| CPC G01N 21/3577 (2013.01) [G01N 21/255 (2013.01); G01N 2021/6471 (2013.01); G01N 2201/0238 (2013.01)] | 10 Claims |

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1. A semiconductor processing tool, comprising:
a chamber;
a viewport through a wall of the chamber; and
a detection module optically coupled to the viewport, wherein the detection module comprises:
an optical bandpass filter with a passband that is up to 10 nm, the optical bandpass filter optically coupled to a light source; and
a first detector optically coupled to the optical bandpass filter; and
a second detector, wherein the second detector is optically coupled to the light source without an intervening optical bandpass filter.
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