Exposure Apparatus Dynamic Model Generation for Overlay Accuracy
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Solution Overview
Problem
Conventional exposure apparatuses face challenges in accurately calculating and efficiently obtaining model equations for exposure aberration, leading to degradation in overlay accuracy due to heat aberration, particularly because they do not adequately consider the pattern shape of the reticle and require extensive time to obtain model equations for various light source and pattern shapes.
Innovation Solution
An exposure apparatus that includes a processor to estimate variations in imaging characteristics using a model determined in advance, with an adjusting device to correct these variations, and the ability to generate additional models if initial adjustments do not meet tolerance, allowing for precise adjustment of the projection optical system based on both reticle and light source shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If model equations are obtained for each effective light source shape and pattern shape of reticle, then exposure aberration can be calculated with high accuracy, but it takes a long time to obtain such model equations
Solution Approach 1:
The patent segments the model equation into two parts: a first model equation obtained without the reticle (representing the projection optical system's basic characteristics) and a second model equation obtained with the reticle (representing the reticle's diffraction effects). This segmentation allows the first model to be obtained quickly without the reticle, while the second model is added only when needed for specific pattern shapes, thus reducing overall time while maintaining accuracy.
Solution Approach 2:
The patent performs preliminary action by obtaining the first model equation in advance without the reticle present. This preliminary model captures the projection optical system's characteristics under different illumination conditions. When actual exposure is performed, this pre-obtained model serves as a baseline, and only additional corrections (second model) are needed for specific reticle patterns, significantly reducing the time required during production.
2Productivity
If the pattern shape of the reticle is not taken into consideration in obtaining a model equation, then the process is simpler and faster, but the exposure aberration in actual exposure cannot be obtained with high accuracy
Solution Approach 1:
The patent implements a dynamic model equation system that adapts to different reticle patterns. The system starts with a basic first model equation that applies to all illumination conditions, then dynamically adds or adjusts a second model equation component when specific reticle patterns are detected. This dynamic approach maintains high productivity by using the simple first model for most cases while achieving high accuracy by activating the pattern-specific second model only when needed.
3Productivity
If exposure is repeated, then production output increases, but variations in imaging characteristic occur due to heating of the projection optical system
Solution Approach 1:
The patent implements periodic measurement and correction cycles during repeated exposure operations. The system periodically measures the actual exposure aberration using the model equation and adjusts the projection optical system's imaging characteristics accordingly. This periodic intervention compensates for heat-induced variations that accumulate during continuous production, maintaining overlay accuracy throughout extended operation periods.
Solution Approach 2:
The patent establishes a feedback loop where the model equation is used to measure exposure aberration, and the measured aberration information feeds back to adjust the projection optical system's imaging characteristics. This feedback mechanism continuously corrects for heat aberrations that develop during repeated exposure, ensuring that manufacturing precision is maintained despite increased production output.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables efficient and precise estimation and adjustment of imaging characteristics, improving overlay accuracy and reducing downtime by generating approximation model equations that account for both reticle and light source shapes, thereby enhancing the performance of the exposure apparatus.
Implementation Method 1
a projection optical system configured to project light from a reticle onto the substrate
Implementation Method 2
variations in imaging characteristic of a projection optical system occur as the projection optical system is heated upon partially absorbing the energy of exposure light
Data Source
AI summary
The present invention provides an exposure apparatus including a projection optical system configured to project light from a reticle onto a substrate, a processor configured to estimate a variation in imaging characteristic of the projection optical system, based on a model determined in advance, and an adjusting device configured to adjust the imaging characteristic of the projection optical system based on the variation estimated by the processor, wherein the processor is configured, if an error of the imaging characteristic of the projection optical system adjusted by the adjusting device based on the variation which is estimated based on a first number of models, for estimating the variation, determined in advance without the reticle, does not fall within a tolerance, to generate a second number of models for estimating the variation, the second number being larger than the first number.