We address current challenges in the fundamental understanding of physical and chemical processes that occur in the fabrication of the transistor gate stack structure. Critical areas include (1) the interface between bulk silicon and high-dielectric-constant (high-ĸ) insulators, (2) the interface between high-ĸ insulators and advanced gate electrodes, and (3) the internal interfaces that form within dielectric stacks with nonuniform material and structure compositions. We approach this topic from a fundamental understanding of bonding and electronic structure at the interfaces, and of film-growth kinetics in comparison with thermodynamics predictions. Implications for the dielectric/electrode interface with metallic gates and issues with integration will also be presented.

The phase equilibria in the ternary Ti-Ga-N have been investigated. Interfacial reactions in Ti/GaN contacts have been studied by diffusion couple experiments. The ternary phase Ti2GaN was confirmed by x-ray diffraction in bulk samples as well as in massive Ti/GaN diffusion couples and annealed Ti thin films on GaN. The diffusion path in samples, annealed at 850°C in Ar gas, is GaN/TiN/Ti2GaN/Ti3Ga/Ti. A planar TiN layer forms in direct contact to GaN and governs the electrical properties of annealed Ti/GaN contacts. Thin film contacts were fabricated by sputtering Ti on MOVPE grown n-GaN (5×1017cm−3) and subsequent rapid thermal annealing in an Argon atmosphere. Initially non-linear current-voltage characteristics become ohmic after annealing and a specific contact resistance of approximately 10−2 Ωcm2, measured with the circular transmission line method, was found after annealing at 9000C for 1 min.