Graded Bottom Antireflective Coating for High NA Photolithography
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Solution Overview
Problem
Conventional photolithography methods face challenges in minimizing reflectance at high numerical aperture (NA) imaging conditions, leading to increased costs and defectivity due to the need for multiple BARC layers or thick BARCs, which are costly and difficult to integrate, especially as feature sizes approach 45 nm and below.
Innovation Solution
The method involves depositing a single bottom antireflective coating (BARC) with graded refractive index and absorbance, modifying its optical properties by illuminating it with light of a wavelength no more than 222 nm, resulting in closer optical properties to the photoresist at the interface, thereby minimizing reflectance while maintaining high resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple BARC layers or thick BARCs are used to minimize reflectance at high NA imaging conditions, then reflectance control is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies local quality by creating a BARC with spatially varying optical properties - the refractive index and absorbance change as a function of depth from the photoresist interface. This gradient structure allows different regions of the BARC to have optimized properties for minimizing reflectance at high NA angles while maintaining manufacturability through a single-layer approach rather than multiple discrete layers.
Solution Approach 2:
The patent utilizes parameter changes by modifying the optical parameters (refractive index and absorbance) of the BARC material as a function of thickness. This is achieved through specialized vapor deposition processes that permit the composition to change during deposition, or through spin-on processes with interfacial segregation, creating a graded structure that optimizes reflectance control without requiring multiple separate layers.
2Object-affected harmful factors
If specialized vapor deposition processes are used to create graded BARCs, then reflectance control is improved, but manufacturing cost and process complexity increase
Solution Approach 1:
The patent employs parameter changes through specialized vapor deposition processes where the composition of the BARC material is controlled to change as a function of thickness during deposition. This creates a graded structure with varying optical properties that effectively minimizes reflectance while using a single deposition process rather than multiple separate layer depositions.
Solution Approach 2:
The patent utilizes composite materials by creating a BARC with non-uniform composition - different materials or compositional gradients are used at different depths of the BARC layer. This composite structure enables optimized optical properties for reflectance control while maintaining a single-layer architecture that simplifies manufacturing compared to multiple discrete layers.
3Object-affected harmful factors
If spin-on processes with interfacial segregation are used to create graded BARCs, then reflectance control is improved, but material control precision requirements increase
Solution Approach 1:
The patent applies parameter changes through spin-on processes where a graded material is produced by interfacial segregation of components in the spin-on formulation. This creates a compositional gradient in the BARC that effectively controls reflectance, with the grading achieved through the physical process of spin coating and subsequent segregation.
Solution Approach 2:
The patent implements local quality through spin-on processes by creating spatial variation in material composition within the BARC layer. The interfacial segregation process naturally creates different material distributions at different locations and depths, providing the desired optical property gradients while using a simple, widely-available spin coating technique.
4Manufacturing precision
If high NA imaging conditions are used to improve resolution at small feature sizes, then resolution is improved, but reflectance from photoresist/BARC interface increases
Solution Approach 1:
The patent resolves this contradiction by applying local quality - creating a BARC where optical properties vary with depth from the photoresist interface. The graded structure provides optimized optical properties specifically at the critical photoresist/BARC interface to minimize reflectance at high NA angles, while maintaining the high NA imaging conditions necessary for small feature size resolution.
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 effective control of reflection with reduced BARC thickness, enhancing throughput and reducing costs by achieving minimal reflectance and improved resolution in photolithography, even at high NA imaging conditions.
Implementation Method 1
BARCs are typically interposed between the target layer and the photoresist so as to serve as a barrier that inhibits the reflected waves from traversing back through the photoresist
Implementation Method 2
Graded BARCs with optical properties that change as a function of the thickness of the BARC
Implementation Method 3
Bottom anti-reflective coatings (BARCs) are known and used to mitigate defects during the patterning of the target layer by attenuating or absorbing the light waves reflected from the target layer surface
Data Source
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AI summary
Photolithography methods using BARCs having graded optical properties are provided. In an exemplary embodiment, a photolithography method comprises the steps of depositing a BARC overlying a material to be patterned, the BARC having a refractive index and an absorbance. The BARC is modified such that, after the step of modifying, values of the refractive index and the absorbance are graded from first values at a first surface of the BARC to second values at a second surface of the BARC. The step of modifying is performed after the step of depositing.