Method and apparatus for measuring the dimensions of patterned features on a lithographic photomask

A system for measuring the dimensions of patterned features on a lithographic photomask comprising a light source, an optical microscope for directing light from said source to said photomask and for receiving reflected light from said patterned features in the photomask, means for mounting the photomask so that the patterned features lie in a plane approximately perpendicular the plane of the beam and so that the unpatterned side of the photomask faces the microscope, means for analyzing the reflected light from the photomask and for providing an output indicative of the dimensions of the patterned features on the photomask, and means for inserting optical plates of varying thicknesses between the photomask and the microscope to compensate for photomask substrate thicknesses of less than a predetermined maximum thickness.

A system for measuring the dimensions of patterned features on a lithographic photomask comprising a light source, an optical microscope for directing light from said source to said photomak and for receiving reflected light from said patterned features in the photomask, means for mounting the photomask so that the patterned features lie in a plane approximately perpendicular the plane of the beam and so that the unpatterned side of the photomask faces the microscope, and means for analyzing the reflected light from the photomask and for providing an output indicative of the dimensions of the patterned features on the photomask, said microscope including an optical system which has been optically corrected for imaging through transparent materials.

A method for measuring the dimensions of the patterned features on a lithographic photomask in an iterative etching process comprising the steps of etching the exposed metal from the photomask so as to provide the patterned features therein, placing the etched photomask in a position to be viewed by an optical microscope using reflected light so that the unpatterned substrate side of the photomask is in a position facing the microscope, obtaining reflectivity information at various points on the patterned layer of the photomask so as to provide information indicative of the dimensions of the features in the patterned layer of the photomask and thereby determining the degree of the etch necessary to complete the etching process, and further etching the exposed metal from the photomask to provide the patterned features with greater accuracy.

A method for measuring the dimensions of the patterned features on a lithographic photomask comprising the steps of placing the photomask in a position to be viewed by an optical microscope using reflected light so that the unpatterned substrate side of the photomask is in a position facing the microscope, locating a first edge of the patterned layer, relatively moving the photomask and the microscope through a scan distance until a second edge of the patterned layer is detected, and determining the distance of relative movement as a measurement of the distance between said first and second edges of the patterned layer.