Lithographic Substrate Table Burl Structures
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Solution Overview
Problem
Lithographic processes face challenges in maintaining tribological properties such as friction and wear resistance on substrate tables, which are crucial for accurate positioning and disengagement of substrates, especially due to the sensitivity of thin wafers and the risk of substrates becoming stuck due to smooth surfaces.
Innovation Solution
The implementation of substrate tables with coarse burls and fine burls, where the fine burls are disposed on the burl-top surfaces of the coarse burls, providing a controlled contact area and surface roughness to manage friction and wear, and potentially incorporating intermediate burls or chemically modified surfaces to enhance separation and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the substrate table surface is made smooth to reduce friction, then ease of substrate disengagement improves, but the substrate may become stuck due to excessive adhesion
Solution Approach 1:
The substrate table surface is equipped with burl structures that create locally rough regions distributed across the surface. These local roughness features reduce the contact area between the substrate and table, thereby reducing adhesion forces and preventing substrate sticking while maintaining controlled friction for secure engagement.
Solution Approach 2:
The surface morphology of the substrate table is changed from smooth to rough by introducing burl structures with specific height and distribution parameters. This parameter change reduces the real contact area and modifies the tribological properties, preventing excessive adhesion while maintaining adequate friction for substrate handling.
2Reliability
If the substrate table surface is made rough to prevent substrate from becoming stuck, then reliability of substrate disengagement improves, but friction increases making substrate positioning more difficult
Solution Approach 1:
Rather than making the entire surface uniformly rough, burl structures are distributed locally across the substrate table surface. This creates regions of increased roughness that prevent sticking while maintaining larger smooth areas that facilitate easy substrate positioning and movement.
Solution Approach 2:
The substrate table surface combines regions of different roughness characteristics - burl structures providing local roughness to prevent sticking, and smoother inter-burl regions facilitating easy positioning. This composite surface structure resolves the contradiction between preventing sticking and enabling easy positioning.
3Manufacturing precision
If a flat substrate table surface is used to meet precision requirements, then manufacturing precision is improved, but tribological properties such as wear resistance deteriorate
Solution Approach 1:
The substrate table surface maintains overall flatness for precision requirements while introducing localized burl structures that provide wear resistance and controlled tribological properties. The burls are distributed features that do not compromise the global flatness needed for lithographic precision.
Solution Approach 2:
Instead of changing the overall flatness of the substrate table surface, the solution introduces vertical dimensionality through burl structures - small height variations on an otherwise flat surface. This dimensional approach provides wear resistance without compromising the horizontal flatness required for manufacturing precision.
Data Source
AI summary
A substrate table for supporting a substrate includes a surface and coarse burls. Each of the coarse burls includes a burl-top surface and fine burls. The coarse burls are disposed on the surface of the substrate table. The fine burls are disposed on the burl-top surface. The fine burls contact the substrate when the substrate table supports the substrate.