Interaction of molecular contaminants with high-k dielectric surfaces
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractAs the device feature size shrinks, films of silicon oxide (SiO₂) will become unsuitable for MOSFET gate dielectric applications and have to be replaced by thicker films of a high-k dielectric material. Among the high-k materials, hafnium oxide (HfO₂) and zirconium oxide (ZrO₂) are the most promising candidates. Molecular contamination can affect the quality of the new gate dielectric films in a manner similar to ultrathin SiO2 films. Therefore, characterization of contaminant adsorption behavior of these high-k films should assist in deciding their potential for successful integration in silicon MOS technology. The interactions of moisture and organic (in particular IPA) contamination with ALCVD(TM) deposited 5-nm HfO₂ and ZrO₂ films were investigated using mass spectrometry. HfO₂ and ZrO₂ were found to have similar moisture adsorption loadings, but significantly higher than that of SiO₂. The new high-k materials also retained a higher portion of the adsorbed moisture after an isothermal nitrogen purge. Almost all the adsorbed moisture could be removed from SiO₂ and HfO₂ after a 300°C bake under nitrogen purge, whereas ZrO₂ surfaces retained significant amounts of the adsorbed moisture. Experiments with ppb-levels of IPA showed that the adsorption loading on the three surfaces had the following order: ZrO₂ > HfO₂ > SiO₂. The relatively slow desorption kinetics of H2O and IPA highlighted the difficulty in removal of these contaminants from HfO₂ and ZrO₂ surfaces. Presence of pre-adsorbed moisture increased IPA adsorption on SiO₂, but reduced adsorption on HfO₂ and ZrO₂. Isotope labeling studies with D₂O showed that IPA reacted with surface hydroxyl groups to form a chemisorbed alkoxy species on all oxides. A multilayer model for adsorption of water and IPA was developed to understand the mechanism of interactions of contaminants with these surfaces. Results indicated that ZrO₂ formed the strongest surface-hydroxyl bond and also physisorbed IPA stronger than HfO₂ and SiO₂. The practical application of the adsorption model is also demonstrated. The results of this work should aid in the selection of the most appropriate dielectric film and design of process/equipment so that it can be more readily integrated into silicon technology.
Degree ProgramGraduate College
Chemical and Environmental Engineering