Asymmetric polarization-based frequency shifting interferometer for microelectronics

Frequency Scanning Interferometry (FSI) generally results in superior optical performance comparing with other 3- dimensional measuring methods as its hardware structure is fixed in operation and only the light frequency is scanned in a specific spectral band without vertical scanning of the target surface or the objective lens. However, it still suffers from optical noise due to polarization characteristic of target surfaces and relatively long processing time due to the number of images acquired in frequency scanning phase. First, a Polarization-based Frequency Scanning Interferometry (PFSI) is proposed for optical noise robustness. It consists of tunable laser for light source, λ/4 plate in front of reference mirror, λ /4 plate in front of target object, polarizing beam splitter, polarizer in front of image sensor, polarizer in front of the fiber coupled light source, λ/2 plate between PBS and polarizer of the light source. Using the proposed system, we can solve the problem of fringe image with low contrast by using polarization technique. Also, we can control light distribution of object beam and reference beam. Second the signal processing acceleration method is proposed for PFSI, based on parallel processing architecture, which consists of parallel processing hardware and software such as Graphic Processing Unit (GPU) and Compute Unified Device Architecture (CUDA). Finally, the proposed system is evaluated in terms of accuracy and processing speed through a series of experiment and the obtained results show the effectiveness of the proposed system and method.