A. R. Chourasia

A study of CrNx thin films by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy has been employed to study the electronic structure of CrNx thin films. The films have been deposited with varying concentration of nitrogen on a stainless steel substrate by a d. c. magnetron sputtering technique. The Cr 2p, Cr LMM Auger, N 1s, and N KLL Auger regions were investigated using Mg Kα radiation. Results indicate changes in the electronic structure of Cr and N in these films. The Auger parameter shows an increasing trend for Cr and a decreasing trend for N. This has been interpreted as increasing charge transfer from Cr to N with increasing content of nitrogen. The full width at half maximum observed for Cr 2p3/2 peak shows an increasing trend with the nitrogen concentration. The density of states at the Fermi level estimated from the asymmetry index of the Cr 2p3/2 peak is larger than that for elemental chromium. However, in the films a decreasing trend is observed for the density of states with increasing nitrogen content. The chemical shift for the Cr 2p3/2 peak shows a decreasing trend while that for the N 1s peak shows an increasing trend. Using the Auger parameter as an approximation for the relaxation shift, the trend in the contribution due to configuration changes in these films has been estimated. The configuration change (hybridization effects) is observed to increase with the increase in the nitrogen content. These changes are interpreted as increasing hybridization of the Cr 3d and 4sp orbitals, with N 2p orbitals as the concentration of nitrogen increases. The observations are corroborated by results on the stoichiometric compound CrN by other studies.

X-ray photoelectron study of TiN/SiO2 and TiN/Si interfaces

The TiN/SiO2 interface has been studied using X-ray photoelectron spectroscopy (XPS). The underlying layer of SiO2 was thermally grown on a Si substrate. A thin film of TiN was then deposited on a SiO2/Si substrate by low-pressure chemical vapor deposition using a mixture of TiCl4, NH3 and NH2 gases. In another type of sample, a reactive sputtering (physical vapor deposition (PVD)) technique was employed to deposit the TiN film on the SiO2/Si substrate. In this process a pure Ti target was sputtered in a N2 and Ar plasma in a d.c. magnetron system. The Ti 2p, N ls, O ls and Si 2p regions were investigated by XPS for chemical reactivity at the TiN/SiO2 interface. In both these samples a shoulder was observed on the high binding energy side of the main N l s peak at the beginning of the TiN/SiO2 interface. The intensity of this shoulder increases while that of the main N ls peak bonded to Ti decreases as a function of depth. No spectral changes were observed for films produced by PVD. The presence of this shoulder is attributed to the formation of silicon oxynitride at the interface. Paulings electronegativity criterion supports this conclusion.

Deposition of diamond films at low pressures and their characterization by positron annihilation, Raman, scanning electron microscopy, and x-ray photoelectron spectroscopy

We have deposited diamond films with micron‐size crystals on Si〈111〉 using low‐pressure hot‐filament‐assisted chemical vapor deposition. These films have been characterized by positron annihilation, Raman spectroscopy, scanning electron microscopy, and x‐ray photoelectron spectroscopy. In addition to the results for the electronic structure and morphology, we also present new results for the lattice defects present in these films.

Characterization of low pressure deposited diamond films by X-ray photoelectron spectroscopy

Abstract X-ray photoelectron spectroscopy (XPS) has been utilized to study the electronic structure of carbon films grown by a low pressure hot filament assisted chemical vapor deposition technique with a view to optimizing the growth parameters for the diamond films. A constant flow of a mixture of high purity methane and hydrogen was maintained at a pressure of 25 Torr in the reaction chamber. The films were prepared at three different concentrations of methane: 0.25%, 0.5%, and 1.0% by density. The XPS C 1s core level and valence band spectra of these films are compared with those of graphite. Diamond has covalent sp 3 bonding while graphite has sp 2 bonding. XPS spectra exhibit features related to the difference in bonding. The plasmon loss shoulder (characteristic of graphite) associated with the main C 1s peak is found to be absent in the spectrum of films grown when the gas composition contains 0.25% methane, while it is found to build up with increasing concentration of methane. The binding energy position of the C 1s peak shows that appreciable charging occurs for the 0.25% methane concentration film. These results show that the films grown with 0.25% methane concentration closely resembled diamond. The valence band region for films grown using a gas composition consisting of 0.25% methane concentration shows considerable s-p mixing as compared with graphite. The core level and valence band results show that the film grown with a gas composition consisting of 0.5% methane concentration represents a composite of diamond and graphite. Scanning electron micrographs and Raman spectra support the conclusions drawn on the basis of XPS investigation.

Scanning tunneling microscopy of the electronic structure of chemical vapor deposited diamond films

This article discusses scanning tunneling microscopy of the electronic structure of chemical vapor deposited diamond films.

