Radiant energy – With charged particle beam deflection or focussing – With detector
Patent
1987-04-10
1988-11-29
Anderson, Bruce C.
Radiant energy
With charged particle beam deflection or focussing
With detector
250310, H01J 37244
Patent
active
047884312
ABSTRACT:
A specimen distance measuring system uses a plate (36) to obstruct the flux of backscattered electrons produced by an electron beam (18), and to cast a shadow across a measurement detector (32) which is sensitive to the position of the shadow. The shadow plate (36) and measurement detector (32) are aligned at an angle of approximately 45 degrees with a substrate (14) in order to allow calibration of the distance measuring system by scanning the electron beam (18). The measuring system is particularly useful as a height sensor (10) in an electron beam lithography apparatus (12) for sensing the height of a substrate (14). The distance measuring system may also include a reference detector (34) which is positioned in order to receive backscattered electron flux without obstruction from the shadow plate (36). The use of such a reference detector (32) is advantageous in allowing compensation of the signals obtained by the measurement detector, in order to allow the height sensor to operate independently of variations in electron beam current, and variations in substrate backscatter coefficient. The reference and measurement detectors (34,32) may be aligned in a vertical or horizontal plane to be either parallel to or perpendicular to the bombardment electron beam (18). Active feedback may be provided from the height sensor (10) to a vertical stage actuator for adjusting the height of the substrate (14).
REFERENCES:
patent: 3876879 (1975-04-01), McAdams et al.
patent: 4137459 (1979-01-01), Allrecht et al.
Carroll Allen M.
Cavan Daniel L.
Eckes William A.
Howard Glen E.
McCarthy Donald J.
Anderson Bruce C.
Berman Jack I.
Grimes Edwin T.
Masselle Francis L.
Murphy Thomas P.
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