Vanadium Nitride Films Formed by Rapid Thermal Processing (RTP): Depth Profiles and Interface Reactions Studied by Complementary Analytical Techniques

Abstract

The nitridation of vanadium films in molecular nitrogen and ammonia using a RTP‐system was investigated. The V films were deposited on silicon substrates covered by 100 nm thermal SiO2. For a few experiments sapphire substrates were used. Nitride formation at high temperatures (900 and 1100 °C) and interface reactions and diffusion of oxygen out of the SiO2‐layer into the metal lattice at moderate temperatures (600 and 700 °C) were studied. For characterisation complementary analytical methods were used: X‐ray diffraction (XRD) for phase analysis, secondary neutral mass spectrometry (SNMS) and Rutherford Backscattering (RBS) for acquisition of depth profiles of V, N, O, C and Si, transmission electron microscopy (TEM) in combination with electron energy filtering for imaging element distributions (EFTEM) and recording electron energy loss spectra (EELS) to obtain detailed information about the initial stages of nitride, oxide and oxynitride formation, respectively, and the microstructure and element distributions of the films. In these experiments the SiO2‐layer acts as diffusion barrier for nitrogen and source for oxygen causing the formation of substoichiometric vanadium oxides and oxynitrides near the V/SiO2‐interface primarily at temperatures ≤ 900 °C. At a temperature of 1100 °C just a small amount of oxynitride forms near the interface because rapid diffusion of nitrogen and fast formation of VN (diffusion barrier for oxygen) inhibit the outdiffusion of oxygen into the metal layer. In the 600 °C regime, in argon atmosphere oxynitride phases observed in the surface region of these films originate from reaction of residual oxygen in the argon gas, whereas NH3 as process gas does not lead to oxide or oxynitride formation at the surface (apart from the oxidation caused by storage). NH3 seems to support the diffusion of oxygen out of the SiO2‐layer. During the decomposition of ammonia at higher temperatures hydrogen is formed, which could attack the SiO2. In contrast, sapphire substrates do not act as oxygen source in the 600 °C regime and change the nitridation behaviour of the vanadium films.

A facile route to VN and V2O3 nanocrystals from single precursor NH4VO3

“…It is found that transition metal nitrides combine the characteristics of both ceramics and metals [1], So they exhibit many attractive properties, such as great abrasion and corrosion resistance, extreme hardness, high melting point, good electric and thermal conductivity, and interesting optical, electronic and magnetic properties [1][2][3]. Besides, vanadium nitride is a superconductor with a transition temperature Tc ranging from 2 to 9 K depending on the nitrogen content [4], and has good catalytic activities to NH 3 synthesis and decomposition, and n-butane dehydrogenation [5,6].…”

A versatile low temperature solid-state synthesis of vanadium nitride (VN) via a “guanidinium-route”: experimental and theoretical studies from the key-intermediate to the final product

“…Thus, these materials present unique physical and chemical traits, which greatly increase their importance in practical applications and fundamental studies, such as for example, their use as raw materials in cutting tools resistant to wear and corrosion. 2,4 Furthermore, since Levy and Boudart, 5 in the 1970s, discovered that tungsten carbide (WC) possesses special catalytic properties, and, from a qualitative point of view electronic properties analogous to those of noble metals, the interest in their electronic and magnetic properties 1 has been greatly on the increase.…”

Carbothermal synthesis of vanadium nitride: Kinetics and mechanism

“…The heat treatment is a critical step in the preparation of these materials from the precursors; therefore, a careful study of the heat treatment would help to clarify the relation between the preparation method and the properties of these materials. Some methods employed recently to synthesize VN are rapid thermal processing [10], thermal reduction/nitration in an autoclave at 500…”