| CPC H01J 37/32917 (2013.01) [G01N 9/00 (2013.01); H01J 2237/24585 (2013.01)] | 20 Claims |

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1. A plasma sensor module comprising:
an upper substrate that is configured to be exposed to plasma;
a lower substrate configured to contact a lower surface of the upper substrate, the lower substrate having a thickness that is thicker than a thickness of the upper substrate;
at least one probe in the lower substrate; and
a printed circuit board (PCB) in the lower substrate, wherein the PCB is configured to apply an alternating current to the at least one probe to detect a density of the plasma, the at least one probe is below an uppermost surface of the lower substrate, and a lower surface of the upper substrate is entirely planar.
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