Dark field inspection apparatus and methods

An apparatus for inspecting a specimen by detecting optical beams scattered from the specimen, comprising:

• a beam generator for providing and directing an incident beam towards a specimen;
• an array subtraction device for substantially subtracting a periodic component from an output beam scattered from the specimen in response to the incident beam, wherein the periodic component corresponds to at least one periodic structure on the specimen, wherein the array subtraction device comprises a spatial light modulator (SLM) or pre-fabricated sinusoidal mask positioned in the Fourier plane of the output beam and configured or arranged to receive the output beam and substantially block transmission of each diffraction peak of the periodic component from the received output beam and to partially and gradually block transmission of the remaining edge portions of each peak from the received output beam so as to cause a gradual decrease in transmission at the remaining edge portions while substantially reducing or eliminating the ringing response;
• and
• a detector for receiving the output beam after it is partially transmitted through the SLM and generating an output image or signal based on the output beam after it is partially transmitted through the SLM.

A method for inspecting a specimen, comprising:

• providing and directing an incident beam towards a specimen;
• splitting an output beam, scattered from the specimen in response to the incident beam, into at least two secondary beams
• spatially shifting the at least two secondary beams relative to each other;
• and
• recombining the secondary beams so as to substantially reduce or eliminate a ringing response from the recombined output beam, wherein the recombining of the secondary beams causes (i) a periodic component, corresponding to at least one periodic structure on the specimen, to be subtracted from the recombined output beam, (ii) a ringing response to be substantially reduced or eliminated from the recombined output beam, and (iii) any actual defect components to be prevented from being subtracted from the recombined output beam;
• and
• receiving the recombined output beam and generating an output image or signal based on the recombined output beam.

A method for inspecting a specimen, comprising:

• providing and directing an incident beam towards a specimen;
• substantially subtracting a periodic component from an output beam scattered from the specimen in response to the incident beam, wherein the periodic component corresponds to at least one periodic structure on the specimen, wherein the subtraction operation is accomplished by receiving the output beam and substantially blocking transmission of each diffraction peak of the periodic component from the received output beam and partially and gradually blocking transmission of the remaining edge portions of each peak from the received output beam so as to cause a gradual decrease in transmission at the remaining edge portions while substantially reducing or eliminating the ringing response;
• and
• receiving the output beam and generating an output image or signal based on the output beam.