Parallel Etching Process

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Background:  Production of an evenly distributed array of ZnO nanowires requires etching an array of seed points into a properly prepared substrate. Using electron beam lithography is time consuming to etch an array with over 25 million elements per cm2. Technology:  Suman Das, Wenzhuo Wu, Yaguang Wei, Zhong Lin Wang, Dajun Yuan, and Rui Guo from the School of Materials Science and Engineering at Georgia Tech have developed a fabrication process for massively parallel etching of array elements using interference patterns generated by a split laser and either laser interference lithography (LIL) or laser interference ablation (LIA) to locate the array elements. A laser is split and the two beams scanned across the substrate to produce a pattern of interference maxima and minima. Using LIL, the laser beams irradiate a substrate covered in photoresist. The resulting areas of high intensity light partially etch the substrate. The substrate is rotated and the process repeated. The places where intensity maxima overlap between the two stages form an array of exposed substrate for growing nanowires. Under the LIA approach, the beams scan a substrate without photoresist. The interference pattern alternatives troughs of high and low intensity light across the substrate. Following partial ablation of the surface, the substrate is rotated and the process repeated. The locations where intensity minima overlapped between the two processing steps form a two dimensional array of surfaces capable of supporting ZnO nanowire growth. Varying processing parameters – laser energy density, laser aperture size, and substrate rotation angle – controls the dimensions of the array. Both approaches produce uniform arrays of ZnO nanowires by hydrothermal decomposition. Typical nanowires average 500 nm in diameter and 5 μm in length. Potential Commercial Applications: ZnO nanowires are a versatile material with broad application in electronics, optoelectronics, and piezoelectronics. Large scale, massively parallel fabrication of ZnO nanowire arrays enables scalable low cost integration of this versatile material into this wide range of applications. Benefits and Advantages Laser interference patterning enables massively parallel and scalable positioning of ZnO nanowire arrays. This process produces highly uniform arrays of ZnO nanowires by hydrothermal decomposition. Pattering occurs either by laser ablation of the substrate surface or by etching of an optical photoresist down to the substrate surface.  Array dimensions can be changed by varying laser aperture and energy density.