Feed-forward lithographic overlay offset method and system
AssigneeInternational Business Machines Corporation
InventorsEdward W. Conrad, Charles J. Parrish, Charles A. Whiting
Life of this patent
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Abstract
A method and system embodying the present invention for predicting systematic overlay affects in semiconductor lithography. This method is a feed-forward method, based on correlation of current and prior aligned levels, to predict optimum overlay offsets for a given lot. Instead of using population averaging, which ignores process variability, it acknowledges the variability and uses prior measurements to advantage. The principle, backed by production data, is that “systematic” overlay errors are just that: Image placement errors which persist through processing and will be predictable through time and processing.
Claims20
A method of predicting systematic lithographic overlay offsets, comprising the steps:
- creating a database of overlay systematics for each lot processed at a first lithographic level and second lithographic level by measuring overlay, and recording these systematic errors and the lot identification;
- creating a correlation between each overlay offset at the second lithographic level relative to the first lithographic level;
- for a new lot, measuring the overlay systematics at the first lithographic level;
- and
- using the correlation between the overlay offsets, and the data from the first lithographic level, to predict the optimum overlay offsets at the second lithographic level.
A system for predicting systematic lithographic overlay offsets, comprising:
- means for creating a database of overlay systematics for each lot processed at a first lithographic level and second lithographic level by measuring overlay, and recording these systematic errors and the lot identification;
- means for creating a correlation between each overlay offset at the second lithographic level relative to the first lithographic level;
- means for measuring, for a new lot, the overlay systematics at the first lithographic level;
- and
- means for using the correlation between the overlay offsets, and the data from the first lithographic level, to predict the optimum overlay offsets at the second lithographic level.
A program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for predicting systematic lithographic overlay offsets, said method steps comprising:
- creating a database of overlay systematics for each lot processed at a first lithographic level and second lithographic level by measuring overlay, and recording these systematic errors and the lot identification;
- creating a correlation between each overlay offset at the second lithographic level relative to the first lithographic level;
- for a new lot, measuring the overlay systematics at the first lithographic level;
- and
- using the correlation between the overlay offsets, and the data from the first lithographic level, to predict the optimum overlay offsets at the second lithographic level.
Dependencies are inferred from the claim text.