Lithographic Encoder Enclosing Device for Refractive Index Stability
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Solution Overview
Problem
The accuracy of position measurement systems in lithographic apparatuses is compromised by temperature and pressure changes in the ambient environment, leading to measurement errors due to variations in the refractive index through which radiation beams travel, especially when one beam travels a longer distance than the other.
Innovation Solution
An encoder system with an optical component and an enclosing device that isolates radiation beams from the ambient environment by propagating them through different media, ensuring equal optical path lengths and minimizing the impact of environmental fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If radiation beams travel through ambient air between encoder and scale, then the encoder can move relative to the scale, but temperature and pressure changes cause refractive index variations leading to measurement errors
Solution Approach 1:
The patent introduces an enclosing device filled with a controlled medium (gas or liquid) as an intermediary between the encoder and scale. This mediator isolates the radiation beams from ambient environmental fluctuations while allowing the beams to travel through a stable refractive index environment, thus resolving the contradiction between enabling relative movement and maintaining measurement precision.
Solution Approach 2:
The patent creates an inert enclosed environment around the radiation beam paths by filling the enclosing device with a controlled gas or liquid medium. This inert environment protects the measurement system from temperature and pressure changes in the ambient air, preventing refractive index variations that would otherwise cause measurement errors while allowing the encoder to move relative to the scale.
2Ease of operation
If one radiation beam travels a longer distance through ambient environment than the other, then the optical paths are asymmetric, but this increases sensitivity to temperature and pressure changes
Solution Approach 1:
The patent applies homogeneity by filling the entire enclosing device with a uniform controlled medium, creating consistent optical conditions for both radiation beams. This homogeneous environment ensures that both beams experience the same refractive index, eliminating differential errors that would arise from asymmetric exposure to ambient temperature and pressure changes.
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 enhances the accuracy of position measurement systems by reducing measurement errors caused by temperature and pressure changes, allowing for more precise positioning in lithographic processes.
Implementation Method 1
The enclosing device is arranged to isolate the first path and the second path from the ambient environment
Implementation Method 2
The encoder is able to detect a change in a phase of the radiation beams when the grating surface moves relative to the encoder
Implementation Method 3
The temperature change and/or the pressure change may influence the refractive index of the medium through which the radiation beams travel
Data Source
AI summary
An encoder includes an optical component and an enclosing device having a first surface portion and a second surface portion. The first surface portion is arranged to receive from an ambient environment a first radiation beam. The second surface portion is arranged to receive from the ambient environment a second radiation beam. The optical component is arranged to combine the first and second radiation beams. The enclosing device is arranged to propagate the first radiation beam along a first path. The first path is between the first surface portion and the optical component. The enclosing device is arranged to propagate the second radiation beam along a second path. The second path is between the second surface portion and the optical component. The enclosing device is arranged to enclose a space, so as to isolate the first path and the second path from the ambient environment.