https://www.diva-portal.org/smash/get/diva2:17175/FULLTEXT02

Ionized physical vapor deposition (IPVD): A review of technology and applications

A method and system for spectroscopic ellipsometry employing reflective optics to measure a small region of a sample by reflecting radiation (preferably broadband UV, visible, and near infrared radiation) from the region. The system preferably has an autofocus assembly and a processor programmed to determine from the measurements the thickness and/or complex refractive index of a thin film on the sample. Preferably, only reflective optics are employed along the optical path between the polarizer and analyzer, a sample beam reflects with low incidence angle from each component of the reflective optics, the beam is reflectively focused to a small, compact spot on the sample at a range of high incidence angles, and an incidence angle selection element is provided for selecting for measurement only radiation reflected from the sample at a single, selected angle (or narrow range of angles). The focusing mirror preferably has an elliptical shape to reduce off-axis aberrations in the focused beam. Some embodiments include both a spectrophotometer and an ellipsometer integrated together as a single instrument. In such instrument, the spectrophotometer and ellipsometer share a radiation source, and radiation from the source can be focused by either the spectrophotometer or the ellipsometer to the same focal point on a sample. Preferred embodiments of the ellipsometer employ a rotating, minimal-length Rochon prism as a polarizer, and include a spectrometer with an intensified photodiode array to measure reflected radiation from the sample, and a reference channel (in addition to a sample channel which detects radiation reflected from the sample).

Focused beam spectroscopic ellipsometry method and system

Electron configurations close to the tetrahedral hybridization are found in pure amorphous carbon at a concentration which depends on preparation conditions. Tetrahedral bonding at levels of approximately 80% is found in amorphous carbons formed from beams of carbon ions with energies in a `window' between 20 eV and approximately 500 eV. Suitable techniques for its formation include cathodic arc deposition, ion beam deposition and laser ablation. Similar material appears to be formed by pressure treatment of fullerene precursors and by displacement damage in diamond. Highly tetrahedral forms of amorphous carbon (ta-C) show electronic, optical and mechanical properties which approach those of diamond and are quite different from amorphous carbons with low content. Useful techniques for determining the content include electron energy loss spectroscopy, electron and neutron diffraction and Raman spectroscopy. Considerable progress has been made in the understanding of this material by simulating its structure in the computer with a range of techniques from empirical potentials to ab initio quantum mechanics. The structure shows departures from an idealized glassy state of diamond which would have a random tetrahedral network structure as used to describe amorphous silicon and germanium. A surprising feature of the structure simulated using ab initio methods is the presence of small rings containing three or four carbon atoms. The electronic and optical properties are strongly influenced by the residual of carbon. Applications to electronic devices are at an early stage with the demonstration of photoconductivity and some simple junction devices. Applications as a wear resistant coating are promising, since the theoretically predicted high values of elastic constants, comparable to but less than those of diamond, are achieved experimentally, together with low friction coefficients.

https://iopscience.iop.org/article/10.1088/0034-4885/59/12/002/pdf

Tetrahedral bonding in amorphous carbon

Ion beam assisted deposition, the bombardment of a thin film with a beam of energetic particles during deposition, provides a powerful technique for modifying the microstructure and properties of thin films and coatings. Various experimental approaches used for ion beam assisted deposition are described and the physical basis for the effects is examined. Observations on modification of nucleation and growth behaviour, microstructure development, compound synthesis, and applications to the modification of properties such as intrinsic stress, adhesion, surface mechanical properties, corrosion and oxidation resistance, optical properties, and electrical properties, are reviewed.

Use of ion beam assisted deposition to modify the microstructure and properties of thin films

The optical properties of the dielectric oxide films SiO2, Al2O3, TiO2, ZrO2, CeO2 and Ta2O5 produced by ion-based techniques have been reviewed. The influence of ion bombardment during deposition is discussed in some detail and the various production techniques are described. Recent results on the deposition and properties of diamond-like carbon films are also reviewed. Finally, some examples of the practical applications of high quality dielectric oxide films are given.

Ion-based methods for optical thin film deposition

Some effects on the properties of electron-beam evaporated thin films produced by ion bombardment of the growing film are reported. Substantial increases in the packing densities of SiO2 , TiO2 , and ZrO2 films have been produced as measured by the reduction in the adsorption of moisture when the films are exposed to a humid atmosphere. In a ZrO2-SiO2 multilayer interference filter, changes in the wavelength of the peak transmittance on exposure to the atmosphere have been reduced from 8 nm for films deposited without ion bombardment to <1 nm for ion-beam-assisted films.

Ion-beam-assisted deposition of thin films.

Mixed thin films of TiO2 and SiO2 were produced by coevaporation from separate electron‐beam sources and simultaneous bombardment of the growing film with oxygen ions. The optical properties of the films were determined during growth by in situ ellipsometry and the surface composition of the deposited films studied by in situ ion scattering spectroscopy, ex situ x‐ray photoelectron spectroscopy, and energy filtered electron diffraction. The correlation between the optical and surface characterization is presented. There is evidence of local variations in the relative concentrations of TiO2 and SiO2. The position of the Si 2p binding energy depends on the TiO2 content in the film, indicating the possible formation of an intimate mixture.

https://espace.library.uq.edu.au/view/UQ:259794/UQ259794_OA.pdf

Ion-assisted deposition of mixed Tio2-Sio2 films

Characteristics of titanium arc evaporation processes

The energy of Ti neutrals and Ti+ ions was determined in the region of the cathode spot of a Ti vacuum arc by measurement of the Doppler broadened profiles of Ti(I) and Ti(II) emission lines using Fabry‐Perot interferometry. Energy analysis of Ti+ and Ti++ was carried out at a distance from the cathode using an electrostatic analyzer. The emission lines showed that the neutrals had energies corresponding to approximately 0.4 eV while the Ti+ ions had a most probable energy of 3 eV. The energy analyzer showed that remote from the cathode spot Ti+ had a most probable energy of 80 eV. This large difference is explained in terms of a simple model for the arc which includes a potential ‘‘hump’’ near the cathode. The charge fraction of the evaporant was measured to be approximately 0.5, and the effect of nitrogen background gas on the energy distribution was observed. Deposited films of Ti and TiN were prepared and the influence of substrate bias investigated. It was found that under high negative bias the Ti films exhibited a preferred 〈110〉 orientation consistent with previous studies of ion‐beam‐induced textures.

Characterization of a Ti vacuum arc and the structure of deposited Ti and TiN films

A versatile ultrahigh‐vacuum thin‐film deposition and analysis system is described. Films are deposited by electron beam evaporation with the possibility of ion beam bombardment of the growing film. Measurements of the reflectance and/or transmittance of the coating surface can be made simultaneously at 16 wavelengths across the visible or infrared spectrum. Ellipsometric measurements can also be made in situ, at a single wavelength and single angle of incidence, by an ellipsometer which can operate in either an automatic rotating analyzer mode or a manual nulling mode. The system is also equipped with an ion gun producing a submillimeter spot, and with a hemispherical sector, ion energy analyzer for ion scattering spectroscopy studies of the film surface. Results obtained during the deposition of a gold film are presented to demonstrate the capability of the system.

C. G. Pacey

Papers

Ion-beam-assisted deposition of thin films.

Ion-assisted deposition of mixed Tio2-Sio2 films

Characteristics of titanium arc evaporation processes

Characterization of a Ti vacuum arc and the structure of deposited Ti and TiN films

Characterization of growing thin films by in situ ellipsometry, spectral reflectance and transmittance measurements, and ion‐scattering spectroscopy