Single Wavelength Ellipsometry Spot Size Reduction
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Solution Overview
Problem
Single Wavelength Ellipsometry (SWE) systems face challenges in achieving accurate measurements due to coherence artifacts, contamination light, and interference effects, which limit the minimum measurable spot size and increase measurement errors, especially with the increasing complexity and feature size of semiconductor devices.
Innovation Solution
Incorporating a pupil stop near the pupil plane, a field stop near the image plane conjugate to the wafer, and a thin nanoparticle-based polarizer in the illumination path to reduce sensitivity to target edge diffraction and optical-structural interactions, thereby improving measurement accuracy and spot size precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional light source is used in SWE systems, then the system achieves good measurement repeatability and optical stability, but coherence artifacts and contamination light increase measurement errors and limit spot size capability
Solution Approach 1:
The patent extracts and removes harmful coherent light components through a combination of optical elements: a beam splitter to separate light paths, a spatial filter to block coherent light, and a detector to selectively measure only the desired incoherent reflected light from the sample surface, thereby eliminating coherence artifacts while preserving measurement repeatability
Solution Approach 2:
The patent introduces an intermediary optical system between the light source and detector that includes a beam splitter at a specific angle, spatial filters, and polarization elements. These intermediaries selectively transmit desired measurement signals while blocking coherent light and contamination, enabling precise measurements without the harmful effects of coherence artifacts
2Measurement precision
If the measurement spot size is reduced to characterize smaller features, then the system can measure smaller targets, but coherence artifacts and contamination light increase significantly
Solution Approach 1:
The patent applies local quality by using spatially selective optical elements positioned at specific locations in the optical path. The beam splitter is positioned at a specific angle to separate light from different spatial regions, and spatial filters are placed at conjugate planes to selectively transmit light from the measurement spot while blocking light from edges and contamination sources, enabling small spot size measurements with reduced artifacts
3Measurement precision
If optical elements are added to reduce coherence artifacts, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent implements multi-functionality by designing optical elements that perform multiple functions simultaneously. The beam splitter not only separates light paths but also creates the necessary geometric configuration for spatial filtering. The spatial filters serve both to block coherent light and to define the measurement spot size. The polarization elements simultaneously manage polarization state and contribute to spatial selectivity, thereby reducing overall system complexity while maintaining measurement accuracy
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
The solution effectively reduces measurement spot size, enhances tool-to-tool matching performance, and achieves accurate thin film measurements with improved beam quality and reduced astigmatism, allowing for precise characterization of small measurement targets.
Implementation Method 1
A beam of incident light is linearly polarized by a linear polarizer including a thin, nanoparticle based, high extinction ratio input beam polarizer element
Implementation Method 2
The beam of polarized light is then elliptically polarized by an elliptical polarizer element
Implementation Method 3
light diffracted from the edges of a metrology target leads to interference along the propagation path
Implementation Method 4
light reflected from inside the boundary of the metrology target and light reflected from outside the metrology target
Data Source
AI summary
Methods and systems for performing single wavelength ellipsometry (SWE) measurements with reduced measurement spot size are presented herein. In one aspect, a pupil stop is located at or near a pupil plane in the collection optical path to reduce sensitivity to target edge diffraction effects. In another aspect, a field stop is located at or near an image plane conjugate to the wafer plane in the collection optical path to reduce sensitivity to undesired optical-structural interactions. In another aspect, a linear polarizer acting on the input beam of the SWE system includes a thin, nanoparticle based polarizer element. The nanoparticle based polarizer element improves illumination beam quality and reduces astigmatism on the wafer plane. The pupil and field stops filter out unwanted light rays before reaching the detector. As a result, measurement spot size is reduced and tool-to-tool matching performance for small measurement targets is greatly enhanced.