Thin Nb2O5-films were deposited on unheated glass, fused silica, and silicon substrates by reactive-low-voltage-high-current-ion-plating (RLVIP). Optical as well as mechanical film properties and their environmental stability are remarkably influenced by deposition parameters like e. g. arc current, deposition rate, gas composition, and total gas pressure. It was found out that an arc current around 50A, gas mixtures with high amount of oxygen, and a deposition rate around 0,3nm/s yielded the best results. Refractive indices were calculated from data obtained by spectrophotometric intensity measurements of the constrained amorphous and homogeneous films. Residual optical absorption in the film's high transmittance range was determined by photothermal deflection spectrometry. Mechanical film stress, for dense films always compressive, was measured by deformation of coated thin silicon discs. Typical obtained values are n550 = 2,39 - 2,40, k515 = 2×10-4, σ = -30MPa. Detailed information is presented in diagrams.
The aim of this investigation was to study the characteristics of a reactive-low-voltage-high-current-ion-plating plasma and to correlate the observed plasma data with the properties of films deposited under such conditions. A Langmuir probe system (Smart Probe - Scientific Systems) was inserted into a Balzers BAP 800 ion plating plant above the e-gun evaporation source close to the insulated substrate holder. In this position during RLVIP deposition, plasma potential, floating potential, self-bias voltage, electron temperature, ion current density, and particle number density were measured and calculated, respectively. All measurements were performed in dependence of arc current (20-80A) and oxygen partial pressure (1 - 36 x 10-4mbar). With rising arc current the number of charged particles, the self-bias voltage between plasma and substrates as well as the energy of the condensing and bombarding species were increased. These data explain the increase of density, refractive index and mechanical stress of RLVIP-metal-oxide-layers, like Ta2O5 and Nb2O5, deposited with higher arc currents. An increase of gas pressure decreased the energy of the particles and therefore reduced slightly film density and refractive index. However, it improved chemistry and eliminated unwanted residual optical absorption and also decreased compressive mechanical film stress.
The density of the material in a deposited film determines many important film properties, for example hardness and abrasions resistance, adherence to the substrate, refractive index, film stress,
flatness and film permeation. Chemical compound films like metal oxides, some nitrides and oxynitrides are mainly produced by reactive PVD processes. The energy input into the growing film strongly influence the density of the resulting film. High energetic coating conditions result e.g. in a high refractive index, but often also in relatively high residual optical absorption and high compressive film stress. In order to obtain films with improved properties immediately after deposition without time consuming post-deposition heat treatments, depositions of RLVIP-Ta2O5 films were carried out under relatively high oxygen pressures and under special rate conditions. The achieved reproducible film properties can practically be accepted for many low loss optical film
In this work the properties of Si3N4 and AIN thin films deposited onto unheated substrates by Reactive Low Voltage Ion Plating (RLVIP) and Reactive DC-Magnetron Sputtering (RDCMS) were investigated. In both experimental setups pure silicon and aluminum were used as starting materials. Working and reactive gas were argon and nitrogen respectively. All Si3N4 films showed amorphous structure in X-ray and electron diffraction whereas AIN films were found to be polycrystalline and could be indexed to the bulk hexagonal AIN lattice. The values of the film refractive index at 550 nm are 2.08 for RLVIP Si3N4, 2.12 for RLVIP AIN, 2.02 for RDCMS Si3N4, and 1.98 or 2.12 for AIN depending on the total pressure in the range of 8 E - 1 Pa and 1 E - 1 Pa during the process. The high optical transmission region for the Si3N4 films lies between 0.23 and 9.5 micrometers , and for AIN films between 0.2 and 12.5 micrometers . Purity and composition were measured by electron microprobe, infrared transmission, nuclear reactions, elastic recoil detection analysis and Rutherford backscattering spectroscopy. Transmission electron micrographs of Pt-C replicas of fracture cross sections of the films show their different microstructure and surface topography. Environmental tests proved the RLVIP Si3N4 films to be very hard, of high density and of strong adherence to glass.
Thin films play an important role in electron microscopy as they are used to improve the electron optical contrast and the structural stability of specimens, and to increase the electrical conductivity of specimen surfaces. They are, however, also the object of structural and microstructural investigations. In order to avoid overlapping of specimen and coating structures, it is necessary to understand how thin films are formed in the various coating technologies, and how to create them reproducibly as part of the different EM-preparation techniques. Electron microscopy is applied to learn more about the structural details of thin films used for instance in the optical coating industry. Heat shock fracturing and Pt-C surface replication of the cross-sections resulted in reliable TEM micrographs of the coating microstructure. These studies demonstrate that, under optimal conditions, it is possible to find a correlation between measured film properties and the microstructure of the coatings. TEM replica investigations reveal single events, so they can be useful if discrepancies in the (statistical) physical data have to be investigated.
Reactive Low-Voltage Ion Plating (RLVIP) is a plasma-assisted evaporation process
that produces anorganic oxide- and nitride films with a closed microstructure. in
order to better understand the process and the resulting film properties a BALZERS
PPM 400 Plasmamonitor, a combination of a quadrupole mass filter and an energy
selective ion optics, has been used to study the relative abundancies and energy
distributions of the ions impinging on the growing film in the RLVIP process. The
device is discussed and preliminary results are presented: The plasma is anisotropic.
Surprisingly it contains ions with higher energies than expected from the
Aluminum nitride films were deposited on fused silica by reactive dc magnetron sputtering from an
Al-target in an Ar/N2 atmosphere.
In-situ measurements during the deposition provide data concerning mechanical stresses inherent to
the growing thin films. By variation of both the composition of the sputtering gas (Ar,N2) and the total
gas flow in the vacuum chamber, the occuring intrinsic stresses could be shifted in magnitude and
direction. Stress values of the thin films ranged from -1.2GPa (compressive) to +1.2GPa (tensile) when
the Ar/N2 ratio was varied between 3:1 and 1:3 for the different total gas flows of 5Osccm, lOOsccm,
and 200sccm (corresponding to total gas pressures of approximately 2x101Pa, 4x101Pa, and 8x101Pa
Investigation of optical film properties, such as refractive index, as well as of structural properties
were carried out and the results were related to the state of stress the films were in. The optical
characterization (n,k) was achieved by photospectrometry. Structure and chemical composition were
analysed by electron diffraction,transmission electron microscopy (ThM) and Auger electron
spectroscopy (AES) respectively.
High quality dielectric films are required today for various interference optical
applications and for planar wave guides in integrated optics. Many inorganic
chemical compounds which were difficult to deposit by conventional techniques in
form of well adherent, dense, hard and stable low-loss films are now routinly synthesized
by reactive gas discharge plasma and energetic ion and/or coating materials
atom processes. A survey over such PVD coating technologies and on the resulting
film properties is given in this paper.