P. Rumsby, B. Baloukas, O. Zabeida, L. Martinu, Polytechnique Montréal, Montreal, Quebec, Canada
Ultra thin metal films play a central role in a wide range of modern photonic and optoelectronic technologies, including low emissivity coatings, transparent conductive electrodes, photovoltaic devices, and plasmonic components. At the thicknesses relevant for these applications, noble metals layers exhibit a complex growth behaviour: they first form isolated nano islands whose optical and electrical properties drastically differ from those of continuous films. As a result, device performance becomes highly sensitive to substrate selection, surface preparation, and deposition conditions. Understanding and characterizing the transitions between the isolated, aggregated, percolated, and continuous regimes is, therefore, critical for optimizing film growth and achieving targeted optoelectronic properties.
In this talk, we describe several optical monitoring approaches able to track the above-mentioned morphological transitions in real time. First, time differential reflectance analysis provides a simple and rapid means to identify changes in growth dynamics, allowing fast comparison of deposition conditions and their effects on island coalescence. Second, in-situ ellipsometry is employed in multiple configurations. Stokes parameter monitoring detects the coupling of p polarized light with localized surface plasmons to identify film percolation, and interference enhanced ellipsometry (IE ISE) tracks changes in film resistivity to identify the formation of continuous layers. However, the interference fringes required for IE-ISE impede the usage of the Stokes parameter approach. To remedy this, we present a simple ellipsometry approach capable of monitoring the formation of conductive metal networks regardless of interference enhancement. Together, these techniques enable us to resolve key morphological transitions under various deposition conditions and during subsequent etching. These findings are corroborated or validated by complementary SEM and AFM imaging, and highlight how advanced optical monitoring approaches can guide the controlled fabrication of ultra thin metal films.
References:
1. S. Hafezian, B. Baloukas, L. Martinu, ""Percolation threshold determination of sputtered silver films using Stokes parameters and in situ conductance measurements"", Appl. Opt., 53(24) (2014) 5367-5374.
2. Phillip Rumsby, Bill Baloukas, Oleg Zabeida, and Ludvik Martinu “Investigating the morphological evolution of ion-thinned Ag films via in situ ellipsometry” J. Appl. Phys. 139, 075306 (2026).
3. Riera, A. “Selectively Absorbing Plasmonic Metal-Island Films” [Master's thesis, Polytechnique Montréal]. PolyPublie (2019). https://publications.polymtl.ca/4119/."