Ultraviolet-assisted processing of dielectric thin-films for metal oxide semiconductor applications

Oxygenation of oxide thin films was studied in this dissertation with application to metal oxide semiconductor technology. One of the main challenges envisioned for future microelectronic devices is finding a replacement gate dielectric for silicon dioxide (SiO₂) on silicon in metal oxide semiconductor applications. Several alternative high-k dielectric materials have been proposed as a solution to this problem because insertion of such a layer would allow thicker layers not subject to tunneling leakage issues encountered with ultrathin SiO₂ layers to be deposited. However, studies have indicated that new problems exist with these alternative layers. Among these issues are the formation of a low-k interfacial dielectric layer and an unacceptable level of oxygen vacancies in the films that contribute to leakage currents. In an attempt to address these issues, a three part experimental procedure has been designed to look at the role of oxygen in the thin film system. First, the formation of an interfacial layer as a function of oxygen concentration in the thin film system has been investigated. Next, ultraviolet radiation was added to a pulsed laser deposition (PLD) system for in-situ ultraviolet-assisted PLD growth of dielectric films. Through the addition of ultraviolet radiation, highly reactive oxygen species are generated which alter the oxygenation conditions and dynamically alter the films properties and final oxygenation conditions. Finally, the application of ultraviolet annealing to already deposited hafnium dioxide (HfO₂) thin films was studied to look at the possibility of more fully oxygenating the film after growth. A variety of characterization techniques indicate that both oxygen trapped in the film and oxygen that passes from the ambient through the film to the interface are responsible for the formation of the interfacial layer. Additionally, the application of ultraviolet radiation to a growth system can alter physical properties of a growing film, such as texturing of a polycrystalline film and overall reduction of trapped oxygen within the film. Furthermore, post-deposition ultraviolet annealing allows for the migration of oxygen species to the interface for growth of the interface and results in an unwanted reduction of the overall electrical properties.