Non-Stoichiometric Metal Nitride Coatings for EUV Mask Conductivity
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Solution Overview
Problem
Current photolithographic mask coatings face challenges in achieving a balance between electrical conductivity, optical transparency, mechanical durability, and adhesion, particularly for extreme ultraviolet (EUV) applications, where surface variations and defects require precise handling and correction.
Innovation Solution
A non-stoichiometric metal nitride coating with a thickness of 5-30 nm, composed of metals like Cr, Ti, or Si, and varying nitrogen content, is deposited using physical vapor deposition, offering improved mechanical resistance, adhesion, and optical transmittance, while maintaining suitable sheet resistance and surface smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick electrically conductive coating is deposited on the substrate, then the sheet resistance decreases (improving electrical conductivity), but the optical transmittance decreases (worsening optical transparency)
Solution Approach 1:
The patent applies parameter changes by controlling the nitrogen content in metal nitride coatings to achieve non-stoichiometric compositions (where nitrogen content is less than the maximum possible). This compositional parameter adjustment allows the coating to maintain electrical conductivity while improving optical transmittance, as the reduced nitrogen content decreases the coating's optical absorption without compromising electrical performance below the required 100 Ω/□ sheet resistance threshold.
Solution Approach 2:
The patent employs composite materials by combining metal nitrides with specific non-stoichiometric compositions in multi-layer configurations. These composite structures integrate materials with different optical and electrical properties, allowing the system to achieve both adequate electrical conductivity and improved optical transmittance through the synergistic arrangement of layers with varying nitrogen contents and material compositions.
2Strength
If a thick coating is deposited to improve adhesion and mechanical resistance, then the coating's durability improves, but the optical transmittance and surface smoothness deteriorate
Solution Approach 1:
The patent uses parameter changes by optimizing the nitrogen content in metal nitride coatings to non-stoichiometric levels, which fundamentally alters the coating's optical properties. This compositional adjustment reduces optical absorption and improves transmittance while maintaining sufficient adhesion and mechanical resistance through the inherent bonding characteristics of the metal-nitrogen structure at controlled nitrogen deficiencies.
Solution Approach 2:
The patent applies local quality by creating coatings with spatially varying nitrogen content or using different metal nitride compositions in specific layers. This allows different regions of the coating system to have optimized properties: layers with higher nitrogen content provide adhesion and mechanical strength, while layers with lower nitrogen content provide optical transmittance, achieving both requirements simultaneously through localized property differentiation.
3Reliability
If the coating composition is optimized for electrical conductivity, then the sheet resistance decreases, but the mechanical resistance and adhesion worsen
Solution Approach 1:
The patent employs composite materials by combining multiple metal nitride layers with different compositions and properties. This composite structure allows one layer to be optimized for electrical conductivity (lower nitrogen content for reduced sheet resistance) while another layer provides mechanical strength and adhesion (higher nitrogen content or different metal composition), achieving both electrical and mechanical performance requirements through material combination.
Solution Approach 2:
The patent applies segmentation by dividing the coating into multiple functional layers, each with specific compositions optimized for particular functions. One layer segment focuses on electrical conductivity with appropriate nitrogen content, while another segment focuses on mechanical resistance and adhesion, allowing each segment to perform its specialized function without compromising the other.
4Reliability
If the nitrogen content in metal nitride coating is increased to improve electrical conductivity, then the sheet resistance decreases, but the optical transmittance and surface smoothness worsen
Solution Approach 1:
The patent applies parameter changes by inverting the conventional approach: instead of increasing nitrogen content to improve electrical conductivity, it reduces nitrogen content to non-stoichiometric levels. This counterintuitive parameter adjustment simultaneously improves both electrical conductivity (by reducing scattering centers) and optical transmittance (by reducing optical absorption), while maintaining adequate mechanical properties through the metal framework structure.
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 coating provides enhanced mechanical resistance, strong adhesion, and controlled optical transmission, enabling precise handling and defect correction of EUV masks without generating particles, and allowing ultra-short laser pulses to penetrate for planarity adjustment.
Implementation Method 1
A non-stoichiometric metal nitride coating with a thickness of 5-30 nm, composed of metals like Cr, Ti, or Si, and varying nitrogen content, is deposited using physical vapor deposition
Data Source
AI summary
The present invention is directed to compositions for photolithographic masks comprising a substrate and a coating having at least one electrical conducting layer comprising a nitride, a boride or a carbide, and methods of making the same.