Characterization of silver films deposited by radio frequency magnetron sputtering

Abstract

Silver thin films have been deposited on various substrates at floating potentials by radio frequency magnetron sputtering of a silver target in pure argon plasma using load-locked sputtering equipment. Under the experimental conditions investigated, the deposition rate of silver films was about 70 nm/min so that metal films as thin as 200 nm could be deposited within easily controllable deposition durations. Film surfaces and cross sections were examined by scanning electron microscopy. The morphology was fully dense. The crystallographic structure was investigated by x-ray diffraction. The grains were preferentially oriented with the (111) lattice planes parallel to the film surface and without preferred azimuthal orientation. The films analyzed by Rutherford backscattering spectroscopy were free of detectable impurities. The residual stresses were determined to be tensile from the measurements of the curvature radius of silicon substrates. The calculated value of the thermal stress showed that the intrinsic stress in the films was compressive. The effective Knoop hardness of 2-μm-thick silver films deposited on glass substrates was in the range 1600–1800 MPa, i.e., three times higher than the hardness of the bulk metal. Pure silver films exhibited an electrical resistivity of 1.5–2 μΩ cm, nearly equal to the bulk resistivity.