Lithographic Projection System Lens Heating Calibration
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Solution Overview
Problem
Current lithographic apparatuses face inefficiencies due to lens heating effects, which introduce aberrations and require lengthy calibration processes, reducing throughput and necessitating frequent idle time for cooling before recalibration.
Innovation Solution
A method involving multiple measurements of a projection system's characteristics before, during, and after exposure, allowing for the separation of heating and cooling effects to calibrate a model that compensates for lens heating, enabling faster and more efficient calibration without initial cooling periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the beam is concentrated into a small region of an optical element to improve projection intensity, then the exposure efficiency is improved, but lens heating effects are intensified causing greater distortion
Solution Approach 1:
The patent applies local quality by differentiating between the irradiated region (exposed to beam) and non-irradiated regions of the optical element. Heaters are applied specifically to non-irradiated regions to compensate for differential heating, creating a controlled temperature distribution that counteracts the distortion caused by concentrated beam heating in high-productivity exposure modes
2Measurement precision
If conventional calibration methods are used requiring test exposures with specific patterns, then calibration accuracy is improved, but the calibration time is significantly increased reducing throughput
Solution Approach 1:
The patent implements preliminary action by pre-heating non-irradiated regions of optical elements using heaters before actual exposure begins. This preliminary thermal compensation establishes the correct temperature distribution in advance, eliminating the need for lengthy test exposures and recalibration, thus maintaining calibration accuracy while dramatically reducing calibration time
Solution Approach 2:
The system performs self-service calibration through automated feedback control. Temperature sensors monitor the thermal state of optical elements, and the controller automatically adjusts heater power to maintain optimal temperature distribution, enabling the system to self-correct without external calibration interventions, thereby reducing calibration time while maintaining accuracy
3Measurement precision
If the projection system is allowed to cool between exposures to maintain stability, then measurement accuracy is improved, but the operational continuity is reduced lowering throughput
Solution Approach 1:
The patent enables continuity of useful action by maintaining the projection system in a continuously heated operational state through compensating heaters. These heaters counteract beam-induced heating in real-time, allowing the system to maintain stable optical characteristics without cooling cycles, thus preserving measurement accuracy while ensuring continuous operation and high throughput
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 reduces the time required for calibration, increases the lithographic apparatus's throughput by allowing continuous operation while modeling and compensating for lens heating effects, and enables the use of previously calibrated models for different recipes without extensive recalibration.
Implementation Method 1
Since the elements of the projection system unavoidably absorb a small percentage of the energy of the beam, these elements will heat up and may thereby distort
Implementation Method 2
these elements will heat up and may thereby distort. Such distortion introduces aberrations into the projection system
Implementation Method 3
allowing the projection system to cool for a period of time
Data Source
AI summary
In a lithographic method, a characteristic of a projection system is measured before and after periods of heating (exposures) and cooling to provide data to calibrate a model of lens heating. The model has a part modeling the effect of cooling and a part modeling the effect of heating on the characteristic.