A method and apparatus for reducing speckle during inspection of articles
used in the manufacture of semiconductor devices, including wafers,
masks, photomasks, and reticles. The coherence of a light beam output by
a coherent light source, such as a pulsed laser, is reduced by disposing
elements in a light path. Examples of such elements include optical fiber
bundles; optical light guides; optical gratings; an integrating sphere;
and an acousto-optic modulator. These various elements may be combined as
desired, such that light beams output by the element combinations have
optical path length differences that are greater than a coherence length
of the light beam output by the coherent light source.