Non-Zero Offset Prediction for Lithography Overlay Control
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Solution Overview
Problem
Semiconductor fabrication processes face instability due to non-zero offset errors in overlay measurements from different metrology tools, leading to performance degradation in process control systems.
Innovation Solution
A process control system that incorporates ADI and AEI data, along with flag data, to predict and adjust for non-zero offset errors, using machine learning algorithms to generate control parameters for maintaining overlay accuracy across layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If overlay control uses data from multiple metrology tools (ADI and AEI), then measurement precision is improved, but non-zero offset errors introduce instability and reduce reliability
Solution Approach 1:
The patent introduces an intermediary correction mechanism that mediates between ADI and AEI measurement systems. A correction value is calculated based on the difference between ADI overlay data and AEI overlay data, then applied to subsequent ADI measurements to reduce non-zero offset errors. This intermediary correction layer allows the system to benefit from both high-throughput ADI measurements and high-precision AEI reference data without direct conflict between the two systems.
Solution Approach 2:
The patent implements a feedback loop where AEI overlay data serves as reference feedback to correct ADI measurements. The system continuously compares ADI and AEI results, calculates correction values, and applies these corrections to maintain alignment accuracy. This feedback mechanism enables the system to adapt to non-zero offset variations while maintaining the benefits of both measurement systems.
2Measurement precision
If low-throughput metrology tools (AEI) are used for high-precision overlay measurement, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The patent creates a corrected overlay measurement system that copies the high-precision AEI measurement approach but applies it through the high-throughput ADI system. By calculating correction values from AEI data and applying them to ADI measurements, the system generates corrected overlay data that mimics AEI precision while maintaining ADI throughput. This allows multiple measurements to be taken rapidly without sacrificing accuracy.
Solution Approach 2:
The patent applies partial AEI measurement action to a subset of samples to generate correction data, then applies these corrections excessively to all subsequent ADI measurements. Rather than measuring every sample with the slow AEI tool, the system measures a representative subset with AEI and uses those results to correct all ADI measurements, achieving high precision at high throughput.
3Device complexity
If non-zero offset errors are not corrected, then device complexity is reduced, but manufacturing precision deteriorates
Solution Approach 1:
The patent performs preliminary correction by calculating offset correction values from AEI data before applying them to ADI measurements. This preliminary action of establishing correction values upfront allows the system to maintain simple operational complexity while achieving high manufacturing precision through pre-computed corrections that are applied systematically to all measurements.
Data Source
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AI summary
A process control system may include a controller configured to receive after-development inspection (ADI) data after a lithography step for the current layer from an ADI tool, receive after etch inspection (AEI) overlay data after an exposure step of the current layer from an AEI tool, train a non-zero offset predictor with ADI data and AEI overlay data to predict a non-zero offset from input ADI data, generate values of the control parameters of the lithography tool using ADI data and non-zero offsets generated by the non-zero offset predictor, and provide the values of the control parameters to the lithography tool for fabricating the current layer on the at least one production sample.