US 4,597,665 A · Dual collector optical flaw detector

Abstract

A flaw detector for optically transmissive surfaces having a first light collector above the surface and a second light collector below the surface. A scanning light beam is directed into the first light collector through a beam entrance aperture and only light scattered from the surface is collected. Light specularly reflected from the surface exits the collector through the beam entrance aperture. Similarly, light passing through the surface enters the second collector, but the axial beam component is dumped through an opening in the second collector, while only diffracted light is collected. Preferably, two-stage light collectors are used with the first stage admitting the beam and generating a scattered or diffracted beam component, with the second stage admitting the scattered or diffracted beam component and integrating the component over a collection surface and sampling the integrated portion at a photoelectric detector. An electrical output signal from the detector may be displayed.

Claims16

Dependent claims

Flaw detector apparatus for detecting particles and holes in thin test members having an optical density such that an inspection beam passes therethrough, but is partially reflected from the surface of the member, comprising,

means for optically scanning a test surface with a beam directed along an optical axis, the beam, upon impingement with the test surface, having an axial component along said optical axis, a specularly reflected component and a scattered component above the surface and a diffracted component through any small holes in the surface,
first light collector means disposed above said surface for admitting the beam into the first light collector means and collecting the scattered light component derived from particles on the surface while simultaneously dumping the beam component specularly reflected from the test surface, and
second light collector means disposed below the surface for admitting the beam into the second collector means transmitted through the surface and collecting light diffracted through holes in the surface while simultaneously dumping the beam component directed along the optical axis.

Flaw detector apparatus for test wafers, films and other test surfaces which can be penetrated by a light beam but are at least partially reflective of the beam comprising,

a light source capable of generating a narrow beam,
a support holding a test surface,
scanning means for sweeping the beam in a path along an optical axis across the test surface,
a first light collector above the test surface, said light collector of the integrating type having a light collection surface exposed to said test surface with an entrance aperture admitting the scanning beam as it is swept in said path, while exiting specularly reflected light, a collected light exit aperture at an angle to the beam entrance aperture having a first detector mounted therein, and
a second light collector below the test surface with a light collection surface exposed to a region of the underside of the test surface proximate to where said beam impinges on the test surface, said second light collector admitting any portion of the scanning beam which projects through the test surface, while exiting light transmitted along the beam optical axis, a collected light exit aperture having a second detector mounted therein, whereby said first light collector collects light scattered from atop the test surface and the second light collector collects light transmitted through the test surface.

2 more elements

Dependencies are inferred from the claim text.

Dual collector optical flaw detector

Life of this patent

Dual collector optical flaw detector

Life of this patent

Abstract

Claims16