Electrical Properties of Anodic Oxide Films of Ta, Nb, Zr, Ti, W, and V Formed by the Ion-Cathode Method

The formation process of Nb~O~ films by metallorganic chemical vapor deposition using pentaethoxy niobium (PEN: Nb(OC~H~)~) as a vapor source and O~ as reactant gas has been analyzed by in situ ellipsometry at substrate temperatures of 200 to 500~ and at O~ flow rates of 0 to 2000 cm~/min. According to the changes in the refractive index and the growth rate of the films, the formation process can be divided into three stages, that is, the nucleation and coalescence, the homogeneous growth, and the surface roughness evolution stages. The refractive index and the growth rate of the films were found to depend on the substrate temperature and the O~ flow rate. The films deposited at 200 to 400~ had amorphous structures, and those deposited at 450 to 500~ contained a 8-Nb~O~ phase in an amorphous matrix. The corrosion resistance of the films in a buffered I-IF solution depended on both the deposition temperature and the O~ flow rate. The film deposited at 450~ in the absence of O~ showed the highest corrosion resistance against the solution.Thin Nb2Q films have been proposed for various applications such as dielectric layers in thin film capacitors, :'2 antireflection coatings for solar cells, 3 and optical waveguides, ~ because of the high dielectric constant (e = 11 to 1007 and high refractive index (2.2 to 2.6 at 546.1 nm)J Moreover, excellent chemical stability of Nb~O~ ~ suggests that this material can be used as corrosion resistant coatings. Several techniques including electron beam evaporation, ~ plasma oxidation, ~' halogen transport, ~ and chemical vapor deposition, ~ have been employed to produce Nh~O~ films. Among these techniques, metallorganic chemical vapor deposition (MOCVD) using the pyrolysis of metal alkoxides is attractive as a preparation method for corrosion resistant oxide coatings, because it offers the following advantages: (i) process simplicity, (it) lower processing temperatures to obtain high density films, (iii) good uniformity and step-coverage of films, and (iv) control of the stoichiometry. However, it is necessary to optimize process parameters to produce metallorganic chemical vapor deposition (MOCVD) oxide films with a good corrosion resistance. ~ It has been reported that the properties of Ta~O~, ~,~0 TiQ, n ZrO~, ~= and AI~O~ ~ films, which were formed by MOCVD using corresponding metal alkoxides, change with deposition time as well as with substrate temperature. It is therefore important to elucidate in situ the change in film properties during deposition under various conditions. The aim of this study is to analyze the growth process and corrosion characteristics of Nb~O~ films formed by MOCVD using pentaethoxy niobium (PEN: Nb(OC~H~)~) as a vapor source. In situ ellipsometry was employed for observing changes in the thickness and optical constants of the films * Electrochemical Society Active Member. during deposition. The dissolution rates of the films were also measured by el]ipsometry in a buffered HF solution. ExperimentalMOCVD apparatus.--Nb20~ films were deposited by MOCV...

Section: Kensuke Isobe Motoaki Tajika Ikumasa Koshiro Hideki Maruymentioning

confidence: 99%

Ellipsometric Analysis of Growth Process and Corrosion Resistance of Nb2 O 5 Films Formed by MOCVD

Hara

Takahashi

Yoon

et al. 1994

“…In addition, highly polarizable oxide dielectrics are generally characterized by considerably high dielectric losses, 15 which also increase with the conductivity in a particular material. 16 All transition metal oxides would be insulating dielectrics if the perfect stoichiometry were obtained. However, achievement of the ideal stoichiometry corresponding to the fully oxidized metals is complicated during low-temperature film deposition processes.…”

mentioning

confidence: 99%

Development of Dielectric Properties of Niobium Oxide, Tantalum Oxide, and Aluminum Oxide Based Nanolayered Materials

Kukli

Ritala

Leskelä

2001

109

Nb2O5, Ta2O5, and Al2O3 solid solutions and nanolaminates were grown using atomic layer deposition technique. Electrical properties of the materials deposited were comparatively characterized by studying the behavior of Al/niobium-aluminum (tantalum) oxide/indium-tin oxide capacitor structures. The films with high Nb content demonstrated high polarizability and leakage current density. The films with high Al content demonstrated low leakage current densities. The leakage currents in Nb-based films were reduced by depositing thin alternate layers of Al2O3 or Ta2O5 and Nb2O5, thereby increasing the number of interfaces between distinct oxide layers. The permittivity of Nb2O5:Al2O3 films could be increased with Nb2O5 concentration without considerable loss in resistivity. © 2001 The Electrochemical Society. All rights reserved.

“…In this paper we would like to report on an ellipsometric study of the plasma oxidation of tantalum. Since the pioneering work of Miles and Smith (1) on the formation of oxides in an oxygen glow discharge there have been several studies of the plasma oxidation of tantalum (2)(3)(4). One of the main problems with these earlier studies has been the technique used to measure the oxide thickness.…”

mentioning

confidence: 99%

Ellipsometric Study of the Plasma Oxidation of Tantalum

Leslie

Knorr²

1974

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.