Characterization of the Solid State Properties of Anodic Oxides on Magnetron Sputtered Ta, Nb and Ta-Nb Alloys

Abstract

Tantalum oxide, niobium oxide and Ta-Nb containing mixed oxides were grown by anodizing sputter-deposited Ta, Nb and Ta-Nb alloys of different compositions. A photoelectrochemical investigation was performed in order to estimate the band gap and the flat band potential of the oxides as a function of their composition. The band gap of the investigated Ta-Nb containing mixed oxides changed monotonically between those estimated for Ta 2 O 5 (4.1 eV) and Nb 2 O 5 (3.4 eV) and in agreement with a proposed correlation between the Band gap of an oxide and the difference of electronegativity of the oxide constituents. From the differential capacitance curves recorded in a wide range of electrode potential and for several frequencies of the alternative signal, the dielectric constant of the investigated oxides were estimated. © 2011 The Electrochemical Society. [DOI: 10.1149/2.031201jes] All rights reserved. Microelectronics is very important for almost all kinds of technology evolutions in the past four decades. In this area, the dielectrics science occupies a prominent place in providing the dominant technology in integrated capacitors or gate insulators. In the last years the main challenge has been to scale down the insulating oxide thickness keeping low values of the leakage current. This task has been partially achieved for metal-oxide-semiconductor field effect transistor thanks to the use of hafnium based dielectrics, while less has been done for dynamic random access memory and metal-insulator-metal capacitors (DRAM MIMCAP). To the last generation DRAM, very low (from 0.5 to 0.35 nm) equivalent thickness is required with the constraint to maintain a very low leakage current. This implies the use of material having high dielectric constant (∼50) and high band gap (>4 eV), which can be obtained by post formation thermal treatment and tuning of the oxide composition. Owing to their high value of dielectric constant, Ta 2 O 5 and Nb 2 O 5 are quite attractive oxides for the development of the next generation of DRAM. Tantalum oxide is a wide band gap (∼4 eV) material with a high dielectric constant (ε = 27 -30) if properly crystallized (T > 750• C). Niobium oxide has a higher dielectric constant (ε = 53) with respect to Ta 2 O 5 but a lower band gap (∼3.3 eV). In recent papers, 1-3 it has been shown that the addition of small amount of Nb in tantalum based oxide decreases the crystallization temperature with small effect on the band gap value of the material. Thus, (Nb (1−x) Ta x ) 2 O 5 have been introduced in the International Technology Roadmap for Semiconductors (ITRS).Tantalum-niobium mixed oxides for microelectronic components are usually prepared by high vacuum techniques (physical and chemical vapour depositions, atomic layer deposition). [4][5][6][7] In this work we propose to prepare these oxides by anodizing in suitable solutions sputter-deposited Nb-Ta alloys. This electrochemical room temperature process allows to grow oxides of controlled thickness and composition, even if a detailed investigation on t...

Critical Review—Photocurrent Spectroscopy in Corrosion and Passivity Studies: A Critical Assessment of the Use of Band Gap Value to Estimate the Oxide Film Composition

“…4, therefore A = 1.35 or A = 2.17 for regular d,d metals and s,p-s,p metals mixed oxides, respectively. In previous papers, [30][31][32] we have shown that conditions such as those mentioned above in the paper of Zunger et al can be encountered in practice in the case of passive films grown on valve-metals alloys where, in suitable electrolytic solutions, the oxide composition maintains the same cation ratio present in the metallic alloy. This is reported in Figures 1-3 for d,d-metals mixed oxides, where the measured optical band gaps as a function of the alloys composition are reported for passive films grown on Ti-Zr and Ta-Nb alloys as well as for physically deposited (Gd x Y (1-x) ) 2 O 3 .…”

“…This is reported in Figures 1-3 for d,d-metals mixed oxides, where the measured optical band gaps as a function of the alloys composition are reported for passive films grown on Ti-Zr and Ta-Nb alloys as well as for physically deposited (Gd x Y (1-x) ) 2 O 3 . [30][31][32][33][34] The amorphous nature of the passive film on Nb-Ta alloys and the absence of any indirectto-direct optical transition crossover in the case of crystalline films grown on Ti-Zr alloys, allowed testing of the suggestion of Zunger and coworkers 25,26 for the regular semiconducting alloys reported above. Figures 1 and 2 show the dependence of experimental E g values of thin anodic passive films vs alloys composition for Ti-Zr and Ta-Nb mixed oxides.…”

Spectroscopic ellipsometry for compositionally induced bandgap tuning of combinatorial niobium–tantalum anodic oxides

“…[8][9][10] Mixing Nb and Ta in their oxidized form during anodization results in extremely interesting behaviors under UV irradiation. 11 Anodic oxides on most valve metals (e.g. Nb and Ta) are amorphous and their crystallization may affect their nal properties.…”

Electrochemical Oxidation of Hf–Nb Alloys as a Valuable Route to Prepare Mixed Oxides of Tailored Dielectric Properties

“…Moreover, as disclosed in Figure b, the highest ε ox is measured for the mixed oxide grown on Hf–39 at% Nb alloy (i.e., 45), which is roughly twice the dielectric constant of pure HfO 2 (20) and comparable to the dielectric constant of Nb 2 O 5 (40–50) …”