The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 27, 2004
Filed:
Oct. 09, 2002
Dale Lindseth, Hollister, CA (US);
Therma-Wave, Inc., Fremont, CA (US);
Abstract
The system and method herein provide a prealigner that has reduced sensitivity to distorting ambient light influences in the environment of a prealigner integrated in a metrology apparatus. A modulated signal is produced by a photo detector in response to modulated light that is partially shielded by wafer positioned in a gap between light source and detector. The pulsed signal is bandpass filtered and demodulated whereby only the difference between high- and low-levels of the pulsed signal are recognized. Flickering and DC components related to ambient light and other distorting operational influences are removed from the analysis unrecognized. Demodulation is synchronously accomplished together with a switching of the light source's power supply. For stable voltage levels of the power supply, a current source is buffered during off-intervals for a constant load on the current source. Also a power steering switch samples the buffers voltage level and takes it as switching condition for the next on-interval of the power supply. Preferably a switched capacitor building block is used as synchronizing element. A final analog output signal is prepared for sampling.