Lithographic Apparatus Vibration Isolation for Position Measurement
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Solution Overview
Problem
Conventional lithographic apparatus position measurement systems are sensitive to dynamic movements and thermal influences, leading to inaccurate position measurements, which result in exposure errors such as focus and overlay errors.
Innovation Solution
A lithographic apparatus with a substrate table position measurement system that includes a substrate table reference element and a first sensor head, mounted on a vibration-isolated sensor frame, to accurately measure the position of the substrate table, and a projection system position measurement system to measure the projection system's position, using a sensor assembly and reference elements to determine their relative positions, thereby reducing sensitivity to vibrations and thermal effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a position measurement system is rigidly mounted on the metrology frame, then the measurement system is stable and easy to install, but it becomes sensitive to dynamic movements and thermal influences resulting in inaccurate position measurement
Solution Approach 1:
A vibration isolation table is introduced as an intermediary component between the sensor head and the metrology frame. This mediator absorbs and isolates vibrations and thermal influences from the measurement system, allowing the sensor head to maintain stable and accurate position measurements even during dynamic operations of the lithographic apparatus.
2Measurement precision
If the sensor head is rigidly mounted on the metrology frame, then the device structure is simple, but position measurement accuracy deteriorates due to sensitivity to vibrations and thermal effects
Solution Approach 1:
The vibration isolation table serves as a mediator that adds minimal structural complexity while significantly improving measurement precision. It is positioned between the sensor head and the metrology frame, providing vibration isolation without requiring complex active control systems or multiple sensor heads.
3Speed
If position measurement is performed during substrate table movement, then real-time position data is obtained, but measurement accuracy decreases due to dynamic movements and thermal influences
Solution Approach 1:
The vibration isolation table enables real-time position measurement during substrate table movement by isolating the sensor head from vibrations generated during dynamic operations. This mediator allows the measurement system to maintain accuracy even when the lithographic apparatus is actively scanning or positioning substrates.
Solution Approach 2:
The patent replaces rigid mechanical mounting with a vibration isolation system that uses passive mechanical isolation techniques. This substitution allows the measurement system to float independently from vibration sources while maintaining stable measurements during dynamic operations.
Data Source
AI summary
A lithographic apparatus including a substrate table position measurement system and a projection system position measurement system to measure a position of the substrate table and the projection system, respectively. The substrate table position measurement system includes a substrate table reference element mounted on the substrate table and a first sensor head. The substrate table reference element extends in a measurement plane substantially parallel to the holding plane of a substrate on substrate table. The holding plane is arranged at one side of the measurement plane and the first sensor head is arranged at an opposite side of the measurement plane. The projection system position measurement system includes one or more projection system reference elements and a sensor assembly. The sensor head and the sensor assembly or the associated projection system measurement elements are mounted on a sensor frame.