Slit Illumination Uniformity Compensation in Lithography
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Solution Overview
Problem
Current methods for compensating slit illumination uniformity in lithographic apparatuses rely solely on critical dimension uniformity (CDU) monitor results, leading to potential errors in spot sensor conversion factor (SSCF) compensation, which can result in product defects and wafer rework or scrap.
Innovation Solution
A method that involves recording initial and optimized slit uniformity profiles, calculating a calibration factor based on their differences, and offsetting the optimized profile to generate a working profile that matches the initial profile's mean value, thereby providing a more reliable compensation factor for slit illumination uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If slit uniformity optimization is performed using traditional methods (adjusting UIP, UNICON plate, or gradient filter), then the slit uniformity is improved, but the SSCF compensation accuracy deteriorates due to reliance solely on CDU monitor results
Solution Approach 1:
The patent implements a feedback mechanism where the system continuously monitors slit uniformity using multiple measurement points and adjusts the SSCF compensation factor based on the difference between initial and optimized slit uniformity profiles. This closed-loop feedback ensures accurate compensation by directly measuring the actual uniformity changes rather than relying on indirect CDU monitor results.
Solution Approach 2:
The system performs self-calibration by automatically generating its own reference data through the slit uniformity measurement process. The initial slit uniformity profile serves as a self-generated baseline that the system uses to calculate compensation factors, eliminating the need for external reference standards and reducing dependency on potentially inaccurate CDU monitor procedures.
2Device complexity
If SSCF compensation is performed based solely on CDU monitor results, then the compensation process is simplified, but the product critical dimension accuracy deteriorates due to potential errors in compensation values
Solution Approach 1:
The patent replaces the indirect mechanical measurement approach (CDU monitor) with a direct optical measurement system that captures slit uniformity profiles at multiple points. This substitution provides more accurate and direct measurement of the actual illumination uniformity, leading to better SSCF compensation factors and improved product critical dimension accuracy.
Solution Approach 2:
The system transitions from one-dimensional CDU monitor measurements to multi-dimensional slit uniformity profiling by measuring at multiple positions across the slit. This dimensional expansion provides a more comprehensive view of the illumination uniformity, enabling more accurate compensation factor calculation while maintaining process simplicity through automated data processing.
3Measurement precision
If multiple measurement points are used to generate slit uniformity profiles, then the compensation accuracy is improved, but the measurement time and process complexity increase
Solution Approach 1:
The system performs preliminary measurements to establish an initial slit uniformity profile before optimization. This pre-established baseline allows for rapid comparison with post-optimization profiles, enabling quick calculation of compensation factors without requiring repeated complex measurements. The preliminary action captures the essential reference data needed for accurate compensation.
Solution Approach 2:
The patent changes the measurement parameters by focusing on key statistical features of the slit uniformity profile (such as mean and standard deviation) rather than processing every individual measurement point in detail. This parameter transformation reduces computational complexity and measurement time while preserving the essential information needed for accurate SSCF compensation.
Data Source
AI summary
A method for compensating a slit illumination uniformity includes executing a first lithography operation and recording an initial slit uniformity profile; executing a slit uniformity optimization process and recording an optimized slit uniformity profile; and offsetting the optimized slit uniformity profile to obtain a working slit uniformity profile such that the working slit uniformity profile has a mean value closest to that of the initial slit uniformity profile.