On-Tool Wavefront Aberration Measurement System
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Solution Overview
Problem
Optical systems in semiconductor process tools suffer from wavefront aberrations, leading to false defect detections and reduced reliability in detecting nanoscale defects due to varying signal-to-noise ratios and aberrations, which affect the inspection tools' ability to differentiate between true and false defects.
Innovation Solution
An on-tool measurement system using a moveable deflection element with a highly transparent region to project differential images onto a sensor, allowing for the measurement and calculation of local wavefront gradients, which compensates for de-focus and jitter aberrations, enabling accurate wavefront aberration measurement and correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If short wavelength DUV lasers are used to detect nanoscale defects, then detection sensitivity and resolution are improved, but the optical system becomes more sensitive to wavefront aberrations causing false detections
Solution Approach 1:
The system performs preliminary wavefront aberration measurements using a Shack-Hartmann sensor before defect inspection, characterizes the aberrations, and applies compensation algorithms to correct them, thereby reducing false detections while maintaining high sensitivity
Solution Approach 2:
The system implements a feedback loop where wavefront aberrations are continuously measured and used to adjust compensation parameters, enabling dynamic correction of optical distortions that cause false defect detections
2Measurement precision
If conventional wavefront measurement methods are used, then wavefront aberrations can be characterized, but the measurement process is time-consuming and reduces inspection throughput
Solution Approach 1:
The system combines wavefront aberration measurement and defect inspection into a single integrated optical path, allowing both functions to be performed sequentially without requiring separate measurement setups, thereby maintaining measurement accuracy while improving throughput
Solution Approach 2:
The system uses a moveable deflection element that can dynamically switch between measurement and inspection modes, enabling rapid transition between wavefront characterization and defect detection without mechanical reconfiguration
3Reliability
If on-tool wavefront measurement is implemented, then real-time aberration monitoring is enabled, but device complexity increases
Solution Approach 1:
The system uses a multi-functional optical setup where the same optical components serve both wavefront measurement and defect inspection purposes, reducing the need for separate dedicated measurement equipment and thereby limiting complexity increase
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 improves the detection stability, repeatability, and reliability of semiconductor process inspection tools by accurately measuring and correcting wavefront aberrations, enhancing the ability to distinguish between true and false defects and maintaining process yields.
Implementation Method 1
The deflection element includes a first surface configured to project a first image of at least one object onto a sensor
Implementation Method 2
the highly transparent region includes a second surface configured to project a second image of the at least one object onto the sensor
Implementation Method 3
a sensor configured to capture the first and second images
Data Source
AI summary
An on-tool measurement system and a method for measuring optical system's wavefront (WF) aberrations are disclosed. The on-tool measurement system includes an optical setup comprising a moveable deflection element further comprising a highly transparent region. The deflection element includes a first surface configured to project a first image of at least one object onto a sensor and the highly transparent region includes a second surface configured to project a second image of the at least one object onto the sensor. The on-tool measurement system includes a sensor configured to capture the first and second images and a controller configured to measure differential displacements between the first and second images at each deflection element position and to calculate the optical setup local WF gradients that depend on the measured differential displacements.