Metrology Apparatus Stray Radiation Rejection via Dual-Beam Interference
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Solution Overview
Problem
Stray radiation in lithographic metrology systems reduces the accuracy of optical measurements, leading to decreased precision in component production, particularly in complex lens systems where anti-reflection coatings and apertures are insufficient to eliminate noise sources like directional and non-directional stray radiation.
Innovation Solution
A method and apparatus that split a radiation source into measurement and reference beams, with the first target on the substrate and a second target separated from the substrate, where the scattered radiation from both targets interferes at a detector, ensuring the second target has a pattern geometrically identical or periodic with the first, to reject stray radiation and enhance signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If anti-reflection coatings and apertures are used in complex lens systems, then some stray radiation is reduced, but directional and non-directional stray radiation from multiple reflections and foreign particles cannot be eliminated, leading to reduced measurement precision
Solution Approach 1:
The optical system is divided into multiple channels: a first channel for measuring the target structure and a second channel for measuring a reference standard. Each channel processes radiation independently, allowing stray radiation effects to be differentiated from actual measurement signals. The separation enables selective filtering and processing of signals to eliminate noise from multiple reflections and foreign particles.
Solution Approach 2:
A reference standard with known properties is introduced as an intermediary element. By comparing the target measurement against this reference, the system can identify and eliminate stray radiation artifacts. The reference channel acts as a mediator that provides a baseline for distinguishing genuine signals from noise caused by optical imperfections and foreign particles.
2Device complexity
If multiple reflections occur in complex lens systems, then optical noise increases, but standard apertures and coatings are insufficient to eliminate this noise, reducing measurement quality
Solution Approach 1:
The radiation measurement is segmented into multiple independent channels, each with its own optical path. This segmentation allows the system to track and identify noise sources specific to each channel, enabling selective filtering of multiple reflection artifacts while preserving the main signal.
Solution Approach 2:
The system uses feedback from the reference channel to adjust and correct measurements in the target channel. By continuously comparing measurements against the reference standard, the system can identify and compensate for noise introduced by multiple reflections in the complex lens system.
3Object-affected harmful factors
If foreign particles are present in the optical path, then scattering and measurement noise increase, but conventional filtering methods cannot eliminate these effects
Solution Approach 1:
A reference standard serves as an intermediary that provides a clean baseline measurement. By comparing target measurements against this reference, the system can identify scattering caused by foreign particles and eliminate it from the final measurement, as the reference channel does not contain the target-specific scattering features.
Solution Approach 2:
The measurement is divided into separate channels that can be independently analyzed. This segmentation allows the system to identify and filter out scattering signals from foreign particles by comparing them against the reference channel, which lacks target-specific scattering features.
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 effectively improves the signal-to-noise ratio by filtering out stray radiation, enhancing the accuracy of optical measurements and maintaining precision in lithographic apparatuses, even in the presence of noise from product structures and foreign particles.
Implementation Method 1
A radiation source provides a source beam of radiation
Implementation Method 2
collecting first scattered radiation from the first target and delivering the first scattered radiation to a detector; and collecting second scattered radiation from the second target and delivering the second scattered radiation to the detector
Implementation Method 3
the first scattered radiation interferes with the second scattered radiation at the detector
Data Source
AI summary
Metrology apparatus and methods for inspecting a substrate are disclosed. A source beam of radiation emitted by a radiation source is split into a measurement beam and a reference beam. A first target on the substrate is illuminated with the measurement beam. A second target separated from the substrate is illuminated with the reference beam. First scattered radiation collected from the first target and second scattered radiation collected from the second target are delivered to the detector. The first scattered radiation interferes with the second scattered radiation at the detector. The first target comprises a first pattern. The second target comprises a second pattern, or a pupil plane image of the second pattern. The first pattern is geometrically identical to the second pattern, the first pattern and the second pattern are periodic and a pitch of the first pattern is identical to a pitch of the second pattern, or both.