TiO2-SiO2 Substrate for EUV Mask Flatness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional photolithography methods using visible or ultraviolet light are nearing their resolution limits, making it difficult to create fine patterns for advanced semiconductor devices, and EUV lithography is needed for patterns below 45 nm, but it requires a substrate with specific properties such as low thermal expansion and minimal striae to maintain precision during EUV exposure.
Innovation Solution
A substrate made of TiO2-SiO2 glass with a thermal expansion coefficient of 0±200 ppb/°C and a fictive temperature less than 1,000°C, produced using a two-step forming method and optimized for low stress and surface roughness, is used for EUV mask blanks, ensuring minimal deformation and high precision during EUV exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithography using visible or ultraviolet light is used, then the manufacturing process is simpler and equipment cost is lower, but the resolution limit is about 45 nm and cannot achieve finer patterns
Solution Approach 1:
The patent changes the fundamental parameter of light wavelength from visible/ultraviolet range to extreme ultraviolet (EUV) range (10-20 nm, particularly 13.5 nm). This parameter change enables突破 the resolution limit of conventional photolithography and achieves finer pattern resolution required for advanced semiconductor devices
Solution Approach 2:
The patent employs a composite substrate structure made of silica glass containing specific amounts of TiO2 (1-12 mass%) and ZrO2 (0.1-10 mass%). This composite material composition provides both the required optical properties for EUV lithography and mechanical stability, resolving the complexity issue through material science advancement
2Stability of the object's composition
If a substrate with low thermal expansion coefficient is used for EUV mask, then deformation under EUV irradiation is reduced, but the substrate material selection and manufacturing become more difficult
Solution Approach 1:
The patent precisely controls the compositional parameters of the glass substrate, specifying TiO2 content (1-12 mass%) and ZrO2 content (0.1-10 mass%), to achieve a thermal expansion coefficient of 0±200 ppb/°C. This parameter control enables both thermal stability and manufacturability
Solution Approach 2:
The patent differentiates between the surface quality area (where patterns are formed) and other areas of the substrate. The surface area is optimized for EUV exposure with specific flatness and stress characteristics, while other areas can have different properties, allowing flexible manufacturing approaches
3Manufacturing precision
If the surface roughness of the substrate is reduced to improve flatness, then mask quality is improved, but the manufacturing process becomes more complex and time-consuming
Solution Approach 1:
The patent incorporates flatness control measures during the glass forming process itself, rather than relying solely on post-forming polishing. By controlling the forming temperature, cooling rate, and annealing conditions, the substrate achieves inherent flatness with surface roughness (rms) ≤ 2 nm in the surface quality area, reducing the need for extensive subsequent processing
Solution Approach 2:
The patent optimizes multiple processing parameters including forming temperature (800-1,200°C), cooling rate (≤10°C/hr average rate), and annealing conditions to achieve both low surface roughness and high manufacturing efficiency. The fictive temperature is controlled to be less than 1,000°C, which facilitates the achieving of excellent flatness
4Manufacturing precision
If the stress in the substrate is minimized to prevent deformation, then pattern accuracy is improved, but the manufacturing process control becomes more difficult
Solution Approach 1:
The patent controls the stress in the substrate by optimizing the compositional parameters (TiO2: 1-12 mass%, ZrO2: 0.1-10 mass%) and thermal processing parameters (forming temperature, cooling rate, annealing conditions). These parameter changes reduce the standard deviation of stress to ≤0.04 MPa in the surface quality area, improving pattern accuracy
Solution Approach 2:
The patent uses a standardized substrate design with defined surface quality area and non-surface quality area, allowing the same manufacturing process to produce multiple substrates with consistent stress distribution and flatness characteristics, simplifying overall process control
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 substrate provides excellent flatness and stability, inhibiting the influence of EUV reflection light and enabling the formation of high-quality masks for EUV exposure, thereby overcoming the resolution limits of conventional photolithography.
Implementation Method 1
a material having a low thermal expansion coefficient and thereby showing no deformation even under EUV light irradiation
Implementation Method 2
a catoptric system, i.e. a combination of a reflective photomask (hereinafter referred to as 'EUV mask') and a mirror
Implementation Method 3
an absorber layer to absorb EUV light
Data Source
AI summary
A substrate that is suitable for an EUV mask or an EUV mask blank and excellent in flatness, is provided.A substrate for an EUV mask blank, which is made of a silica glass containing from 1 to 12 mass % of TiO2, wherein the surface roughness (rms) in a surface quality area of the substrate is at most 2 nm, and the maximum variation (PV) of the stress in the surface quality area of the substrate is at most 0.2 MPa.