Lithography Stage Rotation Compensation via Abbe Error Minimization
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Solution Overview
Problem
Current lithography apparatuses face errors in substrate alignment measurement due to rotation and tilt errors, which lead to decreased overlay accuracy and positioning errors influenced by Abbe errors and changes in the mounting state of components over time or heat.
Innovation Solution
A lithography apparatus with a movable stage and a controller that estimates and compensates for rotation and tilt shifts by adjusting the stage's position based on low-magnification measurements, allowing high-magnification alignment without influencing Abbe errors, by shifting the stage in perpendicular directions to maintain optical axis alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the stage is rotated based on low-magnification measurement result to correct rotation shift, then the rotation alignment is improved, but the verticality between the bar mirror and optical axis deteriorates, causing Abbe error
Solution Approach 1:
The system performs preliminary low-magnification measurement to detect rotation shift, then calculates and stores the rotation shift amount before high-magnification measurement. This preliminary detection allows the system to compensate for rotation errors without physically rotating the stage, thereby avoiding Abbe error while maintaining alignment accuracy.
Solution Approach 2:
The system creates a virtual correction by calculating the rotation shift amount from low-magnification measurement and applying it as a coordinate transformation during high-magnification measurement. Instead of physically rotating the stage, the system copies the correction effect through computational adjustment of measurement coordinates, eliminating Abbe error.
2Measurement precision
If high-magnification alignment measurement is performed to check rotation error, then the alignment accuracy is improved, but the measurement time increases
Solution Approach 1:
The system performs preliminary low-magnification measurement to grasp the magnitude of rotation error before high-magnification measurement. This preliminary step allows the system to pre-calculate the rotation shift amount and adjust the measurement strategy, reducing the time required for high-magnification measurement by focusing only on necessary shots.
Solution Approach 2:
The system performs high-magnification measurement only on representative sample shots rather than all shots. By selecting representative samples that capture the rotation error characteristics, the system achieves sufficient alignment accuracy without the time cost of measuring every shot at high magnification.
3Productivity
If the position of representative sample shots is measured to predict overall array tendency, then the measurement speed is improved, but the alignment accuracy decreases
Solution Approach 1:
The system performs preliminary low-magnification measurement on representative sample shots to detect rotation shift. This preliminary action on samples allows the system to calculate a correction value that is then applied to all shots, achieving both fast sampling and accurate overall alignment through the correction step.
Solution Approach 2:
The system uses the rotation shift amount detected from representative sample shots as feedback to correct the alignment of all shots. The measurement result from samples feeds into a correction algorithm that adjusts the positioning of subsequent measurements, ensuring high accuracy while maintaining fast sampling speed.
Data Source
AI summary
A lithography apparatus includes: a stage configured to hold the substrate; a scope configured to measure a position of a mark formed on a surface of the substrate; and a controller configured to control movement of the stage to form the pattern based on the position of the mark. When there is a rotation shift of the surface of the substrate about a first axis of one of X-, Y-, and Z-axes with respect to the stage, the controller estimates the position of the mark in a direction of a second axis perpendicular to the first axis based on an amount of the rotation shift, moves the stage in the direction of the second axis based on the estimated position of the mark, and then measures the position of the mark by the scope.