The authors report the development of two fabrication processes for creating high-aspect-ratio lightpipes in a 10 μm thick SiO2 layer, with smooth, uniform, and straight vertical sidewalls. Both processes require only standard optical lithography, without the need for advanced electron beam or deep-UV lithography. One process employs a dielectric etch mask and the other uses a negative photoresist as the etch mask. The experiments show that the CF4 -based reaction gases are best for deep etching with high selectivity and etch rate. Trenches with diameters or width of 1.5 μm are demonstrated, with an aspect ratio of 7.2:1 and a sidewall angle of 87.4°. The authors also achieve cylindrical lightpipes with an aspect ratio of 3.8:1 and a sidewall angle of 89.5°. They anticipate that these high-aspect-ratio lightpipe structures would be useful for complementary metal-oxide semiconductor image sensors, where they would increase the efficiency of light collection, and reduce interpixel cross-talk.
Journal of Vacuum Science & Technology B
Department of Electronics

Ye, W.N, Duane, P. (Peter), Wober, M. (Munib), & Crozier, K.B. (Kenneth B.). (2011). Fabrication of high-aspect-ratio lightpipes. Journal of Vacuum Science & Technology B, 29(3). doi:10.1116/1.3589809