| CPC H01J 37/32972 (2013.01) [G01J 3/443 (2013.01); H01J 37/32146 (2013.01); H01J 37/32926 (2013.01); H01J 37/32963 (2013.01); H01L 21/67253 (2013.01)] | 20 Claims |

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1. A method of processing a substrate, the method comprising:
exposing the substrate in a plasma processing chamber to a plasma powered by applying a first power to a first electrode of the plasma processing chamber for a first time duration; and
after the first time duration, determining a process endpoint, the determining comprising:
while exposing the substrate to the plasma by applying the first power to the first electrode, applying a second power to a second electrode of the plasma processing chamber for a second time duration, the second time duration being shorter than the first time duration; and
obtaining an optical emission spectrum from the plasma while applying the second power to the second electrode, wherein an energy of the second power over the second time duration is less than an energy of the first power over a sum of the first time duration and the second time duration by a factor of at least 2.
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