Fast and accurate measurement of high aspect ratio MEMS trench array with optical lattice illumination

The high aspect ratio (HAR) micro-electro-mechanical system trench array is a key component for the miniaturization of micro sensors, actuators, and other advanced precision equipment, with broad application prospects in defense, security, aerospace, energy, and other fields. Therefore, accurate and efficient measurement of the aspect ratio of microstructures will become a crucial method for monitoring and ensuring the reliability and stability of the device fabrication process. This paper presents a novel method that combines the lattice light field generated by a micro-axicon array with microscopic imaging technology to accurately measure the width and depth of HAR micro-trench structures. We designed and constructed a dedicated experimental system, initially using monochromatic microscopic imaging and edge extraction algorithms to obtain the width information of the trenches. Subsequently, the trench depth was measured using the diffraction lattice light field generated by the micro-axicon array. Experimental results indicate that as the light field propagates from the top to the bottom of the trench, the light spots in the lattice light field shift in position due to the presence of diffraction angles, with the displacement being closely related to the trench depth. A mapping between the displacement and depth is established through geometric relationships, enabling the calculation of the trench depth. We tested nine trench samples with different aspect ratios, with the maximum aspect ratio reaching 58.12. The experimental results, compared with the scanning electron microscope measurement values, show that the measurement errors are all <9%.