Deposition-time-dependent structural and electrical characteristics of terbium oxide (Tb4O7) films for high-k MOS applications

The effects of varying deposition time (15, 30, 45 and 60 min) towards terbium oxide (Tb 4 O 7 ) by radio frequency (RF) magnetron sputtering were investigated as a high dielectric constant (k) film for silicon-based metal-oxide-semiconductor (MOS) capacitor and subjected to post-deposition annealing in nitrogen/nitrogen+oxygen/nitrogen (N 2 /N 2 +O 2 /N 2 ) ambient. The incorporation of nitrogen into the oxygen vacancies inhibited further oxidation of the Si surface, diminishing the growth of the SiO 2 interfacial layer (IL) by forming a nitrogen barrier layer. However, an excessive nitrogen accumulation occurred in the Tb 4 O 7 film deposited for 15 min, leading to a degradation in interface quality. The increase of deposition time enhanced the total oxide thickness of the Tb 4 O 7 film deposited for 30, 45, and 60 min, diminished gradually the adsorption and diffusion of nitrogen, and further triggered the interaction of oxygen and the Si substrate. Therefore, the interface quality was optimized with the reduction of interface trap density. The highest k value of 18 in this work was achieved by the Tb 4 O 7 film deposited for 45 min, attributable to the optimized thickness of high-k Tb 4 O 7 film and low k SiO 2 IL at an appropriate nitrogen composition, the relatively high breakdown field (E B ∼ 2.25 MV/cm), as well as nearly the lowest interface trap density (D it ∼ 3.57 × 10 12 eV -1 cm -2 at 0.40 eV), which proposed its potential as a high-k film for MOS devices. Corresponding effects were also systematically investigated by physical and electrical properties of the Tb 4 O 7 film at different deposition times in this work.