| CPC H01J 37/32651 (2013.01) [H01L 21/32051 (2013.01); H01L 21/32131 (2013.01); H01L 21/67259 (2013.01)] | 20 Claims |

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1. An apparatus, comprising:
a chamber;
a wafer support stage inside the chamber for supporting a wafer;
a shield disposed over the wafer support stage, the shield having a first opening exposing at least a portion of the wafer support stage;
a cover ring disposed over the shield, the cover ring having a second opening exposing the portion of the wafer support stage;
a position sensor for determining whether the shield and the cover ring are aligned such that a radial offset of the cover ring with respect to the shield is less than an established value, wherein the established value is between 0 millimeters (mm) and 0.3 mm, and a signal from the position sensor triggers an alarm when the radial offset is greater than the established value;
a position adjustment mechanism; and
a controller programmed to:
determine the radial offset using the position sensor;
compare the radial offset to the established value stored in an electronic memory; and
instruct the position adjustment mechanism to adjust a position of at least one of the shield and the cover ring when the radial offset is greater than the established value.
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