Lithographic Alignment Sensors for Real-Time Substrate Positioning
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Solution Overview
Problem
Lithographic apparatuses face challenges in reducing measurement overhead and positioning errors, which limit throughput and increase costs due to separate measurement and exposure operations, and are prone to errors from temperature fluctuations and stage mismatches.
Innovation Solution
A lithographic apparatus with alignment sensors that measure and recognize alignment marks on the substrate during relative motion, allowing for updated measurements to be used in real-time to accurately position the substrate and patterning device, reducing the need for separate measurement stages and minimizing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate measurement and exposure operations are performed, then measurement precision can be improved, but productivity decreases due to measurement overhead
Solution Approach 1:
The patent combines measurement and exposure operations into a single integrated process. Alignment sensors continuously measure alignment marks on the substrate during the exposure operation itself, eliminating the need for separate measurement steps. This merging allows the system to maintain high measurement precision while significantly improving productivity by removing measurement overhead time.
Solution Approach 2:
The alignment sensors operate continuously during the exposure process, performing measurements without interrupting the useful action of pattern transfer. The system maintains continuous measurement and positioning capability throughout the exposure operation, ensuring that alignment data is always current while maximizing throughput.
2Measurement precision
If separate measurement and exposure operations are performed, then measurement precision can be improved, but loss of time increases due to separate operations
Solution Approach 1:
The patent merges measurement and exposure operations so that alignment measurements are performed during the exposure process itself. This eliminates the time loss associated with separate measurement operations while maintaining measurement precision through continuous sensing during the pattern transfer operation.
Solution Approach 2:
The alignment sensors are positioned and configured in advance to measure alignment marks during the exposure operation. The system prepares the measurement capability beforehand so that no additional time is required during the actual exposure process, eliminating measurement overhead time while ensuring precision measurements are taken at the appropriate moment.
3Productivity
If dual wafer tables are used for parallel measurement and exposure, then productivity can be improved, but device complexity increases
Solution Approach 1:
The patent combines measurement and exposure functions into a single wafer table system, eliminating the need for dual wafer tables. By integrating alignment sensors that operate during the exposure process, the system achieves high throughput without the complexity of multiple tables, coordinate systems, and table swapping mechanisms required by dual-table approaches.
4Measurement precision
If measurement operations are performed before exposure, then measurement precision can be improved, but reliability decreases due to temperature fluctuations and stage mismatches
Solution Approach 1:
The alignment sensors perform measurements continuously during the exposure operation itself, ensuring that alignment data is obtained at the exact moment when the pattern is being transferred. This eliminates time delays between measurement and exposure that could allow temperature fluctuations and stage drift to degrade alignment accuracy, thereby improving reliability while maintaining precision.
Solution Approach 2:
The system uses real-time feedback from alignment sensors during exposure to continuously update positioning information. This feedback mechanism ensures that alignment corrections are applied immediately based on current conditions, compensating for any temperature changes or stage movements that occur during the exposure process and maintaining high alignment reliability.
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 reduced measurement delays and improved accuracy, enhancing throughput and reducing errors caused by temperature changes and stage mismatches, while allowing for real-time alignment and positioning, thus improving the overall efficiency and precision of the lithographic process.
Implementation Method 1
a measuring subsystem comprises one or more alignment sensors directed at the substrate, wherein the alignment sensor(s) is(are) operable in the course of said sequence of movements to recognize and measure alignment marks on the substrate
Data Source
AI summary
A lithographic apparatus is arranged to transfer a pattern from a patterning device onto a substrate, in which a measuring subsystem includes one or (preferably) more alignment & level sensors (AS, LS) directed at the substrate near a patterning location of a patterning subsystem. The alignment sensor(s) is operable to recognize and measure alignment marks (P1) on the substrate passing by the sensor during relative motion of the substrate and patterning subsystem under control of the positioning subsystem. A processor combines measurements of relative locations of a plurality of said marks to provide measurement results with an accuracy sufficient for the positioning subsystem to position at least a first substrate portion at said patterning location relative to said alignment marks. A preliminary step obtains position relative to a known pattern (M1) on the patterning device. Measurements are taken and updated in real time during exposure of successive substrate portions.