Microscope Device for Opaque Silicon Thickness Measurement
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Solution Overview
Problem
Current optical measurement techniques struggle with accurately measuring the thickness of materials like silicon and patterns with high aspect ratios in microelectronics and microsystems, as they are either opaque to visible wavelengths or have limitations in depth resolution due to optical diffraction and parasitic reflections.
Innovation Solution
A microscope device integrating a low-coherence infrared interferometer with a measurement beam that intercepts the object through a distal lens, allowing for simultaneous topography, layer thickness, and pattern height measurements using infrared wavelengths, while minimizing the impact of parasitic reflections through a coherence window definition and adjustable magnification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional visible wavelength optical measurement techniques are used, then imaging and interferometry can be performed with affordable cameras and optics, but materials like silicon that are opaque to visible light cannot be measured
Solution Approach 1:
The patent changes the optical wavelength parameter from visible to infrared range. The interferometer is configured to operate at infrared wavelengths where silicon and other semi-conductor materials become transparent, enabling thickness measurements that were previously impossible with visible light. This parameter change allows the same measurement system to handle both transparent and opaque materials.
2Measurement precision
If high numerical aperture optical beams are used to measure high aspect ratio patterns, then depth resolution is improved, but the beam cannot reach the bottom of deep structures under usable conditions
Solution Approach 1:
The patent introduces an intermediary measurement approach by using infrared interferometry through the distal lens. Instead of relying on high numerical aperture beams that cannot penetrate deep structures, the system uses infrared wavelengths that can transmit through the distal lens and reach the bottom of deep patterns, enabling measurement of high aspect ratio features without requiring extremely high NA optics.
3Adaptability or versatility
If interferometric measurement is performed through the distal lens, then simultaneous topography and thickness measurements are enabled, but parasitic reflections from the distal lens surface can interfere with measurement accuracy
Solution Approach 1:
The patent converts the harmful parasitic reflections from the distal lens surface into a beneficial feature by using the low-coherence infrared interferometer. The coherence window of the infrared source is specifically tuned to reject the parasitic reflections while maintaining the ability to measure through the distal lens. This allows the system to simultaneously perform topography and thickness measurements with high accuracy despite the presence of the distal lens interface.
4Measurement precision
If the measurement beam is focused to a small region for precise location, then measurement positioning accuracy is improved, but the field of view is reduced
Solution Approach 1:
The patent segments the measurement function from the imaging function. The distal lens provides a wide field of view for imaging, while the infrared interferometer provides precise point measurements at specific locations within that field. This segmentation allows the system to maintain both a wide field of view for context and precise positioning accuracy for measurements, as the two functions operate independently at different wavelengths.
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
Enables precise, non-contact measurements of materials opaque to visible light, such as silicon, and high aspect ratio patterns, providing accurate three-dimensional representations and overcoming limitations of conventional optical techniques.
Implementation Method 1
a low-coherence infrared interferometer, including a measurement beam with a plurality of infrared wavelengths, capable of producing measurements by means of interferences between retroreflections of said measurement beam and at least one separate optical reference
Implementation Method 2
optical imaging means capable of producing, on the camera, an image of the object according to a field of view, which optical imaging means include a distal lens arranged on the side of the object
Data Source
AI summary
A microscope device for inspecting structured objects, including: a camera; an optical imager capable of producing, on the camera, an image of the object according to a field of view, and including a distal lens arranged on the side of the object; and a low-coherence infrared interferometer including a measurement beam capable of producing measurements by means of interferences between retroreflections of the measurement beam and at least one separate optical reference. The device also includes coupler for injecting the measurement beam into the optical imaging means in such a way that the beam passes through the distal lens, and the low-coherence infrared interferometer is balanced in such a way that only the measurement beam retroreflections, taking place at optical distances close to the optical distance covered by the beam to the object, produce measurements.