SiC Wafer Photoluminescence Inspection for Buffer-Layer BPD Detection
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Solution Overview
Problem
Existing defect inspection technologies struggle to accurately distinguish basal plane dislocations (BPD) in the buffer layer from those continuing to the drift layer in SiC epitaxial wafers, and to detect BPDs present only in the buffer layer, which are critical for improving semiconductor device manufacturing yield and reliability.
Innovation Solution
A defect inspection apparatus and method that utilizes excitation light to generate photoluminescence, filters specific wavelength bands (420 nm to 430 nm and near-infrared light) to form images, and employs image processing to discriminate defects based on length ranges and machine-learning algorithms, enabling differentiation between BPDs in the buffer and drift layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional photoluminescence inspection is used to detect BPDs in the drift layer, then BPD detection in the drift layer is achieved, but BPDs in the buffer layer cannot be detected
Solution Approach 1:
The inspection method segments the detection process by wavelength bands. The first wavelength band (420-430 nm) is used to detect BPDs in both buffer and drift layers, while the second wavelength band (near infrared) is used to detect BPDs specifically in the drift layer. This segmentation allows differentiated detection capabilities for different layers.
Solution Approach 2:
The invention adds the wavelength dimension to the inspection process by using multiple wavelength bands. By inspecting at different wavelengths (visible range 420-430 nm and near infrared range), the system can differentiate between BPDs in the buffer layer and those in the drift layer, effectively adding a spectral dimension to the spatial detection.
2Measurement precision
If BPD conversion to SSF is performed to detect BPDs in the buffer layer, then buffer layer BPD detection is achieved, but the inspection process becomes extremely complicated
Solution Approach 1:
The invention replaces the mechanical/chemical conversion process (BPD to SSF transformation requiring complex processing) with an optical detection method. By using photoluminescence inspection at specific wavelength bands, the system directly detects BPDs in the buffer layer without requiring any physical or chemical conversion processes, thereby eliminating the complexity associated with conversion procedures.
Solution Approach 2:
The invention changes the detection parameter from structural transformation (BPD conversion to SSF) to optical property measurement (photoluminescence intensity at different wavelengths). By measuring photoluminescence characteristics at specific wavelength bands, the system can identify buffer layer BPDs directly based on their optical signature, avoiding the need for complex conversion processes.
3Measurement precision
If photoluminescence light in the 420-430 nm wavelength band is used for inspection, then buffer layer BPDs can be detected, but the relationship with TEDs in the drift layer cannot be established
Solution Approach 1:
The inspection system performs multiple functions using the same photoluminescence measurement setup. By analyzing photoluminescence data at different wavelength bands, the system can both detect buffer layer BPDs (using 420-430 nm band) and establish their relationship with drift layer TEDs (using near infrared band), making the inspection process universally applicable to multiple detection objectives.
Solution Approach 2:
The system uses feedback from comparative analysis between wavelength bands. By comparing the spatial distribution and characteristics of defects detected at 420-430 nm with those detected in the near infrared range, the system can determine whether a buffer layer BPD continues into the drift layer as a TED, using the near infrared detection results as feedback to interpret the visible range detection data.
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
Accurately discriminates between BPDs in the buffer and drift layers, improving defect detection and enhancing the reliability of SiC epitaxial wafers by identifying BPDs that are converted to threading edge dislocations at the interface, thereby improving device characteristics.
Implementation Method 1
an irradiation optical system configured to irradiate a sample including a silicon carbide substrate, a buffer layer formed on the silicon carbide substrate, and a drift layer formed on the buffer layer with excitation light
Implementation Method 2
a filter unit configured to control a wavelength band to transmit photoluminescence light generated from the sample, the filter unit transmits the wavelength band including 420 nm or longer and 430 nm or shorter in the photoluminescence light
Data Source
AI summary
A defect inspection apparatus according to the present embodiment includes: an irradiation optical system configured to irradiate a sample including a SiC substrate, a buffer layer formed on the SiC substrate, and a drift layer formed on the buffer layer with excitation light; a filter unit configured to control a wavelength band to transmit photoluminescence light generated from the sample; a detection optical system configured to detect the photoluminescence light transmitted through the filter unit; and an image processing unit configured to form an image from the detected photoluminescence light and to discriminate a defect captured in the formed image, and the image processing unit discriminates the defect based on whether a length of the defect is L1=(D1+D2)/tan θ or L2=D2/tan θ.