LPP-EUV Inspection Device Luminance Correction
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Solution Overview
Problem
The use of LPP-EUV light sources in lithography mask inspection devices results in non-uniform luminance distribution and timing jitter, leading to errors in luminance correction and pattern defect inspection due to varying illumination intensity and pulse emission periods, which complicates the optical system and affects the accuracy of TDI sensors.
Innovation Solution
An inspection device with a pulse enable circuit that controls the emission timing of the LPP light source asynchronously with the transfer timing, using a simple detector with a position recording shift register and luminance register to record pixel positions and luminance, allowing for accurate luminance correction and image data acquisition without overlapping transfer and emission timings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If LPP-EUV light source is used for illumination, then high intensity pulsed light is achieved, but luminance distribution becomes non-uniform and timing jitter increases
Solution Approach 1:
A luminance detection unit detects the luminance of the illumination light, and a correction unit corrects the image data based on the detected luminance values. This feedback mechanism compensates for pulse-to-pulse luminance variations and timing jitter, maintaining reliable inspection despite the unstable LPP-EUV light source characteristics.
2Measurement precision
If TDI mode is used for imaging, then sensitivity is improved, but timing synchronization becomes difficult due to emission period jitter
Solution Approach 1:
The system performs preliminary luminance detection and correction before final image inspection. By detecting luminance variations and correcting image data in advance, the system prepares compensated image data that accounts for timing jitter, enabling accurate inspection without complex real-time synchronization mechanisms.
3Illumination intensity
If critical illumination is employed, then luminance is ensured, but luminance distribution becomes non-uniform in the visual field
Solution Approach 1:
The correction unit applies position-dependent correction factors to different regions of the image data based on detected luminance distribution. This local correction approach compensates for spatial non-uniformity caused by critical illumination, ensuring uniform inspection accuracy across the entire visual field while maintaining high luminance.
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 enables accurate luminance correction and high-accuracy inspection by maintaining consistent emission timing with the transfer timing, reducing errors caused by luminance variations and timing jitter, and allowing for precise luminance measurement using a simple detector.
Implementation Method 1
An LPP light source configured to emit illumination light including pulsed light by applying laser light to a droplet
Implementation Method 2
An LPP-EUV light source is a pulsed light source that applies plasma-producing laser light to a tin droplet discharged from a droplet generator and uses EUV light produced from tin that has turned into plasma
Implementation Method 3
a detector for inspection configured to include a plurality of pixels arranged on a light receiving surface including a transfer direction and a direction orthogonal to the transfer direction, and acquire image data by transferring charge produced by light received by the plurality of pixels
Data Source
AI summary
An inspection device according to the present disclosure includes a detector for inspection that includes a plurality of pixels arranged on a light receiving surface and acquires image data by transferring charge produced by light received by the plurality of pixels in a transfer direction at a specified transfer timing, a light source that emits illumination light including pulsed light, a pulse enable circuit that controls emission timing for the light source to emit the illumination light based on the transfer timing, an illumination optical system that illuminates an object to be inspected with the illumination light, a condensing optical system that condenses, on the detector for inspection, light from the object to be inspected illuminated with the illumination light, and a processing unit that inspects the object to be inspected by using the image data of the object to be inspected.