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Thermophotovoltaic (TPV) systems consume near infrared (NIR) filters, which are key components for high conversion efficiency. Bandpass filters employing annular aperture array (AAA) on a fused silica substrate are one of candidates for matching GaSb cells in high-temperature TPV. It is often placed independently between the emitter and cell, and thus spectral control and heat insulation are simultaneously realized. For high efficiency, the smaller the characteristic size and the larger the size is beneficial for the filter. Novel sidewall lithography based on conventional interference lithography and ion-beam etching is first proposed and used for cost-effective fabrication. An AAA filter with a 80 nm critical dimension in a 100 mm × 160 mm area has been fabricated successfully. After the annealing process at 500 °C, the peak transmittance is increased to 70% from 65%, and no deformation is observed in the structural parameters of the filter before and after annealing, and calculated results demonstrate that the spectral efficiency is about 61%. [ABSTRACT FROM AUTHOR]

In this work, we experimentally investigate the surface nano-roughness during the inductively coupled plasma etching of fused silica, and discover a novel bi-stage time evolution of surface nano-morphology. At the beginning, the rms roughness, correlation length and nano-mound dimensions increase linearly and rapidly with etching time. At the second stage, the roughening process slows down dramatically. The switch of evolution stage synchronizes with the morphological change from dual-scale roughness comprising long wavelength underlying surface and superimposed nano-mounds to one scale of nano-mounds. A theoretical model based on surface morphological change is proposed. The key idea is that at the beginning, etched surface is dual-scale, and both larger deposition rate of etch inhibitors and better plasma etching resistance at the surface peaks than surface valleys contribute to the roughness development. After surface morphology transforming into one-scale, the difference of plasma resistance between surface peaks and valleys vanishes, thus the roughening process slows down. [ABSTRACT FROM AUTHOR]

In this paper, we systematically investigate the morphological characteristics and evolution process of plasma induced pitting damage (PIPD) during the inductively coupled plasma (ICP) etching of fused silica with subsurface damage (SSD). Plasma induced pits are found to have uniform diameter as opposed to SSD induced pits. PIPD evolves differently in physical and reactive etching. In physical etching, the pit diameter increases linearly with etching time due to the etching of pit sidewall, while the depth remains constant. In CHF 3 plasma, depth also increases with etching time. This is due to the redistribution of F-based etchant caused by the pit sidewall, which enhances the local etching rate at the pit bottom. The fact that with increasing etching time the diameter increases linearly but remains uniform implies that all the pits are generated at the same time. More particularly, the fitted line suggests that PIPD forms at the beginning of plasma process. [ABSTRACT FROM AUTHOR]

In this work, we introduce an optimum ICP etching technique that successfully removes the subsurface damage (SSD) layer of fused silica without causing plasma induced surface damage (PISD) or lateral etching of SSD. As one of the commonest PISD initiators, metal contamination from reactor chamber is prevented by employing a simple isolation device. Based on this device, a unique low-density pitting damage is discovered and subsequently eliminated by optimizing the etching parameters. Meanwhile etching anisotropy also improves a lot, thus preventing the lateral etching of SSD. Using this proposed technique, SSD layer of fused silica is successfully removed with a surface roughness of 0.23 nm. [ABSTRACT FROM AUTHOR]