We introduced a new method called divided-aperture dual-differential confocal microscopy (DADDCM), which delivered large sensing measurement range and high axial focusing capability for profile measurement. There are three virtual pinholes, one is on the optical axis and the other two are placed either side of the optical axis. The signal from each off-axis will be processed with the on-axis one, and the processed signals are added up to acquire the axial intensity response curve with large linear sensing range. So, it can realize the large-scale non-axial fast sensing scanning with an axial focusing capability of ~2 nm and an improved linear sensing range up to 2.1 times that of divided-aperture differential confocal microscopy (DADCM). Benefiting from this large linear sensing range, a non-axial scanning imaging detection of microstructures is implemented, which leads to a high scanning speed. This method provides a new high precision and fast measurement method for the three-dimensional morphology of microstructure.
The localisation accuracy of axial peaks is an important factor for height determination in a confocal microscope. Several algorithms have been proposed for height extraction in surface topography measurements. However, some algorithms ignore the influence of error and discrete sampling on the accuracy. This paper analyzes the localisation accuracy of some common algorithms under different aberrations and random errors, and discusses the effect of axial scanning interval on the accuracy of each algorithm. Finally, we get the application scope of each algorithm. Our results offer a reference for selecting algorithms for confocal metrology.
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