Patent ID: 6368763
Filing Date: 2002-04-09
Classification: G03F,Y10S

Abstract:
A method of detecting aberrations of an optical imaging system, comprising the steps ofarranging a test object, which comprises at least one closed single figure having a phase structure, in the object plane of the system; providing a photoresist layer in the image plane of the system; imaging the test object by means of the system and an imaging beam; developing the photoresist layer; observing the developed image by means of a scanning detection device having a resolution which is considerably larger than that of the imaging system; subjecting the observed image to a Fourier analysis in order to ascertain at least one of different types of changes of shape in the image of the single figure, each type of shape change being indicative of a given kind of aberration, which is represented by a specific Fourier harmonic being a combination of a number of Zernike polynominals each preceded by a weighting factor, the measurement of the Zernike coefficients being carried out by the steps: setting at least one of the illumination parameters successively at a number of different values, the number being at least equal to the number of Zernike polynomials to be determined; measuring a same Fourier harmonic for each of said different values, and calculating the Zernike coefficients from of the measured values for the said Fourier harmonic and by means of stored weighting factors which have been obtained by a previously carried out simulation program.