Browse Prior Art Database

RETICLE INSPECTION USING DIFFRACTION PATTERN MASKING

IP.com Disclosure Number: IPCOM000025227D
Original Publication Date: 1984-Feb-29
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 127K

Publishing Venue

Xerox Disclosure Journal

Abstract

Described is an electro-optical system for the inspection of reticles used in integrated circuit wafer fabrication. The system utilizes diffraction patterns generated by the reticle to differentiate between valid patterns on the reticle and defects.

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At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 57% of the total text.

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XEROX DISCLOSURE JOURNAL

RETICLE INSPECTION USING DIFFRACTION PATTERN MASKING U.S. C1. 356/138 Warren M. Sterling
William D. Turner

Proposed Classification

Int. C1. GOlb 11/26

-.-.-

- M2

------

fH,N, LASER

SPAT I A L

FILTER V-

 DEFECT DETECT I ON

POSITIONER LOGIC'

WHITE LIGHT LASER LIGHT

WHITE LIGHT

SOURCE BEAM

 VIDEO MONITOR

J p3

SPLITTER

COMPUTER CONTROL Y x- - -

, TIMING CLOCK SIGNAL

Described is an electro-optical system for the inspection of reticles used in integrated circuit wafer fabrication. The system utilizes diffraction patterns generated by the reticle to differentiate between valid patterns on the reticle and defects.

Current state of the art in reticle inspection systems concentrates on manual inspection which compares the reticle under test to either a master reticle known, or assumed, to be defect free, or a digital representation of a defect-free master reticle. In the system disclosed now, no reference article is used. Instead,

I Volume 9 Number 1 January/February 1984 65

BS2

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RETICLE INSPECTION USING DIFFRACTION PATTERN MASKING (Cont'd)

knowledge of the diffraction patterns generated by proper patterns on the reticle is used to differentiate between such patterns and defects. For the purposes of this discussion, the diffraction pattern is the light pattern obtained when a small portion of the reticle is illuminated with focused laser light. The diffraction patterns are determined strictly by the size and orientation of patterns on the reticle.

The figure shows an optical layout for the reticle inspection station. Laser light

Panchromatic

t white) incoherent light is used to image portions of the reticle for the operator to view the defects directly. A HeNe laser generates a polarized and coherent light beam which is directed by turning mirror h41. Wavefront aberrations are removed with a pinhole spatial filter, and the beam is focused on the reticle, using confocal optics L1 and L2. Panchromatic light for reticle imaging is conditioned with condensing lens L3 and injected into the optical path with beam combiner BS1. The reticle is mounted in plane P1 on a two axes positioning stage under computer control. Beam splitter BS2 is used to split off half of the light for imaging the reticle. The portion of the reticle centered about the focused laser spot is imaged with lens L6 on the vidicon at plane P3 via mirror M2, magnified appropriately....