Donald M Mccarthy

US Patent:

47884312, Nov 29, 1988

Filed:

Apr 10, 1987

Appl. No.:

7/036731

Inventors:

William A. Eckes - Hayward CA
Lee Veneklasen - Castro Valley CA
Glen E. Howard - Pleasanton CA
Donald J. McCarthy - Hayward CA
Allen M. Carroll - Oakland CA
Daniel L. Cavan - Woodside CA

Assignee:

The Perkin-Elmer Corporation - Norwalk CT

International Classification:

H01J 37244

US Classification:

250397

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).