Graded Spin-On Antireflective Coating for High NA Lithography
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Solution Overview
Problem
High numerical aperture (NA) optical lithography systems face challenges with substrate reflectivity and reflective notching, leading to non-uniform photoresist linewidths and image quality issues due to light scattering and interference effects, especially when using monochromatic light on reflective substrates with topography.
Innovation Solution
A single-layer spin-on graded antireflective coating (ARC) with varying optical properties throughout its thickness, composed of polymers with chromophore and transparent moieties, is applied to reduce reflectivity and enhance feature control below 65 nm, segregating components to the ARC-photoresist and ARC-substrate interfaces to minimize radiation reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single-layer antireflective coating is used, then the coating process is simple, but the reflectivity control at high NA angles is insufficient
Solution Approach 1:
The patent applies local quality by creating a graded index of refraction within the single ARC layer, where the refractive index varies continuously from the substrate interface to the photoresist interface. This gradient structure locally optimizes optical properties at different depths to control reflectivity across all angles of incidence, including high NA angles, without requiring multiple discrete layers.
Solution Approach 2:
The patent implements parameter changes by varying the refractive index parameter through the thickness of the ARC layer. The graded index profile transitions smoothly from the substrate side to the photoresist side, transforming the optical characteristics to minimize reflection at all angles while maintaining a single-layer structure.
2Reliability
If monochromatic light is used to eliminate chromatic aberration, then chromatic aberration is reduced, but standing waves and interference effects increase
Solution Approach 1:
The patent converts the harmful standing wave effects into beneficial outcomes by designing the graded ARC to specifically target and suppress reflection at the critical interfaces. The gradient structure creates a continuous transition that prevents the formation of strong standing waves, transforming the potential harm of monochromatic light into improved image quality through enhanced reflectivity control.
3Measurement precision
If high NA optical systems are used to increase resolution, then resolution capability is improved, but reflectance and scattering increase
Solution Approach 1:
The graded ARC applies local quality by optimizing optical properties at different depths to handle the angular spread inherent in high NA systems. The refractive index gradient is specifically designed to minimize reflectance across the full angular range from normal incidence to high oblique angles, enabling high resolution imaging without the reflectance penalties of conventional single-layer coatings.
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 graded ARC effectively controls feature sizes below 65 nm by reducing reflectivity and scattering, improving linewidth uniformity and image quality, while simplifying the processing and reducing costs compared to multilayer or graded CVD BARCs.
Implementation Method 1
the radiation intensity that is reflected at the ARC-photoresist interface is substantially decreased, while the light that penetrates the ARC layer is absorbed
Implementation Method 2
constructive and destructive interference is particularly significant when monochromatic or quasi-monochromatic light is used for photoresist exposure
Data Source
AI summary
An antireflective coating that contains at least two polymer components and comprises chromophore moieties and transparent moieties is provided. The antireflective coating is useful for providing a single-layer composite graded antireflective coating formed beneath a photoresist layer.