| 摘要 |
<p>The invention relates to a method and apparatus for determining the centre and displacement of rectilinear structures or images and the relative concentricity of structures or images during photolithography. The method and apparatus is sufficiently sensitive to measure image centres and thus reduce overlay errors. Additionally improvements are achieved in the accuracy of instances where tool or processing conditions have adversely altered the apparent symmetry of an image. The invention lies in the realisation that in instances of low contrast and/or strong asymmetry and thus where symmetry and/or detail has been degraded, existing techniques can be used providing one compensates by improving the nature of the image line that is used for the purpose of the measurements and is specifically achieved by using a second order derivative of an image cross section profile. Thus in one instance the invention presents a method for determining displacement between rectilinear marks or images by firstly adding or averaging a number of image signals in at least a part of a given row and/or column above a given axis and then using the Laplacian function so as to provide an improved 2D image of said mark.</p> |
