Method of measuring spherical aberration in projection system

Abstract

There is provided a method of measuring spherical aberration in a projection system in which a mask pattern is projected in a reduced scale with a light having a wavelength of λ, including the steps of (a) projecting a first mask pattern onto a photosensitive object in a reduced scale, the first mask pattern being defined by light-permeable portions and light-impermeable portions each sandwiched between the light-permeable portions, each of the light-permeable portions having a width equal to the wavelength λ, (b) projecting a second mask pattern onto the photosensitive object in a reduced scale, the second mask pattern being defined by light-permeable portions and light-impermeable portions each sandwiched between the light-permeable portions. each of the light-permeable portions having a width equal to λ/2, (c) exposing the photosensitive object to the light having a wavelength of λ, and developing the photosensitive object, (d) measuring a first location of the photosensitive object at which a width of the light-impermeable portions of the first mask pattern is focused in a minimum, and a second location of the photosensitive object at which a width of the light-impermeable portions of the second mask pattern is focused in a minimum, and (e) measuring spherical aberration, based on the first and second locations. The method makes it possible to accurately measure spherical aberration in a projection system through the use of Levenson type mask patterns having different sizes.

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