METHOD OF DETERMINING THE OVERLAY ACCURACY OF MULTIPLE PATTERNS FORMED ON A SEMICONDUCTOR WAFER
First Claim
1. A method of determining the overlay accuracy of multiple patterns formed within an arrangement of exposure fields on a semiconductor wafer, comprising:
- providing a test wafer to an overlay measurement tool, the test wafer comprising the exposure fields with the patterns and a plurality of overlay targets formed with the patterns across the test wafer;
measuring first shifts of each of the overlay targets;
determining a first set of correctable and/or non-correctable overlay errors from the measured first shifts of the plurality of overlay targets;
selecting a number of overlay targets from said plurality of patterns and forming at least two different subsets thereof, wherein each subset comprises overlay targets residing in at least three of the exposure fields;
for each of the subsets performing the steps a) to c);
a) obtaining the measured first shifts, which correspond to said selected overlay targets, b) calculate a second set of correctable and/or non-correctable errors from the measured first shifts of the selected overlay targets, c) comparing the second set of correctable and/or non-correctable errors with the first set of correctable and/or non-correctable errors;
selecting one of the subsets in dependence of the comparison results;
providing the semiconductor wafer and measuring second shifts of those overlay targets, whose positions on the semiconductor wafer coincide with positions of the overlay targets of the selected subset on said test wafer;
assessing the quality of said semiconductor wafer based on said measured second shifts.
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Accused Products
Abstract
From a plurality of overlay targets formed with patterns on a test wafer, subsets are formed and for each overlay target contained in the subsets, the measurement results of overlay shifts are obtained. Mean shifts, residual data and ranges are calculated for each subset and compared with the 100% full field results. The subset that represents the full field results to highest agreement is selected and used to measure the overlay of a second or any further wafer. A most preferred embodiment relates to selecting each of the subsets in a form such that the overlay target positions are concentric about the wafer center. In a further advantageous aspect, each of the subsets is confined to concentric areas about the wafer center, e.g., an inner circle and/or one or more outer rings. A distribution of selected overlay targets placed in representative regions on the wafer is thus guaranteed.
24 Citations
18 Claims
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1. A method of determining the overlay accuracy of multiple patterns formed within an arrangement of exposure fields on a semiconductor wafer, comprising:
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providing a test wafer to an overlay measurement tool, the test wafer comprising the exposure fields with the patterns and a plurality of overlay targets formed with the patterns across the test wafer;
measuring first shifts of each of the overlay targets;
determining a first set of correctable and/or non-correctable overlay errors from the measured first shifts of the plurality of overlay targets;
selecting a number of overlay targets from said plurality of patterns and forming at least two different subsets thereof, wherein each subset comprises overlay targets residing in at least three of the exposure fields;
for each of the subsets performing the steps a) to c);
a) obtaining the measured first shifts, which correspond to said selected overlay targets, b) calculate a second set of correctable and/or non-correctable errors from the measured first shifts of the selected overlay targets, c) comparing the second set of correctable and/or non-correctable errors with the first set of correctable and/or non-correctable errors;
selecting one of the subsets in dependence of the comparison results;
providing the semiconductor wafer and measuring second shifts of those overlay targets, whose positions on the semiconductor wafer coincide with positions of the overlay targets of the selected subset on said test wafer;
assessing the quality of said semiconductor wafer based on said measured second shifts. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of determining the overlay accuracy of multiple patterns, which are formed within exposure fields being arranged in a matrix on a semiconductor wafer, comprising:
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providing a test wafer to an overlay measurement tool, the test wafer comprising the patterns and plurality overlay targets formed with the patterns in each of the exposure fields across the test wafer;
measuring first shifts of each of the overlay targets;
determining a first set of correctable and/or non-correctable errors from the measured first shifts of the plurality of overlay targets;
selecting each three or more exposure fields comprising overlay targets having first positions from the matrix arrangement and forming at least two subsets thereof;
for each of the subsets performing the steps a) to c);
a) obtaining the measured first shifts of the overlay targets, which are contained within the selected exposure fields of the subset, b) determining a second set of correctable and/or non-correctable errors from the measured first shifts, c) comparing the second set of correctable and/or non-correctable errors with the first set of correctable and/or non-correctable errors;
selecting one of the subsets of exposure fields in dependence of the comparison results;
providing the semiconductor wafer and measuring second shifts of those overlay targets, whose positions on the semiconductor wafer coincide with positions of the overlay targets of the selected subset of exposure fields on the test wafer;
assessing the quality of the semiconductor wafer based on the measured second shifts. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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Specification