Lithographic method and apparatus

1. 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 relative 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.

2. The method of claim 1 , wherein the measuring intensities comprises:

using a plurality of radiation poles to illuminate the diffraction grating;

coupling at least two different resulting diffraction orders per radiation pole through the projection system; and

using the projection system to project the diffraction orders onto the target grating, such that a pair of combination diffraction orders is formed by diffraction of the diffraction orders.

3. The method of claim 1 , wherein the first direction is perpendicular to the second direction.

4. The method of claim 1 , wherein the displacing and measuring second intensities are repeated a number of times.

5. The method of claim 1 , wherein:

the plurality of detector modules are arranged in a linear configuration;

neighboring detector modules are separated by a first distance and other neighboring detector modules are separated by a second distance, and

the second distance differs from the first distance by a distance variation which is significantly smaller than the first distance and the second distance.

6. The method of claim 1 , further comprising, before the measuring first intensities, determining a position of the target grating using an alignment sensor.

7. The method of claim 6 , wherein the target grating comprises first portions usable by the mask sensor apparatus and second portions usable by the alignment sensor.

8. The method of claim 1 , wherein a first portion of the plurality of radiation poles is arranged in a substantially linear configuration along the first direction.

9. The method of claim 1 , wherein the target grating is provided on a substrate.

10. The method of claim 1 , wherein the target grating is provided on a component of the lithographic apparatus.

11. The method of claim 10 , wherein the target grating is provided on a substrate stage of the lithographic apparatus.

12. A lithographic apparatus 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 relative 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 relative to the target grating along the first direction.

13. 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 relative 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.

14. 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 relative 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 relative to the target grating along the first direction.

15. A non-transitory computer-readable medium comprising machine-readable instructions for causing a processor to perform 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 relative to the target grating along the first direction.