Ellipsometric Study of the Plasma Oxidation of Tantalum

Abstract

We have shown that it is possible to grow a uniform Ta oxide film up %o a thickness of 1500A by plasma oxidation. The average speed of growth was 0.1 A/sec, which is comparable to earlier studies. Our experiments show that there is no significant contamination of the oxide due to sputtering from the cathode and that there is no evidence of sputter etching of the sample oxide due to the sample facin~g the cathode. These results are in opposition to the reports of earlier investigators. We find that our ellipsometric measurements on the oxide growth indicate that the Ta oxide being formed is a single, uniform layer with an index of refraction of 2.21. This result is in contrast to the earlier work of Lee etal., who fitted their ellipsometric measurements on plasma-grown Ta oxide with a two-layer model with layer indices of 1.89 and 2.22.

Tantalum nitride films integrated with transparent conductive oxide substrates via atomic layer deposition for photoelectrochemical water splitting

“…This discrepancy in the growth rates is due to the fact that the as-deposited films are amorphous TaO x N y , whereas ammonolysis transforms the films to crystalline Ta 3 N 5 which has 22% smaller molar volume per Ta atom than Ta 2 O 5 . 41,42 …”

High-Temperature Ammonolysis of Thin Film Ta2O5 Photoanodes: Evolution of Structural, Optical, and Photoelectrochemical Properties

“…The absorption at higher wavelengths is attributed to optical interference inside the films. The maxima of the interference fringes are located at different wavelengths due to differences in thickness (Ta 3 N 5 has a 22% smaller molar volume per Ta atom than Ta 2 O 5 ) and refractive index (2.2 and 3.0 for Ta 2 O 5 and Ta 3 N 5 , respectively, at 632 nm). , In addition, substitutional N O defects (N O represents a nitrogen on an oxygen site) may also contribute to the observed sub-bandgap absorption. ,− In this process, an electron localized on N O (which has an effective charge of −1) is excited from a sub-bandgap state to the conduction band by absorption of a photon: N O  + h ν → N O + e – . − On the basis of the current data, we cannot accurately distinguish between interference and defect-induced optical absorption, but the shape of the optical spectra in Figure strongly suggest that interference is the dominant effect. A more detailed quantitative analysis is beyond the scope of this study.…”

“…The maxima of the interference fringes are located at different wavelengths due to differences in thickness (Ta 3 N 5 has a 22% smaller molar volume per Ta atom than Ta 2 O 5 ) and refractive index (2.2 and 3.0 for Ta 2 O 5 and Ta 3 N 5 , respectively, at 632 nm). 33,34 In addition, substitutional N O defects (N O represents a nitrogen on an oxygen site) may also contribute to the observed sub-bandgap absorption. 28,35−39 In this process, an electron localized on N O (which has an effective charge of −1) is excited from a sub-bandgap state to the conduction band by absorption of a photon: N O  + hν → N O + e − .…”

Anodic Oxidation as a Means to Produce Memristive Films

“…To calculate oxide thickness from reflectance spectra, metal oxide refractive indexes are needed. The following values of refractive index at 550 nm were chosen: n Ti = 2.2, n Nb = 2.3, n Ta = 2.1 (21)(22)(23)(24)(25)(26).…”