Light-Field Sensor for Lithography Alignment
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Solution Overview
Problem
Current lithographic apparatuses require multiple measurements across substrates to achieve accurate position alignment, which reduces throughput due to the need for different focus settings for each alignment sensor, as substrates are not perfectly flat.
Innovation Solution
Incorporating a light-field imaging system with a data processor that processes pixel data to derive focused images and position measurements, allowing for simultaneous measurement and correction of depth dependencies, enabling a single pass alignment and focus control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple alignment sensors are operated with different focus settings to capture images of marks at various heights, then measurement precision is improved, but the time required for multiple measurements increases, reducing productivity
Solution Approach 1:
The patent merges multiple alignment sensors with different focus settings into a single sensor that captures light-field data containing information from multiple depths simultaneously. This combining approach allows the system to obtain position measurements for marks at various heights in a single capture, eliminating the need for sequential measurements with multiple sensors or repeated captures, thereby improving both measurement precision and productivity
Solution Approach 2:
The patent transitions from conventional 2D imaging to 3D light-field imaging, adding the depth dimension to the measurement capability. By capturing light-field data that encodes spatial information from multiple focal planes, the system can extract position measurements for marks at different heights simultaneously, resolving the contradiction between measurement precision and measurement time
2Measurement precision
If multiple images are captured at different focus settings to achieve accurate position measurements across a non-flat substrate, then measurement precision is improved, but the measurement time increases, reducing productivity
Solution Approach 1:
The patent combines multiple focus settings into a single light-field capture operation. The light-field sensor simultaneously records optical information from multiple depth planes, allowing the extraction of accurate position measurements for marks at various heights without requiring multiple sequential image captures, thereby reducing measurement time while maintaining precision
Solution Approach 2:
The patent replaces the mechanical approach of physically moving the sensor or substrate between multiple focus settings with a computational approach using light-field imaging. By capturing all depth information in a single shot and using computational algorithms to extract position data, the system eliminates the time-consuming mechanical adjustments while maintaining measurement accuracy
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 approach enhances throughput by reducing measurement time and improving overlay performance by allowing simultaneous alignment and focus control across multiple marks without the need for multiple images at different focus settings.
Implementation Method 1
an imaging optical system and an image detector for capturing an image formed by the imaging optical system
Implementation Method 2
an imaging optical system and an image detector for capturing an image formed by the imaging optical system
Data Source
AI summary
A lithographic apparatus includes a number of sensors for measuring positions of features on a substrate prior to applying a pattern. Each sensor includes an imaging optical system. Position measurements are extracted from pixel data supplied by an image detector in each sensor. The imaging optical system includes one or more light field modulating elements and the processor processes the pixel data as a light-field image to extract the position measurements. The data processor may derive from each light-field image a focused image of a feature on the substrate, measuring positions of several features simultaneously, even though the substrate is not at the same level below all the sensors. The processor can also include corrections to reduce depth dependency of an apparent position of the feature include a viewpoint correction. The data processor can also derive measurements of heights of features on the substrate.