Techniques for analysing particle size to find inconsistencies in silicon carbide (SiC), a wide-bandgap semiconductor utilised in microelectronics.
FREMONT, CA: Considering its unique features, SiC is widely used in microelectronic devices. However, the low yield and high cost of the SiC manufacturing process are important obstacles that must be overcome in order to achieve mass production of high-quality SiC devices. Malignant flaws that occur during the crystal formation process have an impact on the performance of SiC devices. Thus, advancements in crystal formation processes are critical for lowering defect density. Additionally, post-growth inspection techniques must be used in the manufacturing process to discover and find faults.
The primary errors in SiC are surface flaws near or at the wafer surface and crystallographic flaws within the SiC wafer itself. Grain boundaries, micropipes, threading screw dislocations (TSDs), threading edge dislocations (TEDs), stacking faults, and basal plane dislocations (BPDs) are examples of crystallographic flaws.
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For SiC wafer quality, epitaxial layer growth factors are crucial. Scratches, polytype inclusions, and carrot defects are examples of surface flaws that can result from crystallographic contamination and flaws that spread to the epitaxial layer and wafer surface during growth operations. These flaws have a negative impact on the performance of SiC devices.
Defects have an adverse effect on the wafer's quality and the performance of the devices that were built on it. For instance, whereas polytype inclusions and carrots lower the blocking voltage, micropipes increase the leakage current and limit the operating current. Similar to surface scratches, dependability problems can result from them.
Point shortcomings in SiC can shorten the device carrier lifespan, causing junction leakage currents to increase and reduce breakdown voltages. By streamlining the manufacturing process and utilising quick and accurate defect inspection techniques, the impact of these flaws can be diminished.
Defect Detection Using Image Particle Analysis
To characterise the particle size distribution in a sample, particle size analysis can be used. Particle size analysis regulates quality, establishes the effectiveness of the production process, and assesses the finished product's performance in several sectors. Image particle analysis is a method for analysing particle sizes that produce data by taking pictures of each particle. The analysis can provide incredibly high sensitivity and resolution. Optical and TEM microscopy are the two main techniques employed for image particle analysis.
TEM
A nanoscale-resolution view of the sample's subsurface structure can be obtained through TEM. The SiC sample surface, which is elastically scattered from the underlying structure, is penetrated by electrons with high energy and ultra-short wavelength.
Stacking faults, TSDs, and BPDs, among other crystallographic flaws, can be found in SiC using TEM. In order to find limitations in SiC, a scanning transmission electron microscope (STEM) can also be deployed. STEM uses high-angle annular dark-field imaging (HAADF) to achieve atomic-level resolution. Partial dislocations and a trapezoidal stacking fault in 3C-SiC have been clearly seen in TEM images, while HAADF-STEM images have shown the presence of three different types of stacking faults made up of three, two and one defective atomic layers.
Although TEM can be a useful tool for finding SiC faults because it only offers one cross-sectional image at a time, employing this method to find defects over an entire SiC wafer can be quite time-consuming. In addition, the preparation of the sample is difficult and time-consuming due to the TEM mechanism's requirement for an exceedingly thin sample with less than one micrometre in thickness. As a result, TEM is not a useful instrument for in-line or extensive inspection.
Optical Microscopy
Surface inadequacy in SiC can be identified using optical microscopy. Using this method, images can be created in phase mode, bright-field mode, and dark-field mode. When all available photos are combined, it is possible to discover the majority of surface flaws. photos produced in a single mode provide specific defect information.
When the inspection light illuminates the SiC surface, the dark-field mode catches the dispersed light caused by surface imperfections. As a result, the image has a dark background, except for the unscathed light and bright objects that show the location of the flaw.
The bright-field mode, in contrast to the dark-field mode, catches the unscattered light and displays an image with a white background and black objects due to the scattering of defects. A phase-contrast image is produced by the phase mode, which records images with phase shifts caused by contamination on the surface of the SiC wafer.
The scattering image helps in lateral resolution in optical microscopy, but the phase-contrast picture mainly assesses the smoothness of the wafer surface. Several investigations have shown that it is possible to find surface flaws using optical microscopy. For instance, optical microscopy's benefits in lateral resolution make it possible to find flaws in very thin micropipes or carrots.
