Micro/Nano profile measurement by structured illumination microscopy utilizing time-domain phase-shift technique

Overview: With the wide application of micro/nanostructures and the rapid development of a micro/nano technique, micro/nano measurement technologies continue to innovate to satisfy increasing needs for a micro/nano optical measurement method, which is widely used in manufacturing, material science, biology, and other fields. The existing micro/nano optical measurement approaches mainly include the laser confocal method, a white light interferometry, and a structured illumination microscopy (SIM). Aiming at the technical difficulties in the rapid detection and reconstruction of three-dimensional micro-nano devices that are difficult to achieve both high precision and high speed, this paper proposes a structured light detection method based on time-domain phase shift technology. The detection and reconstruction of three-dimensional micro-nano devices are realized combined with time-domain phase shift technology. The measurement system is composed of a light source, a digital mirror device (DMD), a microscope and a CCD sensor. The phase of space light from illumination is modulated by the DMD and the special structural light is vertically illuminated onto the micro-nano devices under testing. The reflexed rays from micro-nano devices under testing are detect by the CCD sensor. The innovation of this method is that the micro-nano devices under testing are drive by a piezo transformer (PZT), measuring rays is modulated by DMD and the height information is tested. The basic principle of SIM is to project a set of sinusoidal grating fringes generated by the DMD onto the sample. While the sample is scanned vertically, the modulation of the image keeps changing, which can be extracted by a modulation decoding algorithm. Theoretically, the peak position of the modulation curve coincides with the focus position and the exact peak position can be obtained by Gaussian curve fitting. Afterward, a 3D shape of the object can be restored by acquiring the exact focus position of each pixel. Compared with the traditional structured light detection method, this technology uses the spatial light modulator to measure the phase shift while the sample is scanned axially, so as to ensure the measurement accuracy and improve the measurement efficiency. By analyzing the measurement data, this method can quickly realize three-dimensional shape detection and reconstruction, and the measurement accuracy can be better than 10 nm. After all, this method can enable a simpler measurement system, faster measurement speed, and better adaptability, because only one fringe pattern is projected at each scanning step and a Fourier transform method based on local analysis is applied to extract the modulation curve. To verify the performance of the proposed method, simulations and experiments have been carried out.