AlN and High-k Thin Films for IC and Electroacoustic Applications
Abstract: Further, a highly selective dry etch process for etching Al on AlN has been developed for the fabrication of MIM, MIS, SAW and BAW test structures for electrical and electroacoustic characterization of the films. A dielectric constant of 10 for AlN and 25 for Ti doped Ta2O5 have been measured. With respect to electroacoustic characterization, BAW measurements gave a longitudinal velocity of 11350 m/s and a TCD of -25ppm/K. AlN thin film test structures on SiO2/Si yielded a SAW velocity of around 5000 m/s, while those on polycrystalline diamond exhibited a SAW velocity of 11800 m/s. The latter results illustrate one of the biggest advantages of thin film SAW technology, namely one can exploit both the piezoelectric properties of the film and the acoustic properties of the substrate and hence devise components with superior performance.The explosive development of personal communications systems, navigation, satellite communications as well as personal computer and data processing systems together with the constant demand for higher speeds and larger bandwidths has driven the fabrication technology to its limits. This in turn necessitates the development of novel functional materials for the fabrication of devices with superior performance and higher capacity at reduced manufacturing costs. This thesis focuses on the synthesis and characterization of such materials for IC and electroacoustic applications. Specifically, AlN thin films as well as Ti doped Ta2O5 thin films have been grown using both RF and pulsed-DC reactive sputter deposition on a variety of substrate materials. AlN is a piezoelectric material and hence its crystallographic structure and film texture are of prime interest, while Ta2O5 is a material with a relatively high dielectric constant. A significant part of the work deals with the optimization of the deposition processes. The latter have been optimized both empirically and theoretically by modeling the reactive sputter process. Subsequently, highly textured AlN thin films have been synthesized and characterized. The films were fully c-axis oriented with a typical value for the FWHM of the (002) rocking curve of 1.6°. In addition, epitaxial AlN films have been grown on sapphire at 500oC with relatively low defect density.
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