EUV Photomask Etching with Self-Mask Tantalum Oxide Layer
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Solution Overview
Problem
EUV mask fabrication faces challenges in etch CD bias control, uniformity, cross-sectional profiles, etch selectivity, and defectivity due to limitations in photoresist materials, leading to high costs and low production yields.
Innovation Solution
A method involving a multi-material EUV photomask structure with a self-mask layer and a bulk absorber layer, where the self-mask layer comprises tantalum and oxygen, and the bulk absorber layer comprises tantalum with no oxygen, utilizing distinct etch processes to achieve high selectivity and reduce etch CD bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a soft photoresist mask is used for EUV mask fabrication, then the patterning process is simpler, but etch CD bias control deteriorates due to photoresist erosion during etching
Solution Approach 1:
The patent segments the absorber layer into two distinct layers: a bulk absorber layer (tantalum with no oxygen) and a self-mask layer (tantalum oxide). This segmentation allows each layer to serve a specific function—the bulk layer provides absorption while the self-mask layer protects against etching, thereby resolving the contradiction between manufacturing simplicity and etch CD bias control.
Solution Approach 2:
The self-mask layer is formed in-situ through oxidation of the bulk absorber layer, creating a protective mask that serves itself during the etch process. This self-service mechanism eliminates the need for separate photoresist materials and their associated erosion problems, achieving both simplicity and precision.
2Manufacturing precision
If a thinner resist layer is used to control non-uniformity, then etch selectivity deteriorates because more resist is consumed during pattern transfer
Solution Approach 1:
The self-mask layer is designed as a sacrificial protective layer that is consumed during etching to protect the bulk absorber layer. This disposable approach allows the use of thin layers for non-uniformity control while maintaining sufficient pattern transfer fidelity, as the self-mask layer is specifically engineered to provide the necessary protection.
Solution Approach 2:
The patent changes the material parameters by creating a tantalum oxide layer with distinct chemical composition and etch resistance properties. This parameter change enables the self-mask layer to provide adequate protection even at thin thicknesses, resolving the contradiction between non-uniformity control and pattern transfer fidelity.
3Manufacturing precision
If a hard mask is used to improve CD control, then manufacturing complexity increases due to additional process steps and selective removal requirements
Solution Approach 1:
The patent merges the absorber layer and mask layer into a single integrated structure where the self-mask layer is formed in-situ on the bulk absorber layer. This merging eliminates the need for separate hard mask deposition and removal processes, achieving CD control without increasing fabrication complexity.
Solution Approach 2:
The self-mask layer automatically forms through oxidation and automatically serves as the protective mask during etching, eliminating the need for external hard mask materials and their associated complex removal processes. This self-service mechanism resolves the contradiction between CD control and fabrication complexity.
4Strength
If a hard mask is used to protect the absorber layer, then etch selectivity requirements increase, making the process more challenging
Solution Approach 1:
The patent changes the chemical composition parameter by oxidizing the bulk absorber layer to form tantalum oxide, which has distinctly different etch resistance properties. This parameter change provides inherent etch selectivity between the self-mask layer and underlying layers, reducing the stringency of selectivity requirements while maintaining strong protection.
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 method achieves improved critical dimension control and uniformity, reducing etch CD bias to near zero and enhancing pattern transfer fidelity, while maintaining high etch selectivity, thus addressing the limitations of conventional EUV mask fabrication techniques.
Implementation Method 1
etching the self-mask layer using a first etch process; and etching the bulk absorber layer using a second etch process different than the first, wherein the etch rate of the bulk absorber layer is greater than the etch rate of the self-mask layer during the second etch process
Implementation Method 2
the self-mask layer comprises tantalum and oxygen and the bulk absorber layer comprises tantalum and essentially no oxygen, utilizing distinct etch processes to achieve high selectivity and reduce etch CD bias
Data Source
AI summary
Embodiments of methods of etching EUV photomasks are provided herein. In one embodiment, a method of etching an extreme ultraviolet photomask includes providing a photomask comprising, in order, a substrate, a multi-material layer, a capping layer, and a multi-layer absorber layer, the multilayer absorber layer comprising a self-mask layer disposed over a bulk absorber layer, wherein the self-mask layer comprises tantalum and oxygen and the bulk absorber layer comprises tantalum and essentially no oxygen; etching the self-mask layer using a first etch process; and etching the bulk absorber layer using a second etch process different than the first, wherein the etch rate of the bulk absorber layer is greater than the etch rate of the self-mask layer during the second etch process.