| CPC G03F 7/70608 (2013.01) [G03F 1/66 (2013.01); G03F 1/82 (2013.01); G03F 7/70491 (2013.01); G03F 7/70741 (2013.01); G03F 7/7085 (2013.01); G03F 7/70925 (2013.01)] | 20 Claims |

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16. A system, comprising:
a gas source;
a moving stage configured to hold a mask pod;
a gas nozzle coupled to the gas source;
an imager; and
one or more controllers, wherein:
the one or more controllers are configured to perform:
moving the moving stage holding the mask pod such that the moving stage stops at each location of a plurality of locations under an outer surface of the mask pod for a predefined amount of time;
at each location of the plurality of locations,
directing a stream of gas from the gas nozzle to the outer surface of a mask pod;
capturing an image of scattered air from each location of the plurality of locations of the outer surface of the mask pod using the imager; and
determining a number of particles in the scattered air as a sampled number of particles based on the captured image; and
generating a map of particles on the outer surface of the mask pod based on the sampled number of particles at each of the plurality of locations.
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