Method for forming a critical dimension test structure and its use
First Claim
Patent Images
1. A method of forming a critical dimension test structure (CDTM) image comprising:
- providing an exposure system having an image plane and an object plane;
providing an image forming layer overlying a substrate disposed in said image plane, said image forming layer requiring a nominal exposure energy to form an image;
providing a first feature disposed in said object plane wherein said first feature has a first orientation and a first critical dimension;
projecting said first feature onto said image forming layer at a first exposure energy less than the nominal exposure energy; and
providing a second feature disposed in said object plane wherein said second feature has a second orientation and a second critical dimension;
projecting said second feature onto said imaging forming layer at a second exposure energy less than the nominal energy wherein a doubly exposed region in said image forming layer is formed where said first feature and said second feature overlap, said doubly exposed region being exposed with a total exposure energy approximately equal to the nominal exposure energy; and
forming said CDTM image in said image forming layer, the CDTM image comprising said doubly exposed region, and having a dimension representative of the average of the first critical dimension and the second test critical dimension.
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Abstract
A method for forming a critical dimension test mark, and the use of the mark to characterize and monitor imaging performance is provided. Methods in accordance with the present invention encompass an exposure of an essentially standard critical dimension bar at each of two overlapping orientations that are rotated about an axis with respect to each other. The overlapped portion forming a critical dimension test mark that is useful for enabling low cost, rapid determination of sub-micron critical dimensions for characterizing exposure tool imaging performance and in-process performance monitoring using optical measurement systems.
27 Citations
17 Claims
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1. A method of forming a critical dimension test structure (CDTM) image comprising:
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providing an exposure system having an image plane and an object plane; providing an image forming layer overlying a substrate disposed in said image plane, said image forming layer requiring a nominal exposure energy to form an image; providing a first feature disposed in said object plane wherein said first feature has a first orientation and a first critical dimension; projecting said first feature onto said image forming layer at a first exposure energy less than the nominal exposure energy; and providing a second feature disposed in said object plane wherein said second feature has a second orientation and a second critical dimension; projecting said second feature onto said imaging forming layer at a second exposure energy less than the nominal energy wherein a doubly exposed region in said image forming layer is formed where said first feature and said second feature overlap, said doubly exposed region being exposed with a total exposure energy approximately equal to the nominal exposure energy; and forming said CDTM image in said image forming layer, the CDTM image comprising said doubly exposed region, and having a dimension representative of the average of the first critical dimension and the second test critical dimension. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for monitoring imaging performance of an exposure tool comprising:
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providing an image forming layer overlying a substrate in an image plan of said exposure tool, said image forming layer characterized in part by an image forming empirical constant determined for said image forming layer and image processing thereof; blanking a portion of an exposure field while exposing, at a nominal exposure energy, a remaining portion of said image forming layer in said exposure field through a reticle positioned in an object plane of said exposure tool; performing a first exposure of a first feature, at a first exposure energy, within said previously blanked portion, said first feature having a first critical dimension and a first orientation, wherein said first exposure energy is less than said nominal exposure energy; performing a second exposure of a second feature, at a second exposure energy, within said previously blanked portion, said second feature having a second critical dimension, approximately equal to said first critical dimension, and a second orientation, wherein said second orientation overlaps a portion of said first orientation and is rotated with respect to said first orientation by a predetermined angle, and wherein said second exposure energy is less than said nominal exposure energy and wherein a sum of said first and second exposure energies is approximately equal to said nominal exposure energy; forming a critical dimension test structure (CDTM) of said overlap portion; measuring a dimension of said CDTM; and determining a critical dimension from said measured CDTM using a linear relationship that provides for;
space="preserve" listing-type="equation">K.sub.il ×
CD=L sin (α
/2)where Kil is the empirical constant of the image forming layer; L is the dimension of the CDTM, and α
is the predetermined angle. - View Dependent Claims (14, 15)
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16. A method for monitoring image performance of an exposure tool comprising:
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providing an image forming layer overlying a substrate in an image plane of said exposure tool, said image forming layer characterized in part by an image forming empirical constant determined for said image forming layer and image processing thereof; blanking a portion of an exposure field while exposing, at a nominal exposure energy, a remaining portion of said image forming layer in said exposure field through a reticle positioned in an object plane of said exposure tool; performing a first exposure of a first feature, at a first exposure energy, within said previously blanked portion, said first feature having a critical dimension and a first orientation, wherein said first exposure energy is less than said nominal exposure energy; performing a second exposure of a second feature, at a second exposure energy, within said previously blanked portion, said second feature having a second critical dimension, approximately equal to said first critical dimension, and a second orientation, wherein said second orientation overlaps a portion of said first orientation and is rotated with respect to said first orientation by a predetermined angle, and wherein said second exposure energy is less than said nominal exposure energy and wherein a sum of said first and second exposure energies is approximately equal to said nominal exposure energy; forming a critical dimension test structure (CDTM) of said overlap portion; measuring a dimension of said CDTM; and determining a critical dimension from said measured CDTM. - View Dependent Claims (17)
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Specification