Self-Differential Confocal Tilt Sensing for Rough Sample Leveling
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Solution Overview
Problem
Current tilt sensors in charged particle beam systems face challenges in accurately measuring the tilt of samples with rough surfaces or those that are only slightly tilted, due to insufficient sensitivity and interference from surface irregularities.
Innovation Solution
The implementation of a self-differential confocal tilt sensor system that uses a common mode reference beam to compensate for source power variations and employs a confocal aperture to enhance sensitivity and reduce ambient light interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional tilt sensor is used to measure sample tilt, then the device structure is simple, but the measurement precision is insufficient for rough surfaces or slight tilts
Solution Approach 1:
The optical path is segmented into multiple beams (reference beam and measurement beam) that travel different paths. The reference beam reflects off a reference surface while the measurement beam reflects off the sample surface. This segmentation allows independent measurement of each path, enabling precise tilt detection by comparing the two beams while compensating for common disturbances like source power variations.
Solution Approach 2:
A confocal aperture is introduced as an intermediary element in the optical path. The aperture is positioned at the focal plane of the lens and acts as a spatial filter that blocks ambient light and scattered light from rough surfaces while allowing the focused measurement beam to pass through. This intermediary element enables measurement of slight tilts by filtering out noise from surface irregularities.
2Measurement precision
If a confocal aperture is added to enhance sensitivity, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The confocal aperture is merged with the focal plane of the existing lens in the optical system. By positioning the aperture at the focal plane, it utilizes the existing optical focusing capability without requiring separate focusing mechanisms. This integration enhances sensitivity by blocking ambient light while maintaining a relatively simple optical structure that leverages the lens's inherent focal properties.
3Reliability
If a common mode reference beam is used to compensate for source power variations, then the reliability of measurement improves, but the device complexity increases
Solution Approach 1:
The light beam is segmented into two separate paths: a reference beam path and a measurement beam path. The reference beam reflects off a stable reference surface while the measurement beam reflects off the sample. Both beams originate from the same light source, so they experience identical source power variations. By comparing the intensities of the two beams, the system reliably measures tilt while compensating for source fluctuations, as the common-mode variations cancel out in the differential measurement.
4Measurement precision
If the sensor uses a confocal aperture to reduce ambient light interference, then the measurement precision improves, but the difficulty of detecting and measuring increases
Solution Approach 1:
The confocal aperture serves as an intermediary spatial filter positioned at the focal plane of the lens. It selectively transmits the focused measurement beam while blocking ambient light and scattered light from rough surfaces. The aperture's position at the focal plane creates a natural focus-point correspondence that simplifies alignment: the aperture automatically filters light based on its spatial coordinates, reducing the need for complex alignment procedures while maintaining high signal-to-noise ratio.
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 improves the accuracy and sensitivity of tilt measurements, allowing for more precise sample leveling and reducing errors in charged particle beam systems, even for samples with rough surfaces.
Implementation Method 1
a lens configured to focus light from the light source, and the lens may be arranged between the second optical element and an aperture
Implementation Method 2
the aperture may be arranged between the third optical element and the second sensing element, and the aperture may be arranged at a focal plane of the lens
Implementation Method 3
a first beam splitter configured to transmit light toward a sample, and to reflect light toward a second beam splitter
Data Source
AI summary
A sensor may be used to measure a degree of tilt of a sample. The sensor may include an apparatus having a light source, first, second, and third optical elements, a lens, and an aperture. The first optical element may supply light from the light source toward the sample, and may supply light input into the first optical element from the sample toward the second optical element. The second optical element may supply light toward first and second sensing elements. An aperture may be arranged on a focal plane of the lens. A light beam incident on the first sensing element may be a reference beam.