| CPC G01J 3/32 (2013.01) [G01J 3/0291 (2013.01); G01N 21/255 (2013.01); G01N 21/68 (2013.01); G01N 21/9501 (2013.01); G01J 3/443 (2013.01); G01N 21/211 (2013.01); G01N 2021/8416 (2013.01)] | 20 Claims |

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1. An apparatus comprising:
a base component; and
a plurality of collimators housed within the base component, each collimator of the plurality of collimators corresponding to a respective location of a plurality of locations of a wafer in an etch chamber, wherein the plurality of locations comprises a center location of the wafer, a plurality of inner ring locations along an inner ring of the wafer associated with a first set of radially symmetric optical emission spectroscopy (OES) signal sampling paths, and a plurality of outer ring locations along an outer ring of the wafer associated with a second set of radially symmetric OES signal sampling paths.
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