Interferometer with pixelated phase shift mask

1. A phase shift interferometer comprising:

a phase mask positioned for either a reference beam or a test beam prior to pass through before being combined in a combined beam or for the combined beam to pass through, the phase mask having an array of pixels, each pixel in the array of pixels being adapted to produce one of a number of predetermined phase shifts between the test beam and the reference beam in the combined beam, wherein the pixels in the array of pixels are arranged to include all of the predetermined phase shifts in repeating horizontal linear groups of pixels that are one column wide and repeating vertical linear groups of pixels that are one row high;

a detector positioned in a plane of an image of a sample to receive the combined beam, the detector comprising an array of pixels aligned to the array of pixels of the phase mask and that receive the image of the sample that comprises interleaved interferograms that differ as a function of the predetermined phase shifts between the test beam and the reference beam in the combined beam and are grouped in repeating horizontal linear groups of pixels and repeating vertical linear groups of pixels; and

at least one processor coupled to the detector, the at least one processor configured to receive signals for each pixel in the array of pixels in the detector and is configured to perform an interferometric measurement based on repeating groups of the interleaved interferograms.

2. The phase shift interferometer of claim 1 , wherein the at least one processor is further configured to:

determine an orientation of a pattern in a portion of the sample; and

select for the interferometric measurement of the portion of the sample the interleaved interferograms grouped in either the repeating horizontal linear groups of pixels or the repeating vertical linear groups of pixels based on the orientation of the pattern in the portion of the sample.

3. The phase shift interferometer of claim 2 , wherein the pattern on the sample are lines having a horizontal orientation or a vertical orientation in the portion of the sample, and wherein the interleaved interferograms in either the repeating horizontal linear groups of pixels or the repeating vertical linear groups of pixels based on the orientation of the pattern in the portion of the sample are selected to match the horizontal orientation or the vertical orientation of the lines in the portion of the sample.

4. The phase shift interferometer of claim 1 , wherein the pixels in the array of pixels are arranged to further include all of the predetermined phase shifts in repeating block groups of pixels that include pixels in multiple rows and columns, and wherein the at least one processor is further configured to:

determine a portion of the sample does not have a resolved pattern; and

select for the interferometric measurement of the portion of the sample the interleaved interferograms grouped in the repeating block groups of pixels.

5. The phase shift interferometer of claim 1 , wherein the phase mask is positioned to receive the combined beam and the pixels in the phase mask are linear polarizers having one of a number of polarizer orientations to produce the predetermined phase shifts between the test beam and the reference beam.

6. The phase shift interferometer of claim 1 , wherein the phase mask is positioned to receive the one of the reference beam or the test beam prior to being combined in the combined beam and the pixels in the phase mask are phase delay elements having one of a number of phase delays to produce the predetermined phase shifts between the test beam and the reference beam.

7. The phase shift interferometer of claim 1 , wherein the at least one processor is further configured to communicate a signal to a process tool that causes the process tool to adjust a process parameter associated with a fabrication process step of a sample fabrication sequence based on the interferometric measurement.

8. The phase shift interferometer of claim 1 , wherein the interferometric measurement produces an average surface height for the pixels in each repeatable pixel group.

9. The phase shift interferometer of claim 1 , wherein the at least one processor is further configured to use the interferometric measurement to at least one of detect a defect on the sample, a roughness of the sample, and a characteristic of a feature on the sample.

10. A phase shift interferometer comprising:

means for producing one of a plurality of predetermined phase shifts between a test beam that is incident on a sample and a reference beam that is incident on a reference surface and are combined to produce a combined beam, wherein all of the plurality of the predetermined phase shifts occur in an array of pixels with repeating horizontal linear groups of pixels that are one column wide and repeating vertical linear groups of pixels that are one row high;

means for detecting an image of the sample from the combined beam as interleaved interferograms that differ as a function of the predetermined phase shifts between the test beam and the reference beam in the combined beam and are grouped in repeating horizontal linear groups of pixels and repeating vertical linear groups of pixels; and

means for performing an interferometric measurement based on the interleaved interferograms based on received signals from each pixel in the array of pixels.

11. The phase shift interferometer of claim 10 , wherein the plurality of predetermined phase shifts comprises a number (N), the horizontal linear groups of pixels are 1×N pixels and the vertical linear groups of pixels are N×1 pixels.

12. The phase shift interferometer of claim 10 , wherein the means for performing the interferometric measurement is configured to:

select the interleaved interferograms grouped in the repeating horizontal linear groups of pixels and the repeating vertical linear groups of pixels;

perform the interferometric measurement on the selected interleaved interferograms;

determine an orientation of a pattern in a portion of the sample; and

select the interleaved interferograms grouped in the repeating horizontal linear groups of pixels and the repeating vertical linear groups of pixels by being configured to select the interleaved interferograms based on the orientation of the pattern in the portion of the sample.

13. The phase shift interferometer of claim 12 , wherein the pattern in the portion of the sample are lines having a horizontal orientation or a vertical orientation on the sample, and the interleaved interferograms are selected to match the orientation of the lines on the sample.

14. The phase shift interferometer of claim 10 , wherein the means for performing the interferometric measurement is configured to:

select the interleaved interferograms grouped in the repeating horizontal linear groups of pixels and the repeating vertical linear groups of pixels;

perform the interferometric measurement on the selected interleaved interferograms;

determine a portion of the sample does not have a resolved pattern; and

select the interleaved interferograms grouped in the repeating horizontal linear groups of pixels and the repeating vertical linear groups of pixels by being configured to select repeating groups of pixels in the portion of the sample based on the portion of the sample not having a resolved pattern.

15. The phase shift interferometer of claim 10 , wherein the means for producing one of the plurality of predetermined phase shifts is positioned to receive the combined beam and the pixels in the in the array of pixels are linear polarizers having one of a number of polarizer orientations to produce the predetermined phase shifts between the test beam and the reference beam.

16. The phase shift interferometer of claim 10 , wherein the means for producing one of the plurality of predetermined phase shifts is positioned to receive the one of the reference beam or the test beam prior to being combined in the combined beam and the pixels in the in the array of pixels are phase delay elements having one of a number of phase delays to produce the predetermined phase shifts between the test beam and the reference beam.

17. The phase shift interferometer of claim 10 , wherein the means for performing the interferometric measurement is configured to communicate a signal to a process tool that causes the process tool to adjust a process parameter associated with a fabrication process step of a sample fabrication sequence based on the interferometric measurement.

18. The phase shift interferometer of claim 10 , wherein the interferometric measurement produces an average surface height for the pixels in each repeatable group of pixels.

19. The phase shift interferometer of claim 10 , wherein the means for performing the interferometric measurement is configured to use the interferometric measurement to at least one of detect a defect on the sample, a roughness of the sample, and a characteristic of a feature on the sample.