Patent ID: 8760642
Filing Date: 2014-06-24
Classification: G01N,G03F

Abstract:
1. A substrate inspection apparatus comprising a stage for supporting a substrate to be inspected, an illumination optical system for projecting an illumination beam toward the substrate, an objective lens for focusing transmitted light through the substrate or reflected light by the substrate, light detection means for receiving the transmitted light or the reflected light emitted from the objective lens, a driving device for driving the objective lens along its optical axis, a position sensor for detecting a position of the objective lens along its optical axis to produce an objective position signal for representing the position of the objective lens along its optical axis, and an autofocus system for controlling the position of the objective lens along its optical axis during the inspection of the substrate, wherein: said stage or the objective lens moves in a first scan direction, a second scan direction whose scanning direction is opposed to that of the first scan direction and a third direction which is perpendicular to the first and second scan directions in a zigzag fashion to scan on scan lines which respectively extend in the first or second scan direction and are set in the third direction one by one, and the inspection data for the substrate and the position data of the objective lens along its optical axis are acquired for each scan line during the scanning of respective scan lines, said autofocus system comprises focus error detection means for detecting a focus error between the objective lens and a surface of the substrate so as to generate a focus error signal, and focus control signal generation means for generating a focus control signal which is used to control the position of the objective lens along its optical axis using a focus data signal comprising of the objective position signal or the objective position signal to which the focus error signal is added, said autofocus system further comprises target value generation means for generating a target value which is used to form the focus control signal by use of the focus data signal, and said target value generation means comprises smoothing means for smoothing the focus data signal so as to output a smoothed focus data signal as the target value, when “i” is assumed as a positive integer and “m” is assumed as a natural number, the focus control signal which is used to scan an (i+2m)-th scan line is formed using the focus data signal which was acquired during the scanning period of an i-th scan line, and said focus control signal generation means generates the focus control signal using the target value which is formed for each scan line.