Soft X-ray appearance potential study of Ni74Fe26

Abstract Soft X-ray appearance potential spectroscopy (SXAPS) has been exploited to study the electronic structure of the Ni 74 Fe 26 alloy. The SXAPS spectra of Ni and Fe in the elemental metals and in the alloy are presented in the L 2,3 energy regions. The L 3 core levels have been used for the measurements. The spectra of Ni and Fe in the alloy are compared with the corresponding elemental spectra. The binding energy of Ni shifts towards lower energy side while that of Fe shifts towards higher energy side in the alloy. The full width at half maximum (FWHM) of the SXAPS positive going peak is a measure of the unoccupied density of states at the Fermi level. The FWHM of Ni decreases and that of Fe increases. Both these results indicate a charge transfer from Fe to Ni in the alloy. The total charge transfer at the Ni site is less than 0.6 electrons per site. The intensity of the L 3 peaks suggests enrichment of the Fe concentration and depletion of the Ni concentration on the surface of the alloy as compared to the bulk composition. A surface state feature is observed for Fe spectra in both the elemental state and the alloy. The negative dip in the alloy spectra increases for Ni but decreases for Fe. This has been interpreted as the shifting of the 4sp band towards E F in the case of Ni and away from E F in case of Fe in the alloy, consistent with the directions of shift observed for the above core levels. The data lend support to the rigid-band model commonly used for 3d transition metals.

X‐ray Photoelectron Study of TiN

Thin films of TiN were deposited from TiCl4, NH3, and H2 in a lamp heated single wafer ‘‘warm wall’’ low pressure chemical vapor deposition reactor. The deposition was carried out on a TiSi2/Si sample. The thickness of the films is estimated to be 100 nm. The films were analyzed by x‐ray diffraction, Rutherford backscattering spectroscopy, and x‐ray photoelectron spectroscopy. The XPS data in Ti 2p, N 1s, Ti L3M23V, and Ti L3M23M23 regions are presented.

X-Ray Photoemission Study of the Oxidation of Hafnium

About 20  of hafnium were deposited on silicon substrates using the electron beam evaporation technique. Two types of samples were investigated. In one type, the substrate was kept at the ambient temperature. After the deposition, the substrate temperature was increased to 100, 200, and . In the other type, the substrate temperature was held fixed at some value during the deposition. For this type, the substrate temperatures used were 100, 200, 300, 400, 500, 550, and . The samples were characterized in situ by the technique of X-ray photoelectron spectroscopy. No trace of elemental hafnium is observed in the deposited overlayer. Also, there is no evidence of any chemical reactivity between the overlayer and the silicon substrate over the temperature range used. The hafnium overlayer shows a mixture of the dioxide and the suboxide. The ratio of the suboxide to dioxide is observed to be more in the first type of samples. The spectral data indicate that hafnium has a strong affinity for oxygen. The overlayer gets completely oxidized to form at substrate temperature around for the first type of samples and at substrate temperature greater than for the second type.

Study of the Ti/Si interface using x‐ray photoelectron and Auger electron appearance potential spectroscopies

Thin films of titanium silicide have been grown by evaporative deposition of high‐purity Ti on a Si 〈111〉 substrate under high‐vacuum conditions and annealing at ∼300 °C for 15 min. The growth of TiSi2 on the top 1000 A of Si was studied for its stoichiometry as a function of thickness by x‐ray photoelectron spectroscopy (XPS) and Auger electron appearance potential spectroscopy (AEAPS). A sputter profiling technique using Ar ions was employed to determine the composition of the overlayer as a function of depth. Results of the study indicate the presence of both TiO2 and SiO2 on the top layers in addition to Ti and Si (which may be bonded to each other). The concentrations of TiO2 and SiO2 are found to decrease with depth, the former decreasing much more rapidly than the latter. The atomic percentage composition measurements indicate the formation of TiSi2 in the Ti overlayer. However, no appreciable shift is observed in the core binding energies of the Ti 2p3/2 and Si 2p peaks. AEAPS, which probes the lo...

X‐ray photoelectron spectroscopy study of the Ni/Si oxide/Si interface

The electronic structure of the Ni/Si oxide/Si interface has been investigated using x‐ray photoelectron spectroscopy. This interface represents a more realistic situation encountered in semiconductor device processing technology. Approximately 35 A of high‐purity Ni was sputter deposited on 〈111〉Si (covered with a thin native oxide layer) at room temperature. A sputter profiling technique was employed to determine the composition and reactivity as a function of depth. The measurements show considerable reactivity at the Ni/Si oxide/Si interface, even at room temperature. The Ni 2p3/2 peak exhibits a gradual shift to higher binding energy which indicates that the overlayer cannot be regarded as a single unique nickel silicide phase. The large positive shift of the Ni 2p3/2 and the small shift of the corresponding Si 2p peak suggest that ionicity plays a nominal role in the Ni–Si chemical bond. The valence‐band spectra show a dominant 3d‐derived feature which gradually shifts to higher binding energy. The ...