Patent ID: 8597859

Claim:
A method for cleaning a photomask unit that includes: a photomask having an inner major surface which has a circuit pattern; a pellicle frame extending from the photomask to surround the circuit pattern and to terminate at a mounting end; a pellicle film having a periphery that is connected to the mounting end, to thereby define a sealed space; and at least one ventilation port disposed in the pellicle frame to fluidly communicate with the sealed space, the method comprising: mounting the photomask unit in a receiving space of a chamber, the chamber having inlet and outlet holes to permit a cleaning gas to flow into and out of the chamber, respectively; and generating a temperature differential between the receiving space and the sealed space so as to permit the cleaning gas to flow out of or into the ventilation port; wherein the temperature differential is generated intermittently by irradiating the photomask unit with infrared ray.