SiC wafer cutting speed up to 100 times faster than dicing

Silicon Carbide (SiC) is being developed as a material for next-generation power devices. Although SiC has excellent semiconductor characteristics, it is extremely hard and the dicing process for SiC wafers takes a considerable amount of time. Mitsuboshi Diamond Industries, which has recently entered the semiconductor industry proposes a cutting process called “scribing and breaking,” which is completely different from conventional dicing. The company, which has long been engaged in cutting glass and LCD panels and has refined its “cutting technology,” says that its method can speed up the cutting speed of SiC wafers up to 100 times faster than conventional methods. 

SiC has good characteristics, but it is an extremely hard material. 

SiC power devices are increasingly used in power conditioners for solar power generation systems and inverters for electric vehicles (EVs). SiC has excellent semiconductor characteristics, with a dielectric breakdown field strength 10 times greater and a band gap three-times greater than that of Si (silicon). The use of SiC in power devices has spurred development and adoption because of its ability to achieve higher breakdown voltages and lower losses than conventional Si power devices. According to a forecast released in September 2023 by Yole Group, the SiC power device market will continue to grow at a compound annual growth rate (CAGR) of 31% from 2022 to 2028. 

Although SiC power devices are expected to grow steadily, there are some challenges. One of the major challenges is that SiC is extremely hard. On the Mohs hardness scale, which indicates the hardness of materials, SiC is 13 — the third hardest after diamond (15), the hardest, and boron carbide (14), the second hardest. In other words, SiC wafers are so hard that processing such as dicing to cut a die from a wafer takes a considerable amount of time. The long processing time is one of the reasons for the high cost of SiC power devices. If this process can be sped up, the UPH in mass production can be higher and costs can be reduced. 

Mitsuboshi Diamond Industry is trying to bring about a revolution in the cutting process. 

Osaka-based Mitsuboshi Diamond Industry was founded in 1935 as a manufacturer of glass cutters. The company’s strength lies in its ability to propose processing methods suited to materials, including highly-difficult processes such as deformed processing and drilling. The company develops and manufactures processing tools and equipment. The company has a particularly high market share in the LCD panel field, having supplied a cumulative total of approximately 6,000 units of equipment, mainly for LCD panel cutting. 

Mitsuboshi Diamond Industries is going on the offensive in the semiconductor market with its “cutting technology,” which it has been refining since its founding. The company will first target the field of SiC wafer cutting.  The company’s “Scribe and Break” cutting technology can increase cutting speed up to 100 times faster than conventional dicing. “It is a completely different cutting method from conventional dicing,” emphasizes Masayuki Wakabayashi, president and representative director. The company will market the Scribe and Break method under the brand name “SnB (S and B).” 

SnB is common in glass cutting, but new in semiconductors. 

Scribing and breaking literally consists of two processes: scribing and breaking. In scribing, a circular cutter called a scribe wheel is used to make shallow cuts on the wafer surface. The purpose of this process is to generate the cracks necessary to break up the wafers, and these cut lines are called scribe lines. Then, in the “break” process, the wafer is turned over and stress is applied from directly behind the scribe lines to separate the wafers along the scribe lines.  

Scribe and break is a process that has been used in glass cutting for more than 80 years. However, for the semiconductor world it is something completely new. Mitsuboshi Diamond Industries is enthusiastic that this “common sense” method in the field of glass will drastically change the way SiC wafers are cut. 

Solving dicing challenges in one step 

Dicing SiC wafers have several challenges. First, chipping, which is cracking or chipping of the corners and periphery of the chips, is a major problem. Chipping of about 20 μm width occurs,” says Mitsuboshi Diamond Industrial Co. 

In addition, dicing tends to increase the kerf width and the street width, which corresponds to the width of the wafer being diced, by 80 to 100 μm. This means that wafers are wasted (kerf loss) by the amount of kerf width and street width. 

Hard SiC wafers are also difficult to cut at high speeds: the average dicing speed for Si wafers is 100 to 200 mm/sec, but for SiC wafers the speed drops to 3 to 10 mm/sec. The cutting speed is also much faster: SnB cuts at 100 to 300 mm/sec, which is up to 100 times faster than dicing at 3 to 10 mm/sec, and will significantly improve SiC power device productivity.   In addition, dicing is a wet process, in which wafers are cut while water is flowing through the wafer, generally uses 6 to 7 liters of water per minute to cut a single wafer.  On the other hand, SnB is a dry process giving it another big advantage over dicing.  

