Patent ID: 7019521

Claim:
A method for locating defects in an electric circuit, the method comprising the steps of: providing a scanning magnetic microscope for obtaining micrographic images of magnetic fields, said scanning magnetic microscope including a magnetic probe selectively displaceable relative to a specimen securing stage; obtaining from a first region of a reference circuit secured to said specimen securing stage a reference micrographic image of a first magnetic field emitted therefrom responsive to a first test current, said first region spatially located on said reference circuit relative to a first fiducial thereon, said first micrographic image including a predetermined number of pixels; obtaining from a second region of a circuit-under-test secured to said specimen securing stage a test micrographic image of a second magnetic field emitted therefrom responsive to a second test current, said circuit-under-test circuit being substantially identical in construction to said reference circuit, said second region spatially located on said circuit-under-test relative to a second fiducial thereon, said second fiducial located at a relative location of said circuit-under-test equivalent to the relative location of the first fiducial to said reference circuit, said second test current being substantially equivalent in direction and magnitude to said first test current, said second micrographic image including said predetermined number of pixels; selecting a spatial displacement value to apply to said test micrographic image; and, applying a spatial transform to said test micrographic image for producing a transformed micrographic image of a spatially displaced magnetic field thereof, said spatial transform computing pixel values for said transformed micrographic image via an interpolation function determined from said predetermined number of pixels of said test micrographic image, said interpolation function computing an estimated magnetic field value for a spatial coordinate of said second magnetic field offset by said spatial displacement value; computing a registration error measure from a difference between said transformed micrographic image and said reference micrographic image; and repeating the method at said spatial displacement value selecting step until said registration error measure is minimized.