Patent ID: 7430052

Claim:
A method for correlating a line width roughness of gratings, comprising the steps of: (a) generating a characteristic curve of a predetermined grating having a predetermined line width roughness; (b) performing a comparing process to select a matching simulated diffraction spectrum matched with the characteristic curve from a plurality of simulated diffraction spectrums with known line width, and setting a virtual line width of the characteristic curve by using the line width of the matching simulated diffraction spectrum; (c) changing a measuring angle and repeating steps (a) and (b) to generate a virtual line width curve, and calculating a deviation of the virtual line width curve; (d) changing the line width roughness of the predetermined grating and repeating steps (a), (b), and (c) to obtain a predetermined number of deviations of the virtual line width curves; and (e) correlating the line width roughness with the deviation of the virtual line width curve.