Coplanar Sensor Displacement Measurement for Lithography
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Solution Overview
Problem
Current lithographic apparatuses face challenges in achieving high accuracy and stability in position measurement of substrate and mask tables due to deformation and thermal expansion, which decreases throughput and accuracy in sub-100 nm lithography.
Innovation Solution
A displacement measuring system with at least three sensor heads positioned coplanar with the x-y plane and perpendicular to the connection line with the center of the substrate table, allowing for continuous high accuracy measurement in three coplanar degrees of freedom (x, y, Rz), making the system insensitive to radial expansion and deformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-axis interferometers are used to measure position in all 6 DOF with sub-nanometer resolution, then measurement precision is improved, but the system requires frequent recalibration which decreases productivity
Solution Approach 1:
The patent extracts the measurement function from a complex 6-DOF interferometer system and implements it using a simplified configuration with only three coplanar sensors measuring in the x-y plane. This extraction eliminates the need for complex recalibration procedures while maintaining sufficient measurement precision for the lithographic process.
Solution Approach 2:
The patent applies local quality by positioning the three sensors in specific locations on the substrate table (at the corners and center) with specific orientations. This localized sensor arrangement provides adequate measurement capability for the specific application requirements without the overhead of full 6-DOF measurement systems.
2Length of moving object
If sensors are positioned at the corners of the substrate table to cover the entire working range, then the measurement range is improved, but the substrate table deformation and thermal expansion negatively influence measurement accuracy
Solution Approach 1:
The patent segments the measurement function across three distributed sensors rather than using a single comprehensive sensor. This segmentation allows the system to achieve both wide measurement range through spatial distribution and improved accuracy by using multiple measurement points that can be processed to compensate for table deformations.
Solution Approach 2:
The patent combines the measurements from three coplanar sensors to achieve accurate position determination. By merging the data from multiple sensors positioned at strategic locations, the system compensates for individual sensor limitations and table deformations, achieving both wide range and high accuracy.
3Ease of manufacture
If optical or magnetic incremental encoders are used for coarse positioning, then ease of manufacture is improved, but absolute accuracy and thermal stability over long travel ranges are not achievable
Solution Approach 1:
The patent replaces traditional mechanical incremental encoders with an optical measurement system using interferometric sensors. This substitution maintains the ease of implementation while achieving the required absolute accuracy and thermal stability through optical measurement principles that are inherently more stable over long travel ranges.
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 configuration enables continuous high accuracy displacement measurement with reduced sensitivity to substrate table deformations and thermal expansion, improving the throughput and accuracy of the lithographic apparatus by minimizing recalibration time and maintaining nanometer resolution.
Implementation Method 1
A displacement measuring system with at least three sensor heads positioned coplanar with the x-y plane and perpendicular to the connection line with the center of the substrate table
Data Source
AI summary
A lithographic apparatus includes a displacement measuring system to measure a position of a moveable object with respect to a reference frame of the lithographic apparatus, in at least three coplanar degrees of freedom (x, y, Rz) of an orthogonal x-y-z coordinate system centered in the center of the moveable object. The moveable object includes a support structure configured to support a patterning device or a substrate table configured to support a substrate. The displacement measuring system includes at least three sensor heads, each sensor head being positioned with a measuring direction substantially coplanar with the x-y plane of the coordinate system and each sensor head being furthermore positioned with the measuring direction substantially perpendicular to a connection line connecting the sensor head with the center of the movable object and extending coplanar with the x-y plane.