EUV Projection Optical Elements With Precise Grating Step Heights
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Solution Overview
Problem
The production of grating structures for EUV projection exposure apparatuses is complex, and there are fluctuations in step height and deviations from specified values, leading to suboptimal optical properties and reflectivity.
Innovation Solution
An optical element with a substrate, shaping layers, etch stop layers, and an EUV radiation-reflecting layer, where the shaping layers form a grating structure with sharp transitions and precise layer thicknesses, minimizing rounding and surface roughness to enhance reflectivity and suppress unwanted radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods are used to produce grating structures, then production complexity is reduced, but manufacturing precision deteriorates due to step height fluctuations and rounding at transitions
Solution Approach 1:
The patent applies a shaping layer before etching to predefine the desired grating structure geometry. This preliminary action establishes the step height and transition profiles before the etching process begins, ensuring that the final grating structure achieves the required manufacturing precision without complex real-time control during etching.
Solution Approach 2:
The shaping layer acts as an intermediary between the substrate and the etching process. It transfers the desired grating pattern to the etching layer, enabling precise reproduction of the grating structure while simplifying the overall production process by decoupling the pattern definition from the material removal step.
2Reliability
If conventional etching methods are used, then production simplicity is maintained, but optical properties deteriorate due to rounding at the transition from bottom region to flank
Solution Approach 1:
The shaping layer is applied in advance with a profile that includes sharp transitions (radius of curvature ≤ 5 μm) before etching. This preliminary definition of sharp edges ensures that the final grating structure maintains the required optical reflectivity without needing complex etching control to achieve sharp transitions.
Solution Approach 2:
The patent replaces mechanical/chemical etching processes that struggle to produce sharp transitions with a deposition-based shaping layer approach. The shaping layer is deposited to define the grating geometry, and subsequent etching simply follows this pre-defined pattern, eliminating the rounding issue inherent in direct etching methods.
3Reliability
If shaping layers with rounded transitions are used, then manufacturing ease is maintained, but optical properties worsen due to reduced reflectivity and increased stray light
Solution Approach 1:
The shaping layer is deposited with a predetermined sharp transition profile (radius of curvature ≤ 5 μm) before any etching occurs. This preliminary establishment of sharp edges ensures that the final optical element achieves the required EUV reflectivity and minimal stray light, as the sharp transitions are preserved through the subsequent etching process.
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 improves the precision of the grating structure, enhancing EUV reflectivity and reducing stray light losses, allowing for improved optical properties and simplified production processes.
Implementation Method 1
an EUV radiation-reflecting layer, wherein the EUV-radiation-reflecting layer is applied at least to the bottom region and to the front side of the grating structure
Data Source
AI summary
In a method for producing an optical element for an EUV projection exposure apparatus, a shaping layer (221) is applied onto a substrate (20) so as to have a surface roughness of at most 0.5 nm rms directly after the application of the shaping layer onto the substrate.