Charles Benjamin

US Patent:

43575404, Nov 2, 1982

Filed:

Dec 19, 1980

Appl. No.:

6/218322

Inventors:

Charles E. Benjamin - Poughkeepsie NY
David J. Crawford - Poughkeepsie NY

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

H01J 3700

US Classification:

2504911

Abstract:

This describes an automatic beam alignment and defect inspection system for masks. The system causes each field or sub-field to be individually aligned for inspection irrespective of the previous alignment of the mask or any other field or sub-field. This is accomplished by scanning a preselected portion of each field of sub-field, with a beam and adjusting the position of the deflection based on the reflected signal while scanning a pre-established portion of the selected field or sub-field. In this way a portion of each selected field or sub-field is used as an alignment mark and stepping errors avoided. Once alignment is achieved a beam spot, comparable to the size of the minimum defect to be detected is scanned over the selected field or sub-field with an overlapping scan to find defects such as mask material in improper places or points where the mask material is missing.