Traceable Nanomechanical Metrology of GaN Micropillar Array

This work reports on the nanomechanical metrology of vertically aligned gallium nitride micropillar arrays with high homogeneity and well-controlled geometry. The GaN micro-building blocks are top-down fabricated by combining photolithography, inductively coupled plasma dry reactive ion etching (ICP-DRIE) with SF6/H-2 gases, and post-wet chemical etching treatment by a KOH-based solution. A nanoindenter with a three-sided pyramid Berkovich tip is employed to precisely measure the mechanical properties of the GaN micropillars directly from their top surfaces, hence an additional preparatory work to transfer them on a foreign substrate is not necessary. From the obtained experimental results, the insight of the indentation pop-in phenomenon on the micropillars is carefully investigated. Besides, a confocal laser scanning microscope (CLSM) and an atomic force microscope (AFM) are utilized to confirm the high homogeneity of the micropillar arrays before indentation and to characterize the morphologies of their top surfaces after stress relaxation, respectively. Therefore, the obtained experimental results can be employed as the prior knowledge to be compared with the bulk counterparts, in which the GaN micropillars can be further developed for mechanical force sensors, since the performed measurement techniques have provided the existent mechanical circumstance of the microstructures when a vertical force is applied.