Lithographic Apparatus Mirror Block Slip Reduction
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Solution Overview
Problem
Conventional lithographic apparatuses experience slip between the mirror block and the substrate table due to high acceleration forces, leading to positional errors and incorrect substrate exposure.
Innovation Solution
The introduction of burls with increased flexibility and stiffness between the mirror block and the substrate table, along with optimized clamping mechanisms, such as reduced burl count, high friction coatings, and varying burl stiffness, to absorb deformation and minimize slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the substrate table is clamped by vacuum to the mirror block via burls, then the substrate can be held and moved for projection, but high acceleration forces cause local slip between the mirror block and substrate table
Solution Approach 1:
The patent introduces a flexible membrane structure (bellows) between the mirror block and substrate table that can deform elastically under acceleration forces. This membrane acts as a compliant connection that maintains the vacuum seal while accommodating relative motion tendencies, preventing slip between the mirror block and substrate table during high-speed movements.
Solution Approach 2:
The patent modifies the clamping mechanism by introducing a variable stiffness connection through the bellows structure. The effective stiffness and damping characteristics of the vacuum connection are changed to optimize the balance between holding force and compliance, allowing the system to maintain reliability during high-acceleration operations.
2Productivity
If higher accelerations are applied to move the substrate faster, then throughput is improved, but slip between mirror block and substrate table increases causing positioning errors
Solution Approach 1:
The flexible membrane (bellows) structure provides a compliant vacuum connection that can dynamically respond to acceleration forces. During high-speed substrate movement, the membrane deforms to absorb inertial forces, maintaining the vacuum seal integrity and preventing slip that would compromise positioning precision, thus enabling high throughput without sacrificing manufacturing precision.
Solution Approach 2:
The bellows structure acts as a pre-designed cushioning element that anticipates and absorbs the effects of high acceleration forces before they can cause slip. The membrane's elastic properties provide a buffer that protects the rigid connection between mirror block and substrate table during rapid movements, ensuring positioning accuracy is maintained even at high speeds.
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
Significantly reduces slip between the mirror block and the substrate table, ensuring accurate and precise substrate positioning and exposure, thereby enhancing the throughput and reliability of the lithographic apparatus.
Implementation Method 1
The burls are provided with a high friction coating to reduce slip between the mirror block and the substrate table
Implementation Method 2
The substrate table is clamped by vacuum to the mirror block (also called encoder block) via burls
Data Source
AI summary
A lithographic apparatus includes an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a mirror block provided with a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, wherein the mirror block is constructed and arranged to reduce slip between the mirror block and the substrate table. Slip can occur if the acceleration of the mirror block is high and the substrate table slips locally with respect to the mirror block. Slip may lead to exposure errors since the position of the substrate is no longer determined with the desired accuracy.