Optical metrology with purged reference chip

1. An apparatus comprising:

a chuck for holding a sample and positioning the sample with respect to an optical metrology device;

a reference chip for the optical metrology device, the reference chip being movable to various positions with respect to the optical metrology device, wherein one of the various positions is within an optical path of the optical metrology device when the reference chip is measured by the optical metrology device for calibration and another of the various positions is not within the optical path of the optical metrology device while the optical metrology device is measuring the sample held on the chuck; and

a reference chip purge device that provides a flow of purge gas or air that is directed to the reference chip while the reference chip is in the various positions.

2. The apparatus of claim 1 , wherein the reference chip is mounted to the chuck and is movable to the various positions with respect to the optical metrology device by movement of the chuck.

3. The apparatus of claim 1 , wherein the chuck moves with Polar coordinates, the reference chip is mounted to the chuck and has a linear direction of travel between the various positions, wherein the reference chip purge device does not move with respect to the optical metrology device and is aligned with the linear direction of travel of the reference chip to provide the flow of the purge gas or air directed to the reference chip while the reference chip is in the various positions.

4. The apparatus of claim 3 , wherein the reference chip purge device comprises a linear purge tube having a plurality of apertures through which the purge gas or air is directed over the reference chip while the reference chip is moved in a linear direction.

5. The apparatus of claim 4 , wherein the reference chip purge device further comprises a pair of tubes coupled to the linear purge tube and are located to sides of the optical path of the optical metrology device so as to not obstruct the optical path of the optical metrology device, the pair of tubes having a second plurality of apertures through which the purge gas or air is directed over the reference chip while the reference chip is positioned in the optical path of the optical metrology device.

6. The apparatus of claim 5 , wherein the pair of tubes have a third plurality of apertures through which the purge gas or air is directed over a window or lens of the optical metrology device.

7. The apparatus of claim 1 , wherein the reference chip and the reference chip purge device are coupled to the chuck and are together movable to the various positions with respect to the optical metrology device by movement of the chuck.

8. The apparatus of claim 7 , wherein the reference chip purge device comprises a nozzle that at least partially surrounds the reference chip, the nozzle comprising at least one aperture that directs the purge gas or air over the reference chip.

9. The apparatus of claim 7 , wherein the reference chip purge device comprises an enclosure around the reference chip, the enclosure comprising at least one aperture that directs the purge gas or air over the reference chip and an exit aperture through which the purge gas or air exits the enclosure and through which the optical metrology device samples the reference chip.

10. The apparatus of claim 1 , wherein the apparatus is an integrated metrology module.

11. An integrated metrology module comprising:

a chuck for holding a sample and moving the sample in a linear direction to position the sample with respect to an optical metrology device;

a reference chip for the optical metrology device, the reference chip being mounted to the chuck and movable in the linear direction to various positions with respect to the optical metrology device; and

a reference chip purge device comprising a linear purge tube aligned in the linear direction and having a plurality of apertures through which purge gas or air is directed over the reference chip while the reference chip is moved in the linear direction.

12. The integrated metrology module of claim 11 , wherein the reference chip purge device further comprises a pair of tubes coupled to the linear purge tube that are located to sides of an optical path of the optical metrology device so as to not obstruct the optical path of the optical metrology device, the pair of tubes having a second plurality of apertures through which the purge gas or air is directed over the reference chip while the reference chip is positioned in the optical path of the optical metrology device.

13. The integrated metrology module of claim 12 , wherein the pair of tubes have a third plurality of apertures through which the purge gas or air is directed over a window or lens of the optical metrology device.

14. An integrated metrology module comprising:

a chuck for holding a sample and positioning the sample with respect to an optical metrology device;

a reference chip for the optical metrology device, the reference chip coupled to the chuck and being movable to various positions with respect to the optical metrology device by movement of the chuck; and

a reference chip purge device coupled to the chuck and movable with the reference chip to the various positions with respect to the optical metrology device by movement of the chuck, the reference chip purge device comprising at least one aperture through which purge gas or air is expelled over the reference chip while the reference chip is in the various positions.

15. The integrated metrology module of claim 14 , wherein the reference chip purge device comprises a nozzle that at least partially surrounds the reference chip, the nozzle comprising the at least one aperture that directs the purge gas or air over the reference chip.

16. The integrated metrology module of claim 14 , wherein the reference chip purge device comprises an enclosure around the reference chip, the enclosure comprising the at least one aperture that directs the purge gas or air over the reference chip and an exit aperture through which the purge gas or air exits the enclosure and through which the optical metrology device samples the reference chip.