Method and system for phase/amplitude error detection of alternating phase shifting masks in photolithography

A method for detecting phase and amplitude error of an alternating phase shifting mask, the method comprising:

• passing a collimated light beam through a pair of adjacent, phase shifted openings in the phase shifting mask;
• recording, as a function of angular position, beam intensities of diffracted light passed through said pair of adjacent openings, said beam intensities further being used to plot an angular distribution of diffraction curve with respect to an arc of constant radius about a centerline between said pair of adjacent openings;
• determining, from said angular distribution of diffraction curve, an angle α at which a first diffraction order and a second diffraction order occurs, wherein a represents a deviation from a pair of symmetrically distributed diffraction orders;
• and
• determining, from said angular distribution of diffraction curve, a minimum intensity and a maximum intensity;
• wherein the phase error is calculated from the determined value of a, and the amplitude error is calculated from said minimum intensity and said maximum intensity.

A system for detecting phase and amplitude error of an alternating phase shifting mask, comprising:

• an optical source for directing a collimated light beam through a pair of adjacent, phase shifted openings in the phase shifting mask;
• a photo detector for detecting, through an arc of constant radius about a centerline between said pair of adjacent openings, beam intensities of diffracted light passed through said pair of adjacent openings;
• and
• a test apparatus for recording, as a function of angular position, said beam intensities, said test apparatus further using said beam intensities to plot an angular distribution of diffraction curve;
• wherein the phase error and the amplitude error are determined from said angular distribution of diffraction curve.