Industry news 2022-03-10

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8-inch GaN-on-Si wafer fabrication technology

Gallium Nitride (GaN) is a wide-bandgap semiconductor material with superior properties and performance compared to silicon, including high efficiency, fast switching rates, excellent thermal management, and a compact footprint and weight. Before GaN-based devices can be widely adopted in power applications, some challenges, mainly related to high-volume production and price reduction, must be addressed.

Innoscience was established in December 2015, focusing on gallium nitride technology. Innoscience has two fabs dedicated to 8-inch GaN-on-Si device fabrication for a variety of applications and voltages - low voltage (as low as 30V) and high voltage (up to 650V).

“GaN-based devices are primarily fabricated on (old) 6-inch lines. With our brand new 8-inch silicon wafer line and high volumes, we can get huge volumes, which, combined with economies of scale, allows us to have very Cost-effective device," said Denis Marcon, managing director of Innoscience Europe.

He added: “The fact that we are using 8-inch and advanced [ASML] scanners allows us to shrink the gate length and other dimensions of GaN devices that other manufacturers can do with traditional 6-inch production lines. This is especially important for LV devices (<100V) to achieve low on-resistance. By utilizing 8-inch silicon fabrication technology, we can also achieve high yields.”

According to Innoscience, production is currently at 10,000 wafers per month, but will reach 14,000 wafers per month by the end of this year and 70,000 wafers per month by 2025. Because it owns and controls two fabs, the company can support very high volume production even as the market demand for GaN surges.

“We started construction of our second factory in 2018 with the thought in advance that the market would be there. Several other players are still using 6 inches and it will take some time for them to migrate to 8 inches, which is not trivial, and/ Or increase capacity to the level we already have today," Marcon said.

Gallium Nitride Technology
The overall cost can be reduced by processing more devices simultaneously on each wafer. From the outset, Innoscience has strategically adopted the 8-inch wafer size, resulting in an 80% increase in the number of devices per wafer compared to 6-inch wafers (see Figures 1 and 2). This decision inevitably had a direct impact on device cost, allowing Innoscience to make GaN device technology more affordable.

Marcon said Innoscience was able to offer GaN technology at a very competitive price thanks to the optimizations they made and the economies of scale they used. They offer this technology at an affordable price to tap into many different markets and applications.

Since its establishment at the end of 2015, Innoscience has recruited 1,400 people, including more than 300 people in the R&D department. The company holds, licenses or has filed over 500 patents. Innoscience has sales and application engineering teams in Shenzhen to support customers in making evaluation boards and similar products.

“We really want to work with customers and partners to enable system solutions based on GaN technology. We really want to be a good partner for any company that wants to promote GaN technology, and we are here to offer them our capabilities and technology," Marcon said.

Essentially, Innoscience is an IDM, which means it is a fully integrated company. It does its own epitaxy, device design, wafer processing, and failure and reliability testing. The only thing Innoscience currently outsources is packaging. According to Marcon, the standard packaging technology is highly appreciated by customers because they are very familiar with it. That's why Innoscience does not use special packages, but uses standard DFN for high voltage 650V equipment and FCSP, WLCSP or LGA for low voltage equipment.

According to Innoscience, other GaN chip makers are using very special packages in an attempt to keep the devices as small as possible to keep costs down. Innoscience is also working in this direction, but using standard packages and paying close attention to heat dissipation.

"We think it's an evolution, we're supporting and serving several design houses in China to embed our devices with (Si) drivers, controllers, temperature protection, everything into one package, a basically system level packaging," Marcon said.

According to Innoscience, GaN-based devices are normally-on (d-mode), but the market requires normally-off (e-mode) devices. There are basically two ways to solve this obvious problem. The first Cascode-based solution includes co-packaging of d-mode GaN devices with LV Si MOS. The second is developing normally-off devices, which is exactly what Innoscience has done — developing p-GaN-based normally-off/enhancement mode (e-mode) technology.

To keep the price down, Innoscience leveraged two key factors. The first is to use facilities optimized for large-scale manufacturing capabilities, leveraging the optimizations that silicon has achieved over the past 30 years to compress fab yields to the maximum. The second is to use a larger wafer size. By using 8" wafers, you can get more chips than with 6" wafers.

"What we've developed on top of GaN technology is the introduction of a strain enhancement layer, which is basically a layer that we deposit after the gate is formed, to increase the 2DEG density. By doing this, we were able to reduce the resistivity of the device without affecting the resistivity of the device. Other parameters, such as threshold voltage and leakage current," Marcon said.

One of Innoscience's factories has been certified for the production of auto parts, and the company is working with automotive customers to have automotive-compliant equipment ready in the coming months. Automotive GaN applications include DC/DC high voltage converters (650 V/950 V), DC/DC 48-V/12-V converters, on-board chargers and lidars.