Two-dimensional Fourier domain Ronchi ruling measurement using Talbot-based crossing point modeling

We propose a direct two-dimensional Fourier domain fitting-free method to determine the period of a Ronchi ruling. A precise method to measure a spatial frequency target's quality and fidelity is highly desired as the pattern period directly affects every aspect of a spatial frequency target-based metrology, including the accuracy and precision of the measurement or evaluations. A standard Talbot experimental apparatus and the Talbot effect are used to obtain and model our data. To determine the period of the ruling directly, only a common digital camera, with a protective glass and an air gap in front of the sensor array, and a Ronchi ruling of chrome deposited on a glass substrate are required. The Talbot effect-based crossing point modeling technique requires no calibration or a priori information but simply the pixel size of the digital camera and a precise means of measuring the spatial frequency from a Talbot image. For a Ronchi ruling with a period specification of 0.1 mm, the nanometric measurement was found to be 0.100010 mm with an error level of 5 nm.