Patent ID: 8417018

Claim:
A method for inspecting a photomask blank or an intermediate thereof having a film on a substrate to be inspected for stress, comprising the steps of: (A) measuring a surface topography of a photomask blank or intermediate having a film to be inspected for stress, (B) removing all the film to be inspected from the photomask blank or intermediate to provide a treated substrate, (C) measuring a surface topography of the treated substrate after removal of the film, and (D) comparing the surface topography of the photomask blank or intermediate prior to said film removal with the surface topography of the treated substrate after said film removal, thereby evaluating a stress in the film, wherein the stress in the film to be inspected is evaluated by (1) measuring each of the outermost surface of the photomask blank or intermediate prior to removal of the film to be inspected and the outermost surface of the treated substrate after removal of the film, by a surface topography measuring device, obtaining XYZ three-dimensional coordinate data of each outermost surface, (2) computing a least square plane of each outermost surface from the coordinate data of each outermost surface, (3) while the relative position between the coordinates of the outermost surface of the photomask blank or intermediate and the least square plane thereof, and the relative position between the coordinates of the outermost surface of the treated substrate and the least square plane thereof are fixed, arranging the coordinates and the least square plane such that (i) two least square planes are positioned on XY plane of a XYZ three-dimensional imaginary space, (ii) both the center of an outermost equivalent region of the photomask blank or intermediate providing the former least square plane and the center of an outermost equivalent region of the treated substrate providing the latter least square plane are positioned at the origin, and (iii) the two outermost equivalent regions are arranged in overlay with their diagonal directions in alignment so that the four corners of the two outermost equivalent regions correspond to each other, respectively, before and after removal of the film to be inspected, (4) within the range of the coordinate data arranged as above, for each pair of coordinates between the coordinates of the outermost surface of the photomask blank or intermediate and the coordinates of the outermost surface of the treated substrate that are coincident in X and Y values, computing the difference (Z 1 -Z 2 ) between a Z value (Z 1 ) of the outermost surface of the photomask blank or intermediate and a Z value (Z 2 ) of the outermost surface of the treated substrate, and (5) determining a sum of the magnitude of maximum and the magnitude of minimum of the difference (Z 1 -Z 2 ) of Z values that represents a warpage change, wherein the surface topographies are compared in terms of the warpage change for evaluation.