A comparative study of the electrical properties of TiO_2 films grown by high-pressure reactive sputtering and atomic layer deposition

摘要

Oxide-semiconductor interface quality of high-pressure reactive sputtered (HPRS) TiO_2 films annealed in O_2 at temperatures ranging from 600 to 900℃, and atomic layer deposited (ALD) TiO_2 films grown at 225 or 275℃ from TiCl_4 or Ti(OC_2H_5)_4, and annealed at 750℃ in O_2, has been studied on silicon substrates. Our attention has been focused on the interfacial state and disordered-induced gap state densities. From our results, HPRS films annealed at 900℃ in oxygen atmosphere exhibit the best characteristics, with D_(it) density being the lowest value measured in this work (5-6 x 10~(11) cm~(-2) eV~(-1)), and undetectable conductance transients within our experimental limits. This result can be due to two contributions: the increase of the SiO_2 film thickness and the crystallinity, since in the films annealed at 900℃ rutile is the dominant crystalline phase, as revealed by transmission electron microscopy and infrared spectroscopy. In the case of annealing in the range of 600-800℃, anatase and rutile phases coexist. Disorder-induced gap state (DIGS) density is greater for 700℃ annealed HPRS films than for 750℃ annealed ALD TiO_2 films, whereas 800℃ annealing offers DIGS density values similar to ALD cases. For ALD films, the studies clearly reveal the dependence of trap densities on the chemical route used.