Method and apparatus for positioning and biasing an electro-optic modulator of an electro-optic imaging system

摘要

An imaging method creates a two-dimensional image of a voltage distribution or a capacitance distribution of a substrate under test using an electro-optic modulator. A coarse modulator calibration determines the effect of non-uniformities in the modulator and determines a look-up table relating the gap distance between the modulator and the substrate to the intensity of the light emerging from the modulator. A positioning means calibration determines a look-up table relating control voltage to response by the positioning means. The modulator is moved over a portion of the substrate and then undergoes a positioning step, a fine onsite calibrating step, and a measuring step. The positioning step can be accomplished using the intensity of emerging light to determine modulator gap distance, and the response verses control voltage look-up table to determine a control signal to vertically position the modulator. The look-up tables permit the modulator to be position substantially parallel to the substrate at a desired gap distance using one step positioning.