Method and apparatus for focusing a wafer stepper

Claim 2

Apparatus for focusing a lens system in which a lens projects an image of a mask to create a lithographically-defined pattern on a wafer, said lens having a focal plane which is substantially parallel to a wafer received in said system, said apparatus comprising: means for adjusting the position of the lens focal plane and a surface of the wafer relative to one another; a reticle having a plurality of parallel, opaque rectangles formed thereon; a plurality of elongate, transparent segments disposed between said rectangles and having elongate edges which define edges of adjacent rectangles, said rectangles having a width bearing a ratio to the width of said segments of in excess of 2:1.

Claim 3

The apparatus of claim 1 wherein said ratio is substantially 4:1.

Claim 4

The apparatus of claim 2 wherein said apparatus further includes additional opaque rectangles formed on said reticle coaxial with each of said parallel rectangles.

Claim 5

The apparatus of claim 3 wherein said reticle includes additional opaque rectangles oriented at substantially 90 degrees to each other.

Claim 6

The apparatus of claim 1 wherein said transparent segments each have a width of approximately 2.5 microns.

Claim 9

The method of claim 6 wherein the step of using the lens to project an image of alternating light bands comprises the step of projecting such an image in which the ratio of the distance between adjacent light bands to the width of said light bands is substantially 4:1.

Claim 10

The method of claim 7 wherein the step of using the lens to project an image of alternating light bands comprises the step of projecting alternating light bands oriented at 90 degrees to each other.

Claim 11

The method of claim 7 wherein the step of using the lens to project an image of alternating light bands comprises the step of positioning a reticle adjacent said lens on a side of said lens opposite said wafer.

Claim 12

A reticle for projecting a focusing image on a wafer comprising: a substantially planar film; a plurality of parallel, opaque rectangles formed on said film; first, third and fifth rows of said rectangles in which the rectangles are positioned end-to-end with a transparent film section separating one rectangle end from the end of the next adjacent rectangle, each rectangle in one of the rows being aligned with a rectangle in each of the other two rows; and second, fourth and sixth rows of said rectangles in which the rectangles are positioned end-to-end with a transparent film section separating one rectangle end from the next, each rectangle in one of the second, fourth and sixth rows being aligned with a rectangle in each of the other two of said second, fourth and sixth rows and the rectangles in said second, fourth and PG,19 sixth rows further being staggered relative to the rectangles in said first, third and fifth rows.

Claim 13

A reticle for projecting a focusing image on a wafer comprising: a substantially planar film; a plurality of parallel, opaque rectangles formed on said film; first, third and fifth rows of said rectangles in which the rectangles are positioned end-to-end with a transparent film section separating one rectangle end from the end of the next adjacent rectangle, each rectangle in one of the rows being aligned with a rectangle in each of the other two rows; and second, fourth and sixth rows of said rectangles in which the rectangles are positioned end-to-end with a transparent film section separating one rectangle end from the next, each rectangle in one of the second, fourth and sixth rows being aligned with a rectangle in each of the other two of said second, fourth and sixth rows and the rectangles in said second, fourth and PG,19 sixth rows further being staggered relative to the rectangles in said first, third and fifth rows.

Claim 14

The reticle of claim 10 wherein said reticle further includes an elongate, transparent film segment disposed between each row of rectangles and having elongate edges which define the edges of adjacent rectangles.

Claim 15

The reticle of claim 11 wherein said rectangles have a width bearing a ratio to the width of said segments of in excess of 2:1.

Claim 16

The reticle of claim 12 wherein said ratio is substantially 4:1.