SiC-based production process of power semiconductors

SiC-based production process of power semiconductors – Cheersonic

It can be divided into the following steps:

(1) Raw material generation: (PVT gas phase formation, many structures, difficult to control)

The high-purity silicon powder and high-purity carbon powder are uniformly mixed according to the process formula, and at a high temperature above 2,000 ℃, a specific reaction process is carried out in the reaction chamber to remove the residual trace impurities in the reaction environment and adsorbed on the surface of the reaction fine powder. Silicon powder and carbon powder are reacted in a predetermined stoichiometric ratio to synthesize silicon carbide particles of specific crystal form and particle size. After crushing, sieving, cleaning and other processes, high-purity silicon carbide powder raw materials that meet the requirements of crystal growth are obtained. Each batch is sampled to test for purity, particle size, etc.

(2) Crystal growth

Chinese companies generally use the PVT method to prepare silicon carbide single crystals. The PVT method heats the silicon carbide powder at a high temperature above 2,300°C and a low pressure close to vacuum in a closed growth chamber by induction heating, so that it sublimates to produce Si, Si2C , SiC2 and other reaction gases with different gas phase components, through the solid-gas reaction to generate a silicon carbide single crystal reaction source; due to the different gas-phase partial pressures of the Si and C components formed by the solid-phase sublimation reaction, the Si/C stoichiometric ratio varies with the thermal field. There are differences in distribution, and the gas phase components need to be distributed and transported according to the designed thermal field and temperature gradient, so that the components are transported to the predetermined crystallization position of the growth chamber; in order to avoid disordered gas phase crystallization to form polycrystalline silicon carbide, A silicon carbide seed crystal (seed) is set on the top of the growth chamber, and the gas phase components transported to the seed crystal are atomically deposited on the surface of the seed crystal under the driving of the supersaturation of the gas phase components, and grow into a silicon carbide single crystal.

The entire solid-gas-solid reaction process of the above silicon carbide single crystal preparation is in a complete and airtight growth chamber. The parameters of the reaction system are coupled with each other. Any fluctuation of growth conditions will lead to changes in the entire single crystal growth system, affecting the The stability of silicon carbide crystal growth; in addition, the different close-packed structures of silicon carbide single crystals in their crystal orientations have various atomic connection and bonding methods, thereby forming more than 200 crystal forms of silicon carbide isomeric structures, and The energy conversion barrier between different crystal forms is extremely low. Therefore, the transformation of different crystal forms easily occurs in the PVT single crystal growth system, resulting in serious quality problems such as disorder of the target crystal form and various crystal defects. Therefore, it is necessary to use special testing equipment to detect the crystal form and various defects of the ingot.

(3) Ingot processing

The silicon carbide ingot is oriented with an X-ray single crystal orientation instrument, and then ground and rounded by precision machining, and processed into a silicon carbide ingot with standard diameter size and angle. The size, angle and other indicators of all formed ingots are tested.

(4) Ingot cutting

Under the premise of considering the subsequent machining allowance, the silicon carbide ingot is cut into different thicknesses to meet the customer’s needs using fine diamond wire, and the warp (Warp), bow (Bow), Thickness Change (TTV) isosurface inspection.

(5) Cutting blade grinding

The cutting sheet is thinned to the corresponding thickness by the grinding liquid of its own process formula, and the line marks and damages on the surface are eliminated. Use automatic testing equipment and non-contact resistivity tester to test the surface and electrical properties of all cutting sheets.

(6) Abrasive polishing

Mechanical polishing and chemical polishing are carried out on the abrasive sheet with a well-proportioned polishing liquid, which is used to eliminate surface scratches, reduce surface roughness and eliminate processing stress, etc., so that the surface of the abrasive sheet can reach nano-level flatness. Use X-ray diffractometer, atomic force microscope, surface flatness tester, surface defect comprehensive tester and other equipment to detect various parameters and indicators of the silicon carbide polishing sheet, and judge the quality level of the polishing sheet accordingly.

(7) Polishing sheet cleaning

In the 100-class clean room, the polishing sheet in the cleaning machine is cleaned with a specific ratio of chemical reagents and deionized water to remove dust particles, metal ions, organic contaminants, etc. on the surface of the polishing sheet, and then dry and package. In a clean wafer box, a silicon carbide substrate is formed that can be used by customers out of the box.

Author: Yao Donglai

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.