Photosensitive Resist Under-layer for EUV Lithography Focus Compensation
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Solution Overview
Problem
The challenge in EUV lithography is to increase the numeric aperture (NA) to achieve smaller critical dimensions and features, but this is limited by the reduced depth of focus (DoF), which affects the focus latitude and leads to issues with feature separation and critical dimension uniformity.
Innovation Solution
A photosensitive resist under-layer with a lower exposure threshold than the resist itself is used, allowing the resist under-layer to change properties during exposure, such as becoming more hydrophilic, which aids in the development process and compensates for the low DoF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the numeric aperture (NA) is increased to achieve smaller critical dimensions, then the feature size decreases, but the depth of focus (DoF) reduces
Solution Approach 1:
The patent divides the resist system into two separate functional layers: a top resist layer for pattern formation and a bottom resist under-layer for focus compensation. This segmentation allows each layer to be independently optimized - the top resist for critical dimension definition and the under-layer for depth of focus extension through its lower exposure threshold and hydrophilic properties.
Solution Approach 2:
The resist under-layer acts as an intermediary between the substrate and the top resist. It mediates the exposure process by absorbing excess radiation and undergoing chemical changes that compensate for focus variations, thereby protecting the top resist layer from focus-related defects and enabling larger NA operation.
2Manufacturing precision
If the exposure dose is reduced to lower line width roughness, then the line width uniformity improves, but the feature separation may be compromised
Solution Approach 1:
The patent changes the exposure threshold parameter of the under-layer relative to the top resist. By designing the under-layer with a lower exposure threshold, it becomes more sensitive to radiation and undergoes chemical changes at lower doses, creating a contrast effect that enhances feature separation while allowing the top resist to maintain smooth line widths at reduced exposure doses.
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 allows for the use of higher NA in EUV systems, improving the separation of features and critical dimension uniformity, while also enabling a lower radiation dose during exposure, which reduces line width roughness.
Implementation Method 1
the exposure threshold of the resist under-layer is lower than the exposure threshold of the resist
Implementation Method 2
a photosensitive resist under-layer with a lower exposure threshold than the resist itself is used, allowing the resist under-layer to change properties during exposure
Data Source
AI summary
A substrate arrangement for use in a lithographic apparatus, the substrate arrangement including: a resist; a photosensitive resist under-layer; and a substrate, wherein an exposure threshold of the resist under-layer is lower than an exposure threshold of the resist. The resist and the resist under-layer may be both photosensitive to EUV radiation.