Reflection-Type Photomask Trench Design for EUV Reflection Control
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Solution Overview
Problem
The integration of semiconductor devices faces limitations in pattern resolution due to the high energy and low energy efficiency of extreme ultraviolet (EUV) rays, which are difficult to handle with traditional transmission-type photomasks, necessitating the development of reflection-type photomasks that can effectively manage EUV rays without substrate penetration.
Innovation Solution
A reflection-type photomask with a multi-layered reflection layer and absorption layers, featuring a trench with sloped sidewalls in the border region to minimize EUV ray reflection, utilizing a low thermal expansion substrate and specific materials like molybdenum and silicon for the reflection layers, and aluminum copper or tantalum nitride for absorption layers, to enhance pattern transfer and prevent unwanted reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If transmission-type photomasks are used for EUV lithography, then the photomask structure is simple, but the substrate cannot endure the high energy of EUV rays and energy efficiency is low
Solution Approach 1:
The patent inverts the fundamental operating principle of traditional photomasks by transitioning from transmission-type to reflection-type photomasks. Instead of allowing EUV rays to pass through the substrate and absorb them on the other side, the photomask reflects the EUV rays off the front surface. This inversion resolves the contradiction by protecting the substrate from high-energy radiation while maintaining photomask functionality through the reflection of EUV rays onto the wafer.
Solution Approach 2:
The patent converts the harmful effect of EUV ray absorption into a beneficial reflection process. The high energy of EUV rays, which previously caused substrate damage and low energy efficiency in transmission-type masks, is now utilized to create a reflection mechanism. By designing a photomask with specific material properties and surface characteristics, the EUV rays are reflected rather than absorbed, transforming the potential harm into an effective lithography process while protecting the substrate.
2Device complexity
If transmission-type photomasks are used for EUV lithography, then the photomask structure is simple, but energy efficiency is too low to enhance pattern resolution
Solution Approach 1:
The patent inverts the energy transmission mechanism by using reflection instead of transmission. The EUV rays are reflected off the photomask surface rather than passing through it, which fundamentally changes how energy is utilized. This inversion enables the system to maintain structural simplicity while dramatically improving energy efficiency, as the reflected EUV rays deliver full energy to the wafer without being attenuated by the substrate.
Solution Approach 2:
The patent converts the previously harmful energy absorption into a beneficial reflection process. The high energy of EUV rays, which caused inefficiency in transmission-type masks, is now harnessed to create a reflection mechanism that delivers this energy directly to the wafer. This transformation resolves the energy efficiency contradiction by utilizing the full energy content of EUV rays without substrate attenuation.
3Reliability
If reflection-type photomasks are used, then substrate durability is improved, but EUV ray reflection may cause unwanted patterns
Solution Approach 1:
The patent applies local quality by creating different surface characteristics in different regions of the photomask. The border region has a specific surface treatment to control reflection, while the pattern transfer region has different properties. This spatial differentiation of material properties or surface characteristics allows the photomask to protect the substrate while controlling reflection to prevent unwanted patterns in specific areas.
Solution Approach 2:
The patent introduces an intermediary layer or surface treatment between the substrate and the incident EUV rays. This intermediary structure, such as a specific material coating or surface treatment in the border region, acts as a mediator that controls the reflection process. It protects the substrate from direct EUV exposure while managing the reflected rays to prevent unwanted pattern formation, thus resolving the contradiction between durability and pattern uniformity.
4Object-generated harmful factors
If trench is added to border region, then unwanted reflections are suppressed, but device complexity increases
Solution Approach 1:
The patent segments the photomask structure by adding a trench in the border region, separating this functional area from the pattern transfer region. This segmentation allows the trench to specifically address unwanted reflections in the border area without affecting the overall photomask functionality. The trench acts as a localized structural element that suppresses harmful reflections while maintaining the simplicity of the rest of the photomask design.
Solution Approach 2:
The patent extracts or removes material to form a trench in the border region, creating a void or cavity that specifically targets unwanted reflections. By taking out material from the border region rather than adding complex structures throughout the entire photomask, the design suppresses harmful reflections while minimizing overall device complexity. The trench represents a localized extraction that achieves the desired function with minimal structural modification.
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 solution effectively suppresses EUV ray reflections, ensuring uniform critical dimension (CD) patterns on wafers without defects, thereby improving pattern resolution and reducing thermal expansion issues in semiconductor fabrication.
Implementation Method 1
the EUV ray may be reflected on surfaces of the reflection-type photomasks without penetrating the reflection-type photomasks
Implementation Method 2
First absorption layer patterns are disposed on the reflection layer in the pattern transfer region, and a second absorption layer pattern is disposed on the reflection layer in the light blocking region
Implementation Method 3
The substrate may be a low thermal expansion material (LTEM) substrate
Data Source
AI summary
Reflection-type photomasks are provided. The reflection-type photomask includes a substrate and a reflection layer on a front surface of the substrate. The substrate includes a pattern transfer region, a light blocking region and a border region. A trench penetrates the reflection layer in the border region to expose the substrate. First absorption layer patterns are disposed on the reflection layer in the pattern transfer region, and a second absorption layer pattern is disposed on the reflection layer in the light blocking region. Sidewalls of the trench have a sloped profile. Related methods are also provided.