Ellipsometer Beamsplitter Focusing System
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Solution Overview
Problem
Conventional ellipsometer focusing systems require precise alignment, which is expensive and prone to inaccuracies due to stray light and systematic errors, and fail to produce a small illuminating spot size on the sample.
Innovation Solution
An improved focusing system that uses an image of the measurement spot to determine the best focal position by splitting the reflected measurement signal before analysis, allowing for real-time focus position measurement using a two-dimensional sensor and processor to adjust the focal position based on the spot's location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an independent focusing system with precise alignment is used, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines the focusing system with the existing ellipsometer optical path by using a beam splitter to direct part of the reflected light to a focus detector. This integration eliminates the need for separate independent focusing systems while maintaining measurement precision, thereby reducing device complexity and cost.
Solution Approach 2:
The ellipsometer's optical components serve dual purposes: the main optical path performs ellipsometric measurement while the same reflected light path (via beam splitter) provides focusing information. This multi-functionality reduces the need for additional dedicated components, simplifying the overall system.
2Productivity
If a position sensitive device or quad cell is used as focus detector, then real-time focus detection is enabled, but measurement precision deteriorates due to stray light sensitivity
Solution Approach 1:
The patent extracts only the necessary focusing information from the reflected light beam using a beam splitter, separating the focus detection function from the main measurement path. This allows the use of position-sensitive detectors for real-time feedback while the main measurement path remains unaffected by stray light issues.
Solution Approach 2:
The beam splitter acts as an intermediary that divides the reflected light into two paths: one for main measurement and one for focus detection. This intermediary component enables real-time focus monitoring without exposing the main measurement system to stray light sensitivity.
3Device complexity
If only the outer part of the beam is sampled by the detector, then device complexity is reduced, but measurement precision worsens due to systematic errors from the mirror
Solution Approach 1:
The patent segments the reflected light beam using a beam splitter, directing a portion of the beam to the focus detector while maintaining the integrity of the full beam cross-section. This segmentation allows comprehensive beam sampling without requiring complex mirror systems, improving measurement precision while keeping device complexity manageable.
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 provides high precision and real-time focus adjustment, minimizing inaccuracies and achieving a smaller spot size, thus enhancing the measurement accuracy and precision of the ellipsometer.
Implementation Method 1
a beamsplitter positioned in the path of the reflected beam after the compensator, the beam splitter positioned to receive the reflected beam and to direct a first portion of the reflected beam to a focusing system and to direct a second portion of the reflected beam to an analyzer
Implementation Method 2
a lens system that receives the first portion of the reflected beam, the lens system magnifies any deviation from a best focus position of the ellipsometer
Implementation Method 3
the lens system magnifies any deviation from a best focus position of the ellipsometer
Implementation Method 4
a compensator disposed in the path of the sample beam or the reflected beam, the compensator induces phase retardations of a polarization state of the light
Implementation Method 5
a polarizer that polarizes the light to produce a sample beam that interacts with a sample
Data Source
AI summary
An ellipsometer includes a focusing system that uses an image of the measurement spot to determine a best focal position for the ellipsometer. The focus signal is produced by splitting off the ellipsometer measurement spot before the signal is analyzed by a polarizer thereby avoiding imagining the spot with a modulated intensity. The focus signal is imaged on a sensor array and based on the position of the spot on the sensor array, the focal position of the ellipsometer may be determined. A single image may be used to determine the focal position of the ellipsometer permitting a real time focus position measurement.