Patent ID: 8592770

Claim:
A method for transmittance mapping of a photomask which is at least partially transparent to deep ultraviolet radiation, the method comprising: directing a wide-band deep ultraviolet incoherent radiation so as to illuminate different areas of an array of successive areas of the photomask; using a non-imaging optical detector with a wide dynamic range of 3 or more orders of magnitude and that is positioned on an opposite side of the photomask with respect to the radiation source to detect the wide-band deep ultraviolet radiation that is transmitted by the photomask and that emerges from the opposite side of the photomask; processing signals from the optical detector to determine the transmittance of the radiation through the different areas of the array of successive areas of the photomask; and repeating determination of the transmittance to determine changes in the transmittance so as to monitor degradation of the photomask.