Chipping has been improved to a level where it can be said that it almost never occurs,” says the company. Scribing only cuts a line on the wafer, so there is almost no chipping or cracking,” says the company. The street width is 30 µm, less than half that of dicing, and there is virtually no kerf loss. 

Many of our customers are very interested in improving kerf loss and productivity. The higher the cutting speed, the more wafers can be processed, which increases the mass production speed of power devices. Therefore, SnB can be cut at the same speed as Si wafers. 

The side walls is also smoother than dicing. The surface roughness index “Rz” is 1.43μm (horizontal direction) / 1.47μm (vertical direction) for dicing, whereas it is 0.17μm / 0.07μm for SnB. The reason why the side walls are so clean is that SnB is cut using the “cleavage” property of crystals. Crystals have the property of breaking along the surface where the bonding force between atoms is weak. This is called cleavage. Dicing is like cutting a crystal by forcefully crushing it regardless of the cleavage. SnB, on the other hand, cuts by forcibly separating atomic bonds. “It is like cutting a piece of fibrous cheese,” says the company. This means that there is little damage to the side walls. 

One of the reasons for these features is the material and shape of the scribe wheel developed by the company. When cutting SiC wafers with a conventional scribe wheel that cuts glass, the blade wears out after only a few meters of cutting. However, the scribe wheel we developed can maintain its cutting performance for about 3,000 meters,” says the company. This is the strength of a manufacturer that develops processing tools. 

Up to 13% more dies can be obtained 

Since SnB has a smaller street width and almost no kerf loss the number of dies that can be obtained from a single wafer increase. For example, a 6-inch SiC wafer dicing 0.75mm square die yields 23,936 dies.  Using SnB yields 27,144 or about 13% more. This will contribute to lower costs for SiC power semiconductors and other products. 

Reduces equipment footprint by 75%. 

Mitsuboshi Diamond Industries has already released a semiconductor wafer precision cutting system “DIALOGIC” that uses SnB and has already delivered approximately 20 units of SnB equipment to a SiC power device manufacturers. 

DIALOGIC will help reduce the footprint. Assume a production line that processes 90 million 6-inch wafers per month to cut out 1mm square dies. With DIALOGIC, only three dicing machines are needed, reducing the footprint by 75% to 16.5 m². 

DIALOGIC’s production capacity “can process about 10 wafers per hour when manufacturing power semiconductor chips,” according to the company. 6-inch and 8-inch wafers are both supported, in anticipation of larger-diameter SiC wafers. 

DIALOGIC requires periodic replacement of tools such as scribe wheels. Mitsuboshi Diamond Industries is also planning to offer services such as periodic maintenance. 

 Exhibited at CS Mantech 2024 and will exhibit ICSCRM 2024 for the first time 

Mitsuboshi Diamond Industrial Co., Ltd. exhibited at CS Mantech 2024 (International Conference on Compound Semiconductor Manufacturing Technology) to be held at the JW Marriott Starr Pass Resort in Tucson, Arizona from May 20 to 23, 2024 and will also exhibit for the first time at ICSCRM2024 to be held at Raleigh convention center from Sept 29 to Oct 4, 2024.  

Mr. Wakabayashi said, “After the growth of the LCD market settled down, we set semiconductors as the next axis of growth. Since then, we have been developing technologies to enter the semiconductor market for about 10 years. Now we have finally settled on SiC as our target market,” he said. We have focused our research and development not only on which semiconductor materials to cut, but also on which materials to cut with. This is one of our strengths as a developer of processing tools. We can also develop equipment to make the best use of these tools. We would like everyone in the semiconductor industry to know our company name and technology,” said Wakabayashi. 

The company aims to achieve sales of approximately 10 billion yen in the SiC wafer processing business alone between 2025 and 2030. The company has also established an office in San Diego, California, in the United States. We are serious about the semiconductor business,” Wakabayashi emphasized. 

As the semiconductor industry searches for ways to lower the cost of SiC power devices and improve their mass production, Mitsuboshi Diamond Industries’ SnB should be a major step forward in bringing innovation to the industry. 

“At first, people don’t believe that we can cut SiC wafers so fast because the semiconductor industry is not aware of the scribe-and-break process,” said Wakabayashi. “However, when they actually see it, they sometimes applaud.” 

Seeing is believing — so why not visit ICSCRM 2024 and take a look at the SnB process for yourself?