Hans K. Pulker

Optical coatings deposited by ion and plasma PVD processes

Abstract Evaporation and sputter deposition and a considerable number of technologically innovative variants of these basic processes are today available for thin film deposition by PVD. Particularly their reactive modes for stoichiometric compound film formation are important. In industrial film manufacture, however, only a limited but clearly growing number of them is in use. The reasons are mainly problems with economy and reliability. Ion and plasma processes with controlled kinetic particle energy of some tens of electron volts are often preferred in reactive evaporative deposition for densification of the layers and improvement in adherence, hardness, abrasion resistance and stoichiometry. Ion beam assisted deposition with various broad-beam ion sources, ion plating, particularly the reactive low-voltage ion plating process, and more recently plasma assisted evaporative coating techniques, as the advanced plasma source process are used mainly for the production of various environmental stable dielectric multilayer products in instrument optics and ophthalmics. For extremely low-loss film products as for instance durable, all-dielectric mirrors, ion beam sputtering is today the most advanced technology. In industrial film production standard bell jar and box coating plants are more and more replaced by modern fully automatic production systems which are designed exactly for the applied process including layer type and layer sequence, and the shape, size and number of the parts to be coated. High rate sputter technologies replace to an increasing degree the traditional evaporative deposition for metal mirror fabrication. New technological solutions as for instance the medium frequency powered twin-magnetron technique are available to overcome troubles in reactive mode DC-sputtering, so that reliable sputtering of dielectric films can be performed in production with improved manufacturing efficiency. Large area coating onto rigid substrates, e.g. for the production of transparent conductive films for liquid crystal display applications, and for the production of various architectural window coatings, is a domain for sputtering and advances assure that it will continue into the future.

Properties of reactively d.c.-magnetron-sputtered A1N thin films

Abstract In this work the dependence of the properties of reactively d.c.-magnetron-sputtered A1N films on their deposition parameters was investigated. In this set-up, argon was used as the sputtering gas and nitrogen as the reactive gas. The argon-to-nitrogen ratios varied between 1 to 3 and 3 to 1, at three different total gas flows: 50 sccm, 100 sccm and 200 sccm. The d.c. power was kept constant at 1 kW. All films showed a polycrystalline hexagonal structure; the refractive index at 550 nm of the series grown at 50 sccm was scattered around 2.12, for the series grown at 100 sccm around 2.05, and for the series grown at 200 sccm around 1.97. Localized gap states appeared in films grown at 50 sccm with an Ar-to-N 2 ratio of 3 to 1. The films grown at flows of 100 sccm and 200 sccm showed tensile stresses (up to 1 GPa). The films grown at 50 sccm showed a transition from compressive ( −1.3 GPa) to tensile stress (0.3 GPa) if the Ar-to-N 2 ratio was increased to more than 2 to 1.

Fundamental optical absorption edge of reactively direct current magnetron sputter‐deposited AlN thin films

Aita et al. [J. Appl. Phys. 66, 4360 (1989)] studied the ultraviolet optical behavior of rf sputter‐deposited AlN thin films. The same optical behavior is found for reactively dc magnetron sputter‐deposited AlN thin films at different total gas flows for constant Ar/N2 ratios. The microcrystallites of these films exhibit diameters between 5 and 20 nm.

Reactive low voltage ion plating of aluminium nitride films and their characteristics

Abstract By means of reactive low voltage ion plating, AlN films were deposited onto unheated BK-7 glass, fused silica, and Si wafers. The obtained films were investigated mainly with respect to possible optical applications. Refractive index and absorption values were determined from spectrophotometric measurements. Hexagonal film structure, high density and smooth film surface and bulk film morphology were found by electron optical investigations. Mechanical characterization showed high hardness, good adherence to glass and compressive intrinsic film stress.

Mechanical stress in thin SiO2 and Ta2O5 films produced by reactive-low-voltage-ion-plating (RLVIP)

SiO2 and Ta2O5 films on unheated glass substrates deposited by reactive low voltage ion plating (RLVIP) have high compressive stresses of more than 1.2 GPa for film thicknesses < 100 nm. With increasing film thickness to 700 nm the stresses decrease exponentially to 0.7 GPa for SiO2 and 0.55 GPa for Ta2O5. Increasing the ion current density to 0.45 mA cm−2 during film deposition while maintaining (gas pressure and gas composition) increases the number (ion—molecule-reactions in the plasma) of energetic particles, increase the film density but also the compressive film stress. However, while maintaining stoichiometry parameter sets could be found for dense and therefore stable films with acceptable low compressive stress.

Film Deposition Methods

Thin films of elements, alloys and chemical compounds can be formed on solid substrates by various wet and dry chemical and physical deposition methods. Depending on the applied process, depositions are performed in air or in environmentally controlled atmosphere, under reduced pressure or in vacuum.

Plasma diagnostic of ion and plasma PVD processes

Abstract The aim of this work was to compare different plasma PVD processes in respect to their plasma properties in dependence on the process parameters. The processes under investigation were reactive d.c. pulsed magnetron sputtering magnetically assisted, arc source ion plating, reactive multi plasma supported d.c. magnetron sputtering and reactive low voltage ion plating. The experiments were carried out in specially designed plants under variable vacuum and plasma conditions. The plasma properties, like ion mass, ion energy distribution, ion and electron densities of the different processes were investigated by mass spectroscopy with additional energy distribution analysis (PPM421-Inficon) and a Langmuir probe system (Smart Probe-Scientific Systems). The magnetically forced and medium frequency pulsed biased d.c. magnetron sputter deposition variants, showed a relatively large amount of single and double charged positive ions with kinetic energies up to 55 and 95 eV, as consequence of the applied modifications. The arc source process, even when performed at high pressures of approximately 10 −1 mbar, showed a remarkable amount of ions with energies up to 75 eV.

Density-related properties of metal oxide films

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 applications.

Flash Evaporation. Ein-Quellen-Verdampfungstechnik zur Aufdampfung komplexer Schichten

Flash evaporation is a one-source evaporation technique to deposit complex multicomponent film materials in a relatively simple way onto various substrates. To perform this technique special material preparation and special devices are required. Die Flash-Verdampfung ist eine Ein-Quellen-Verdampfungstechnik, welche in relativ einfacher Weise die Aufdampfung komplexer, multikomponenter Schichtmaterialien ermoglicht. Dazu ist aber eine spezielle Vorrichtung und eine spezielle Materialaufbereitung des Schichtmaterials notwendig.

Stress-related phenomena in reactively dc-magnetron-sputtered aluminum nitride thin films

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 respectively). 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.