The speckle effect occurring in holographic lithography process for sub-nano pattering of photoresist layer deposited on bare sapphire substrate is reported. Thin photoresist layer was exposed in the holographic setup with wavelength of 355 nm to produce the surface relief grating. We observed well-defined valleys and ridges of diffraction grating in SPR700 deposited on GaN grown by metalloorganic vapour phase epitaxy on Al/sub 2/O/sub 3/ whereas the whole structure on sapphire was strongly affected by the speckles created by reflection from the unpolished back surface of the sapphire substrate. Latter, we confirmed with transmission spectroscopy, that even small amount of light transmitted through the substrate, which is back reflected by the unpolished back-surface of sapphire, can strongly disturb nano-sized features in photoresist.
Holographic lithography for grating coupler fabrication in gallium nitride grown on sapphire substrate
2005-01-01
607685 byte
Conference paper
Electronic Resource
English
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