Polarization Filter for Lithography Mirror Temperature Measurement
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Solution Overview
Problem
Existing projection exposure apparatuses for semiconductor lithography face challenges in accurately measuring the surface temperature of optical elements due to interference from thermal radiation reflected from surroundings, leading to insufficient accuracy in determining the differential temperature.
Innovation Solution
The apparatus incorporates a temperature recording device equipped with a filter, such as a polarization filter, to selectively allow only the thermal electromagnetic radiation from the optical element's surface to be detected, thereby filtering out disturbing radiation and improving measurement accuracy. Additionally, the use of a lock-in amplifier and emissivity adjustments can enhance the accuracy further.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an infrared camera is used to detect the temperature of the mirror surface, then temperature measurement is enabled, but the measurement accuracy deteriorates due to reflected thermal radiation from surroundings
Solution Approach 1:
A polarizing filter is introduced as an intermediary component between the infrared camera and the mirror surface. This filter selectively transmits thermal radiation based on its polarization state, allowing the camera to detect emitted radiation from the mirror while blocking reflected radiation from surrounding objects. The filter acts as a mediator that separates the desired signal (emitted radiation) from the unwanted interference (reflected radiation).
Solution Approach 2:
The solution changes the polarization parameter of the thermal radiation being detected. By using a polarizing filter oriented at a specific angle (typically 45 degrees relative to the mirror surface normal), the system exploits the polarization characteristics of emitted versus reflected radiation. Emitted thermal radiation from the mirror surface has a different polarization state compared to reflected radiation from surroundings, allowing differentiation and selective detection.
2Productivity
If the throughput of the projection exposure apparatus is increased, then productivity improves, but thermal load increases causing more imaging aberrations
Solution Approach 1:
The system implements a feedback mechanism where the infrared camera continuously monitors the temperature of the mirror surface, and this temperature information is fed back to the control system. Based on the measured temperature, the system can adjust operational parameters or activate cooling mechanisms to maintain the mirror within optimal temperature ranges, thereby compensating for the increased thermal load resulting from higher throughput operations.
Solution Approach 2:
The patent replaces direct mechanical contact temperature measurement methods with non-contact infrared thermography. This substitution allows for continuous, real-time temperature monitoring without physically interfering with the optical path or introducing additional thermal conduction paths that could affect the mirror temperature.
3Manufacturing precision
If optical assemblies are used to correct imaging aberrations, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
Instead of adding more optical assemblies, the system corrects imaging aberrations by changing the temperature parameter of existing optical elements. By precisely controlling and adjusting the temperature of mirrors and other optical components, the system exploits thermal expansion and refractive index changes to dynamically correct optical path differences and imaging aberrations, thereby achieving high manufacturing precision without increasing device complexity.
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 solution significantly improves the accuracy of surface temperature measurement on optical elements, allowing for more precise thermal management and reduced imaging aberrations in projection exposure apparatuses, thereby enhancing the overall performance and reliability of semiconductor lithography processes.
Implementation Method 1
detecting a temperature on a surface of the optical element via the thermal electromagnetic radiation emanating from the surface of the optical element
Implementation Method 2
a filter for filtering the electromagnetic radiation
Implementation Method 3
a filter, such as a polarization filter, to selectively allow only the thermal electromagnetic radiation from the optical element's surface to be detected
Data Source
AI summary
A projection exposure apparatus for semiconductor lithography comprises an optical element and a temperature recording device for detecting a temperature on a surface of the optical element via electromagnetic radiation emanating from the surface of the optical element. The temperature recording device can comprise a filter for filtering the electromagnetic radiation.