| 摘要 |
A pattern testing apparatus and method are provided to perform exact focus detection even in case the line width and pitch of the pattern of the object image is less than the wavelength of the optical system. A pattern testing apparatus(10) comprises first and second sensors, a first imaging optical system(30), a second imaging optical system(60), a focus detection circuit(80), and a focus control circuit(83). The first and the second sensor convert the optical image of a subject(W) imaged on the incidence surface into an image signal and outputs the image signal. The first imaging optical system forms the optical image on the first sensor. The second imaging optical system branches the optical image from the first imaging optical system to the second sensor, and branches the optical image into two moreover so that a front side focus image and a back side focus image of the optical image of the first sensor are formed on the second sensor. The focus detection circuit performs the respective differentiation of a front side sensor image signal at a front side focus zone and a back side sensor image signal at a back side focus zone obtained from the second sensor. The focus detection circuit also calculates the difference of each focus evaluation value as a focus variation. The focus control circuit controls the focus of the first imaging optical system based on the calculated focus variation.
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