Substrate Support Dither Device Friction Control
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Solution Overview
Problem
Conventional lithographic apparatuses face challenges in achieving precise substrate positioning due to substrate load grid deformation, leading to overlay errors and increased wear on the support surface and substrate, primarily caused by high friction between the substrate and the burls during loading and projection processes.
Innovation Solution
A substrate support system incorporating a clamping device and a dither device to provide a clamping force and reduce friction by vibrating the substrate during loading and unloading, allowing for improved positioning and reduced wear by altering the clamping force and using pressure waves to facilitate sliding over the burls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the friction between the substrate and burls is reduced to facilitate sliding during loading, then the substrate can be more easily positioned on the support surface, but the substrate may slide during projection due to high accelerations and decelerations
Solution Approach 1:
The friction coefficient is made variable rather than constant. The support surface changes its frictional properties dynamically: high friction during loading to prevent substrate movement, and low friction during projection to allow substrate sliding. This is achieved by using a belt-like support surface that can be driven at different speeds relative to the substrate, creating controlled friction conditions at different operational stages.
Solution Approach 2:
The system employs periodic alternation between high-friction and low-friction states. During loading, the support surface is driven to create high friction for stable substrate positioning. During projection, the driving speed is reduced or reversed to create low friction, allowing the substrate to slide freely over the burls. This periodic switching of friction conditions resolves the contradiction between stable loading and stable projection.
2Shape
If a vacuum clamp or electrostatic clamp is used to flatten the substrate on the support surface, then the substrate shape is improved, but the friction increases making it difficult for the substrate to slide over the burls
Solution Approach 1:
The clamping force is made variable rather than continuously applied. The vacuum or electrostatic clamp is activated only during specific phases: applied during loading to flatten the substrate and improve its shape, then reduced or deactivated during projection to allow the substrate to slide freely. This dynamic control of clamping force resolves the contradiction between achieving good substrate flatness and enabling substrate sliding.
3Ease of manufacture
If the substrate is loaded on three loading pins extending above the support surface, then the loading process is simplified, but the substrate shape changes during loading causing positioning inaccuracies
Solution Approach 1:
The loading pins are extended above the support surface before substrate loading, allowing the robot to place the substrate without precise positioning. The substrate is initially supported by the extended pins, then the pins are retracted to transfer the substrate to the support surface. This preliminary extension of pins simplifies the loading operation while the subsequent retraction and flattening process corrects any shape changes, achieving both ease of loading and positioning accuracy.
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 solution enhances substrate positioning accuracy, reduces overlay errors, and minimizes wear on both the substrate and support surface by optimizing friction levels during loading and the lithographic process, thereby improving the overall performance of the lithographic apparatus.
Implementation Method 1
a dither device to vibrate the clamping force
Implementation Method 2
reduce friction by vibrating the substrate during loading and unloading
Implementation Method 3
a clamping device to provide a clamping force to hold the substrate on the support surface
Data Source
AI summary
A substrate support for supporting a substrate. The substrate support includes a main body, a clamping device and a dither device. The main body includes a support surface for supporting the substrate. The clamping device is arranged to provide the clamping force to clamp the substrate on the support surface. The dither device is configured to dither the clamping force. The dither device may be configured to dither the clamping force while the substrate is being loaded onto the support surface.