Silicon carbide is superior to silicon in some applications as it has higher thermal conductivity, a wider band gap, is thermally and chemically inert, and features a higher breakdown field. These characteristics make it appealing for use in transistors (JFETS, MOSFETs, etc.), for applications like high temperature electronics, as well as in rapid high voltage devices for more effective power transmission. At present, it is utilized in a range of fields, including next generation power electronics for transportation solutions.
Challenges Facing Silicon Carbide
Silicon carbide's properties depend on its crystal structure (it can exist in a number of polytypes), on the crystal quality, and on the types and number of defects present. Silicon carbide raw material and device manufacturers must regulate and control these properties to improve their yield.
The Power of Raman Spectroscopy
As a first step in controlling these parameters, they need to be determined repeatably and in a quantifiable manner. The Raman systems from Renishaw are the ideal solution for this. The analysis of laser light scattered from the silicon carbide enables the quality, the crystal form, and the nature of defects to be determined.
This can be done conveniently, rapidly and in a non-destructive manner. A small region or a complete wafer can be analyzed, and both surface and subsurface information can be revealed in three dimensions.
Key Features of Renishaw’s Raman Systems
The key benefits of using Renishaw’s Raman systems for SiC analysis are:
- The crystal polymorphs and polytypes present can be determined
- Their distribution can be revealed
- The complex defects in three dimensions can be analyzed
- Depth profiles, interfaces, and layers can be studied
- It can be used for both development and as FA, QA tools
- Stress or strain can be determined
- Measurement of electronic properties, such as free carrier concentration and dopant levels is possible
- Rapid mapping of large wafers possible
Figures 1 to 6 show Raman spectra for different applications:
Figure 1. Raman spectra clearly differentiate 15R, 4H, and 6H, allowing for detailed high resolution identification and mapping.
Figure 2. Large wafers in high definition - Approximately 1 mm square Raman image showing inclusions of 6H-Silicon carbide, 3C-Silicon carbide or Si (red), voids (black), and strain distribution (blue to green).
Figure 3. 3D Raman image of core inclusion, showing: 3C-SiC inclusion (red); 4H- SiC epilayer (green); doped 4H-SiC substrate (blue). Sample courtesy of Prof. Noboru Ohtani, Kwansei Gakuin University, Japan.
Figure 4. Stress regions surrounding the defect (grey) and 4H/3C boundary. Compressive stresses (red), tensile stresses (blue)
Figure 5. Fast results - whole 2 inch wafer of silicon carbide scanned in less than 30 minutes. The Raman image highlights non-uniformity, such as variations in doping level and the presence of defects such as other polytypes and foreign material.
Figure 6. See defects in high detail - ‘comet’ defect, showing doped 4H-SiC substrate (green), 4H-SiC epilayer (blue), and 3C-SiC inclusion (red/orange). The mapped region is 70 × 25 × 7 µm3.
inVia - The ideal Raman Imaging tool
Figure 7 shows the Renishaw inVia Raman microscope.
Figure 7. The Renishaw inVia Raman microscope
The key features of the inVia are:
- Research grade Raman microscope
- High confocality StreamLineHR™ imaging for observing minute details
- Flexibility of switching between standard and high confocal imaging
- Measurements can be lined up to maximise data collection
- StreamLine™ imaging technology for high speed mapping, including whole wafers
- Surface option for acquiring superior quality images from uneven surfaces
- StreamLine imaging with Slalom for obtaining a general idea of the samples
This information has been sourced, reviewed and adapted from materials provided by CRenishaw - Raman Spectroscopy.
For more information on this source, please visit Renishaw - Raman Spectroscopy.