Object-side based differential axial measurement based on parallel confocal microscopy

Abstract

The differential confocal microscopic imaging technology can obtain high axial measurement accuracy. However, existing differential confocal microscopic imaging techniques mainly employed to laser scanning confocal microscopy can not satisfy requirements of non-contact online and on-site measurement for workpieces during micro-nano machining processes. Axial measurement methods that were applicable to parallel confocal technology were proposed based on the analysis that differential confocal microscopic imaging system could realize axial measurement principle. In the method, a uniform white light illumination was used. The image space only needed a camera as detector, and the object space made twice imaging of samples before and after the focal point by moving the objective table, then the height of the object surface could be obtained according to the scaled differential curve in advance. Both the theoretical simulation and experimental results are indicated that the method can realize axial measurement with high accuracy. For the measurement of step samples with 500 nm, the average error is 2.9 nm and the relative error is 0.58%. The method is simple and low-cost with high measurement accuracy, thus can be used for general microscope and be easy to realize rapid restoration and measurement of three-dimensional images for samples.