Lithographic Stage Level Sensor Height Map Resolution
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Solution Overview
Problem
Conventional level sensors in lithographic apparatuses provide insufficiently accurate height maps, particularly near the edges of substrates, due to limited resolution, which can affect the precise positioning of substrates in the focal plane during exposure processes.
Innovation Solution
A combination of a stage and a level sensor system that projects a measurement beam onto a substrate, with a detector system receiving reflected portions from sub-areas within the measurement area, and a signal processing system that processes output signals to determine the height level by consecutively retrieving signals from each sub-area, allowing for improved resolution without compromising measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional level sensor projects a measurement beam onto a substrate to measure height profile, then the measurement process is simple and fast, but the spatial resolution is insufficient particularly near substrate edges
Solution Approach 1:
The detector system is divided into multiple detection elements arranged in a two-dimensional array, where each element corresponds to a specific sub-area of the measurement spot. This segmentation allows independent measurement of height at different locations within the measurement spot, thereby improving spatial resolution without requiring multiple separate sensors or complex mechanical scanning systems.
Solution Approach 2:
The invention transitions from one-dimensional height measurement (single averaged value) to two-dimensional height mapping by arranging detection elements in a two-dimensional array. This dimensional expansion enables resolution of height variations across the measurement spot area, particularly improving edge region measurements where height variations are most critical.
2Reliability
If the measurement spot size is increased to improve signal detection, then detector sensitivity is enhanced, but the height map resolution deteriorates
Solution Approach 1:
The measurement spot is effectively segmented into multiple sub-areas, each monitored by a corresponding detection element. This allows the system to maintain a large measurement spot size for high signal strength and detector sensitivity while simultaneously achieving high resolution by processing height information from multiple segmented regions independently.
Solution Approach 2:
The invention combines the advantages of large measurement spot size (high signal-to-noise ratio) with high spatial resolution by merging multiple detection elements into a unified two-dimensional array system. Each element contributes to the overall sensitivity while collectively providing detailed height mapping across the measurement area.
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 spatial resolution of height measurements, providing a more accurate height profile near the edges of substrates, thereby improving the precision of substrate positioning during the exposure process.
Implementation Method 1
a light source configured to project a light beam onto a surface of a substrate; a detector configured to detect a reflection of the light beam from the surface of the substrate
Data Source
AI summary
Combination of a stage and a level sensor configured to sense a height level at a target location on an object is described, the stage comprising an object table configured to hold the object and a positioning device for displacing the object table relative to the level sensor in a first direction, the level sensor comprising a projection system configured to project a measurement beam onto a measurement area of the object, the measurement area having a measurement area length in the first direction, a detector system configured to receive different portions of the measurement beam after being reflected off different sub-areas within the measurement area, the different sub-areas being arranged in the first direction, and to supply output signals representative of the different portions received, a signal processing system configured to process the output signals from the detector system.