Optical Element Surface Measurement With Pressure Matching
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Solution Overview
Problem
The challenge of accurately measuring the surface shape of optical elements with cooling channels under varying pressure conditions, particularly in EUV systems, is exacerbated by pressure differences and refractive index mismatches, leading to deformation and unwanted reflections, which affect optical performance.
Innovation Solution
A method and apparatus that adjust the cooling channel pressure to match a target pressure difference by controlling coolant pressure, using hydraulic, pneumatic, or electric pumps, and selecting coolant refractive index to minimize reflections, ensuring precise measurement under EUV conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling channels are formed in the substrate to prevent heating during EUV operation, then thermal deformation is reduced, but measurement precision deteriorates due to pressure differences causing surface deformation
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the cooling channel pressure parameter to match the measurement environment pressure. This involves monitoring pressure differences between the cooling channels and measurement environment, then modifying the cooling channel pressure to eliminate deformation during measurement, thereby enabling high-precision surface shape measurement while maintaining the cooling function during operation
2Temperature
If cooling channels are formed in the substrate to dissipate heat, then optical performance is maintained during operation, but measurement precision deteriorates due to refractive index mismatches causing unwanted reflections
Solution Approach 1:
The patent introduces an intermediary substance (coolant) filled in the cooling channels with specific refractive index properties. The coolant acts as an intermediary medium that matches the refractive index of the substrate material, thereby eliminating unwanted reflections at the interface between the cooling channels and substrate during interferometric measurement, while still providing effective heat dissipation during EUV operation
3Temperature
If pressure difference is maintained in cooling channels during EUV operation, then cooling effectiveness is improved, but measurement precision deteriorates due to pressure-induced surface deformation
Solution Approach 1:
The patent implements dynamics by making the cooling channel pressure adjustable and adaptable to different operational conditions. The system dynamically transitions between two states: during EUV operation, pressure is maintained to ensure effective cooling; during measurement, pressure is adjusted to match the measurement environment, eliminating deformation. This dynamic pressure control enables the system to optimize for different functions as needed
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
Enables reliable and high-precision measurement of optical elements by aligning actual pressure differences with target values, reducing deformations and reflections, thereby maintaining optical performance.
Implementation Method 1
at least one cooling channel for receiving a coolant is formed in the substrate
Implementation Method 2
an interferometer, with which a measurement of at least a partial surface of a surface of the optical element is able to be carried out by interferometric superposition of a test wave
Implementation Method 3
selecting coolant refractive index to minimize reflections
Data Source
AI summary
A method for measuring a surface shape of an optical element, wherein the optical element has a main body with a substrate and a reflective surface, and wherein at least one cooling channel for receiving a coolant is formed in the substrate, comprising: a) recording a cooling channel pressure, b) recording a measurement environment pressure, c) determining a pressure difference based on the cooling channel pressure and the measurement environment pressure, d) comparing the pressure difference with a predetermined target pressure difference, e) monitoring for a deviation between the pressure difference and the target pressure difference, wherein, if a deviation greater than a predetermined limit value is detected, the cooling channel pressure is adapted in such a way that the deviation becomes less than or equal to the predetermined limit value, and f) measuring the surface shape if the deviation is less than or equal to the predetermined limit value.