Lithographic Method and Apparatus

A method for measuring a position of a target grating with a mask sensor apparatus which comprises a plurality of detector modules each comprising a diffraction grating located at a mask side of a projection system of a lithographic apparatus and an associated detector, the method comprising:

• measuring first intensities of a combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along a first direction;
• displacing the mask sensor apparatus relative to the target grating in a second direction, wherein a size of the relative displacement is proportional to a spatial frequency of a potential error;
• and
• measuring second intensities of the combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along the first direction.

A lithographic apparatus comprising configured to carry out a method for measuring a position of a target grating with a mask sensor apparatus which comprises a plurality of detector modules each comprising a diffraction grating located at a mask side of a projection system of a lithographic apparatus and an associated detector, the apparatus comprising:

• a measuring device configured to measure first intensities of a combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along a first direction;
• a displacing device configured to displace the mask sensor apparatus relative to the target grating in a second direction, wherein a size of the relative displacement is proportional to a spatial frequency of a potential error;
• and
• the measuring device is configured to measure second intensities of the combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along the first direction.

A method of manufacturing devices wherein device features and target gratings are formed on a series of substrates by a lithographic process, wherein properties of the target gratings on one or more processed substrates are measured by the method for measuring a position of a target grating with a mask sensor apparatus which comprises a plurality of detector modules each comprising a diffraction grating located at a mask side of a projection system of a lithographic apparatus and an associated detector, the method comprising:

• measuring first intensities of a combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along a first direction;
• displacing the mask sensor apparatus relative to the target grating in a second direction, wherein a size of the relative displacement is proportional to a spatial frequency of a potential error;
• and
• measuring second intensities of the combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along the first direction, and
• wherein the measured properties are used to adjust parameters of the lithographic process for the processing of further substrates.

A mask sensor apparatus comprising at least one diffraction grating usable in a method for measuring a position of a target grating with a mask sensor apparatus which comprises a plurality of detector modules each comprising a diffraction grating located at a mask side of a projection system of a lithographic apparatus and an associated detector, the apparatus comprising:

• a measuring device configured to measure first intensities of a combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along a first direction;
• a displacing device configured to displace the mask sensor apparatus relative to the target grating in a second direction, wherein a size of the relative displacement is proportional to a spatial frequency of a potential error;
• and
• the measuring device configured to measure second intensities of the combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along the first direction.

A computer program product containing one or more sequences of machine-readable instructions for implementing a determining step of a method for measuring a position of a target grating with a mask sensor apparatus which comprises a plurality of detector modules each comprising a diffraction grating located at a mask side of a projection system of a lithographic apparatus and an associated detector, the instructions causing a processor to perform operations comprising:

• measuring first intensities of a combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along a first direction;
• displacing the mask sensor apparatus relative to the target grating in a second direction, wherein a size of the relative displacement is proportional to a spatial frequency of a potential error;
• and
• measuring second intensities of the combination of diffraction orders diffracted from the target grating while the mask sensor apparatus is moved relatively to the target grating along the first direction.