Investigation of the interfacial structure of ultra-thin platinum films using X-ray reflectivity and X-ray photoelectron spectroscopy

Abstract Ultra-thin films of platinum deposited on highly polished 100 silicon have been investigated using X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS) as part of a study on the interface structure of multilayers used for X-ray mirrors. In this paper results are presented for films deposited by electron beam evaporation and by DC-magnetron sputtering. The reflectivity was fitted by assuming an intermediate platinum silicide layer exists between the platinum and the silicon. XPS data clearly confirmed the existence of such a platinum silicide layer. According to the XRR data this layer was estimated to be approximately 10 A thick for e-beam samples and approximately 30 A thick for magnetron samples. For e-beam films the fitted density for the platinum silicide layer was found to decrease from 16.4 g·cm−3 for a nominal 80 A film down to 2.65 g·cm−3 for a nominal 20 A film. For magnetron sputtered films the fitted density was always within the range of 6.1–6.8 g·cm−3. The fitted density of the platinum layer from the e-beam results was always within 5% of the density of bulk platinum whereas for the magnetron sputtered films the density decreased uniformly with decreasing film thickness for films with a nominal thickness less than 30 A. The XPS data show that the magnetron deposited platinum penetrates through the native oxide layer and into the silicon substrate to a far greater degree than the e-beam deposited platinum.