Lithographic Level Sensor Using Projection Grating and Sensor Array
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Solution Overview
Problem
Conventional level sensors in lithographic apparatuses are complex and bulky due to the use of detection gratings and focusing optics, which increases costs and complexity, and can lead to inaccuracies in height measurement due to differing spectral sensitivities of separate detectors.
Innovation Solution
A level sensor with a projection unit that projects a measurement beam with a periodically varying intensity distribution, received by a sensor array with sensing elements arranged at a pitch smaller than or equal to half the period, eliminating the need for detection gratings and focusing optics, and using a processing unit to determine the substrate height from sensor signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a detection grating and separate detectors are used to receive the reflected measurement beam, then the height measurement can be performed, but the device becomes bulky and complex
Solution Approach 1:
The invention extracts and removes the detection grating from the detection unit, eliminating the need for this complex optical component. The sensor array directly receives the reflected patterned measurement beam without requiring a detection grating to split it into different parts, thereby simplifying the device structure while maintaining height measurement capability
Solution Approach 2:
The sensor array serves multiple functions: it directly detects the reflected patterned measurement beam, determines height information from the beam pattern, and eliminates the need for separate detection gratings and focusing optics. This multi-functional approach reduces device complexity while maintaining measurement precision
2Measurement precision
If separate detectors with different spectral sensitivities are used, then the reflected measurement beam can be detected, but measurement inaccuracies occur
Solution Approach 1:
The invention applies local quality by ensuring all sensing elements in the sensor array have matching spectral sensitivities. This uniformity in local detection characteristics across the entire array eliminates measurement inaccuracies that would arise from varying spectral responses, thereby improving both precision and reliability
Solution Approach 2:
The sensor array employs homogeneous sensing elements with matching spectral sensitivities throughout the array. This homogeneity ensures consistent detection characteristics across all elements, eliminating the measurement inaccuracies that occur when separate detectors with different spectral sensitivities are used
3Measurement precision
If detection gratings and focusing optics are included, then the reflected beam can be processed, but the device size increases
Solution Approach 1:
The invention extracts and removes the detection grating and focusing optics from the detection unit, eliminating these bulky optical components. The sensor array directly receives and processes the reflected patterned measurement beam without requiring these additional elements, thereby significantly reducing the device volume while maintaining measurement capability
Solution Approach 2:
The invention uses a simplified detection approach where the sensor array directly captures the reflected beam pattern without requiring complex optical copying mechanisms. This direct detection method eliminates the need for detection gratings and focusing optics, reducing device size while preserving height measurement functionality
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 solution results in a less complex and more compact level sensor with reduced power requirements, improved accuracy, and matching spectral sensitivity of sensing elements, enabling precise height measurements without the need for separate detectors.
Implementation Method 1
a projection grating having a period P, the projection grating being configured to impart the measurement beam, thereby obtaining a patterned measurement beam having a periodically varying intensity distribution
Implementation Method 2
a detection unit to receive a reflected patterned measurement beam after reflection on the substrate
Implementation Method 3
a sensor array configured to receive the reflected patterned measurement beam having the periodically varying intensity distribution, whereby the sensor array comprises a plurality of sensing elements
Data Source
AI summary
A level sensor to determine a height level of a substrate, that includes a projection unit including a projection grating having a period P, the projection grating configured to provide a patterned measurement beam, to the substrate, having a periodically varying intensity distribution in a first direction having the period P; a detection unit to receive a reflected patterned measurement beam after reflection on the substrate, the reflected patterned measurement beam having a periodically varying intensity distribution in a second direction, having the period P, wherein the detection unit has a sensor array to receive the reflected patterned measurement beam, the sensor array including a plurality of sensing elements arranged along the second direction at a pitch p smaller than or equal to half the period P, and a processing unit to determine the height level of the substrate based on a signal from the sensor.