Silicon carbide (SiC) wafers are used in power electronics, EVs, power inverters, and PVs. Silicon carbide wafers are feats of modern science, as their thermal properties, high breakdown voltage and temperature survival allows for the production of our modern efficient and reliable electronics in all these applications. Here’s how they are made.
Step 1: Raw Material Selection and Preparation. It all start with the selection of good quality raw materials. Petroleum coke is mixed with high purity silica. The Acheson process is an example of a chemical process commonly used to “grow” the crystals at high temperature. Around 2500 degrees Celsius is typical of these commercial processes. Electric furnaces produce small crystals. Step 2: Crystal Growth – Sublimation Method. The crystals are then grown. “Sublimation,” or “Physical Vapor Transport (PVT),” is used to produce many of the higher quality SiC wafers. Silicon carbide powder is placed in a furnace and idled at high temperatures typically in the range of 2000-2500 degrees C. Over time the hot SiC itself vaporizes and crystallizes on the existing seed crystal, gradually producing the large single crystal ‘wafer’ used in exploitation. This method is crucial to the production of the high purity, single crystal silicon carbide wafers. Step 3: Crystal Orientation and Cutting. The SiC crystals have been grown, and cut into the thin wafers we need. SiC crystals are carefully oriented so that the slices cut from them will have the desired characteristics.This orientation of the SiC crystals is necessary to obtain the required properties of the resulting wafers for use in electronic devices. Often the crystals are sliced into wafers of the desired thickness (normally in the range of 300 to 500 microns thick, although it may be thicker, or other desired thickness depending on the individual application required) using a diamond coated saw. Step 4: Polishing or Surface Preparation
Once sliced, wafers are then polished to a smooth, flat surface, etc., as required for the intended further processing, such as the manufacture of semiconductors or the production of power devices such as high voltage power semiconductors. Such polishing may take various forms; several steps may be involved, for example mechanical polishing, followed by chemical mechanical polishing (CMP); the latter being important in order to ensure good, defect free, scratch free, and uncontaminated surfacesSiC raw material is manufactured by “heat” and intimately mixing together silicon and carbon powders with a mix rich in silicon forming a metal. This quantity of silicon metal is typically to hand at all manufacturing locations as a by-product; it may well also exist more “locally to hand” for that use, at an additional second payback.
Crystal growth. The growth of the crystal itself for the SiC wafer is then performed by either a solution or a sublimation process performed in an inert atmosphere. Since normal use of SiC in will be at around 2000 °C, a high vacuum process can be used to render the resulting material pure. By clever uses of” seeding of the liquid, or whatever material the zuill to be created is to start as a blob of, a small unfinalized section of crystal may then be seeded, and thus grow (or beotherwise come to be formed) around that seeding.
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