In situ growth of evaporated TiO2 thin films using oxygen radicals: Effect of deposition temperature

Abstract

The growth and characterization of TiO2 thin films deposited by electron-beam evaporation of TiO2 have been studied. The growing film was exposed to a flux of atomic oxygen supplied from an oxygen radical beam source at a total deposition pressure of 1×10−5 mbar. The properties of as-deposited 1000 Å thick films on silicon substrates have been studied in the growth temperature interval 100–680 °C. X-ray diffractometry demonstrated a phase evolution as a function of growth temperature, from amorphous (100 °C) to anatase (300 °C) and eventually rutile (680 °C). While the amorphous film surface had a smooth film surface as evidenced by atomic force microscopy, the anatase and rutile specimens exhibited a grain-like morphology. No apparent difference in surface roughness was observed between the anatase and rutile phase. Secondary ion mass spectrometry indicated that silicon diffused into the rutile film grown at the highest temperature. Ellipsometry measurements revealed that the crystallized films exhibited significantly larger refractive index and absorption than the amorphous film. Current–voltage (C–V) measurements demonstrated that the leakage was very high in the amorphous and anatase films (3–5 A/cm2 at 0.3 MV/cm). With increasing amount of rutile phase, the leakage current decreased resulting in a leakage current density of 70 nA/cm2 at an electrical field of 0.3 MV/cm for rutile films grown at 680 °C. High-frequency C–V measurements on rutile films resulted in typical metal-insulator- semiconductor behavior with a measured static dielectric constant of 39.

Dielectric and infrared properties of TiO2films containing anatase and rutile

“…Similar observations have been reported by others [9]. As-deposited, zero bias films show a featureless spectrum typical of an amorphous network and is shown in figure 3(a).…”

Atomic Layer Deposition of Titanium Oxide from TiI4 and H2O2

“…[5,12,13] With reference to factors affecting the physical properties, an interesting aspect in TiO 2 growth has been the stability of various crystallographic phases such as anatase and rutile. These phases possess different electro-optical properties.…”

“…These phases possess different electro-optical properties. For instance, although uniform anatase films can be grown with a quite high permittivity value (70), [4] the anatase is still characterized by a lower dielectric constant, [12] higher leakage current, [5] and lower breakdown field strength, [12] than rutile. At the same time, pure anatase is optically less absorbent than rutile.…”

“…[2,3,14] Possibly the lowest reported in-situ processing temperature of pure rutile has been 300 C in laser ablation, [15] or rutile mixed with anatase in films evaporated at 300 C and above. [5,16] The stabilization of rutile in CVD has usually been possible at temperatures above 500 C, or after post-deposition heat treatment. [1,4,12,14,17] The composition of the substrate may also have an influenceÐit has been noted that, at rather low temperatures (around 300 C), high Al 2 O 3 and Na 2 O contents in the substrate material favor the formation of rutile and anatase phases, respectively.…”

“…[1,4,12,14,17] The composition of the substrate may also have an influenceÐit has been noted that, at rather low temperatures (around 300 C), high Al 2 O 3 and Na 2 O contents in the substrate material favor the formation of rutile and anatase phases, respectively. [7] Recently, rutile TiO 2 has been produced by low-pressure CVD from titanium-tert-butoxide on SnO 2 (of rutile structure) substrates at temperatures as low as 290 C and on glass at 322 C. [4] Anatase and rutile thin films have been obtained by physical methods such as reactive sputtering [6,13] and electron beam evaporation, [5] or by various chemical methods such as ambient air hydrolysis of metal precursors, [9] hydrolysis in aqueous medium, [2,8] chemical beam epitaxy (CBE), [10] and CVD. [ sors have been used in CVD, including b-diketonate complexes, [1,18] TiCl 4 , [9,16,19] Ti(NO 3 ) 4 , [14] Ti(OC 2 H 5 ) 4 , [12] or Ti(OC 3 H 7 ) 4 .…”