.

Nano-crystalline carbon films possessing a prevailing diamond or a graphite character, depending solely on substrate temperature and deposition time, can be deposited from a methane–hydrogen mixture by the direct current glow discharge plasma chemical vapor deposition method. In this study we investigate the evolution of nano-crystalline carbon films deposited in the 800–950 °C temperature range onto silicon substrates aiming to enlight the physicochemical processes leading to the formation of nano-diamond films. While at a deposition temperature of ∼880 °C the formation of a thin precursor graphitic film is followed by deposition of a film of diamond character, at higher and lower temperatures the films maintain their graphitic character. The morphology of the films and their growth rate vary with deposition temperature: slower growth rates and higher film roughness are obtained at lower temperatures suggesting the importance of kinetic effects during the growth process. For deposition times longer than ∼60 min, similar morphologies are obtained irrespectively of the deposition temperature. A preferred spatial alignment of the basal planes of the graphitic film at the interface with the silicon substrate was determined. The alignment was found to differ with deposition temperature: at 800 and 880 °C the alignment occurs along the graphitic â axis perpendicular to the silicon substrate, while at 950 °C the ĉ axis is aligned perpendicular to the silicon substrate. However, it was determined that for films a few hundred nm thick close to the evolving surface the films display a preferred alignment of the basal planes vertical to the surface, irrespectively of their orientation at the interface. The reason for this alignment is suggested to be associated with a stress relaxation mechanism in the graphitic films. It was determined that film growth is accompanied by the evolution of large local stresses which obtain a maximum value for the films deposited at 880 °C. The relaxation of these stresses is suggested to lead to the transformation of the graphitic material into the diamond phase. The narrow range of temperatures (880+/−10 °C) which enables the formation of the diamond phase indicates the importance of hydrogen adsorption/desorption processes in the nucleation and growth of the nano-crystalline diamond films. The morphological evolution of the films was analyzed by atomic force microscope. By electron diffraction and high-resolution transmission electron microscopy the phase composition of the films and their microstructure were examined. The alignment of the graphitic films within the near-surface region of the evolving films as a function of the deposition time and temperature was investigated by angle-resolved near edge x-ray absorption fine structure measurements. Raman spectroscopy was applied to determine the presence of stresses within the films and their phase composition.

Nanocrystalline carbon films possessing a prevailing diamond or graphite character, depending on substrate temperature, can be deposited from a methane hydrogen mixture by the direct current glow discharge plasma chemical vapor deposition method. While at a temperature of ∼880 °C, following the formation of a thin precursor graphitic film, diamond nucleation occurs and a nanodiamond film grows, at higher and lower deposition temperatures the films maintain their graphitic character. In this study the hydrogen content, density and nanocrystalline phase composition of films deposited at various temperatures are investigated. We aim to elucidate the role of hydrogen in nanocrystalline films with a predominant diamond character. Secondary ion mass spectroscopy revealed a considerable increase of the hydrogen concentration in the films that accompanies the growth of nanodiamond. It correlates with near edge x-ray adsorption spectroscopy measurements, that showed an appearance of spectroscopic features associated with the diamond structure, and with a substantial increase of the film density detected by x-ray reflectivity. Electron energy loss spectroscopy showed that nanocrystalline diamond films can be deposited from a CH4/H2 mixture with hydrogen concentration in the 80%–95% range. For a deposition temperature of 880 °C, the highest diamond character of the films was found for a hydrogen concentration of 91% of H2. The deposition temperature plays an important role in diamond formation, strongly influencing the content of adsorbed hydrogen with an optimum at 880 °C. It is suggested that diamond nucleation and growth of the nanodiamond phase is driven by densification of the deposited graphitic films which results in high local compressive stresses. Nanodiamond formation is accompanied by an increase of hydrogen concentration in the films. It is suggested that hydrogen retention is critical for stabilization of nanodiamond crystallites. At lower deposition temperatures an excess of hydrogen in the deposited layers helps to prevent the densification of the films and accumulation of microstresses and consequently the films maintains its graphitic character. At higher temperatures the hydrogen content in the films is relatively low and the film maintains its graphitic character.

No abstract