Method of and apparatus for article inspection including speckle reduction

In the inspection of a patterned article used in the manufacture of semiconductor devices, a method of reducing speckle, said method comprising:

• effecting relative movement between an illuminating beam and said patterned article, said illuminating beam being obtained by modifying a coherent light beam so as to reduce, at least partially, its coherence;
• said modifying of said coherent light beam comprising:
• disposing an acousto-optic modulator in a light path between a source of said coherent light beam and said inspected article so as to effect changes in wavelength and direction of said coherent light beam such that optical path length differences between output beams from said acousto-optic modulator are greater than a coherence length of said coherent light beam.