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.