Reducing speckle in an excimer light source

A photolithography exposure apparatus comprising:

• an optical source configured to produce a light beam made up of pulses and having a wavelength in the deep ultraviolet range, each pulse having a first temporal coherence defined by a first temporal coherence length and each pulse being defined by a pulse duration;
• an optical arrangement comprising an illumination module, a reticle, and a projection stage aligned along an optical axis with a wafer stage;
• and
• a coherence reduction system in the path of the light beam of pulses and configured to, for each of the pulses in the light beam, modulate an optical phase over the pulse duration of the pulse to produce a modified pulse having a second temporal coherence defined by a second temporal coherence length that is less than the first temporal coherence length of the pulse;
• wherein a wafer positioned at the wafer stage is configured to receive a light beam of pulses formed from the modified pulses.