Sidewall lithography of micron-sized features in high-aspect-ratio meso-scale channels using a three-dimensional assembled mask

We report a fabrication technique for dense, detailed lithographic patterning on high-aspect-ratio vertical sidewalls, and illustrate its use through the fabrication of etched array of micro-dimples on the sidewalls of aluminum channels. A photoresist etch mask was spray-coated inside the channel, and patterned using a silicon-fabricated three-dimensional mask which includes a diffuser and a reflector to uniformly redistribute the vertically incident source light in the channel. All the lithographic processes from photoresist coating to development have been carried out without disassembling the channel. Arrays of 107.5 μm-deep circular dimples were isotropically etched onto the sidewalls of a 31 mm-tall, 3.2 mm-wide aluminum channel.