Apparatus and methods for removing optical abberations during an optical inspection

Abstract

Disclosed are methods and apparatus for altering the phase and/or amplitude of an optical beam within an inspection system using one or more spatial light modulator(s) (SLMs). In one embodiment, an apparatus for optically inspecting a sample with an optical beam is disclosed. The apparatus includes a beam generator for directing an incident optical beam onto the sample whereby at least a first portion of the incident optical beam is directed from the sample as an output beam and a detector positioned to receive at least a portion of the output beam. The detector is also operable to generate an output signal based on the output beam. The apparatus further includes one or more imaging optics for directing the output beam to the detector and a programmable spatial light modulator (SLM) positioned within an optical path of the incident or output beam. The SLM is configurable to adjust a phase and/or amplitude profile of the incident beam or the output beam. The apparatus also has a control system operable to configure the SLM to alter the phase and/or amplitude profile of the incident beam or the output beam. For example, the SLM may be configured to alter the illumination profile of the incident beam to achieve different inspection modes. In another example, the SLM may be configured to alter the phase and/or amplitude profile of the output beam so as to substantially eliminate aberrations produced by the imaging optics. In other embodiments, the apparatus may include two or more SLM's which are configurable to alter the phase and/or amplitude profile of both the incident beam and the output beam.