System and method for monitoring the topography of a wafer surface during lithographic processing

1. A system for monitoring wafer surface topography during a lithographic process comprising:

projection optics that illuminate a portion of the wafer surface, said projection optics having an axis of illumination;

at least one off-axis wafer surface gauge that monitors wafer surface height relative to said projection optics;

at least one backplane gauge that monitors wafer position relative to a backplane;

a filter that translates time-domain measurements of said at least one off-axis wafer surface gauge and said at least one backplane gauge into space-domain measurements;

a coordinate transformer that transforms said space-domain measurements into a single coordinate system;

a computational element that combines said space-domain measurements with a focus set-point to determine correction data; and

a delay line for storing the correction data until the wafer has moved a first predetermined distance.

2. The system of claim 1 , wherein said at least one off-axis wafer surface gauge is located a first distance from said axis of illumination, and wherein said first distance is substantially equal to said first predetermined distance.

3. The system of claim 1 , further comprising at least one stalk gauge that monitors the distance between said projection optics and said backplane.

4. The system of claim 3 , wherein said at least one stalk gauge comprises three stalk gauges.

5. The system of claim 1 , wherein said filter is a finite-impulse-response filter.

6. The system of claim 5 , wherein said finite-impulse-response filter has a width that is controllable based on a velocity associated with movement of the wafer relative to said projection optics.

7. The system of claim 5 , wherein said finite-impulse-response filter outputs said space-domain measurements in response to a spatial interrupt triggered by a space clock determiner.

8. The system of claim 7 , wherein said space clock determiner triggers said spatial interrupt when said wafer moves a second predetermined distance along a predetermined axis of movement.

9. The system of claim 8 , wherein said predetermined axis of movement is approximately parallel to the surface of the wafer.

10. The system of claim 8 , wherein said second predetermined distance is between about 0.1 and 1.0 millimeters.

11. The system of claim 10 , wherein said second predetermined distance is equal to about one-half of a millimeter.

12. A method of monitoring wafer surface topography during a lithographic process comprising the steps of:

(a) capturing wafer position and surface data at a first time when the wafer is at a first wafer location; wherein said capturing wafer position and surface data step includes capturing backbones position data;

(b) generating correction data for a second wafer location prior to the wafer reaching the second wafer location;

(c) storing the correction data in a spatial delay line; and

(d) moving the wafer based on the correction data when the wafer is at said second wafer location at a second time.

13. The method of claim 12 , wherein said step (a) includes capturing backplane position data with a plurality of stalk gauges.

14. A method of monitoring wafer surface topography during a lithographic process comprising the steps of:

(a) capturing wafer position and surface data at a first time when the wafer is at a first wafer location;

(b) generating correction data for a second wafer location prior to the wafer reaching the second wafer location, wherein the generating step includes converting the wafer position and surface data captured during said step (a) from a time-domain into a space-domain and transforming at least some of the data captured during said step (a) from a first coordinate system into a second coordinate system such that all of the data captured during said step (a) is associated with a single coordinate system;

(c) storing the correction data in a spatial delay line; and

(d) moving the wafer based on the correction data when the wafer is at said second wafer location at a second time.

15. The method of claim 14 , further comprising the step of combining the wafer surface data and the wafer position data with focus set-point data in order to produce the correction data.