Optical constants and roughness study of dc magnetron sputtered iridium films

Abstract

Extremely smooth thin films of iridium have been deposited onto superpolished fused silica substrates using dc magnetron sputtering in an argon plasma. The influence of deposition process parameters on film microroughness has been investigated. In addition, film optical constants have been determined using variable angle spectroscopic ellipsometry, over the spectral range from vacuum ultraviolet to middle infrared ͑140 nm-35 m͒. Because the Ir films were optically thick and the surface roughnesses were measured by atomic force microscopy then accounted for in the optical model, the as-determined film optical constants are expected to be the best available for Ir bulk metals, minimally affected by surface overlayers or microstructure.

Optical modeling of iridium thin film erosion under oxygen plasma exposure

“…Moreover, iridium films could be made thicker, taking even longer to become transparent. However, the tradeoff is that increasing film thickness increases surface roughness, 9 which is certainly not desired for substrates. The ultimate goal is to find a good balance between film thickness and surface roughness.…”

“…19 Details on the iridium film optical constant determination are described elsewhere. 9 In this work, spectroscopic ellipsometric data were taken as a function of time, t, during plasma exposure (see Fig. 2).…”

“…In this model, the iridium film optical response was represented by a classical Drude dispersion layer, along with seven Gaussian oscillators, to account for both free carrier and interband absorptions, respectively. 9 Surface roughness was modeled using a Bruggeman effective medium approximation (EMA) layer, using the rms thickness values taken directly from AFM results, assuming 50% iridium and 50% void. We realized that AFM and optical models may not yield the same values for roughness; however, they are closely related.…”

“…8 As reported by our group recently, extremely smooth thin films of iridium were deposited using dc magnetron sputtering, and their optical constants determined using variable angle spectroscopic ellipsometry ͑VASE ® ͒, over the spectral range from vacuum ultraviolet (UV) to middle infrared (IR) ͑140 nm-35 um͒. 9 The effects of roughness on apparent optical constants were carefully removed in the film analysis; therefore the final determined optical constants are expected to be the best available for Ir metals, minimally affected by surface overlayers or surface microstructure.…”

Growth, characterization and micro-pattern fabrication of iridium/Si3N4/Si(100) thin films

“…[2] It is anticipated that iridium films will play an increase important role in the development of the new electronic devices, especially the devices working under harsh environmental conditions. So far, various techniques have been employed in iridium thin films deposition including ion beam assisted deposition, [3] metal-organic chemical vapor deposition (MOCVD), [4] DC [5] and RF [6,7] magnetron sputtering. Among these techniques, magnetron sputtering is especially attractive due to its superior features such as high deposition rate and excellent adhesion of the sputtered films to the substrate.…”