Immersion Lithography Edge Speed Control
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Solution Overview
Problem
In immersion lithography, liquid loss from the space between the projection system and the substrate can lead to imaging defects due to the formation of bubbles, which interfere with the pattern imaging on the substrate.
Innovation Solution
A controller adjusts operating conditions, such as scanning or stepping speed, and fluid handling parameters to minimize liquid loss and bubble formation, particularly at the edges of the substrate, by optimizing the motion and fluid flow dynamics during the imaging process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the substrate is scanned at high speed through the immersion liquid, then productivity is improved, but liquid loss increases leading to bubble formation and imaging defects
Solution Approach 1:
The patent applies dynamics by making the scan speed variable rather than constant. The controller dynamically adjusts the scan speed based on the position of the substrate relative to the immersion liquid space, reducing speed at edges where liquid loss is more likely to occur. This allows high productivity during central scanning while preventing bubble formation at critical edge positions.
Solution Approach 2:
The patent implements feedback through the controller that monitors substrate position and adjusts scan speed accordingly. The system uses information about the substrate's location relative to the immersion liquid boundaries to modulate scanning parameters, creating a closed-loop control system that prevents liquid loss while maintaining high throughput.
2Reliability
If the scanning speed is reduced to minimize liquid loss, then imaging quality improves, but productivity decreases
Solution Approach 1:
The patent resolves this contradiction by making scan speed dynamic rather than static. High scan speeds are maintained during central regions where liquid loss is minimal, while speeds are reduced only at edge positions where bubble formation is problematic. This spatially-dependent speed adjustment maximizes productivity while ensuring imaging quality.
Solution Approach 2:
The patent applies local quality by treating different regions of the substrate differently. The scan speed is optimized locally for each position based on its proximity to liquid boundaries, allowing fast scanning in safe zones and reduced speed only where necessary to prevent liquid loss and bubble formation.
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 reduces the risk of imaging defects by minimizing liquid loss and bubble formation, thereby improving the accuracy and reliability of the lithographic process.
Implementation Method 1
immersion the substrate in the lithographic projection apparatus in a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the final element of the projection system and the substrate... the exposure radiation will have a shorter wavelength in the liquid... increasing the effective numerical aperture (NA) of the system
Data Source
AI summary
A method of operating a lithographic apparatus is disclosed. The method includes moving a substrate table supporting a substrate relative to a projection system and adjusting the scanning speed between the substrate table and the projection system during imaging of a target within a predefined area at or near an edge of the substrate, or adjusting the stepping speed between adjacent target positions in a predefined area at or near the edge of the substrate, or both. The adjusting the scanning and/or stepping speed may comprise lowering the speed. The projection system is configured to project a patterned beam of radiation on to a target portion of the substrate.