[OPTICAL REVIEW Vol. 8, No. 4 (2001) 227-234]

Measurement of Wave-Front Aberrations in Lithography Lenses with an Overlay Inspection Tool

Hiroshi NOMURA*

Process & Manufacturing Engineering Center, Semiconductor Company, Toshiba Corporation, 8 Shinsugita-cho, Isogo-ku, Yokohama, 235-8522 Japan

(Received January 30, 2001; Accepted April 20, 2001)

Measurement methods using overlay inspection tools have been established for wave-front aberrations in optical lithography lenses used for integrated circuit manufacturing. Three-beam interferometry and asymmetric two-beam interferometry can transform the wave-front aberrations at selected points on the lens pupil to lateral image shifts for fine grating objects. A technique of overlapped exposures makes the image shifts of inner lines of the grating images optically measurable, even if the images are too fine to be resolved optically. These methods are available in the fields of integrated circuit manufacturing and lithography tool assembling. This paper sums up measurement methods for wave-front aberrations. It is experimentally estimated that the methods are equally matched with the phase measuring interferometry widely used in the tool assemblies respecting accuracy and precision.

Key words : photolithography, wave-front aberration, overlay inspection tool, Zernike polynomials