METHOD FOR IDENTIFYING AND USING PROCESS WINDOW SIGNATURE PATTERNS FOR LITHOGRAPHY PROCESS CONTROL
First Claim
1. A set of process window signature patterns, comprising:
- a plurality of patterns in a circuit device area of a mask, wherein a collective response of the plurality of patterns to a lithography process uniquely identifies any deviation from nominal in process condition parameters of the lithography process.
2 Assignments
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Accused Products
Abstract
A method for identifying process window signature patterns in a device area of a mask is disclosed. The signature patterns collectively provide a unique response to changes in a set of process condition parameters to the lithography process. The signature patterns enable monitoring of associated process condition parameters for signs of process drift, analyzing of the process condition parameters to determine which are limiting and affecting the chip yields, analyzing the changes in the process condition parameters to determine the corrections that should be fed back into the lithography process or forwarded to an etch process, identifying specific masks that do not transfer the intended pattern to wafers as intended, and identifying groups of masks that share common characteristics and behave in a similar manner with respect to changes in process condition parameters when transferring the pattern to the wafer.
154 Citations
27 Claims
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1. A set of process window signature patterns, comprising:
a plurality of patterns in a circuit device area of a mask, wherein a collective response of the plurality of patterns to a lithography process uniquely identifies any deviation from nominal in process condition parameters of the lithography process.
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2. A method for identifying process window signature patterns, comprising:
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performing simulations of a lithography process, using a representation of a device area of a mask, at two or more non-nominal locations and at nominal condition in a process window to produce simulation results;
determining simulated values from the simulation results for at least one metric at the two or more non-nominal locations and at nominal condition in the process window, wherein the simulated values for the at least one metric are determined at a plurality of locations within the device area;
for each of the plurality of locations within the device area, determining a difference between simulated values for the at least one metric at the two or more non-nominal locations in the process window and the simulated value for the at least one metric at nominal condition;
identifying a number of locations within the device area where the difference for the at least one metric is above a threshold;
if the number of identified locations is greater than a predetermined number, modifying the threshold and identifying the locations within the device area where the difference for the at least one metric is above the threshold until the number of identified locations within the device area is less than the predetermined number; and
assigning patterns associated with the number of identified locations within the device area that is less than the predetermined number to be signature patterns. - View Dependent Claims (3, 4, 5, 6)
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7. A method for monitoring changes in a lithography process, comprising:
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performing simulations of a lithography process, using a representation of a device area of a mask, at two or more non-nominal locations and at nominal condition in a process window to produce simulation results;
determining simulated values from the simulation results for at least one metric at the two or more non-nominal locations and at nominal condition in the process window, wherein the simulated values for the at least one metric are determined at a plurality of locations within the device area;
for each of the plurality of locations within the device area, determining a difference between simulated values for the at least one metric at the two or more non-nominal locations in the process window and the simulated value for the at least one metric at nominal condition;
identifying a number of locations within the device area where the difference for the at least one metric is above a threshold;
if the number of locations is greater than a predetermined number, modifying the threshold and identifying the locations within the device area where the difference for the at least one metric is above the threshold until the number of identified locations within the device area is less than the predetermined number;
assigning patterns associated with the number of identified locations within the device area that is less than the predetermined number to be signature patterns;
obtaining measured values of the at least one metric for the signature patterns, the measured values being obtained from measurements of the signature patterns printed on a wafer processed by the lithography process using the mask;
finding a location in the process window where a total difference measure between the measured values of the at least one metric for all of the signature patterns and the simulated values of the at least one metric for all of the signature patterns at the location in the process window is minimized; and
determining a change between the location in the process window where the total difference measure is minimized and nominal condition to determine a change in the lithography process. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A method for identifying deviations from nominal values of process condition parameters of a lithography process, comprising:
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processing a wafer using a lithography process and a mask;
measuring a metric associated with each of a plurality of signature patterns of a device area of the mask on the processed wafer, producing measured values of the metrics, wherein the plurality of signature patterns collectively provide a unique response to changes in a set of process condition parameters to the lithography process;
simulating the lithography process using a representation of the device area of the mask at a plurality of values of the set of process condition parameters to produce simulated results;
determining simulated values for each metric associated with each of the plurality of signature patterns of the device area of the mask using the simulated results;
identifying a location in the process window such that a total difference measure between the measured values for the metrics and the simulated values for the metrics is minimized; and
determining a deviation between the location in the process window where the total difference measure is minimized and nominal condition. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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21. A computer-readable medium including instructions for performing:
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performing simulations of a lithography process, using a representation of a device area of a mask, at two or more non-nominal locations and at nominal condition in a process window to produce simulation results;
determining simulated values from the simulation results for at least one metric at the two or more non-nominal locations and at nominal condition in the process window, wherein the simulated values for the at least one metric are determined at a plurality of locations within the device area;
for each of the plurality of locations within the device area, determining a difference between simulated values for the at least one metric at the two or more non-nominal locations in the process window and the simulated value for the at least one metric at nominal condition;
identifying a number of locations within the device area where the difference for the at least one metric is above a threshold;
if the number of locations is greater than a predetermined number, modifying the threshold and identifying the locations within the device area where the difference for the at least one metric is above the threshold until the number of identified locations within the device area is less than the predetermined number;
assigning patterns associated with the number of identified locations within the device area that is less than the predetermined number to be signature patterns;
storing measured values of the at least one metric for the signature patterns, the measured values being obtained from measurements of the signature patterns printed on a wafer processed by the lithography process using the mask;
finding a location in the process window where a total difference measure between the measured values of the at least one metric for all of the signature patterns and the simulated values of the at least one metric for all of the signature patterns at the location in the process window is minimized; and
determining a change between the location in the process window where the total difference measure is minimized and nominal condition to determine a change in the lithography process. - View Dependent Claims (22, 23, 24, 25, 26, 27)
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Specification