# US 4,999,510 A · Apparatus for detecting foreign particles on a surface of a reticle or pellicle

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- Number: US 4,999,510 A
- Document ID: US4999510A
- Status: Granted
- Kind: A
- Application number: 07/427,365
- Filed: 1989-10-27
- Granted: 1991-03-12
- Earliest claimed: 1987-01-29
- Assignees: Nikon Corporation
- Inventors: Fuminori Hayano; Kazunori Imamura; Sunao Murata; Kinya Kato
- Web page: https://patentgrep.com/patent/US4999510A

## CPC

- G03F 1/62: Pellicles, e.g. pellicle assemblies, e.g. having membrane on support frame; Preparation thereof
- G01N 21/94: Investigating contamination, e.g. dust (G01N21/85 takes precedence)
- G03F 1/84: Inspecting
- G01N 2021/4721: {using a PSD}
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

An apparatus for detecting foreign particles on a surface of a reticle or pellicle comprises an optical system through which a light beam forms a light spot on the surface. The surface and the light spot are shifted relatively so that the light spot scans the surface. Light detectors receive light scattered by a foreign particle and directed in different directions, respectively, and generated photoelectric outputs by which the presence of the foreign particle is discriminated. Beam diameter and scanning speed are varied to provide the most effective operation for particles of different sizes.

## Claims

### Claim 1

An apparatus for detecting foreign particles on a surface of a reticle or pellicle, comprising:
a supplying means for supplying a light beam which forms a light spot on said surface;
a scanning means for shifting said surface and said light spot relatively so that said light spot scans the surface;
a plurality of light detectors for receiving light scattered by a foreign particle on said surface and directed in different directions, respectively, and for generating photoelectric outputs, respectively;
changing means for changing the diameter of said light beam; and
a discriminating means for discriminating the presence a foreign particle on said surface on the basis of each of said photoelectric outputs.

### Claim 2 (depends on 1)

An apparatus as set forth in claim 1, wherein said discriminating means includes a comparing means for comparing each of said photoelectric outputs with a reference output level, and a correcting means for correcting said comparing means by changing said photoelectric outputs and said reference output level relatively in accordance with said changing means.

### Claim 3 (depends on 1)

An apparatus as set forth in claim 1, wherein said scanning means changes speed of said shifting in accordance with changing of said beam diameter.

### Claim 4 (depends on 1)

An apparatus as set forth in claim 1, wherein said changing means includes an aperture diaphragm retractable with respect to said beam.

### Claim 5 (depends on 1)

An apparatus as set forth in claim 1, wherein said changing means includes a plurality of beam expanders having different expansions and means for selectively passing said light beam through any one of said beam expanders.

### Claim 6 (depends on 1)

An apparatus as set forth in claim 1, wherein said changing means includes variable expansion beam expander means.

### Claim 7 (depends on 1)

An apparatus as set forth in claim 1, wherein said supplying means includes a light source and an objective optical system fixed in said apparatus and arranged opposite to said surface, wherein said light beam is transmitted from said light source through said objective optical system to said surface, and wherein said changing means comprises optical means between said light source and said objective optical system for changing a numerical aperture of said supplying means.