PLD of high-k dielectric films on silicon

Thin films of high-k materials praseodymium oxide (PrxOy) and hafnium oxide (HfOx) were deposited on silicon (100) surfaces by pulsed laser deposition (PLD), using the third harmonic of a Nd:YAG laser. The two materials are compared with respect to their morphology, in dependence on the substrate temperature during deposition, and their chemical composition and crystalline structure, in particular at the interface. The films of both oxides exhibit a grainy structure when deposited at substrate temperatures below 750 degreesC, with the grain size increasing from approximate to 40 nm at room temperature to approximate to 100 nm at 750 degreesC. However, the PrxOy films are much more uniform than hafnia, the latter exhibiting increasingly larger holes, reaching several nm into the silicon substrate. For a substrate temperature of 900 degreesC, the film morphology for PrxOy completely changes to much larger crystalline areas, while for HfOx the role of holes in the film becomes substantial. Also, the interface chemistry is significantly different for both materials: a silicate formation for PrxOy and a rich abundance of SiO2 and a silicide for hafnia. Finally, our PrxOy-films exert compressive stress on the substrate, for HfOx-films tensile stress is observed which, however, may also result from interfacial SiO2.