Projection Exposure Apparatus Pressure Fluctuation Decoupling
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Solution Overview
Problem
Pressure fluctuations caused by mechanical vibrations during the scanning process in projection exposure apparatuses for semiconductor lithography negatively impact the optical imaging quality, particularly in systems operating in the scan mode, where high accelerations can lead to significant disturbances affecting the optical components and polarization of electromagnetic radiation.
Innovation Solution
A mechanism is introduced to decouple parts of the illumination system and projection lens from pressure fluctuations by creating a closed-off space around the mask stage, filling it with a gas of higher sound absorption than air, and using flexible mountings or active correction systems to neutralize sound waves, along with the use of pellicles to shield against contamination and mechanical decoupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the mask stage is moved at high acceleration to save time in scan mode, then productivity is improved, but pressure fluctuations increase which deteriorate optical imaging quality
Solution Approach 1:
The system is divided into two separate stages: a first stage for high-acceleration movement to achieve fast scanning and productivity, and a second stage for fine positioning to ensure optical imaging quality. This segmentation allows each stage to be optimized for its specific function without compromising the other.
Solution Approach 2:
The mask stage acceleration profile is dynamically adjusted by selectively activating only necessary lens elements during the scan. This dynamic optimization reduces the overall acceleration requirements and associated pressure fluctuations while maintaining the required scan speed and productivity.
2Loss of time
If high acceleration is used during scanning to reduce exposure time, then exposure time is reduced, but mechanical vibrations and pressure fluctuations increase affecting optical components
Solution Approach 1:
The exposure process is segmented into a fast scanning phase and a fine positioning phase. During the scanning phase, high acceleration is applied to minimize exposure time. During the fine positioning phase, the system settles to ensure optical quality, effectively separating the time-critical and precision-critical operations.
Solution Approach 2:
The system dynamically optimizes the acceleration profile by selectively using only necessary lens elements during scanning. This reduces the mass that needs to be accelerated and minimizes mechanical vibrations and pressure fluctuations while maintaining short exposure times.
3Productivity
If the diameter of the wafer is increased to process larger substrates, then productivity is improved, but larger accelerations occur during scanning which increase pressure fluctuations
Solution Approach 1:
For large diameter wafers, the scanning process is divided into a high-speed scan phase and a fine positioning phase. The segmentation allows the system to handle large substrates efficiently while managing acceleration levels to control pressure fluctuations during the critical exposure period.
Solution Approach 2:
The system dynamically adjusts the acceleration profile based on the wafer diameter and selected lens elements. By using only necessary lens elements during the scan, the system reduces the effective mass and minimizes pressure fluctuations even when processing large diameter wafers for improved productivity.
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 approach significantly reduces the influence of pressure fluctuations on the optical imaging quality, allowing for faster movement of the mask stage without compromising the quality of micro- and nanostructures produced on semiconductor substrates, even for larger wafers, by minimizing mechanical disturbances and maintaining high optical imaging standards.
Implementation Method 1
filling it with a gas of higher sound absorption than air
Data Source
AI summary
The invention relates to a projection exposure apparatus for semiconductor lithography, comprising an illumination system for illuminating a mask arranged on a movable mask stage, and comprising a projection lens for imaging the mask onto a semiconductor substrate, wherein at least one means is present for at least partly decoupling at least parts of the illumination system and/or of the projection lens from the influence of pressure fluctuations in the medium surrounding the projection lens or the illuminated system, the pressure fluctuations being attributed to movements of the mask stage during the operation of the apparatus.