Apparatus and process for determination of dynamic lens field curvature
A technique for the determination of dynamic lens field curvature uniquely associated with a photolithographic scanner is described. A series of lithographic exposures is performed on a resist coated silicon wafer using a photolithographic scanner. The lithographic exposures produce an array of focusing fiducials that are displaced relative to each other in a unique way. The resulting measurements are fed into a computer algorithm that determines the dynamic lens field curvature (ZDLC) perpendicular to the scanning direction in an absolute sense. Furthermore, the effects of wafer flatness, wafer surface non-uniformity, and stage error are considered. The ZDLC information can be used to improve lithographic modeling, overlay modeling, and advanced process control techniques related to scanner stage dynamics.
1. A method of determining dynamic lens field curvature associated with a photolithographic scanner having a projection lens, the method comprising:
exposing at least one row of an array of focusing fiducials in a reticle of the scanner onto a substrate that is coated with a recording media;
shifting the substrate and exposing the focusing fiducials to create at least one row of printed overlapped focusing fiducials on the substrate; and
determining dynamic lens field curvature of the projection lens in accordance with focal plane deviation (FPD) values determined from measurement of the focusing fiducials on a developed substrate.
2. A method as defined in claim 1 , wherein the substrate comprises a semiconductor wafer.
3. A method as defined in claim 1 , wherein the substrate comprises a flat panel display substrate.
4. A method as defined in claim 1 , wherein the substrate comprises an optical plate.
5. A method as defined in claim 1 , wherein the substrate comprises a recording media.
6. A method as defined in claim 1 , wherein the photolithographic scanner comprises a stepper.
7. A method as defined in claim 1 , wherein the photolithographic scanner comprises an electron beam imaging system or direct write machine.
8. A method as defined in claim 1 , wherein the photolithographic scanner comprises an extreme ultra-violet imaging apparatus.
9. A method as defined in claim 1 , wherein the photolithographic scanner comprises an electron-beam projection lithography tool.
10. A method as defined in claim 1 , wherein the photolithographic scanner comprises an x-ray imaging system.
11. A method as defined in claim 1 , wherein exposing the focusing fiducials comprises multiple dynamic scans that create a printed focusing fiducial array.
12. A method as defined in claim 1 , wherein the focusing fiducial comprises a reduced transmission reticle.
13. A method as defined in claim 12 , wherein exposing the focusing fiducials comprises multiple dynamic scans that create a printed focusing fiducial array.
14. A method as defined in claim 1 , wherein exposing the focusing fiducials comprises dynamically exposing the focusing fiducial using a sub threshold exposure dose.
15. A method as defined in claim 1 , wherein the substrate is shifted by an amount such that flatness of the substrate over the shifted distance does not vary beyond a desired amount.
16. A method of controlling a photolithographic projection scanner comprising:
exposing at least one row of an array of focusing fiducials in a reticle of the scanner onto a substrate that is coated with a recording media;
shifting the wafer substrate and exposing the focusing fiducials to create at least one row of printed overlapped focusing fiducials on the substrate;
determining dynamic lens field curvature of the projection lens in accordance with focal plane deviation (FPD) values determined from measurement of the focusing fiducials on a developed substrate; and
adjusting the scanner in accordance with the determined dynamic lens field curvature of the projection lens so as to minimize the effects of the dynamic lens field curvature of the scanner.
17. A method as defined in claim 16 , whereby the substrate comprises a semiconductor wafer.