Substrate Holder Release Control for Flat Wafer Burl Support
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Solution Overview
Problem
In lithographic apparatuses, substrates often exhibit non-flatness due to in-plane stresses and burls on substrate holders, leading to imaging errors and overlay issues during pattern projection.
Innovation Solution
A substrate holder design with a main body having first and second burls, where the distal end surfaces of a subset of the first burls are initially separated from the substrate to relax stresses, and then controlled forces are applied to deform the main body, allowing the substrate to be supported by both subsets of burls to achieve flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the substrate is placed on the substrate holder with all burls in contact, then the substrate is supported firmly, but in-plane stresses and deformations occur leading to non-flatness
Solution Approach 1:
The burls are divided into two subsets: a first subset that contacts the substrate to provide support, and a second subset that is separated from the substrate to allow stress relaxation. This segmentation enables different functional zones on the substrate holder surface, resolving the contradiction between firm support and stress-induced deformation.
Solution Approach 2:
Different regions of the substrate holder have different properties: areas with first subset burls provide support contact while areas with second subset burls provide separation for stress relief. This local differentiation allows the substrate to be held firmly in some regions while remaining stress-free in others, achieving both stability and flatness.
2Manufacturing precision
If the substrate holder main body is deformed to create gaps between burls and substrate, then stress relaxation occurs improving flatness, but the substrate support firmness is reduced
Solution Approach 1:
The burls are segmented into two functional groups: first subset burls that maintain contact with the substrate for stability, and second subset burls that are separated to enable stress relaxation through main body deformation. This segmentation allows the system to achieve both flatness and clamping stability simultaneously.
Solution Approach 2:
Instead of separating all burls from the substrate, only a portion (the second subset) is separated while the first subset maintains contact. This partial action is sufficient to relieve in-plane stresses and improve flatness, while the remaining contact points maintain adequate clamping stability.
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 in-plane deformations and stresses in the substrate, improving overlay performance and enabling more precise pattern projection by ensuring the substrate is held flat and in contact with all burls.
Implementation Method 1
generating a first force to attract the substrate holder to the support surface
Implementation Method 2
generating a second force to attract the substrate to the substrate holder
Implementation Method 3
controlling at least one of the first force and the second force in a release step to deform the main body between the second burls
Data Source
AI summary
A method including: generating a first force to attract a substrate holder to a support surface, the holder including a body having opposing first and second body surfaces, first burls at the first body surface, wherein each first burl has a distal end to support a substrate, and second burls at the second body surface to support the substrate holder on the support surface through contact with distal ends of the second burls; generating a second force to attract the substrate to the substrate holder; and controlling the first force and/or second force in a release step to deform the body between the second burls such as to create a gap between the distal ends of a first subset of the plurality of first burls and the substrate and such that the substrate is supported on distal ends of a second subset of the plurality of first burls.