Multi-channel grating interference alignment sensor

An alignment sensor having a fixed reference grating and a movable wafer grating receiving electromagnetic radiation from a coherent illumination source. The illumination source is split into two beams by a beamsplitter. One beam is directed to a fixed reference grating and the diffracted orders are collected. The other beam from the beamsplitter is directed to a movable wafer grating. The diffracted orders from the movable wafer grating are collected and caused to interfere with the diffracted orders from the fixed reference grating, causing a phase shift indicative of the wafer movement or misalignment with respect to the fixed reference grating. Multiple channels having discrete wavelengths or colors are used to optimize detection and alignment irrespective of wafer processing variables. A polarization fixture on the illumination source and a central polarizing portion on the beamsplitter is used to provide contrast optimization, or alternately a latent image metrology mode. The alignment sensor improves alignment accuracy irrespective of processing variables and provides flexibility improving efficiency in the manufacture of semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a portion of a photolithography system utilizing the present invention.

FIG. 2 is a schematic illustration illustrating the alignment sensor of the present invention.

FIG. 3 is a plan view illustrating diffraction orders collected from the diffraction gratings.

FIGS. 4A and 4B schematically illustrates the change in phase of a plane wave due to horizontal displacement of the diffraction grating.

FIG. 5 is a block diagram illustrating a method to increase production efficiencies in aligning a mask and wafer.

1. An alignment sensor comprising:

2. An alignment sensor as in claim 1 wherein:

3. An alignment sensor as in claim 2 wherein:

4. An alignment sensor as in claim 1 wherein:

5. An alignment sensor as in claim 1 wherein:

6. An alignment sensor as in claim 1 wherein:

7. An alignment sensor as in claim 1 wherein:

8. An alignment sensor as in claim 7 wherein:

9. An alignment sensor comprising:

10. An alignment sensor as in claim 9 wherein:

11. A transformable alignment sensor comprising:

12. An alignment sensor as in claim 11 wherein:

13. A method of aligning a mask and wafer in photolithography comprising the steps of:

14. A method as in claim 13 wherein:

15. A method as in claim 13 wherein:

16. A method of optimizing detection of alignment information for aligning a mask and wafer for use in photolithography comprising the steps of:

17. A method of optimizing detection of alignment information for aligning a mask and wafer for use in photolithography as in claim 16 further comprising the step of:

18. An apparatus for optimizing detection of alignment information for aligning a mask and wafer for use in photolithography comprising:

19. An apparatus for optimizing detection of alignment information for aligning a mask and wafer for use in photolithography as in claim 18 further comprising: