Method and Device for Pupil Illumination in Overlay and Critical Dimension Sensors

A metrology system, comprising:

• a polarizing beam splitter (PBS) configured to divide an illumination beam into a first sub-beam and a second sub-beam;
• an illumination mode selector (IMS) having a plurality of apertures, each aperture configured to transmit either the first sub-beam or the second sub-beam and the IMS being configured to be arranged in a plurality of illumination positions, each of the plurality of illumination positions corresponding to an illumination mode;
• a reflective spatial light modulator (SLM) having a pixel array, the pixel array being configured to modify a spatially-resolved beam characteristic of the first sub-beam and the second sub-beam and to reflect either or both of the first sub-beam and the second sub-beam back to the IMS and PBS along a return path, wherein, along the return path, the PBS, IMS, and SLM cooperate to control a complex amplitude or intensity spatial profile of at least the first sub-beam or the second sub-beam;
• an objective projection system configured to receive the first sub-beam and the second sub-beam from the IMS and PBS and direct the first sub-beam and the second sub-beams towards a substrate having a target structure thereon;
• and
• a detector configured to receive an image or diffracted image of the target structure.

A method for inspection comprising:

• splitting, via a polarizing beam splitter (PBS), an illumination beam into a first sub-beam and a second sub-beam;
• transmitting either the first sub-beam or the second sub-beam through an aperture of illumination mode selector (IMS), wherein the IMS is arranged in illumination position corresponding to an illumination mode;
• generating a desired a complex amplitude or intensity spatial profile of the transmitted first sub-beam or the second sub-beam via a reflective spatial light modulator (SLAT) having a pixel array by reflecting a portion of the transmitted first or second sub-beam to the IMS and the PBS;
• directing, via an objective projection system, the portion of the transmitted first sub-beam or second sub-beam from the and PBS towards a substrate having a target thereon;
• and
• detecting an image or diffracted image of the target structure.