1. Overview of silicon carbide substrate processing technology
The current silicon carbide substrate processing steps include: grinding the outer circle, slicing, chamfering, grinding, polishing, cleaning, etc. Slicing is an important step in semiconductor substrate processing and a key step in converting the ingot to the substrate. At present, the cutting of silicon carbide substrates is mainly wire cutting. Multi-wire slurry cutting is the best wire cutting method at present, but there are still problems of poor cutting quality and large cutting loss. The loss of wire cutting will increase with the increase of substrate size, which is not conducive to the silicon carbide substrate manufacturers to achieve cost reduction and efficiency improvement. In the process of cutting 8-inch silicon carbide substrates, the surface shape of the substrate obtained by wire cutting is poor, and the numerical characteristics such as WARP and BOW are not good.
Slicing is a key step in semiconductor substrate manufacturing. The industry is constantly trying new cutting methods, such as diamond wire cutting and laser stripping. Laser stripping technology has been highly sought recently. The introduction of this technology reduces cutting loss and improves cutting efficiency from the technical principle. The laser stripping solution has high requirements for the level of automation and requires thinning technology to cooperate with it, which is in line with the future development direction of silicon carbide substrate processing. The slice yield of traditional mortar wire cutting is generally 1.5-1.6. The introduction of laser stripping technology can increase the slice yield to about 2.0 (refer to DISCO equipment). In the future, as the maturity of laser stripping technology increases, the slice yield may be further improved; at the same time, laser stripping can also greatly improve the efficiency of slicing. According to market research, the industry leader DISCO cuts a slice in about 10-15 minutes, which is much more efficient than the current mortar wire cutting of 60 minutes per slice.
The process steps of traditional wire cutting of silicon carbide substrates are: wire cutting-rough grinding-fine grinding-rough polishing and fine polishing. After the laser stripping process replaces wire cutting, the thinning process is used to replace the grinding process, which reduces the loss of slices and improves processing efficiency. The laser stripping process of cutting, grinding and polishing of silicon carbide substrates is divided into three steps: laser surface scanning-substrate stripping-ingot flattening: laser surface scanning is to use ultrafast laser pulses to process the surface of the ingot to form a modified layer inside the ingot; substrate stripping is to separate the substrate above the modified layer from the ingot by physical methods; ingot flattening is to remove the modified layer on the surface of the ingot to ensure the flatness of the ingot surface.
Silicon carbide laser stripping process
2. International progress in laser stripping technology and industry participating companies
The laser stripping process was first adopted by overseas companies: In 2016, Japan's DISCO developed a new laser slicing technology KABRA, which forms a separation layer and separates wafers at a specified depth by continuously irradiating the ingot with laser, which can be used for various types of SiC ingots. In November 2018, Infineon Technologies acquired Siltectra GmbH, a wafer cutting startup, for 124 million euros. The latter developed the Cold Split process, which uses patented laser technology to define the splitting range, coat special polymer materials, control system cooling induced stress, accurately split materials, and grind and clean to achieve wafer cutting.
In recent years, some domestic companies have also entered the laser stripping equipment industry: the main companies are Han's Laser, Delong Laser, West Lake Instrument, Universal Intelligence, China Electronics Technology Group Corporation and the Institute of Semiconductors of the Chinese Academy of Sciences. Among them, the listed companies Han's Laser and Delong Laser have been in layout for a long time, and their products are being verified by customers, but the company has many product lines, and laser stripping equipment is only one of their businesses. The products of rising stars such as West Lake Instrument have achieved formal order shipments; Universal Intelligence, China Electronics Technology Group Corporation 2, the Institute of Semiconductors of the Chinese Academy of Sciences and other companies have also released equipment progress.
3. Driving factors for the development of laser stripping technology and the rhythm of market introduction
The price reduction of 6-inch silicon carbide substrates drives the development of laser stripping technology: At present, the price of 6-inch silicon carbide substrates has fallen below 4,000 yuan/piece, approaching the cost price of some manufacturers. The laser stripping process has a high yield rate and strong profitability, which drives the penetration rate of laser stripping technology to increase.
The thinning of 8-inch silicon carbide substrates drives the development of laser stripping technology: The thickness of 8-inch silicon carbide substrates is currently 500um, and is developing towards a thickness of 350um. The wire cutting process is not effective in 8-inch silicon carbide processing (the substrate surface is not good), and the BOW and WARP values have deteriorated significantly. Laser stripping is regarded as a necessary processing technology for 350um silicon carbide substrate processing, which drives the penetration rate of laser stripping technology to increase.
Market expectations: SiC substrate laser stripping equipment benefits from the expansion of 8-inch SiC and the cost reduction of 6-inch SiC. The current industry critical point is approaching, and the development of the industry will be greatly accelerated.
Post time: Jul-08-2024