Exposure Stage Grid Error Calibration for Overlay Positioning
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Solution Overview
Problem
Current exposure apparatuses face challenges in maintaining high overlay accuracy and position measurement precision, particularly with larger wafers like 450 mm, as existing position measurement systems are not adaptable to variations in grating pitch and shape over time, leading to difficulties in achieving the required nm-level positioning errors.
Innovation Solution
The exposure apparatus employs a position measurement system with multiple heads placed on a movable body and outside, forming a one-dimensional or two-dimensional grating on the measurement surface, allowing for concurrent measurement of positional information and grid errors, using a reference head and measurement heads to monitor and calibrate differences in measurement values, ensuring accurate positioning and pattern formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional position measurement system with encoder heads is used, then position measurement is achieved, but the system cannot adapt to grating pitch and shape variations over time, leading to positioning errors
Solution Approach 1:
The patent implements a feedback mechanism where the position measurement system continuously monitors the movable body's position and feeds this information back to the control system. The control system uses this feedback to adjust and correct positioning errors in real-time, compensating for grating variations and maintaining measurement precision over long periods.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting measurement parameters and calibration data based on detected grating variations. The system modifies its operating parameters to adapt to changing grating pitch and shape, allowing it to maintain accuracy despite environmental factors and aging effects.
2Productivity
If the wafer stage size is increased to handle larger 450 mm wafers, then productivity is improved, but the permissible positioning error becomes tighter and the scale size increases making grid variation more difficult to control
Solution Approach 1:
The patent divides the large-scale measurement system into multiple encoder heads and scales, each responsible for a specific region. This segmentation allows independent calibration and monitoring of different areas, making it easier to control grid variations across the entire large wafer stage while maintaining tight positioning tolerances.
Solution Approach 2:
The patent introduces additional measurement dimensions by using multiple encoder heads positioned at different locations and orientations. This multi-dimensional measurement approach provides redundant data for detecting and correcting grid errors, enabling precise positioning control on large 450 mm wafer stages.
3Measurement precision
If multiple encoder heads are used to improve measurement accuracy, then positioning precision is improved, but the device complexity increases
Solution Approach 1:
The patent designs the encoder heads and control system to perform multiple functions: primary position measurement, grating variation detection, error calibration, and real-time compensation. This multi-functionality allows the system to achieve high measurement accuracy with multiple encoder heads while managing complexity through integrated design.
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 solution enables precise and accurate positioning of the movable body within the exposure apparatus, maintaining high overlay accuracy and adaptability to larger wafers by continuously monitoring and calibrating grid errors, thus ensuring reliable pattern transfer on semiconductor devices and other microdevices.
Implementation Method 1
the encoder heads measure a position of the substrate table by irradiating measurement beams on a scale which is placed facing the substrate table and receiving return beams from the scale
Data Source
AI summary
In corner sections of first to fourth quadrants whose origin point is a center of an upper surface of a stage, three each of two-dimensional heads are provided. The three each of two-dimensional heads include one first head and two second heads. The stage is driven, while measuring a position of the stage using three first heads that face a two-dimensional grating of a scale plate provided above the stage from the four first heads, and during the driving, difference data of measurement values of the two second heads with respect to the first head in a measurement direction are taken in for head groups to which the three first heads belong, respectively, and using the difference data, grid errors are calibrated.