Substrate Holder Gas Cushion for Lithography Overlay Control
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Solution Overview
Problem
Conventional substrate holders struggle to handle distorted substrates effectively, leading to inconsistent overlay errors and substrate-to-substrate variations during lithographic processes due to uneven clamping and thermal expansion.
Innovation Solution
A substrate holder with a main body and burls that form a gas cushion around the periphery when a substrate is lowered, allowing for even contact and reducing in-plane compression or expansion, thereby stabilizing the substrate and improving thermal coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional substrate holders use direct contact clamping, then strong clamping force is achieved, but substrate distortion and overlay errors increase
Solution Approach 1:
A layer of gas is introduced as an intermediary between the substrate and the substrate holder surface. The gas forms a cushion that allows the substrate to be held firmly against the holder while preventing direct contact that would cause distortion and trapping of contaminant particles. This resolves the contradiction by maintaining strong clamping force through gas pressure while eliminating the harmful effects of direct solid-to-solid contact.
Solution Approach 2:
The invention uses a pneumatic system to generate and control the gas cushion between the substrate and holder. Gas is supplied through channels in the substrate holder to create a pressurized gas layer that provides both the clamping force and the non-contact interface. This pneumatic approach enables strong holding force without the mechanical contact that causes substrate distortion and overlay errors.
2Stability of the object's composition
If substrate is firmly clamped to prevent movement, then positioning stability is improved, but thermal expansion variations increase
Solution Approach 1:
The gas layer acts as a thermal intermediary that decouples the substrate from the holder's thermal mass. While the gas provides mechanical stability by preventing substrate movement, it also provides thermal isolation that reduces heat transfer from the holder to the substrate. This minimizes thermal expansion variations while maintaining positioning stability during the exposure process.
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
The substrate holder reduces substrate-to-substrate overlay differences and improves thermal control, resulting in more consistent substrate behavior and reduced overlay errors, enhancing the performance of lithographic processes even with distorted substrates.
Implementation Method 1
A substrate holder with a main body and burls that form a gas cushion around the periphery when a substrate is lowered
Implementation Method 2
improving thermal coupling
Data Source
AI summary
A substrate holder (WT) for use in a lithographic apparatus and configured to support a substrate, the substrate holder comprising: a main body (20) having a main body surface; and a plurality of burls (21) projecting from the main body surface; wherein each burl has a distal end configured to engage with the substrate; the distal ends of the burls substantially conform to a support plane whereby a substrate can be supported in a substantially flat state on the burls; and a flow control feature (22, 22c, 22d) configured to form a gas cushion adjacent the periphery of the substrate holder when a substrate is being lowered onto the substrate holder.