Lithographic apparatus, multi-wavelength phase-modulated scanning metrology system and method

A lithographic apparatus comprising:

• an illumination system configured to illuminate a pattern of a patterning device;
• a projection system configured to project an image of the pattern onto a substrate;
• and
• a metrology system comprising:
• a radiation source configured to generate radiation;
• a first optical system, comprising at least one reflective, transmissive, or diffractive optical element, and a waveform generator configured to split the radiation into at least first and second beams of radiation;
• one or more phase adjusters configured to impart a phase difference between the first and second beams;
• a second optical system, comprising at least one reflective or transmissive optical element, configured to direct the first and second beams toward a target structure in an off-axis, not fully coherent, manner to produce first and second scattered beams of radiation;
• a third optical system, comprising at least one focusing optical element, configured to interfere the first and second scattered beams at an imaging detector, wherein the imaging detector is configured to generate a detection signal based on the interfered first and second scattered beams, wherein the metrology system is configured to impart the phase difference before or after the first and second beams interact with the target structure;
• and
• a processor configured to analyze the detection signal to determine a property of the target structure based on at least the phase difference.

A method comprising:

• generating radiation;
• splitting the radiation into at least first and second beams of radiation using at least one beam splitter or diffractive optical element, and a waveform generator;
• imparting a phase difference between the first and second beams using one or more phase adjusters;
• directing, using at least one reflective or transmissive optical element, the first and second beams toward a target structure in an off-axis, not fully coherent manner, to produce first and second scattered beams of radiation, wherein the phase difference is imparted before or after the first and second beams interact with the target structure;
• interfering, using at least one focusing optical element, the first and second scattered beams at an imaging detector;
• modulating one or more phase differences of the first and second scattered beams;
• generating a detection signal using the imaging detector;
• and
• analyzing the detection signal to determine a property of the target structure based on at least the modulated one or more phase differences.