Lithographic Substrate Alignment via Diffraction Beam Comparison
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Solution Overview
Problem
Current lithographic apparatuses face challenges in achieving highly accurate substrate alignment due to errors in position measurement systems, which are prone to thermal fluctuations, atmospheric gas turbulences, and inaccuracies in positioning relationships between various elements, limiting the minimum dimensions of structures that can be achieved in subsequent layers.
Innovation Solution
The method involves irradiating a first target portion of the substrate with a first patterned beam to form a first pattern, and a second target portion with a second patterned beam, detecting the diffraction beam resulting from the interaction of the second pattern with the first pattern, comparing it to a desired diffraction beam, and aligning the substrate based on the difference between the two, using a detector and comparator within the lithographic apparatus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional position measurement systems are used to determine substrate alignment, then the alignment process can be performed, but measurement accuracy deteriorates due to thermal fluctuations, atmospheric gas turbulences, and positioning errors
Solution Approach 1:
The patent replaces conventional mechanical position measurement systems with a diffraction-based optical measurement method. Instead of using mechanical encoders or interferometers that are susceptible to thermal and atmospheric disturbances, the system uses diffraction patterns generated when a measurement beam passes through or reflects off the substrate surface. The diffraction pattern characteristics (position, intensity distribution) directly encode alignment information, providing a measurement method that is inherently immune to thermal fluctuations and atmospheric turbulences affecting long measurement paths.
Solution Approach 2:
The patent introduces a diffraction pattern as an intermediary between the substrate and the measurement system. Rather than directly measuring substrate position with beams traveling through turbulent air, the system creates a diffraction pattern that serves as a stable intermediate representation of the substrate's alignment state. This intermediary encodes position information in a form that can be detected with high precision without being affected by the same environmental disturbances that plague direct beam-based measurements.
2Area of stationary object
If multiple position measurement devices and long measurement paths are used to achieve adequate alignment, then coverage is improved, but measurement accuracy deteriorates due to atmospheric gas turbulences and temperature variations
Solution Approach 1:
The patent replaces long-path mechanical beam measurements with localized diffraction-based optical measurement. The measurement beam interacts with the substrate surface to create a diffraction pattern, eliminating the need for long beam paths through turbulent air. This substitution maintains measurement coverage while improving precision by removing the measurement path from the environment's thermal and atmospheric influences.
3Ease of operation
If conventional alignment methods measuring substrate table position are used, then alignment can be performed, but accuracy deteriorates because they measure table position instead of actual substrate position
Solution Approach 1:
The patent enables the substrate itself to provide alignment information through its interaction with the measurement beam. The diffraction pattern is generated by the substrate's own surface features and structure, making the substrate self-descriptive of its position and orientation. This eliminates the need for separate measurement devices that might not accurately reflect the substrate's true position, as the substrate's diffraction pattern directly reveals its alignment state.
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 enhances the accuracy of substrate alignment by directly measuring and correcting for misalignments during the irradiation process, thereby improving the precision of pattern application and the achievable dimensions of subsequent layers.
Implementation Method 1
detecting a diffraction beam due to a diffraction of the second patterned beam on the first pattern
Data Source
AI summary
A method for aligning a substrate in a lithographic apparatus, the method including irradiating a first target portion of the substrate with a first patterned beam to form a first pattern on the substrate. Then, a second target portion of the substrate is irradiated with a second pattern beam to form a second pattern on the substrate. The second target portion at least partly overlaps the first target portion. A diffraction beam is detected during irradiation of the second pattern, due to a diffraction of the second patterned beam on the first pattern. The diffraction beam is compared with a desired diffraction beam, and the substrate is aligned based on a comparison between the detected diffraction beam and the desired diffraction beam.