Influence of bias voltage of APS ion source on performance of hafnium films deposited with ion-assisted technology

With ion beam assisted reactive deposition, hafnia films were prepared at different bias voltages of the APS ion source in the range from 50 V to 140 V on silicon disks and ultraviolet quartz glasses (JGS1) in the Leybold APS 1 104 coating system, where metallic hafnium was used as the starting material. The Lambda 900 spectrophotometer was employed to measure the transmittance spectra of the deposited films. The composition and microstructure were measured with XPS and XRD measurements. AFM was used to characterize the surface morphology and roughness. It is shown that the short ultraviolet optical loss will decrease with the reduction of the bias voltage of the APS ion source when it changes between the two ranges of 140-120 V and 90-50 V, but it is not sensitive to the bias voltage in the range of 110-90 V. At the point of 100 V, the surface roughness and crystal grain size reach maximum values of 5.79 nm and 26.2 nm, respectively. Above 100 V, the hafnia films present noncrystal structure and show a relatively lower level of surface roughness, generally below 2 nm. Below the point, both the surface roughness and the crystal grain size decrease with the reduction of bias voltage. Furthermore, both surface and depth-dependent compositions of all the films investigated show no apparent dependence on the bias voltage.