Determination of best focus for step and repeat projection aligners

Claim 1

A method for macroscopically determining best focus of a projection aligner from a focus/exposure matrix, comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-dimensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of focus, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; and (4) obtaining from the position of said apex on said focus axis an indication of said best focus.

Claim 2

A method for macroscopically determining best focus of a projection aligner from a focus/exposure matrix, comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-dimensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of focus, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; and (4) obtaining from the position of said apex on said focus axis an indication of said best focus.

Claim 7

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner to quantify aberrations and tilt thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-dimensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of focus, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; (4) determining from the position of said apex on said focus axis an indication of best focus; and (5) repeating Steps (1) through (4) at other locations on said lens, by masking said reticle to a field size smaller than the full field and desired lens locations, on additional wfers, whereby any difference in best focus across the field indicates the presence of at least one of aberrations and tilt.

Claim 8

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner to quantify aberrations and tilt thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-dimensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of focus, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; (4) determining from the position of said apex on said focus axis an indication of best focus; and (5) repeating Steps (1) through (4) at other locations on said lens, by masking said reticle to a field size smaller than the full field and desired lens locations, on additional wfers, whereby any difference in best focus across the field indicates the presence of at least one of aberrations and tilt.

Claim 9

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner to quantify lens tilt thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-demensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of foucs, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; (4) determining from the position of said apex on said focus axis an indication of best focus; and (5) repeating Steps (1) through (4) at at least five locations on the field by masking said reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of lens tilt may be extracted by looking for linear variations in said best focus values across said lens.

Claim 10

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner to quantify lens tilt thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-demensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of foucs, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; (4) determining from the position of said apex on said focus axis an indication of best focus; and (5) repeating Steps (1) through (4) at at least five locations on the field by masking said reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of lens tilt may be extracted by looking for linear variations in said best focus values across said lens.

Claim 11

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner to quantify field curvature thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-dimensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of focus, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; (4) determining from the position of said apex on said focus axis an indication of best focus; and (5) repeating Steps (1) through (4) at at least five locations on the field by masking said reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of field curvature may be extracted by looking for second order variations, after removing linear components, in said best focus values across said lens.

Claim 12

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner to quantify field curvature thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-dimensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of focus, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; (4) determining from the position of said apex on said focus axis an indication of best focus; and (5) repeating Steps (1) through (4) at at least five locations on the field by masking said reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of field curvature may be extracted by looking for second order variations, after removing linear components, in said best focus values across said lens.

Claim 13

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner to quantify astigmatism thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-dimensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will b removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of focus, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; (4) determining from the position of said apex on said focus axis an indication of best focus; (5) repeating Steps (1) through (4) with said reticle aligned in different orientations to supply information about sagittal and tangential components; and (6) repeating Steps (1) through (5) at different locations on said lens by masking said reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of astigmatism at any lens location is detemined by the difference between best focus in two orthogonal directions, sagittal and tangential.

Claim 14

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner to quantify astigmatism thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a two-dimensional matrix of resist fields on a polished side of a flat surface of said wafer, employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure along one axis and varying focus along a second axis orthogonal to said first axis, thus transferring multiple images of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will b removed to obtain a parabolic pattern of lined resist fields whose axis and apex lie along the axis of focus, with resist being completely removed during said developing from over-exposed and out-of-focus fields on either side of said parabola; (4) determining from the position of said apex on said focus axis an indication of best focus; (5) repeating Steps (1) through (4) with said reticle aligned in different orientations to supply information about sagittal and tangential components; and (6) repeating Steps (1) through (5) at different locations on said lens by masking said reticle to a smaller field size and desired lens locations, on additional wafers, whereby the magnitude of astigmatism at any lens location is detemined by the difference between best focus in two orthogonal directions, sagittal and tangential.

Claim 15

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner by viewing the whole field simultaneously to quantify aberrations and tilt thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a matrix of maximum-sized resist fields on a polished side of a flat wafer employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit of said resist/aligner system, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure and keeping focus constant, thus transferring an image of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed, to obtain a sequence of fields, some of which are nearly completely covered with a lined resist pattern and some of which are nearly free of all resist; (4) determining for any location the focus value of the center of said fields having resist present at that location, which is an indication of best focus for said location; (5) repeating said determination at all desired locations; (6) exposing additional wafers for all reticle orientations desired and repeating Steps (1) through (5) to obtain additional values of best focus; and (7) comparing the various best focus values obtained, whereby astigmatism is determined by the difference in best focus at any location between best focus for sagittal and tangential lines resulting from reticle orientations and whereby tilt is determined as the linear component of the variation in average of sagittal and tangential best focus across the lens and whereby field curvature is determined by any second order variation remaining after removal of said linear component.

Claim 16

A method of macroscopically diagnosing and characterizing a lens in a step and repeat projection aligner by viewing the whole field simultaneously to quantify aberrations and tilt thereof comprising: (1) forming a layer of resist on a wafer, said resist and said aligner comprising a resist/aligner system having a given resolution limit; (2) forming a matrix of maximum-sized resist fields on a polished side of a flat wafer employing a reticle comprising a plurality of opaque lines and clear spaces of widths slightly above said resolution limit of said resist/aligner system, by sequentially projecting light or other electromagnetic radiation through said reticle, field by field, while varying exposure and keeping focus constant, thus transferring an image of said reticle into said resist; (3) developing said resist so that either exposed or unexposed resist will be removed, to obtain a sequence of fields, some of which are nearly completely covered with a lined resist pattern and some of which are nearly free of all resist; (4) determining for any location the focus value of the center of said fields having resist present at that location, which is an indication of best focus for said location; (5) repeating said determination at all desired locations; (6) exposing additional wafers for all reticle orientations desired and repeating Steps (1) through (5) to obtain additional values of best focus; and (7) comparing the various best focus values obtained, whereby astigmatism is determined by the difference in best focus at any location between best focus for sagittal and tangential lines resulting from reticle orientations and whereby tilt is determined as the linear component of the variation in average of sagittal and tangential best focus across the lens and whereby field curvature is determined by any second order variation remaining after removal of said linear component.