Off-axis levelling in lithographic projection apparatus

A lithogaphic projection apparatus comprising:

• a first object table constructed and arranged to hold a mask;
• a second, movable object table constructed and arranged to hold a substrate and having a physical reference surface fixed thereon;
• a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate;
• a positioning system constructed and arranged to move said second object table between an exposure station, at which said projection system can image said mask portion onto said substrate, and a measurement station;
• a height mapping system, located at said measurement station, constructed and arranged to measure positions of a plurality of points on a surface of said substrate in a first direction substantially perpendicular to said surface, to measure a position of said physical reference surface in said first direction and to measure a position of said second object table in said first direction substantially simultaneously with the measurement of at least one of the positions of the plurality of points on the surface of said substrate and the position of said physical reference surface, said lithographic apparatus constructed and arranged to create a height map, relative to said physical reference surface, from said positions of the plurality of points on the surface of the substrate;
• a position measuring system located at said exposure station constructed and arranged to measure a position of said physical reference surface in said first direction, after movement of said second object table to said exposure station;
• and
• a position controller constructed and arranged to control a position of said second object table in at least said first direction, during exposure of said target portion, in accordance with said height map and said position measured by said position measuring system.

A lithographic projection apparatus comprising:

• a first object table constructed and arranged to hold a mask;
• a second, movable object table constructed and arranged to hold a substrate and having a physical reference surface fixed thereon;
• a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate;
• a positioning system constructed and arranged to move said second object table between all exposure station, at which said projection system can image said mask portion onto said substrate, and a measurement station;
• a height mapping system located at said measurement station and constructed and arranged to measure positions of a plurality of points on a surface of said substrate in a first direction substantially perpendicular to said surface and to measure at a substantially same position in a plane substantially perpendicular to said first direction positions of said second object table in said first direction, said lithographic apparatus constructed and arranged to create a height map, relative to said physical reference surface, from said positions of the plurality of points on the surface of the substrate and said positions of said second object table;
• a position measuring system located at said exposure station constructed and arranged to measure a position of said physical reference surface in said first direction, after movement of said second object table to said exposure station;
• and
• a position controller constructed and arranged to control a position of said second object table in at least said first direction, during exposure of said target portion, in accordance with said height map and said position measured by said position measuring system.

A lithographic projection apparatus comprising:

• a first object table constructed and arranged to hold a mask;
• a second, movable object table constructed and arranged to hold a substrate and having a physical reference surface fixed thereon;
• a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate;
• a positioning system constructed and arranged to move said second object table between an exposure station, at which said projection system can image said mask portion onto said substrate, and a measurement station;
• a height mapping system located at said measurement station and constructed and arranged to measure positions of a plurality of points on a surface of said substrate in a first direction substantially perpendicular to said surface, to measure a position of said physical reference surface in said first direction and to measure at a substantially same position to the measurement of said physical reference surface in a plane substantially perpendicular to said first direction a position of said second object table in said first direction, said lithographic apparatus constructed and arranged to create a height map, relative to said physical reference surface, from said positions of the plurality of points on the surface of the substrate;
• a position measuring system located at said exposure station constructed and arranged to measure a position of said physical reference surface in said first direction, after movement of said second object table to said exposure station;
• and
• a position controller constructed and arranged to control a position of said second object table in at least said first direction, during exposure of said target portion, in accordance with said height map and said position measured by said position measuring system.