Tunable wavelength illumination system

A method to align a wafer in a lithographic apparatus, comprising:

• generating a first high intensity short-pulse radiation;
• propagating the first radiation through a non-linear device to generate a second continuous, broad, and flat spectrum radiation;
• filtering, using an acoustically tunable filter, the second radiation acoustically to generate narrow-band linearly polarized radiation;
• selecting a plurality of narrow-band wavelength set points at a same time or nearly the same time;
• receiving, using a relay and mechanical interface, the narrow-band linearly polarized radiation from the acoustically tunable filter;
• adjusting a profile of the received narrow-band linearly polarized radiation;
• and
• illuminating an alignment target with the narrow-band radiation to enable alignment of the wafer.

An illumination system in a lithographic apparatus, comprising:

• a radiation source configured to convert narrow-band radiation into continuous, flat, and broad-band radiation;
• an acoustically tunable narrow pass-band filter configured to:
• filter the broad-band radiation into narrow-band linearly polarized radiation, wherein the narrow-band linearly polarized radiation is focused on alignment targets of a wafer to enable alignment of the wafer, and
• select a plurality of narrow-band wavelength set points at a same time or nearly the same time;
• and
• a relay and mechanical interface configured to:
• receive the narrow-band linearly polarized radiation from the acoustically tunable narrow pass-band filter;
• and
• adjust a profile of the received narrow-band linearly polarized radiation based on physical properties of the alignment targets.

An alignment system comprising:

• an illumination source configured to provide tunable narrow-band wavelengths over a continuous broad spectral range, wherein the illumination source comprises:
• an acoustically tunable filter configured to:
• filter a broad-band radiation into narrow-band linearly polarized radiation, wherein the narrow band linearly polarized radiation is focused on alignment marks of a wafer to enable alignment of the wafer, and
• select a plurality of narrow-band wavelength set points at a same time or nearly the same time for detecting a position of the alignment mark on the wafer to align the wafer using the alignment mark;
• a relay and mechanical interface confirmed to:
• receive the narrow-band linearly polarized radiation from the acoustically tunable filter;
• and
• adjust a profile of the received narrow-band linearly polarized radiation based on physical properties of the alignment targets;
• and
• an optics system configured to cover the continuous broad spectral range of the illumination source.