Lithographic Apparatus Grating Contamination Barrier
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Solution Overview
Problem
In immersion lithography systems, contamination such as droplets of liquid or particles on the grating or sensor can lead to false measurements due to interference with radiation, causing measurement errors.
Innovation Solution
A lithographic apparatus with a barrier positioned to hinder contamination from reaching the grating or sensor, and a contamination removal device that changes the surface properties to prevent or remove contaminants, such as using surface acoustic waves or electrostatic potential, is employed to ensure accurate positional measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If immersion liquid is used to fill the space between the projection system and substrate, then imaging of smaller features is enabled due to shorter wavelength in liquid, but contamination such as droplets or particles on the grating or sensor can lead to false measurements due to interference with radiation
Solution Approach 1:
A barrier member is introduced as an intermediary element positioned between the immersion liquid environment and the grating/sensor. This barrier prevents contamination from the liquid environment from reaching the measurement components, thereby eliminating the harmful effect of contamination while preserving the beneficial immersion imaging capability
Solution Approach 2:
The measurement system (grating and sensor) is extracted from the direct immersion liquid environment by placing it in a separate, contamination-free zone behind the barrier member. This spatial separation allows the immersion liquid to be used for imaging while preventing it from contaminating the measurement components
2Measurement precision
If a barrier member is introduced to protect the grating and sensor from contamination, then measurement accuracy is maintained, but device complexity increases due to additional components
Solution Approach 1:
The barrier member is designed to perform multiple functions simultaneously: it acts as a physical barrier to prevent contamination, serves as a structural support for mounting the grating and sensor, and maintains the positional relationship between measurement components. This multi-functionality reduces the need for additional separate components
Solution Approach 2:
The barrier member is merged with the existing apparatus structure, such as being integrated into the projection system housing or substrate table assembly. This integration approach combines the protective barrier function with existing structural elements, thereby minimizing the increase in overall 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
The barrier effectively keeps contaminants out of focus and the contamination removal device ensures that they do not interfere with the measurement, maintaining the accuracy of positional readings in the lithographic apparatus.
Implementation Method 1
The barrier effectively keeps contaminants out of focus and the contamination removal device ensures that they do not interfere with the measurement
Implementation Method 2
a contamination removal device that changes the surface properties to prevent or remove contaminants, such as using surface acoustic waves
Implementation Method 3
a contamination removal device that changes the surface properties to prevent or remove contaminants, such as using surface acoustic waves or electrostatic potential
Implementation Method 4
a sensor configured to detect radiation redirected by the grating to measure the relative position between the substrate table and the reference frame
Data Source
AI summary
A difficulty of contamination interfering with a grid plate positional measurement system is addressed. In one embodiment contamination is prevented from coming into contact with the grating or the sensor. In an embodiment, surface acoustic waves are used to detach contamination from a surface of the grating or sensor.