System and method for inspecting a workpiece surface by analyzing scattered light in a front quartersphere region above the workpiece

An optical collection system for use in a surface inspection system for inspecting a surface of a workpiece, the surface inspection system having an incident beam projected through a back quartersphere and toward a desired location on the surface of the workpiece to impinge thereon to create reflected light, extending along a light channel axis in a front quartersphere, and scattered light, the incident beam and the light channel axis forming an incident plane, the optical collection system comprising:

• first wing collector and second wing collector positioned to collect a first portion of scattered light and a second portion of scattered light, the first wing collector and second wing collector being disposed in the front quartersphere, outside the incident plane, and at a null of a bi-directional reflectance distribution function when the incident beam is P polarized;
• and
• at least one of the following collection elements:
• a light channel collector, positioned in the incident plane to simultaneously receive the reflected light, or
• a front collector disposed in the front quartersphere and positioned to simultaneously collect a third portion of the scattered light.

A surface inspection system for inspecting a surface of a workpiece, the surface inspection system comprising:

• a scanning beam source for directing an incident beam through a back quartersphere and toward a desired location on the surface of the workpiece at an oblique angle with respect to the surface to impinge thereon to create reflected light, extending along a light channel axis in a front quartersphere, and scattered light, the incident beam and the light channel axis forming an incident plane;
• a workpiece movement subsystem that moves the workpiece relative to the incident beam;
• an optical collection subsystem comprising a first wing collector and a second wing collector positioned to collect a first portion of scattered light and a second portion of scattered light, the first wing collector and the second wing collector being disposed in the front quartersphere, outside the incident plane, and at a null of a bi-directional reflectance distribution function when the incident beam is P polarized;
• and
• at least one of the following collection elements:
• a light channel collector, positioned in the incident plane to simultaneously receive the reflected light, or
• a front collector disposed in the front quartersphere and positioned to simultaneously collect a third portion of the scattered light;
• a detection subsystem coupled to the optical collection subsystem that detects collector output and generates signals in response;
• and
• a processing subsystem operatively coupled to the detection subsystem for processing the signals.

A method for inspecting a surface of a workpiece, the method comprising:

• scanning an incident beam on the surface of the workpiece to impinge thereon to create reflected light, extending along a light channel axis in a front quartersphere, and scattered light, the incident beam and the light channel axis defining an incident plane;
• collecting a first portion of the scattered light at a wing collector disposed in the front quartersphere, outside the incident plane, and at a null of a bidirectional reflectance distribution function when the incident beam is P polarized;
• simultaneously collecting one of the following:
• a second portion of scattered light at a front collector disposed in the front quartersphere, or
• the reflected light at a light channel collector positioned in the incident plane to receive the reflected light;
• detecting collector output and generating signals in response;
• and
• processing the signals to obtain information about the surface.