In this research, an approach called modulation-based structured-illumination microscopy (MSIM) is proposed to measure the surface and thickness profile of thin film layers. With this method, a sinusoidal fringe pattern generated by digital micro-mirror devices (DMD) is projected on the sample. The modulation estimation of the reflected patterns is implemented for characterizing the surface and thickness profile of the sample. The measurement system is relatively simple and only an ordinary objective is enough to achieve imaging of the sample. In addition, the reflected signals come from the back surface of the film create less disturbance to the front surface compared with white-light interferometry. Consequently, they can be easily distinguished and achieve a successful measurement precisely. Both simulation and experiments are carried out to demonstrate the availability of this MISM method. The results are in excellent agreement with commercial stage profiler and the relative uncertainty is less than 10 nm.

A differential optical sectioning microscopy with structured-illumination (DOSM-SI) with enhanced axial precision is explored in this paper for three-dimensional (3D) measurement. As the segment of data on the linear region of the contrast depth response curve (CDR) is very sensitive to variation of the height information, the DOSM-SI introduces a new CDR2 with an axial shift to intersect the linear region of the CDR1, which is achieved by using two charge-coupled detectors (CCDs) in the optical path. The CCD1 is located on the imaging plane and the CCD2 is displaced from the imaging plane. The difference between the CDR1 and CDR2 for each pixel is defined as the differential depth response curve (DCDR). Further, the zero-crossing point of the DCDR for each pixel is accurately extracted using the line-fitting technique, and finally, the sample surface can be reconstructed with a high resolution and precision. Since the slope around the zero-crossing point of the DCDR is apparently larger than that of near the focal position, an enhanced resolution and precision can be realized in DOSM-SI. The experiments and theoretical analysis are elaborated to demonstrate the feasibility of DOSM-SI.

The application of dual-grating moiré fringe is introduced in lithography alignment. Minute angular displacement between the two alignment marks will lead to the tilt of moiré fringe, which has an influence in high-accuracy alignment. Proposed is a novel measurement method of angular displacement based on the phase of moiré fringe. The relationship between phase of moiré fringe and angular displacement is analyzed. Both simulation and experiment indicate that an angular displacement can be determined to achieve a linear displacement measurement with error of nanometer level.

Spectroscopic reflectometry is widely used in industry to measure film thickness. However, it is still a challenge to quickly obtain accurate thickness information from films with less than 1 micron thickness. In order to achieve fast demodulation of thin-film signals, this letter proposes a signal demodulation method based on deep learning techniques for thin-film measurements with optical path differences of 100–2000 $nm$ . Here, a reflectivity generation model is used to generate a training dataset. The trained neural network can directly recover thickness information from the reflectance spectrum and the speed is 10 times faster than the traditional method. Simulation results show that this method has strong noise robustness. Experimental results indicate that the deep learning method is reliable in different situations and the average error is less than 3 $nm$ .

Microsphere-assisted microscopy serves as an effective super-resolution technique in biological observations and nanostructure detections, and optical trapping is widely used for the manipulation of small particles like microspheres. In this study, we focus on the selection of microsphere types for the combination of the optical trapping and the super-resolution microsphere-assisted microscopy, by considering the optical trapping performances and the super-resolution imaging ability of index-different microspheres in water simultaneously. Finally, the polystyrene (PS) sphere and the melamine formaldehyde (MF) sphere have been selected from four typical index-different microspheres normally used in microsphere-assisted microscopy. In experiments, the optically trapped PS/MF microsphere in water has been used to achieve super-resolution imaging of a 139 nm line-width silicon nanostructure grating under white light illumination. The image quality and the magnification factor are affected by the refractive index contrast between the microspheres and the immersion medium, and the difference of image quality is partly explained by the photonic nanojet. This work guides us in selecting proper microspheres, and also provides a label-free super-resolution imaging technique in many research fields.