Inspecting a workpiece using scattered light
A surface inspection system, as well as related components and methods, are provided. The surface inspection system includes a beam source subsystem, a beam scanning subsystem, a workpiece movement subsystem, an optical collection and detection subsystem, and a processing subsystem. The system features a variable polarization a polarizing relay assembly arranged to selectively permit the scattered light having a selected polarization orientation to pass along a detector optical axis to a light detection unit in the detection subsystem. The system also features a collector output width varying subsystem for varying the width of an output slit in response to changes in the location of the location scanned on the workpiece.
1. An optical collection and detection 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 comprising an scanned spot having a known scanned spot size, the incident beam impinging on the surface to create scattered light that is collected by a collector module, the collector module comprising:
collection optics for collecting and focusing the scattered light to form focused scattered light;
a collector output slit positioned at an output of the collector module and through which the collection optics focus the scattered light, with scattered light associated with the scanned spot forming an imaged spot at the collector output slit; the collector output slit having a width that is selected to be proportional to the scanned spot size to allow passage of the focused scattered light associated with the scanned spot but to exclude the focused scattered light associated with the workpiece regions other than the desired spot;
a collector output width and side-to-side position varying subsystem for varying the width and side-to-side position of the collector output slit in response to changes in the location of the scanned spot, the collector output width and side-to-side position varying subsystem comprising a workpiece height tracker for tracking a relative height of the workpiece and changing at least one of the collector output slit width and side-to-side position in response thereto, the collector output slit thereby tracking the scanned spot size and side-to-side position as the height of the workpiece changes.
2. An optical collection and detection system, as recited in claim 1 , wherein the incident beam impinging on the surface further creates reflected light that is detected by a light channel position sensing detector; and wherein the workpiece height tracker further comprises a control system that uses a signal from the light channel position sensing detector to sense the relative height of the workpiece.
3. An optical collection and detection system, as recited in claim 1 , wherein the collector output slit is disposed at a Scheimpflug angle to match the angle of the imaged spot at the slit relative to the workpiece.