Off axis alignment system for scanning photolithography

An alignment system for use in a scanning photolithographic tool as used in semiconductor manufacturing comprising:

• an illumination source;
• a reticle;
• first lens means for directing light;
• an aperture stop;
• a beamsplitter;
• second lens means for directing light to a wafer and for collecting light reflected and scattered from the wafer, the wafer having plus and minus alignment marks thereon;
• first detector means, associated with said beamsplitter and positioned to receive reflected light over a first predetermined numerical aperture, for detecting light reflected from the wafer;
• second detector means, associated with said beamsplitter and positioned to receive scattered light over a second predetermined numerical aperture, for detecting light scattered from the plus alignment mark on the wafer;
• third detector means, associated with said beamsplitter and positioned to receive scattered light over the second predetermined numerical aperture, for detecting light scattered from the minus alignment mark on the wafer;
• and
• guardband means, positioned between said first detector means and said second and third detector means, for preventing detection of unwanted scattered and reflected light.

An alignment system for use in a scanning photolithographic tool as used in semiconductor manufacturing comprising:

• an illumination source having a bandwidth ranging from 400 to 700 nanometers;
• a reticle having two orthogonal intersecting rectangular apertures therein;
• a first lens;
• an aperture stop following said first lens to limit the numerical aperture of the light delivered to the wafer;
• a beamsplitter positioned to receive light from said first lens;
• an second lens positioned on a side of said beamsplitter opposite said first lens;
• a wafer positioned adjacent said second lens;
• a plurality of wafer alignment marks on said wafer comprised of both plus and minus orientations;
• first detector means, associated with said beamsplitter and positioned to receive reflected light over a first predetermined numerical aperture, for detecting light reflected from said wafer and said plurality of wafer alignment marks;
• first left side scattered light detector means, associated with said beamsplitter and positioned to receive scattered light over a second predetermined numerical aperture, for detecting light scattered into the left direction from the plus alignment mark orientation of said plurality of wafer alignment marks;
• first right side scattered light detector means, associated with said beamsplitter and positioned to receive scattered light over the second predetermined numerical aperture, for detecting light scattered into the right direction from the plus alignment mark orientation of said plurality of wafer alignment marks;
• second left side scattered light detector means, associated with said beamsplitter and positioned to receive scattered light over the second predetermined numerical aperture, for detecting light scattered into the left direction from the minus alignment mark orientation of said plurality of wafer alignment marks;
• second right side scattered light detector means, associated with said beamsplitter and positioned to receive scattered light over the second predetermined numerical aperture, for detecting light scattered into the right direction from the minus alignment mark orientation of said plurality of wafer alignment marks;
• and
• guardband means, positioned between said first detector means and said second and third detector means, for preventing detection of unwanted scattered and reflected light,
• the first predetermined numerical aperture having a value less than the second predetermined numerical aperture.

A photolithographic tool comprising:

• projection optics, said projection optics capable of projecting the image of a pattern onto a wafer, the wafer having a plurality of alignment marks formed thereon, including plus and minus alignment marks;
• alignment optics attached adjacent to said projection optics, said alignment optics receiving alignment illumination from an illumination source, said alignment optics being independent of said projection optics so that the alignment illumination is not substantially collected by said projection optics;
• a plurality of detectors receiving light scattered and reflected from the wafer and the plurality of alignment marks formed thereon and collected by said alignment optics, one of said plurality of detectors detecting light scattered from the plus alignment marks, and another one of said plurality of detectors detecting light scattered from the minus alignment marks,
• whereby the wafer is aligned with the pattern by detection of light received by said plurality of detectors.

A photolithographic tool comprising:

• projection optics, said projection optics capable of projecting the image of a pattern onto a wafer, the wafer having a plurality of plus and minus alignment marks formed thereon;
• alignment optics attached adjacent to said projection optics, said alignment optics receiving alignment illumination from an illumination source used to illuminate the wafer;
• a first detector, said first detector positioned to receive the alignment illumination reflected from the wafer;
• a second detector, said second detector positioned to receive the alignment illumination scattered from one of said plurality of plus alignment marks on the wafer;
• and
• a third detector, said third detector positioned to receive the alignment illumination scattered from one of said plurality of minus alignment marks on the wafer,
• whereby the wafer is aligned with the pattern by detection of light received by said first, second, and third detectors.