Enhanced lithographic displacement measurement system

A lithographic projection apparatus comprising:

• a radiation system configured to provide a beam of radiation;
• a support structure to support a patterning device configured to pattern the beam of radiation according to a desired pattern;
• a substrate holder to hold a substrate;
• a projection system configured to project the patterned beam onto a target portion of the substrate;
• an interferometric measuring system configured to measure displacement of a target object, said target object being a displaceable component of said apparatus;
• a second harmonic interferometer configured to measure atmospheric conditions along an optical path;
• a control system responsive to said second harmonic interferometer configured to apply corrections to measurements of said interferometric measuring system;
• wherein measurement beams of said interferometric measuring system and said second harmonic interferometer are directed against and reflected by a same mirror on said target object;
• and
• wherein said mirror on said target object is provided with a protective coating having a nominal thickness such that the sensitivity of measurements of said second harmonic interferometer to variations in the thickness of said coating is minimized.

A lithographic projection apparatus comprising:

• a radiation system configured to provide a beam of radiation;
• a support structure to support a patterning device configured to pattern the beam of radiation according to a desired pattern;
• a substrate holder to hold a substrate;
• a projection system configured to project the patterned beam onto a target portion of the substrate;
• an interferometric measuring system configured to measure displacement of a target object, said target object being a displaceable component of said apparatus;
• a second harmonic interferometer configured to measure atmospheric conditions along an optical path;
• a control system responsive to said second harmonic interferometer and configured to apply corrections to measurements of said interferometric measuring system;
• wherein said second harmonic interferometer comprises:
• a first Brewster prism to receive the beams of said second harmonic interferometer;
• a first detector to receive radiation reflected by said first Brewster prism;
• a quarter-wave plate configured to introduce a 90° phase shift between two beams transmitted by said first Brewster prism;
• a second Brewster prism to receive beams that have traversed said quarter-wave plate;
• a second detector to receive beams reflected by said second Brewster prism;
• and
• a third detector to receive beams transmitted by said second Brewster prism.

A lithographic projection apparatus comprising:

• a radiation system configured to provide a beam of radiation;
• a support structure to support a patterning device configured to pattern the beam of radiation according to a desired pattern;
• a substrate holder to hold a substrate;
• a projection system to hold the patterned beam onto a target portion of the substrate;
• an interferometric measuring system employing an interferometric measuring beam to measure displacement of a target object, said target object being a displaceable component of said apparatus;
• a second harmonic interferometer employing second harmonic interferometer measuring beams to measure atmospheric conditions along an optical path;
• a control system responsive to said second harmonic interferometer and configured to apply corrections to measurements of said interferometric measuring system;
• and
• a beam combiner for spatially combining said interferometric measuring beam and said second harmonic interferometer measuring beams;
• wherein said beam combiner comprises:
• a dichroic mirror configured to transmit said interferometric measuring beam and reflecting said second harmonic interferometer measuring beams and oriented at 45° to said interferometric measuring beam;
• and
• a wave plate to ensure that the polarization of the beams reflected and transmitted by the dichroic mirror are purely S or P polarized.

A lithographic projection apparatus comprising:

• a radiation system configured to provide a beam of radiation;
• a support structure to support a patterning device configured to pattern the beam of radiation according to a desired pattern;
• a substrate holder to hold a substrate;
• a projection system configured to project the patterned beam onto a target portion of the substrate;
• an interferometric measuring system using an interferometric measuring beam to measure displacement of a target object, said target object being a displaceable component of said apparatus;
• a second harmonic interferometer using second harmonic interferometer to measure beams for measuring atmospheric conditions along an optical path;
• a control system responsive to said second harmonic interferometer configured to apply corrections to measurements of said interferometric measuring system;
• and
• a beam combiner to spatially combine said interferometric measuring beam and said second harmonic interferometer measuring beams;
• wherein said beam combiner comprises:
• a dichroic mirror for transmitting said interferometric measuring beam and reflecting said second harmonic interferometer measuring beams;
• and
• first and second wave plates respectively located between the interferometric measuring and said dichroic mirror and between said second harmonic interferometer and said dichroic mirror for correcting the polarization of the beams reflected and transmitted by the dichroic mirror.

A device manufacturing method, comprising:

• providing a substrate that is at least partially covered by a layer of radiation-sensitive material;
• projecting a patterned beam of radiation onto a target portion of the layer of radiation-sensitive material;
• measuring displacement of a target object using an interferometric displacement measuring system;
• measuring atmospheric conditions along an optical path;
• and
• correcting measurements of said interferometric displacement measuring system responsive to measurements of said atmospheric conditions;
• and
• removing from said measurements of atmospheric conditions any dependence on the length of said optical path before correcting measurements of said interferometric displacement measuring system.