公开(公告)号：US3901814A

公开(公告)日：1975-08-26

申请号：US48350974

申请日：1974-06-27

Applicant: IBM

Inventor： DAVIS DONALD E ,  HABEGGER MILLARD A ,  MOORE RICHARD D ,  WEBER EDWARD V ,  WOODARD OLLIE C

IPC: G05D3/12 ,  H01J37/304 ,  H01L21/027 ,  H01J37/00

CPC classification number: H01J37/304

Abstract: A square-shaped beam of charged particles is passed over a registration mark, which is formed by a depression or a rise in the surface of a semiconductor wafer. When the beam passes over one edge of the mark, a positive peak signal is produced from a pair of diode detectors located with their surfaces orthogonal to the direction of the beam scan and a negative peak signal is produced when the beam passes over the other edge of the mark. The amplitudes of these peak signals are balanced so that they are substantially the same irrespective of the location of each of the diode detectors relative to the mark in comparison with the location of the other of the diode detectors relative to the mark. These peak signals are compared with positive and negative threshold signals in comparators with an output signal being produced from each of the comparators when its threshold signal is crossed. This enables location of each of the marks to be determined. The positive and negative threshold signals are set during the prior scan with the scans being in opposite directions. The peak to peak amplitude across the registration mark in a particular area is sampled during the first scan and used to provide an automatic gain factor for the remainder of the scans across the mark so that a substantially constant peak amplitude signal is transmitted to the comparators.