Thermal behavior of the microstructure and the electrical properties of magnetron-sputtered high-k titanium silicate thin films

Abstract

We report on the high-temperature stability of high-dielectric-constant (high-k) titanium silicate (Ti0.5Si0.5O2) thin films deposited by means of a magnetron sputtering process. We have investigated the effect of substrate deposition temperature Td (in the 20–600°C range) and postdeposition annealing temperature Ta (in the 200–800°C range) on the electrical, microstructural, and optical properties of the films. The Ti-silicate films grown at room temperature were found to exhibit a combination of excellent electrical properties, including a k-value of 16.5, a leakage current as low as 3nA at 1MV∕cm, and a dissipation factor tan(δ)<0.01. On the other hand, when the processing temperature (Td or Ta) is ⩾300°C, the leakage current of the films is found to degrade progressively. The x-ray diffraction, Raman spectroscopy, and transmission electron microscopy characterizations have shown that the Ti-silicate films exhibit an amorphous microstructure up to a temperature of about 600°C. For higher temperatures, (i.e., Td of 600°C or a Ta⩾700°C) some anatase TiO2 nanocrystallites (in the 1.5–5nm size range) formation is evidenced. This TiO2 nanocrystallite precipitation results from a thermally induced phase segregation of TiO2-rich and SiO2-rich environments, which is shown to be initiated at rather low processing temperatures. This progressive phase segregation, which leads to the precipitation of a low band gap and leaky TiO2-rich phase in the films, is believed to be at the origin of the observed degradation of the leakage current of the Ti-silicate films with increasing temperatures (Td or Ta).