Auto Focus Subsystem Using Dual Focus Parameters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optical metrology systems face challenges in achieving accurate and rapid auto focusing of workpieces, particularly with increased requirements for throughput, smaller spot sizes, and lower cost of ownership, which demands optimization in design to enhance measurement capabilities, accuracy, and repeatability.
Innovation Solution
An auto focusing subsystem with a focus detector having a tilt angle and multiple sensors, coupled with a processor that determines focus parameters to calculate the initial position of the workpiece and generate instructions for moving it to the best focus position, utilizing two focus parameters SP and SR to improve focusing accuracy and range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single focus parameter is used for auto focusing, then the focusing process is simple, but the accuracy and range of focus position determination are limited
Solution Approach 1:
The focus detection system is segmented into multiple independent sensors (first sensor and second sensor) that each detect a different focus parameter (first focus parameter and second focus parameter). This segmentation allows each sensor to specialize in detecting specific focus characteristics, improving overall measurement precision while keeping individual sensor designs simple.
Solution Approach 2:
The patent transitions from single-parameter focus detection to multi-parameter focus detection by introducing a second focus parameter orthogonal to the first. This dimensional expansion enables the system to determine focus position with greater accuracy and extended range, as each parameter contributes information from a different dimensional perspective.
2Measurement precision
If the spot size is reduced for higher resolution measurements, then measurement precision improves, but the focusing becomes more sensitive to position variations and harder to control
Solution Approach 1:
The system uses multiple focus parameters detected by separate sensors to provide feedback on the workpiece focus position. The first focus parameter and second focus parameter together create a comprehensive feedback mechanism that guides the focusing process, making it easier to control even with reduced spot sizes by continuously monitoring and adjusting position.
Solution Approach 2:
The patent changes the approach from single-parameter to multi-parameter focus control. By introducing a second focus parameter that is orthogonal to the first, the system gains additional control dimensions, enabling precise focusing with smaller spot sizes while maintaining ease of operation through the enhanced parameter space for control algorithms.
3Adaptability or versatility
If the capture range of the focus detector is increased, then the range of measurement capabilities improves, but the sensitivity to focus position changes may be reduced
Solution Approach 1:
The focus detection range is segmented between two independent sensors, each responsible for detecting a specific focus parameter. The first sensor detects the first focus parameter while the second sensor detects the second focus parameter. This segmentation allows each sensor to maintain high sensitivity within its designated range while collectively providing extended overall capture range.
Solution Approach 2:
The patent extends the capture range by introducing a second focus parameter in an orthogonal dimension to the first parameter. This dimensional expansion allows the system to measure focus positions over a broader range while maintaining sensitivity, as each parameter provides information from a different dimensional perspective that complements the other.
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 enables precise and efficient auto focusing of workpieces, enhancing the accuracy and throughput of optical metrology systems by effectively determining the best focus position using focus parameters SP and SR, thereby improving measurement capabilities and reducing the complexity of focusing processes.
Implementation Method 1
a focus detector having a tilt angle, a capture range, and a plurality of sensors
Implementation Method 2
Optical metrology involves directing an incident beam at a structure on a workpiece, measuring the resulting diffraction signal
Implementation Method 3
Auto focus of a workpiece using two or more focus parameters
Data Source
AI summary
Provided is a method for focusing a workpiece in the Z-axis for optical metrology. The auto focusing subsystem includes a focus detector having a tilt angle, a capture range, and a plurality of sensors. A processor coupled to the focus detector is configured to utilize the plurality of focus signals measured using the focus detector to determine two or more focus parameters. The two or more focus parameters and calibration data are used to determine an initial position of the workpiece and to generate instructions to move the workpiece to a best focus position.