Patterning of light-extraction nanostructures on sapphire substrates using nanoimprint and ICP etching with different masking materials

Sapphire nanopatterning is the key solution to GaN light emitting diode (LED) light extraction. One challenge is to etch deep nanostructures with a vertical sidewall in sapphire. Here, we report a study of the effects of two masking materials (SiO 2 and Cr) and different etching recipes (the reaction gas ratio, the reaction pressure and the inductive power) in a chlorine-based (BCl 3 and Cl 2 ) inductively coupled plasma (ICP) etching of deep nanopillars in sapphire, and the etching process optimization. The masking materials were patterned by nanoimprinting. We have achieved high aspect ratio sapphire nanopillar arrays with a much steeper sidewall than the previous etching methods. We discover that the SiO 2 mask has much slower erosion rate than the Cr mask under the same etching condition, leading to the deep cylinder-shaped nanopillars (122 nm diameter, 200 nm pitch, 170 nm high, flat top, and a vertical sidewall of 80° angle), rather th...

Hao Chen, Qi Zhang and Stephen Y Chou

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