Terahertz Wafer Measurement Using Multi-Photon Excitation Through Silicon
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Solution Overview
Problem
Existing THz signal spectroscopic measuring apparatuses face challenges in accurately measuring ion doping concentration and spatial resolution, particularly when additional material layers are present on semiconductor wafers, as they often rely on single laser beams with short wavelengths that are absorbed or reflected, limiting depth information and resolution.
Innovation Solution
A THz signal measuring apparatus that utilizes a femtosecond laser beam split into multiple sub-laser beams with longer wavelengths, generating multi-photon excitation at the silicon substrate surface, allowing for accurate detection of THz signals through the substrate and overlying layers, and incorporating a THz pump-probe unit to measure changes in absorption, thereby enhancing spatial resolution and enabling depth-dependent doping concentration analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single laser beam with short wavelength is used for THz signal generation, then the apparatus structure is simple, but the spatial resolution and depth information are limited due to absorption and reflection by material layers
Solution Approach 1:
The single laser beam is segmented into multiple sub-laser beams (first, second, third, and fourth sub-laser beams) with different wavelengths. These segmented beams are then combined to illuminate the sample from multiple wavelengths simultaneously, enabling both high spatial resolution through short wavelength beams and depth information penetration through longer wavelength beams that can pass through material layers.
2Device complexity
If a single laser beam with short wavelength is used, then the apparatus is simple, but depth information and doping concentration measurement are limited
Solution Approach 1:
The laser beam is segmented into multiple wavelength components that can penetrate different depths into the sample. The longer wavelength sub-laser beams can pass through material layers to provide depth information, while shorter wavelength beams provide surface resolution, collectively recovering depth information that would be lost with a single beam.
3Measurement precision
If multiple sub-laser beams with different wavelengths are used, then spatial resolution and depth information are improved, but the apparatus complexity increases
Solution Approach 1:
Multiple sub-laser beams with different wavelengths are merged and combined to illuminate the sample simultaneously. This merging of beams from different wavelength sources achieves both high spatial resolution and depth penetration capabilities in a single measurement setup, avoiding the need for separate measurement systems.
Solution Approach 2:
The measuring apparatus is designed with multi-functionality to handle multiple wavelengths and measurement modes. The system can perform both high-resolution surface measurements and depth-dependent doping concentration measurements using the same apparatus configuration, making it universally applicable to various measurement requirements.
4Measurement precision
If multiple sub-laser beams are used for multi-photon excitation, then doping concentration measurement accuracy is improved, but the device complexity increases
Solution Approach 1:
Multiple sub-laser beams are merged to create multi-photon excitation conditions that enhance doping concentration measurement accuracy. The combined beams provide sufficient photon energy and intensity to excite carriers at different depths, enabling accurate doping profile measurement through THz signal detection.
Solution Approach 2:
The system utilizes parameter changes in laser wavelength and intensity to optimize multi-photon excitation conditions. By adjusting the wavelengths and intensities of individual sub-laser beams, the system achieves optimal carrier generation and THz signal emission for accurate doping concentration measurement across different depth regions.
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
The apparatus achieves improved spatial resolution of about 50 nm to 100 nm and accurately measures doping concentration profiles across the depth of semiconductor wafers, even with additional material layers, by using multi-photon excitation and pump-probe techniques.
Implementation Method 1
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
measure changes in absorption, thereby enhancing spatial resolution and enabling depth-dependent doping concentration analysis
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.