摘要： In this letter, we propose a new method based on the optical sectioning microscopy to characterize the multilayer structure with micro-scale air gaps. With this technique, sinusoidal fringe patterns having a predefined shifted phase produced by digital micro-mirror devices are illuminated onto the sample. The contrast response curve (CRC) of the reflected patterns along the scanning direction is determined by the phase-shifting algorithm while the object is scanned through the focus of the microscope. The maximum contrast value of the CRC occurs at the position where the sample is on the focal plane. The peak positions of the CRC are extracted through the Gaussian fitting and then implemented to achieve the surface topography and gap thickness distribution. To suppress the noise influence caused by the environment fluctuations or other factors, the frequency domain analysis (FDA) has been introduced in this work. The simulations and experiments are conducted to verify the feasibility of this technique, demonstrating the potential to be applied in such fields as semiconductor and biochip, where the air gap may play crucial roles.