Patent ID: 6573500
Filing Date: 2003-06-03
Classification: G02B

Abstract:
A method of precision calibration of magnification of a scanning microscope with the use of a test diffraction grating, comprising the steps of positioning and orienting of a test object formed as a test diffraction grating on a stage of microscope so that strips of a test diffraction grating are perpendicular to a direction along which a calibration is performed; scanning a selected portion of the test object along axes X and Y; measuring values of a signal S in dependence on coordinates X and Y in a plane of scanning and storing said values S (x,y) in a digital form as a two-dimensional digital array; transforming the two-dimensional array of signals S(x, y) into a two dimensional array S (u,v) by turning of the axes so that a direction of a new axis U is perpendicular to the strips of grating and a direction of a new axis V coincides with the strips of the grating; line-by-line mathematical processing of the array S(u,v), including separation from it of a one-dimensional array-line S(u) which contains a profile of periodically repeating strips of the test-object; transformation of the array S(u) into an array P(w) in accordance with formula P&af;(w)=&Sum;j=1N-w&it;â€ƒ&it;{[S&af;(j)-S&af;(j+w)]2}where N is a number of members in the array S(u), w is an argument, j is an index of summing, determination of coordinates of w1, w2, w3, w4 of successive maximums of the function P(w) wherein w4>w3>w21>w0, and a determination of an average pitch Tâ€² of the test grating in pixels for selected line S(u) in accordance with the formula Tâ€²=1n&it;&Sum;i+1u&it;â€ƒ&it;(wi+1-wi).where n is a number of minima in the function P(w); moving to a next line S(u) with a new value of a coordinate V and performing the same steps of the line-by-line mathematical processing for the next line; performing a standard statistic processing of obtained set of values Tâ€² corresponding to various lines v with a calculation of an average for all lines value of the pitch Tave and calculating a magnification Mu on an image medium in selected direction u in accordance with the formula Mu=Tave&CenterDot;LT0&CenterDot;N,wherein L is a width of the image carrier in direction of calibration, T0 is a value of pitch of the test object attested by an independent method, and N is a total number of pixels in a line along the direction u.