Etch rate monitor using collimated light and method of using same
First Claim
1. An etch rate monitor for monitoring the etch rate of a substrate being etched in an etch chamber comprisinga) a light transmissive window in said etch chamber;
- b) means for applying a collimated light beam through said window near the periphery thereof to said substrate at a normal angle of incidence to the surface of the substrate being etched;
c) means for collecting reflected light having multiple diffraction orders of time varying intensity through said window at a substantial angle to the path of said collimated light;
d) a photodetector, for said reflected light; and
e) means coupled to said photodetector and responsive to the time varying intensity of the collected light for monitoring etch rate in said chamber.
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Accused Products
Abstract
An etch rate monitor for use with semiconductor wafer etching processes includes a source of light of normal incidence to the wafer surface through a window in the etching chamber. In a first embodiment, a Fresnel or positive lens is used to collect some of the diffraction orders caused by the repetitive patterns on the wafer surface which merge from the window. In alternate embodiments, a concave spherical mirror and/or a photodetector system are used to collect the diffraction orders. A collimating lens applies these diffraction orders of normal incidence to interference filters which reject plasma and ambient light and pass the diffraction orders to a photodetector to monitor etch rate as a function of the cycle period between interference minima or maxima caused by the difference in path length between the etched and not etched surfaces of the wafer.
36 Citations
19 Claims
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1. An etch rate monitor for monitoring the etch rate of a substrate being etched in an etch chamber comprising
a) a light transmissive window in said etch chamber; -
b) means for applying a collimated light beam through said window near the periphery thereof to said substrate at a normal angle of incidence to the surface of the substrate being etched; c) means for collecting reflected light having multiple diffraction orders of time varying intensity through said window at a substantial angle to the path of said collimated light; d) a photodetector, for said reflected light; and e) means coupled to said photodetector and responsive to the time varying intensity of the collected light for monitoring etch rate in said chamber. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of monitoring etch rate during semiconductor substrate processing comprising the steps of:
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a) applying a collimated light beam of normal incidence through a light transmissive window provided in an etch chamber proximate to an edge of said window to the surface of a substrate being processed; b) collecting diffracted light having multiple diffraction orders of time varying intensity therefrom and then detecting the intensity of the diffracted light; and c) detecting changes in the diffracted light intensity to monitor etch rate in the chamber. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification