Inspection Apparatus Autofocus Tracking Delay Reduction
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Solution Overview
Problem
In semiconductor device manufacturing, existing mask inspection apparatuses face challenges with autofocus tracking delays due to shallow depth of focus, leading to defocusing and reduced precision in defect detection, especially when rapid stage movement occurs.
Innovation Solution
An inspection apparatus and method that virtually divide the sample into stripe-shaped regions, allowing for focal position data generation and setting of focus offset values based on shifted coordinate data, enabling precise control of the stage's height position to minimize autofocus tracking delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the stage moves rapidly to enhance inspection speed, then productivity is improved, but autofocus tracking delay occurs causing defocusing and reducing measurement precision
Solution Approach 1:
The system performs preliminary action by predicting the focal position for the current scan position using data from previous scan positions, and pre-adjusts the stage height before the actual inspection point is reached. This anticipatory focus adjustment eliminates tracking delay and maintains sharp focus during rapid stage movement, resolving the contradiction between high inspection speed and focus position accuracy.
2Measurement precision
If the magnification and numerical aperture of the optical system are increased to capture fine patterns, then measurement precision is improved, but the depth of focus becomes shallow making the system sensitive to focus changes
Solution Approach 1:
The system employs feedback by continuously monitoring the focal position during scanning and using this information to dynamically adjust the stage height. The focus position detection circuit provides real-time feedback signals that are processed to generate focus offset values, ensuring that the shallow depth of focus is compensated and stable focus is maintained throughout the inspection process, thus resolving the contradiction between high measurement precision and focus stability.
3Device complexity
If polynomial approximation computation is used for focal position control, then device complexity is reduced, but tracking delay occurs during rapid stage movement reducing productivity
Solution Approach 1:
The system applies preliminary action by computing focus offset values in advance based on previously acquired focal position data, and storing these pre-computed values for immediate application during scanning. This approach eliminates the need for real-time polynomial approximation computation during rapid stage movement, maintaining both low device complexity and high productivity by preparing focus corrections beforehand.
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 reduces autofocus tracking delays, enhances image capturing precision for fine patterns, and improves defect detection accuracy by adjusting the stage's height position based on calculated focus offset values, thereby reducing defocusing and improving defect detection.
Implementation Method 1
an illumination optical system configured to irradiate the sample with light used for optical scanning of the sample
Implementation Method 2
an imaging optical system including a sensor that detects a focal position, and configured to cause the light with which the sample is irradiated to form an image on the sensor
Data Source
AI summary
According to an embodiment, an inspection apparatus includes: a stage; an illumination optical system; an imaging optical system including a sensor that detects a focal position; a detection circuit configured to detect a focal position signal of the light; a setting circuit configured to set a first focus offset value of a first region based on a result obtained by shifting, in an advancement direction of the stage, coordinate data of first focal position data generated based on a result obtained by optically scanning the first region; and a control circuit configured to control a height position of the stage based on the focal position signal and the first focus offset value.