Method and apparatus for measurement of exit pupil transmittance
A method and apparatus for determining the state of the lens transmittance of an optical projection system are described. A lens or imaging objective transmission is determined as a function of exit pupil transverse direction cosine (nx,ny) at multiple field points thereby providing a more complete analysis and correction of a photolithographic exposure system. The entrance pupil of a projection imaging system is uniformly illuminated and the angular dependence of transmission through the imaging system as a function of exit pupil direction cosines is determined. The illumination source includes a light conditioner with an in-situ illumination structure (ISIS), which is an optical structure that can provide uniform illumination of the system's entrance pupil.
1. A method of determining an exit pupil transmittance of a projection imaging system, the method comprising:
providing an illumination source with a substantially uniform illumination with an angular extent that is greater than an angular size of an entrance pupil of the projection imaging system, the illumination source comprising a light conditioner comprising:
a reticle having a top and bottom surface;
a ball lens mounted below the bottom surface of the reticle; and
an aperture plate and means for mounting same to the reticle;
exposing a recording media with illumination from the illumination source that is emitted from an exit pupil of the projection imaging system; and
reconstructing a transmission function of the exit pupil of the projection imaging system from the exposed recording media.
2. The method of claim 1 , wherein the projection imaging system comprises a stepper, a scanner, a scanner configured for immersion lithography, or a stepper configured for immersion lithography.
3. The method of claim 1 , wherein the recording media comprises a photoresist, an electronic device, or a CCD structure.
4. The method of claim 1 , further comprising correcting the exit pupil numerical aperture.
5. The method of claim 4 , wherein the correction comprises adjusting numerical aperture blades.
6. The method of claim 5 , wherein the aperture blades are adjusted to represent the average numerical aperture of all field points measured.
7. The method of claim 5 , wherein the aperture blades are elliptically configured.
8. The method of claim 4 , wherein the correction comprises adjusting a position of the numerical aperture.
9. The method of claim 8 , wherein the numerical aperture position is adjusted to represent an average numerical aperture for all field points measured.
10. The method of claim 1 , further comprising correcting a transmission error of the projection imaging system.
11. The method of claim 10 , wherein correcting comprises placement of a gray-level pupil filter into a pupil plane.
12. The method of claim 1 , wherein exposing comprises multiple sub-exposures.