Patent ID: 6549648
Filing Date: 2003-04-15
Classification: G01B

Abstract:
A method for determining a position P of a structural element on a substrate, in which the substrate is mounted on a measuring stage that is displaceable in an interferometrically measurable fashion in a measuring plane relative to a reference point, the structural element being imaged on a detector array by an imaging system that has its optical axis arranged perpendicular to the measuring plane, with the pixels of said detector array being arranged in rows and columns parallel to the axes of an x/y coordinate system associated with the substrate, the position P being defined by the distance of one edge of the structural element from the reference point, and the position PIPC of the edge on the detector array being determined by evaluation of an intensity profile of the edge image, that is derived from pixels located in a measuring window, and which is perpendicular to the edge direction,wherein a rectangular measuring window is produced having a boundary line aligned in parallel to the edge direction, the direction of another boundary line of the rectangular measuring window, that is perpendicular to the edge direction, being determined in the coordinate system of the detector array by its angle of rotation &thgr;, further wherein a virtual pixel array is formed having fields arranged in rows and columns parallel to the boundary lines of the measuring window when the boundary lines of the measuring window lie non-orthogonally to the rows and columns of the detector array, and further wherein intensity values are assigned to the fields, said intensity values being determined by weighted evaluation of the intensities of those pixels of the detector array which are covered by a field, and further wherein the position PIPC of the edge is determined from its distance from the reference point based on the intensity values associated with the fields, and wherein the position P of the edge in the x,y coordinate system of the substrate is given as a function of the rotational angle &THgr;, the position PIPC, and the x,y position of the reference point in the x,y coordinate system of the substrate by: P=PIPC+L, with L=xÂ·cos &thgr;+yÂ·sin &thgr;.