Auto Focusing Subsystem Using Tilted Sensor Array for Metrology
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 affect the measurement capabilities and repeatability of diffraction signal measurements.
Innovation Solution
An auto focusing subsystem with a focus detector having a tilt angle and a plurality of sensors, coupled with a processor that determines focus parameters to move the workpiece to a best focus position using calculated focus signals and calibration data, enhancing the capture range and sensitivity of the focusing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional auto focusing methods are used, then the system can achieve basic focusing functionality, but the measurement accuracy and repeatability deteriorate with smaller spot sizes and increased throughput requirements
Solution Approach 1:
The focus detector is divided into multiple sensors (first sensor, second sensor, third sensor, fourth sensor) arranged in a specific geometric pattern. Each sensor independently detects focus signals from different regions, and the processor combines these segmented measurements to calculate multiple focus parameters (SP, SR, SL, TR), thereby improving measurement accuracy while maintaining throughput capability
Solution Approach 2:
The patent introduces a tilt angle dimension to the focus detector configuration. The detector is positioned at a specific tilt angle relative to the optical axis, enabling detection of focus signals from multiple angular perspectives. This dimensional addition allows the system to extract more information from the same optical path, improving measurement precision without requiring additional optical components that would reduce throughput
2Area of stationary object
If the focus detector uses a larger capture range, then more of the workpiece can be focused, but the sensitivity to detect precise focus position decreases
Solution Approach 1:
The focus detector is segmented into four sensors positioned at the vertices of a rectangle, with each sensor covering a specific angular range. This segmentation allows the system to maintain high sensitivity within each sensor's local detection range while collectively covering a wide capture range through the combined output of all sensors
Solution Approach 2:
The system calculates multiple focus parameters (SP, SR, SL, TR) from the focus signals detected by different sensors. By changing from a single focus parameter to multiple parameters, the system achieves both wide capture range and high focusing sensitivity, as each parameter provides different information about the focus position
3Measurement precision
If multiple focus parameters are calculated, then the focusing accuracy improves, but the system complexity increases
Solution Approach 1:
The focus detector serves multiple functions simultaneously: it detects focus signals for calculating all four focus parameters (SP, SR, SL, TR), determines the initial workpiece position, and guides the motion control system to the best focus position. This multi-functionality reduces the need for additional dedicated components for each function, thereby improving focusing accuracy without proportionally increasing system complexity
Solution Approach 2:
The processor acts as an intermediary that receives focus signals from the focus detector and performs the complex calculations to derive multiple focus parameters. By centralizing the computational complexity in the processor rather than distributing it across multiple physical components, the system achieves high focusing accuracy while maintaining relatively simple hardware architecture
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, improving the accuracy and speed of measurements in optical metrology systems, particularly for small-spot metrology instruments like reflectometers and ellipsometers, by utilizing focus parameters SP and SR to guide the motion control system to the best focus position.
Implementation Method 1
a focus illumination source generating a focus illumination beam directed to optical focusing component generating a focus projection beam onto a workpiece. The focus projection beam is reflected off the workpiece and focused to form an image of the source spot onto the focus detector
Data Source
AI summary
Provided is an apparatus for auto focusing a workpiece for optical metrology measurements using an optical metrology system. 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. A diffraction signal is measured off a structure on the workpiece using the optical metrology system to determine at least one profile parameter of the structure. The at least one profile parameter is used to modify at least one process variable or equipment setting of a semiconductor fabrication cluster.