Mesa Height Map Correction for Nanoimprint Lithography Inspection
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Solution Overview
Problem
The miniaturization of semiconductor patterns requires high inspection accuracy for mask defects, but the automatic focus mechanism struggles with mesa structures in replica templates used in nanoimprint lithography, leading to blurred pattern images due to focus control issues and variations in atmospheric pressure.
Innovation Solution
An inspection method and apparatus that measures the height of mesa portions using corner positions, creates a height map, corrects the height based on deviations from target values, and controls the focal position to maintain image clarity, while also accounting for temporal variations caused by atmospheric pressure changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high magnification and high numerical aperture are used in the inspection optical system, then inspection accuracy is improved, but focus control becomes more difficult due to deeper focus depth causing image blurring
Solution Approach 1:
The patent implements an automatic focus mechanism that continuously monitors the distance between the optical system and the mask table using a focus detection sensor, and adjusts the table position in real-time based on feedback signals to maintain optimal focus despite atmospheric pressure variations
Solution Approach 2:
The patent replaces manual focus adjustment with an automated electro-mechanical focus control system that uses motor-driven table positioning and electronic feedback loops to maintain precise focus automatically
2Adaptability or versatility
If atmospheric pressure changes occur, then environmental conditions vary, but focal position stability deteriorates leading to image blurring
Solution Approach 1:
The patent uses atmospheric pressure sensors to detect environmental changes and feeds this information to the focus control system, which automatically compensates for pressure-induced focal shifts by adjusting the mask table position
Solution Approach 2:
The patent dynamically adjusts the focal position parameter in response to atmospheric pressure changes, modifying the distance between the optical system and the mask to maintain constant image quality despite environmental variations
3Measurement precision
If the distance between the optical system and the mask varies, then focus control becomes problematic, but inspection accuracy is maintained through automatic focus mechanisms
Solution Approach 1:
The patent employs continuous feedback from focus detection sensors to the table positioning system, creating a closed-loop control mechanism that automatically compensates for distance variations and maintains optimal focus
Solution Approach 2:
The automatic focus mechanism enables the inspection system to self-correct focus errors without external intervention, using built-in sensors and actuators to maintain optimal imaging conditions autonomously
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 enables accurate detection of defects on mesa-patterned samples by maintaining a stable focus and image quality, even with changes in atmospheric pressure, thereby improving the inspection accuracy and productivity in nanoimprint lithography.
Implementation Method 1
irradiating light to the mesa portion through an optical system, and receiving light reflected by the mesa portion for measuring a height of the mesa portion
Implementation Method 2
The light transmitted through or reflected by the mask is imaged on an image sensor through a lens
Data Source
AI summary
A sample, which has a mesa portion having a pattern thereon, is placed on a Z table. Light is irradiated to the mesa portion through an optical system and light reflected by the mesa portion is received to measure a height of the mesa portion. A height map of the mesa portion is created based on a height of a corner position. A height using the height map is corrected based on a deviation of a measured value from a target value, and a temporal variation of a focal position of light irradiated to the mesa portion. An optical image of the pattern is obtained based on the corrected height of the mesa portion. The optical image is compared with a reference image and a defect is determined when a difference value between the optical image and the reference image is more than a predetermined threshold value.