Silver diffusion effects in aluminum nitride/silver films on polydimethylsiloxane gratings via nitrogen–argon sputtering

In this study, we present the effect of silver diffusion into a dielectric medium and its consequent effect on the optical spectra on thin metal-dielectric structures. We show that on a grating pattern, reactive sputter deposition of aluminum nitride immediately following the sputter deposition of a thin layer of silver results in a broadening of the absorption peak of the AlN/Ag gratings which is directly related to diffusion of Ag ions into the overlying AlN layer. Time of Flight Secondary Ion Mass spectroscopy shows that the sample with broadened optical absorption has a significant concentration of Ag within the AlN layer and that the concentration profile follows the error function consistent with Fick’s second law of diffusion. Plasma emission spectroscopy reveal that the use of N₂/Ar mixture instead of an Ar only plasma during RF sputtering reduces the emission of neutral silver atoms, implying that the density of singly ionized silver increases in a nitrogen-containing plasma. However, sputter deposition of AlN following exposure of the underlying silver grating film to ambient atmosphere does not give rise to the same broadening effect in the optical spectra for the AlN/Ag gratings due to the increased concentration of oxygen within the AlN and Ag layers, indicating that oxidation at the AlN/Ag interface inhibits silver migration into the dielectric.