Mask Inspection Sensor Light Fluctuation Correction
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Solution Overview
Problem
Conventional mask inspection methods face challenges in accurately measuring line widths due to light quantity fluctuations, leading to correction errors caused by the mismatch in response frequencies between photodiodes and TDI sensors.
Innovation Solution
A mask inspection apparatus and method that utilize a sensor with a first area for acquiring optical image data and a second area for detecting light quantity fluctuations, allowing for real-time correction of gradation values and accurate line width measurement by generating reference image data and calculating line width errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photodiode is used to detect light quantity fluctuation for correcting TDI sensor output, then light quantity detection is achieved, but correction error occurs due to mismatch in response frequency bands between photodiode and TDI sensor
Solution Approach 1:
The patent introduces a light quantity detecting sensor as an intermediary device that receives light from the light source through a specific optical path. This sensor acts as a mediator between the light source and the TDI sensor, providing accurate light quantity detection data that corresponds to the same time period as the optical image acquisition, thereby enabling precise correction of the TDI sensor output without the frequency mismatch problem caused by photodiodes
Solution Approach 2:
The patent implements a feedback mechanism where the light quantity detecting sensor continuously monitors the light source output, and this detection result is used to correct the TDI sensor output data. The correction unit uses the light quantity detection data to adjust the optical image data, creating a closed-loop feedback system that maintains measurement accuracy despite light source fluctuations
2Measurement precision
If light quantity fluctuation correction is applied to TDI sensor output, then measurement accuracy improves, but correction errors are introduced due to response frequency mismatch
Solution Approach 1:
The light quantity detecting sensor serves as an intermediary that provides accurate light quantity detection data synchronized with the TDI sensor acquisition timing. This intermediary device enables proper correction of gradation values without introducing the frequency mismatch errors that would otherwise degrade line width measurement accuracy
3Reliability
If a separate photodiode device is used for light quantity detection, then light quantity monitoring is achieved, but device complexity increases and correction accuracy decreases
Solution Approach 1:
The patent merges the light quantity detection function with the existing sensor system by using a light quantity detecting sensor that is integrated into the imaging unit. This unified approach combines optical image acquisition and light quantity detection into a single coordinated system, reducing overall device complexity while maintaining reliable light quantity monitoring capability
Solution Approach 2:
The sensor system is designed with multi-functionality, where the imaging unit serves both to acquire optical images and to detect light quantity fluctuations through its light quantity detecting sensor. This universal design eliminates the need for separate dedicated photodiode devices, reducing system complexity while maintaining comprehensive monitoring capability
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 significantly reduces correction errors, enabling precise line width measurement and accurate CD map generation, thereby improving the accuracy of mask inspection processes.
Implementation Method 1
a TDI (Time Delay Integration) sensor can be used as the sensor that acquires the optical image of the mask
Implementation Method 2
A laser light source, wherein the emission wavelength is in an ultraviolet region, or a plasma light source excited by a laser light source can be used as the light source
Data Source
AI summary
An inspection target is illuminated by an illumination optical unit using a light source. Optical image data of a pattern disposed in the inspection target is acquired by an imaging unit by causing light transmitted or reflected to be incident to a first and second area of a sensor. Reference image data is generated, corresponding to the optical image data, from design data of the pattern. The optical image data is corrected by obtaining a fluctuation of a gradation value of optical image data acquired using light incident to the second area, and correcting a gradation value of optical image data acquired using the light incident to the first area. A line width of the pattern of the corrected data, and a line width error which is a difference between the line widths of corrected data and reference image data are obtained by the line width error obtaining unit.