Effect of microscale and macroscale patterns on the radiative heating of multilayer thin-film structures

Patterned thin-film structures, which can be found in biological systems as well as in the microelectronics industry, display spatial variations in radiative properties. In the microelectronics industry, wafers are patterned according to the specifications that were developed to perform electrical functions. The thermal processing of these devices is affected by both the local and overall radiative properties of the wafer. The wing of a butterfly is shingled with scales (approximately 100 μm long) which contain thin-film structures. The overall visible wing pattern is created by variations in scale microstructure. On a microscopic level, these scales are patterned with ridges, cross-ridges, and film thickness variations. For the above examples, radiative property changes are due to changes in the geometry and optical properties of the layered structure. These microscale radiative effects are prominent when the film thicknesses are at most the same order of magnitude as the wavelength of radiation. Most studies in the past have focused on uniform film structures over an area. In this paper, the effect of patterns for different size scales is investigated for biological and microelectronic thin-film structures. These examples illustrate when patterns are important to consider in radiative heating