SiC Epitaxial Wafer Buffer Layer Refractive Index
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Solution Overview
Problem
The existing methods for measuring the layer thickness of silicon carbide (SiC) epitaxial layers, particularly when a buffer layer is present, face difficulties in distinguishing between the active epitaxial layer and the buffer layer, leading to inaccurate measurements and the inability to form SiC epitaxial layers of a predetermined thickness.
Innovation Solution
A method involving the formation of a first and second silicon carbide epitaxial layer with a sufficient rate of change in impurity concentration, allowing for individual layer thickness measurement using Fourier transform infrared spectrophotometry, by ensuring a refractive index difference of at least 20% between the substrate and the epitaxial layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a buffer layer is arranged between the active epitaxial layer and the SiC substrate, then defects of the active epitaxial layer are reduced, but the layer thickness measurement by FT-IR method becomes difficult
Solution Approach 1:
The invention applies local quality by creating a transition region within the buffer layer that has different impurity concentrations. Specifically, the buffer layer is designed with a first region having a first impurity concentration and a second region having a second impurity concentration that differs from the first. This local variation in impurity concentration creates a local refractive index difference that enables light reflection at specific interfaces, allowing the FT-IR method to distinguish and measure the thickness of the active epitaxial layer separately from the buffer layer.
2Ease of manufacture
If the impurity concentration of the buffer layer is made close to that of the active epitaxial layer, then the buffer layer can be formed, but the refractive index difference becomes insufficient for light reflection
Solution Approach 1:
The invention applies parameter changes by intentionally varying the impurity concentration parameter within the buffer layer. The buffer layer is structured with a first region having a first impurity concentration and a second region having a second impurity concentration that is different from the first. This parameter change creates a refractive index difference at the interface between these regions, enabling light reflection to occur at this internal interface. Consequently, the FT-IR method can detect this reflection and use it to measure the thickness of the active epitaxial layer, even when the buffer layer's overall impurity concentration is close to that of the active layer.
3Ease of manufacture
If the impurity concentration of the buffer layer is made close to that of the SiC substrate, then the buffer layer can be formed, but the reflection at the substrate interface becomes difficult to obtain
Solution Approach 1:
The invention applies the intermediary principle by introducing a transition region within the buffer layer that acts as an intermediate structure between the active epitaxial layer and the SiC substrate. This transition region has an impurity concentration that is intermediate between the active layer and the substrate, creating a gradient structure. The interface within the buffer layer between regions of different impurity concentrations serves as an intermediary reflection interface, enabling light reflection to occur at this internal boundary. This allows the FT-IR method to obtain measurement data for the active epitaxial layer thickness without requiring strong reflection from the substrate interface.
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 measurement and formation of multiple silicon carbide epitaxial layers of a predetermined thickness, as the increased refractive index difference allows for clear separation of peaks in the reflection interference analysis, facilitating accurate layer management.
Implementation Method 1
the interference of light is generated by light reflected at the surface of the SiC epitaxial layer and light reflected at the interface between the SiC epitaxial layer and the SiC substrate. In the layer thickness measurement by an FT-IR method, by utilizing the interference of light, the layer thickness of the SiC epitaxial layer is derived.
Data Source
AI summary
The present invention is aimed at providing a method of manufacturing a silicon carbide epitaxial wafer by which a plurality of silicon carbide epitaxial layers of a predetermined layer thickness can be precisely formed. In the present invention, a first n-type SiC epitaxial layer is formed on an n-type SiC substrate so that the rate of change in impurity concentration between the n-type SiC substrate and the first n-type SiC epitaxial layer will be greater than or equal to 20%. A second n-type SiC epitaxial layer is formed on the first n-type SiC epitaxial layer so that the rate of change in impurity concentration between the first n-type SiC epitaxial layer and the second n-type SiC epitaxial layer will be greater than or equal to 20%.