Challenges in SiC Manufacturing: Powder Purity, Crystal Ingot Uniformity, and Beyond

Among the many wide bandgap semiconductor materials, silicon carbide(SiC) has become a material that has attracted much attention, especially in the field of high power conversion. It is widely used in traction inverters and on-board chargers for electric vehicles (EVs), as well as in infrastructure sectors such as DC fast charging, solar inverters, energy storage systems, and uninterruptible power supplies (UPS). Although Silicon Carbide has been used in mass production for over a hundred years, initially primarily as an abrasive material, it has also demonstrated excellent performance for high-voltage and high-power applications.

In terms of physical properties, silicon carbide has high thermal conductivity, high saturated electron drift velocity, and high breakdown electric field (as shown in Figure 1). As a result, silicon carbide-based systems can operate with significantly reduced energy losses and faster switching speeds. Compared to traditional silicon MOSFETs and IGBT devices, silicon carbide is able to achieve these advantages in a smaller size, with higher efficiency and stronger performance.

Fig.1:Properties of silicon and wide bandgap materials

The Opportunities Presented by Silicon Carbide

For manufacturers, silicon carbide is seen as an important competitive advantage, providing an opportunity to build energy-efficient systems while also effectively reducing the size, weight, and cost of the overall system. This is because systems with silicon carbide are generally more energy-efficient, compact, and durable than silicon-based systems, and designers can reduce costs by reducing the size of passive components. More specifically, Silicon Carbide Devices can operate at lower temperatures than traditional solutions for specific applications due to their lower heat generation (as shown in Figure 2).This allows silicon carbide to improve system efficiency while also improving reliability and extending the life of equipment.

Fig.2:Advantages of Silicon Carbide Applications

In the design and manufacturing process, the adoption of new chip connection technologies, such as sintering technology, can help dissipate heat more efficiently and ensure the reliability of the connection. Silicon carbide devices are capable of operating at higher voltages and offer faster switching speeds compared to silicon devices. These benefits allow designers to rethink how to optimize functionality at the system level while improving price competitiveness. Currently, many high-performance devices have adopted silicon carbide technology, including silicon carbide diodes, Silicon Carbide Mosfets, and silicon carbide modules.

Compared to silicon materials, silicon carbide's superior properties open up promising prospects for emerging applications. Silicon carbide devices are typically designed with voltages not less than 650V, especially above 1200V, making silicon carbide the best choice for many applications. Applications such as solar inverters, electric vehicle charging piles, and industrial AC-to-DC conversion will gradually shift to silicon carbide technology in the future. Another area of application is solid-state transformers, where existing copper and magnetic transformers will be gradually replaced by silicon carbide technology, bringing greater efficiency and reliability to power transmission and conversion.

The Challenges Presented by Silicon Carbide

Despite its vast market potential, silicon carbide faces numerous challenges in its manufacturing process. First, the purity of raw materials (i.e., silicon carbide granules or silicon carbide powder) needs to be ensured. This is followed by the generation of silicon carbide ingots with high consistency (as shown in Figure 3) and the accumulation of experience in each subsequent processing step to ensure the reliability of the final product (as shown in Figure 4).

One of the unique challenges of silicon carbide is that it does not have a liquid phase, so crystals cannot be grown through traditional melting methods. The growth of crystals must be carried out under precisely controlled pressure, which makes the fabrication of silicon carbide more complex than silicon. If it remains stable in high and low pressure environments, silicon carbide will decompose directly into gaseous substances without going through liquid phase processes. Due to this property, silicon carbide crystals are often grown using sublimation or physical vapor transfer (PVT) techniques.

In this process, silicon carbide powder is placed in a crucible in a furnace and heated to high temperatures (over 2200°C). When silicon carbide is sublimated, it will crystallize on the seed and form crystals. The key part of growing crystals using the PVT method is the seed, which is similar in diameter to the ingot. It is important to note that the rate of PVT growth is very slow, approximately 0.1 to 0.5 mm per hour.

Fig.3:Silicon carbide powder, crystal ingots, and wafers

The process of manufacturing wafers has become more complicated due to the extremely high hardness of silicon carbide compared to silicon. Silicon carbide is an extremely hard material that is difficult to cut even with a diamond saw, and this hardness is very different from that of many other semiconductor materials. While there are several methods currently available for slicing the ingot into wafers, these methods can often introduce defects into the single crystal, which affects the final quality of the material.

Fig.4:The manufacturing process of silicon carbide from raw materials to the final product

In addition, the scaled production of silicon carbide also faces several challenges. Compared to silicon, silicon carbide has more inherent defects. Its doping process is highly complex, and producing large-sized wafers with fewer defects implies higher manufacturing and processing costs. Therefore, establishing an efficient and stringent development process from the outset is crucial to ensure the production of consistently high-quality products.

Fig.5：Challenges – Silicon carbide wafers and defects