Silicon Carbide Wafer

Bandgap and Thermal Conductivity
With its wide bandgap, silicon carbide wafers can withstand voltages that are up to ten times higher than silicon, which has a breakdown voltage of around 600V. Silicon (Si), a semiconductor that’s long been the material of choice for the wafers used in integrated circuits (ICs) and photovoltaics, has a bandgap of 1.12 eV. Gallium arsenide (GaAs), a semiconductor used in solar cells, has a bandgap of 1.42 eV. By contrast, silicon carbide has a bandgap of 3.26 eV. SiC’s wider bandgap also support faster, more efficient switching and smaller, thinner devices. In addition, silicon carbide’s higher thermal conductivity allows for the more efficient transportation of heat and can reduce or eliminate the need for heat sinks in electronic designs.

Thermal Shock Resistance
With its high thermal conductivity and low thermal expansion, silicone carbide also provides superior resistance to thermal shock, a transient mechanical load caused by a rapid change of temperature. Often, thermal shock occurs when an extreme temperature gradient reaches some but not all of an object. Because of this difference in temperature, parts of the object expand and contract at different rates, which can lead to fracture. Compared to most semiconductor materials, SiC has a low thermal conductivity (3.8 W/m.K minimum) and a high thermal expansion (7.9 to 11 10-6/K).

Physical, Chemical and Electrical Durability
Silicon carbide’s physical durability is demonstrated by its use in non-electronic applications such as the plates in bulletproof vests. With regard to temperature durability, SiC will not sublimate into a vapor phase until around 2700°C, which is significantly higher than the melting point of iron (around 1500°C). SiC is also chemically inert and can resist very aggressive chemicals such as alkalis and molten salts, even at high temperatures up to 800°C. With its high energy bandgap, SiC is extremely resistant to high levels of electromagnetic disturbances and the damaging effects of radiation.

Versatility
Silicone carbide’s superior properties makes it good choice for EV power electronics. Applications include on-board DC/DC converters, off-board DC fast chargers, on-board battery chargers, EV powertrains, and automotive lighting for LEDs. In addition to high-temperature resistance, silicon carbide provides the low power consumption, rigidity, and support for smaller, thinner designs that EV power electronics need. With their greater power densities and higher amounts of heat, 5G electronics are also using SiC wafers.

Hardness
There are numerous advantages to using silicon carbide over more traditional silicon substrates. One of the major advantages is its hardness. This gives the material many advantages, in high speed, high temperature and/or high voltage applications. Silicon carbide wafers have high thermal conductivity, which means they can transfer heat from one point to another well. This improves its electrical conductivity and ultimately miniaturization, one of the common goals of switching to SiC wafers.

Thermal capabilities
Silicon carbide substrates also have a low coefficient for thermal expansion. Thermal expansion is the amount and direction a material expands or contracts as it heats up or cools down. The most common explanation is ice, although it behaves opposite of most metals, expanding as it cools and shrinking as it heats up. Silicon carbide’s low coefficient for thermal expansion means that it does not change significantly in size or shape as it is heated up or cooled down, which makes it perfect for fitting into small devices and packing more transistors onto a single chip. Another major advantage of these substrates is their high resistance to thermal shock. This means they have the ability to change temperatures rapidly without breaking or cracking. This creates a clear advantage when fabricating devices as it is another toughness characteristic that improves the lifetime and performance of silicon carbide in comparison to traditional bulk silicon. On top of its thermal capabilities, it is a very durable substrate and does not react with acids, alkalis or molten salts at temperatures up to 800°C. This gives these substrates versatility in their applications and further assists their ability to out perform bulk silicon in many applications. Its strength at high temperatures also allows it to safely operate at temperatures over 1600°C. This makes it a suitable substrate for virtually any high temperature application.

Larger Wafers, Greater Efficiency
The availability of SiC wafers with larger diameters, reaching up to 150mm and even 200mm, is a game-changer. These larger wafers allow for increased device integration on a single chip, leading to higher production throughput and ultimately reduced manufacturing costs per unit area.

Taming Defects, Refining Quality
The relentless pursuit of reducing defects and improving crystal quality has spurred the development of advanced growth techniques. Techniques like Continuous Feed Physical Vapor Transport (CF-PVT) and refined High-Temperature Chemical Vapor Deposition (HTCVD) minimize defect densities and pave the way for exceptional SiC crystals.

State-of-the-Art Characteristics
Leading manufacturers are delivering SiC wafers with truly impressive characteristics. Low defect densities (often less than 10 micropipes per square centimeter) and high carrier lifetimes are hallmarks of these advanced wafers. This translates to the fabrication of high-performance SiC devices with superior efficiency and reliability.

Epitaxial Growth Takes Center Stage
Significant advancements in epitaxial growth techniques are contributing to the overall quality of SiC wafers. Cutting-edge methods like Chloride-Based Chemical Vapor Deposition (CVD) and Trichlorosilane (TCS) CVD offer unparalleled control over doping profiles, layer thickness, and defect densities within the epitaxial SiC layers.

Doping with Precision
Doping, the process of introducing impurities to control the electrical properties of SiC wafers, has become an art form. Techniques like ion implantation and in-situ doping during epitaxial growth have been meticulously refined, allowing for precise control over dopant concentrations and activation. Common dopants include nitrogen for n-type (electron-rich) and aluminum or boron for p-type (hole-rich) conductivity.

Seeing the Unseen
Advanced Characterization: The relentless pursuit of perfection extends to characterization techniques. Advanced methods like X-ray topography, photoluminescence mapping, and scanning electron microscopy (SEM) are used to not only identify defects but also analyze them in detail. This continuous monitoring allows manufacturers to refine their processes and steadily improve wafer quality, ultimately leading to even better device performance.