Microlithographic Optical Element Heating for EUV Deformation Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
EUV mirrors in microlithographic projection exposure apparatuses experience thermal expansion and deformation due to EUV radiation absorption, leading to imaging property degradation, which existing control methods fail to adequately address.
Innovation Solution
Implement dynamic closed-loop control of heating power to optical elements using a heating arrangement, adjusting setpoint values over time based on a thermal model and real-time system data to compensate for varying operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a heating arrangement with temperature sensors is used to control mirror temperature, then thermal expansion can be compensated, but the measured temperature differs from the actual surface temperature causing insufficient control accuracy
Solution Approach 1:
The patent introduces an optical sensor as an intermediary measurement device that directly measures the mirror surface temperature without physical contact. This intermediary sensor provides accurate temperature data from the actual location where temperature control is needed, eliminating the temperature gradient error inherent in contact sensors placed at remote locations.
Solution Approach 2:
The patent replaces the mechanical contact-based temperature sensing system with an optical measurement system. By using optical sensors that detect thermal radiation or refractive index changes, the system obtains temperature information without physical contact, thereby avoiding the temperature differential between the sensor location and the mirror surface.
2Illumination intensity
If EUV mirrors are used in projection lenses, then imaging at EUV wavelengths is enabled, but absorption of EUV radiation causes thermal expansion and deformation degrading imaging properties
Solution Approach 1:
The patent converts the harmful thermal effect of EUV radiation absorption into a controllable parameter by implementing active heating. Instead of merely compensating for thermal expansion passively, the system uses controlled heating to pre-establish optimal temperature distributions, thereby converting the harmful thermal effect into a manageable and even beneficial control parameter.
Solution Approach 2:
The patent dynamically adjusts the temperature parameter of the EUV mirrors through controlled heating arrangements. By changing the thermal state of the mirrors in response to measured temperature deviations, the system compensates for thermally induced surface deformations and maintains optimal imaging properties despite continuous EUV radiation exposure.
3Temperature
If active mirror heating is applied during low absorption phases, then temperature control is achieved, but heating power must be continuously adjusted which complicates the control system
Solution Approach 1:
The patent implements a feedback control system where optical sensors continuously measure the actual mirror surface temperature, and this measurement feeds back to a controller that adjusts the heating power accordingly. This closed-loop feedback mechanism simplifies the control strategy by using real-time temperature information to automatically modulate heating, eliminating the need for complex predictive control algorithms.
Solution Approach 2:
The system enables the mirror heating control to be self-regulating through feedback from optical temperature sensors. The heating arrangement automatically adjusts its power output based on the measured temperature, making the system self-correcting and reducing the need for external intervention or complex control programming.
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
Effectively reduces thermal deformations and optical aberrations by dynamically adapting heating processes to actual system states, enhancing imaging quality.
Implementation Method 1
Absorption of the radiation emitted by the EUV light source among other reasons can cause the EUV mirrors heat up and undergo an associated thermal expansion or deformation
Implementation Method 2
the actual surface temperature using an optical sensor
Data Source
AI summary
A method of heating an optical element in a microlithographic projection exposure apparatus and an optical system includes using a heating arrangement to introduce a heating power into the optical element. The heating power is regulated based on a setpoint value. The setpoint value is varied over time during the operation of the projection exposure apparatus. Varying the setpoint value for the heating power comprises a simulation of the effects of changes in the heating power relative to the actual value thereof based on a model for the thermal behavior of the optical element.