Method of detecting a mark by an electron beam and an apparatus therefor
AssigneesHitachi, Ltd., Nippon Telegraph & Telephone Public Corporation
InventorsTsuneo Okubo, Nobuo Hamamoto, Kazuo Ichino
Life of this patent
Estimating the term…
Abstract
This invention relates to a method of detecting a mark by an electron beam, the mark being provided on a sample, which includes the steps of scanning the electron beam over an area of the mark in such a manner that the electron beam is subjected to chopping by sampling pulses having a higher frequency than the scanning frequency, eliminating a component of noise from a detected signal representative of the mark, synchronously rectifying the detected mark signal, binary-coding the detected mark signal as compared with a suitable threshold value, and detecting a position of the mark by using the binary-coded signal.
Claims14
A method of detecting a mark on a sample by an electron beam including the steps of:
- scanning the electron beam over an area of the mark provided on the sample in such a manner that the electron beam is subjected to chopping by sampling pulses having a higher frequency than the scanning frequency;
- detecting the electron beam with a detector after the beam has scanned over said mark to produce a detected mark signal representative of the mark;
- eliminating a component of noise from the detected mark signal;
- synchronously rectifying the detected mark signal after removal of the noise component;
- binary-coding the rectified detected mark signal as compared with a threshold value;
- and
- detecting the position of the mark by using the binary-coded signal.
An apparatus for detecting a mark by an electron beam comprising:
- means for scanning the electron beam over an area of the mark provided on the sample;
- means for chopping the electron beam by sampling pulses having a higher frequency than the scanning frequency;
- means for detecting the electron beam with a detector after the beam has scanned over the mark to produce a detected mark signal representative of the mark;
- means for eliminating a component of noise from the detected mark signal;
- means for synchronously rectifying the detected mark signal after removal of the noise component;
- means for binary-coding the rectified detected mark signal as compared with a threshold value;
- and
- means for detecting the position of the mark by using the binary-coded signal.
Dependencies are inferred from the claim text.