High-speed and large range measurement technology of microstructure surface morphology based on laser scanning lateral differential confocal

With the development of precision manufacturing technology, the demand for fast measurement of surface morphology and structure at the micro and nano scale is becoming increasingly important. Laser scanning confocal microscopy is widely used for morphology characterization of micro and nano structures due to its high resolution and no need for special sample processing. In order to ensure the measurement accuracy of the measured sample morphology, confocal microscopy generally uses smaller axial scanning steps and more scanning layers, which increases the measurement time; And for samples with a measured area exceeding the transverse scanning field of view of the galvanometer, multiple fields of view need to be measured and spliced to obtain a complete surface morphology. Therefore, the measurement time is multiplied, which is difficult to meet the needs of large-scale rapid detection and iteration of micro and nano processed products in the field of precision manufacturing. In order to achieve fast and large range measurement of micro/nano structure samples, this paper proposes a method of using the linear region of laser scanning transverse differential confocal curve to quickly measure the surface morphology of a field of view, and combining with displacement stage scanning, feature point detection, and morphology image stitching to achieve rapid measurement of large range micro/nano structure morphology. This method uses a galvanometer to quickly scan and obtain the front and rear focal light intensity signals 𝐼_𝐴 and 𝐼_𝐵. The linear region near the zero point of the differential confocal intensity curve are fitted using a cubic polynomial to obtain a linear sensing curve with good linearity and an accurate correspondence between the zero point and the height of the sample. This enables the fast acquisition of micro/nano structure surface morphology within the effective measurement range of the sensing curve without axial scanning. As for samples with heights exceeding the effective measurement range of the linear sensing curve, measurements can be completed quickly with a larger axial scanning step and fewer scanning layers compared to confocal microscopy. For large range samples, this method first quickly measures the surface morphology within a horizontal field of view, then sets a certain proportion of overlapping areas, switches to a new measurement field by the XY lateral displacement stage, and sequentially completes the scanning of multiple sub areas of the samples. Finally, the SURF feature point detection algorithm is used to extract the feature points of the overlapping areas for morphology map stitching, achieving high-precision and rapid measurement of large range micro/nano structures. The measurement method proposed in this article has fast speed and high accuracy, providing an efficient detection method for the field of precision manufacturing.