Yun Jung Lin

US Patent:

6555828, Apr 29, 2003

Filed:

Nov 17, 1998

Appl. No.:

09/193198

Inventors:

Jeffrey Bokor - Oakland CA
Yun Lin - Berkeley CA

Assignee:

The Regents of the University of California - Oakland CA

International Classification:

G01B 1506

US Classification:

2504922, 2504921, 2504923

Abstract:

An at-wavelength system for extreme ultraviolet lithography mask blank defect detection is provided. When a focused beam of wavelength 13 nm is incident on a defective region of a mask blank, three possible phenomena can occur. The defect will induce an intensity reduction in the specularly reflected beam, scatter incoming photons into an off-specular direction, and change the amplitude and phase of the electric field at the surface which can be monitored through the change in the photoemission current. The magnitude of these changes will depend on the incident beam size, and the nature, extent and size of the defect. Inspection of the mask blank is performed by scanning the mask blank with 13 nm light focused to a spot a few m in diameter, while measuring the reflected beam intensity (bright field detection), the scattered beam intensity (dark-field detection) and/or the change in the photoemission current.