Echelle Diffraction Grating Blaze Angle Offset for UV Stability
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Solution Overview
Problem
Conventional Echelle diffraction gratings used in ArF excimer lasers experience degradation of the reflective coating layer and resin layer, leading to a decrease in diffraction efficiency over time, making it challenging to maintain consistent performance for long-term use.
Innovation Solution
The Echelle diffraction grating is designed with a specific configuration that includes a blazed surface and a counter surface with an apex angle between 85° and 90°, and a second blaze angle set by subtracting an offset value from the first blaze angle to maintain peak diffraction efficiency before surface deformation occurs, using a protective dielectric layer to prevent oxidation and enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional Echelle diffraction grating is used for ArF excimer laser, then initial diffraction efficiency is high, but diffraction efficiency degrades over time due to reflective coating layer deformation
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the blaze angle to be smaller than the optimal value before the grating is put into service. This pre-adjustment compensates for the expected deformation of the reflective coating layer during long-term use, ensuring that the diffraction efficiency remains stable throughout the service life rather than degrading over time.
2Reliability
If the blaze angle is optimized for maximum diffraction efficiency, then initial efficiency is maximized, but the grating becomes sensitive to surface deformation
Solution Approach 1:
The patent applies preliminary anti-action by intentionally setting the blaze angle smaller than the optimal value, which creates a design margin that counteracts the harmful effect of surface deformation. This pre-adjusted configuration ensures that even when the reflective coating layer deforms during use, the diffraction efficiency does not drop below the acceptable threshold, thereby preventing the harmful effect of deformation from compromising performance.
3Reliability
If a reflective coating layer is used on the blazed surface, then diffraction efficiency is improved, but the coating layer degrades due to ultraviolet radiation
Solution Approach 1:
The patent applies the blessing in disguise principle by using a dielectric layer with specific properties (refractive index between 1.3-1.6, thickness 1-10 μm) that converts the harmful effect of ultraviolet radiation into a beneficial protective function. The dielectric layer absorbs and scatters UV radiation, protecting the underlying reflective coating layer from degradation while maintaining high diffraction efficiency.
4Reliability
If the apex angle is set to a large value, then the blazed surface area is increased, but manufacturing precision becomes more difficult to control
Solution Approach 1:
The patent applies parameter changes by optimizing the apex angle to a specific range (85°-90°) that balances diffraction efficiency with manufacturability. This parameter optimization ensures that the blazed surface area is sufficient for high efficiency while keeping the apex angle within a range that can be reliably controlled during the manufacturing process, avoiding the difficulties of precision control at larger angles.
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 configuration maintains diffraction efficiency at 82% or higher, significantly improving upon the conventional efficiency of 66% and ensuring stability and durability, even under ultraviolet radiation, while minimizing manufacturing errors.
Implementation Method 1
Echelle diffraction grating... configured to select the wavelength in an excimer laser
Implementation Method 2
the blazed surface constitutes one side of the triangular section of the grating and has a large influence on the diffraction efficiency
Implementation Method 3
a reflective layer (aluminum film) formed on a surface of the resin layer
Implementation Method 4
using a protective dielectric layer to prevent oxidation and enhance durability
Data Source
Figure 1A~1B
Figure 2~3
Figure 4~5
AI summary
An Echelle diffraction grating (1) has a Littrow configuration. Each grating includes a resin layer (11) made of light curing resin and having a thickness between 2 µm and 10 µm, and a reflective coating layer (12) formed on the resin layer, having a thickness between 120 nm and 500 nm, and made of aluminum. An apex angle (6) between a blazed surface (3) and a counter surface (8) is between 85° and 90°. A first blaze angle is an angle that maximizes diffraction efficiency of a set blazed order for incident light of a wavelength of 193.3 nm. A blaze angle (5) has an initial value of a second blaze angle smaller than the first blaze angle. 0.25°≤bd-ba≤1.2° is satisfied where bd denotes the first blaze angle and ba denotes the second blaze angle.