Confocal THz Doping Measurement Through Silicon and Insulating Layers
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Solution Overview
Problem
Existing THz signal spectroscopic measuring apparatuses face challenges in accurately measuring ion doping concentration as they are limited by the inability to effectively generate THz signals and detect them through material layers, leading to inaccurate or incomplete measurements.
Innovation Solution
A THz signal measuring apparatus and method that utilizes a confocal laser-induced THz emission microscopy (LTEM) unit to generate multi-photon excitation using overlapping femtosecond laser beams, allowing for the generation and detection of THz signals through a silicon substrate and insulating layers, with improved spatial resolution and detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional THz signal spectroscopic measuring apparatus is used, then the measurement can be performed, but the measurement precision of ion doping concentration is insufficient due to inability to effectively generate and detect THz signals through material layers
Solution Approach 1:
The patent segments the laser beam into multiple sub-laser beams (first, second, third sub-laser beams) that are incident on different locations of the silicon substrate. This segmentation allows independent control and optimization of each beam's interaction with the substrate, enabling effective THz signal generation despite the presence of material layers that would otherwise block or attenuate the signal.
Solution Approach 2:
The patent introduces an insulating layer as an intermediary between the silicon substrate and the environment. This insulating layer with controlled thickness (50-200 nm) and material composition serves as a mediator that allows THz signals to pass through while providing necessary electrical isolation, thus enabling reliable signal detection through the material layer without direct contact that would cause signal degradation.
2Loss of information
If the measurement depth is increased to obtain deeper doping concentration profiles, then more comprehensive information is obtained, but the spatial resolution deteriorates
Solution Approach 1:
The patent transitions from conventional single-point measurement to a multi-dimensional measurement approach by incidenting multiple laser beams at different locations simultaneously. This dimensional expansion allows the system to gather doping concentration information from multiple depths and positions in parallel, maintaining high spatial resolution while obtaining comprehensive depth profiles through strategic beam placement and focal point control.
Solution Approach 2:
The patent employs precise control of laser beam parameters including focal point depth, beam intensity, and wavelength to optimize the balance between measurement depth and spatial resolution. By adjusting these parameters, the system can selectively probe different depths within the silicon substrate while maintaining the required 50 nm spatial resolution, thus resolving the trade-off between depth and resolution.
3Stability of the object's composition
If material layers are present on the silicon substrate, then the sample structure is complete, but the THz signal detection is blocked or interfered with
Solution Approach 1:
The patent applies local quality optimization by selecting specific regions on the silicon substrate where the insulating layer thickness and material composition are locally tailored to maximize THz signal transmission. Different areas of the substrate can have different insulating layer characteristics optimized for their specific measurement requirements, allowing signal detection through material layers while maintaining overall sample structural integrity.
Solution Approach 2:
The patent utilizes composite material structures consisting of the silicon substrate combined with insulating layers of specific materials and thicknesses. This composite structure leverages the complementary properties of silicon (high carrier mobility for THz generation) and the insulating layer (signal transmission with electrical isolation), creating a material system that simultaneously preserves sample integrity and enables THz signal detection through the layered structure.
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 accurate measurement of ion doping concentration by generating and detecting THz signals through both the lower and upper surfaces of a silicon substrate, overcoming material layer interference and enhancing spatial resolution to 50 nm, thereby providing precise doping concentration profiling.
Implementation Method 1
a confocal laser-induced THz emission microscopy (LTEM) unit configured to generate multi-photon excitation by splitting the femtosecond laser beam into four sub-laser beams and causing three sub-laser beams among the four sub-laser beams to be incident in an overlapping manner on a measurement position of the sample wafer
Implementation Method 2
a THz pump-probe unit including a beam shutter, a second time difference generator, a THz antenna, a second dichroic mirror, and a second reflective objective lens, the THz pump-probe unit being configured to generate a first THz signal using the second femtosecond laser beam and cause the first THz signal to be incident on the measurement position
Implementation Method 3
the first THz signal may pass through the SiO2 insulating layer to be incident on an upper surface of the silicon substrate
Data Source
AI summary
A measuring apparatus includes a stage including a transmissive wafer chuck on which a sample wafer is provided, where the sample wafer includes a silicon substrate and at least one material layer on the silicon substrate, a light source unit including a light source configured to generate and output a femtosecond laser beam, and a confocal laser-induced terahertz (THz) emission microscopy (LTEM) unit configured to generate multi-photon excitation by splitting the femtosecond laser beam into four sub-laser beams and causing three sub-laser beams among the four sub-laser beams to be incident in an overlapping manner on a measurement position of the sample wafer, where the confocal LTEM unit is configured to generate the multi-photon excitation based on the three sub-laser beams being incident on a lower surface of the silicon substrate.