Research on three-dimensional detection of microscopy using nonparallel light interference illumination

In order to realize rapid and simple measurement on micro-topography, an optical detection method using interference illumination of nonparallel light was proposed. In this method, a spatial light modulator is used to diffract the laser beam, and two diffracted beams with similar intensity are selected to pass through the objective. Fringe which has accurate phase and period approximately equal to resolution can be obtained by dual-beam interference. The surface topography is detected by calculating four fringe images with equal phase difference. This method neither need interferometric objective to produce fringes nor axial scanning device to record fringe changes, therefore the phase adjustment is accurate, and the imaging is intuitive. In addition, because the phase varies linearly with the pixel coordinates, the fringe period does not need to be modified. The adjustment path of fringe parameters is separated from imaging path, hence the system is simple and easy to adjust. To verify the accuracy of the proposed micro-topography method, a module (Ra=100 nm) and a silicon wafer were used as the samples for three-dimensional reconstruction experiments. The results show that the proposed method can achieve a repeatability measurement accuracy of 8.6 nm (2σ) in axial direction.