Infrared Optical Metrology for Buried Structure Measurement
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Solution Overview
Problem
Conventional optical metrology systems face challenges in measuring buried structures within multi-layered devices, particularly in 3D memory technologies like vertical NAND flash, as photons struggle to reach and return from deep within these structures, leading to difficulties in obtaining accurate dimensional information and measuring features like the Tungsten replacement at the bottom of the structure.
Innovation Solution
An optical metrology device utilizing a tunable Quantum Cascade Laser light source producing beams of light with varying wavelengths in the infrared spectral range, combined with oblique incidence and phase modulation, effectively excludes backside reflections by adjusting phase modulators to ensure that only light from the top and buried structures is detected, allowing for the determination of buried structure characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical metrology systems use photons to measure buried structures, then measurement capability is provided, but photons cannot reach deep buried structures and return due to absorption and scattering in multi-layered devices
Solution Approach 1:
The patent changes the wavelength parameter of light to the infrared spectral range (2.5-30 μm) where the sample is at least partially transparent. This parameter change allows photons to penetrate deeper into multi-layered structures and reach buried features that are inaccessible to conventional visible light metrology systems.
2Measurement precision
If light is transmitted through the sample to reach buried structures, then measurement of deep features is enabled, but backside reflections swamp the signals from buried structures
Solution Approach 1:
The patent extracts and eliminates the harmful backside reflection component from the detected light signal. By using optical elements to separate and remove reflections from the bottom surface, the system retains only the useful signals from buried structures while discarding the overwhelming backside reflections.
Solution Approach 2:
The patent introduces intermediate optical elements (such as beam splitters, filters, or spatial separators) that mediate between the detected light and the detector. These intermediaries selectively transmit signals from buried structures while blocking or separating backside reflections before they reach the detector.
3Quantity of substance
If the number of layers in 3D memory devices is increased to increase memory capacity, then memory capacity is improved, but the aspect ratio increases making optical measurement of buried structures more difficult
Solution Approach 1:
The patent changes the operating wavelength parameter to the infrared range where materials in multi-layered memory structures exhibit higher transparency. This allows optical penetration through increased numbers of layers (96 layers or more) while maintaining sufficient signal strength for measurement.
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 enables accurate measurement of buried structures by ensuring that only relevant reflections are detected, overcoming the issue of backside reflections swamping signals and allowing for precise characterization of deep features within multi-layered devices.
Implementation Method 1
a tunable Quantum Cascade Laser (QCL) light source that produces incident light along an optical path as a plurality of sequential produced beams of light each having different wavelengths in an infrared spectral range
Implementation Method 2
at least one phase modulator comprising at least one photoelastic modulator or at least one electrooptic modulator through which the incident light or the reflected light passes, the at least one phase modulator is adjustable based on wavelengths in each beam of light to produce a same retardation of polarization for each sequentially produced beam of light
Implementation Method 3
at least one phase modulator comprising at least one photoelastic modulator or at least one electrooptic modulator
Implementation Method 4
a first set of reflective focusing optics that focuses the incident light to be obliquely incident on a top surface of the sample at an angle of incidence between 40° and 50°
Implementation Method 5
a first set of reflective focusing optics that focuses the incident light
Data Source
AI summary
An optical metrology device produces beams of light with varying wavelengths in a spectral range for measurement of a sample that is at least partially transparent to the spectral range. The light is obliquely incident on the sample, where a portion of the light is reflected off the top surface and a portion is transmitted through the sample and is reflected off the bottom surface. The incident light and/or reflected light is polarized and a phase modulator, such as a photoelastic modulator or electrooptic modulator, is adjusted based on the wavelengths in each beam of light to produce a same retardation of polarization for each beam of light. The reflected light that is received by a detector does not include light reflected from the bottom surface of the sample. A characteristic of a buried structure below the top surface of the sample is determined using the detected reflected light.