EUV Lithography Film Stack with Selective Middle Layer
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Solution Overview
Problem
Current EUV lithography techniques face challenges with line edge roughness and line width roughness, leading to linewidth fluctuations that affect device characteristics, and have lower etch selectivity compared to traditional 193i processes, necessitating improved materials and methods for patterning substrates with increased selectivity.
Innovation Solution
The method involves a film stack with a bottom layer of diamond-like carbon, a middle layer that can be selectively etched and converted to increase selectivity, and a patterned photoresist exposed to EUV radiation, followed by plasma treatment to enhance etch selectivity, allowing for precise patterning of substrates with high selectivity over the photoresist and bottom layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If EUV lithography is used for patterning, then fewer masks are required compared to traditional 193i process, but etch selectivity is lower and throughput is slower
Solution Approach 1:
The patent divides the patterning process into multiple etch steps with different selectivity requirements. A first etch process with lower selectivity is used to etch through the mandrel layer, followed by a second etch process with higher selectivity to etch through the target layer. This segmentation allows each etch step to be optimized independently, resolving the contradiction between using fewer masks and maintaining high etch selectivity.
Solution Approach 2:
The patent introduces a mandrel layer as an intermediary structure between the photoresist and the target layer. This mandrel layer enables the use of a lower selectivity etch process while still achieving the desired patterning result, as the mandrel provides structural support and defines the pattern before the final target layer etch.
2Reliability
If polymer dump process is used to achieve higher selectivity, then etch selectivity improves, but line edge roughness and line width roughness increase
Solution Approach 1:
The patent changes the material parameters of the mandrel layer from polymer-based materials to inorganic materials such as silicon oxide or silicon nitride. This parameter change allows the use of lower selectivity etch processes without experiencing the line width roughness issues associated with polymer dump processes, as inorganic materials provide more stable etch profiles and better line edge definition.
3Productivity
If critical dimensions are shrunk to meet tightening dimensional tolerances, then device density increases, but line width variations become too large to be acceptable
Solution Approach 1:
The patent performs preliminary patterning to form the mandrel layer with the desired pattern before conducting the final target layer etch. This preliminary action establishes a stable pattern template that guides the subsequent etch process, ensuring that even as critical dimensions are shrunk, the line width variations remain controlled and within acceptable tolerances.
Solution Approach 2:
The patent replaces direct photoresist-to-target etching with a two-step process involving a mandrel layer. This substitution allows for better control of the etch mechanics, as the mandrel layer provides a more stable structure that reduces line edge roughness and line width roughness during the etch process, enabling smaller critical dimensions with acceptable precision.
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 achieves high selectivity in etching, reducing linewidth fluctuations and improving device characteristics by selectively etching the middle and bottom layers, thereby addressing the limitations of current EUV lithography techniques.
Implementation Method 1
the coated substrate is exposed to a source of activating radiation, which causes a chemical transformation in the exposed areas of the surface
Implementation Method 2
The photoresist residue is removed by exposing the substrate to a plasma comprising one or more of O2, N2, H2 or HBr
Implementation Method 3
The patterned middle layer is exposed to an oxidizing agent to convert the patterned middle layer to a modified patterned middle layer. The oxidizing agent comprises an inductively coupled O2 plasma
Implementation Method 4
The oxidizing agent comprises an inductively coupled O2 plasma
Data Source
AI summary
Methods and film stacks for extreme ultraviolet (EUV) lithography are described. The film stack comprises a substrate with a hard mask, bottom layer, middle layer and photoresist. Etching of the photoresist is highly selective to the middle layer and a modification of the middle layer allows for a highly selective etch relative to the bottom layer.