8-inch GaN-on-Si Wafers Manufacturing Technology

Article By : Maurizio Di Paolo Emilio

Some challenges must be addressed before GaN-on-Si devices can be widely adopted in power applications.

Gallium nitride (GaN) is a wide-bandgap semiconductor material with exceptional features and performance when compared to silicon, including high efficiency, rapid switching rate, great thermal management, and a compact footprint and weight. Some challenges, mostly related to large-volume production and price reduction, must be addressed before GaN-based devices can be widely adopted in power applications.

Founded in December 2015, Innoscience is focusing on gallium nitride technology. With two fabs dedicated to 8-inch GaN-on-Si device manufacturing, Innoscience produces normally-off (e-mode) GaN devices for a wide range of applications and voltages — low voltages (down to 30V) and high voltages (up to 650V).

“GaN-based devices are mainly fabricated on (old) 6-inch lines. By having our brand new 8-inch silicon wafer manufacturing line and big capacity, we can get a great throughput which, together with the economies of scale, allows us to have very cost-effective devices,” said Denis Marcon, general manager of Innoscience Europe.

He added, “The fact that we use 8-inch and advanced [ASML] scanners, allows us to shrink the gate length and other dimensions of GaN devices beyond what other players can do with a conventional 6-inch line. This is particularly important for LV devices (<100V) to obtain low on-resistance. And by leveraging 8-inch silicon manufacturing technology, we can get high yield too.”

GaN-on-Si
Figure 1: InnoGaN devices

According to Innoscience, production today stands at 10,000 wafers per month, but it 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 large volume production, even with a big increase in the market demand of GaN.

“We started building up our second fab in 2018, thinking ahead that the market would be there. Several other players are still on 6-inch, and it will take some time for them to move to 8-inch, which is not trivial, and/or increase capacity to the level that we already have today,” said Marcon.

GaN technology

By simultaneously processing more devices per wafer, overall cost can be lowered. From the very beginning, Innoscience has strategically adopted 8-inch wafer size, obtaining 80% more devices per wafer with respect to what would be possible with a 6-inch wafer (see Figures 1 and 2). This decision has inevitably had a direct impact on the device cost, allowing Innoscience to make GaN device technology much more affordable.

According to Marcon, Innoscience can offer GaN technology at a very competitive price thanks to the optimization they did and the economies of scale they were using. They are offering this technology at a reasonable price in order to penetrate many different markets and applications.

GaN-on-Si
Figure 2: 8-inch GaN wafer provides higher yield

Since its foundation at the end of 2015, Innoscience has enrolled 1,400 people, out of which 300+ are in the R&D department. The company holds, has a license or has submitted over 500+ patents. Innoscience has a sales and application engineering team in Shenzhen, which supports customers making evaluation boards and similar products.

“We really want to collaborate 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 widespread the GaN technology and we are here to offer our capacity and technology to them,” said Marcon.

By nature, Innoscience is an IDM, meaning it is a fully integrated company. It does its own epitaxy, device design, wafer processing, and also failure and reliability testing. The only thing that Innoscience is currently outsourcing is packaging. According to Marcon, standard package technology is highly appreciated by the customers, because they are very familiar with it. That’s the reason why Innoscience does not use exotic packages, but rather standard DFN for the high voltage 650V devices, and FCSP, WLCSP, or LGA for low voltage devices.

According to Innoscience, other GaN chipmakers are using a very specific package, trying to make the device as small as possible in order to reduce costs. Innoscience is also working in that direction, but using standard packages and keeping an eye on the thermal dissipation.

“What we see as an evolution, and we are supporting, serving several design houses in China, is the co-packaging of our device together with the (Si) driver, the controller, the temperature protection, everything embedded into one package, a system-in-package basically,” said Marcon.

According to Innoscience, GaN-based devices are normally-on (d-mode), but market demand normally-off (e-mode) devices. There are basically two ways to solve this apparent issue. The first one is based on the Cascode solution, consisting in the co-packaging of a d-mode GaN device with a LV Si MOS. The second one consists in developing a normally-off device, which is what Innoscience has done – developing a normally-off/enhancement-mode (e-mode) technology based on p-GaN.

In order to reduce the price, Innoscience leverages two key factors. The first one is to use facilities optimized for large manufacturing capabilities, taking advantage of the optimization achieved by silicon over the past 30 years to squeeze the fab throughput to the maximum. The second one is to use a larger wafer size. By using 8-inch wafer, you can get many more dice per wafer than you can get with a 6-inch wafer.

“What we have developed on top of the GaN technology is the introduction of a strain enhancement layer, which is basically a layer that we deposit after the gate formation in order to increase the 2DEG density. And by doing so, we are able to reduce the specific resistance of the device, without impacting other parameters, such as threshold voltage and leakage current,” said Marcon.

One of Innoscience’s fab is already certified for automotive part production, and the company is working with an automotive customer to have automotive-qualified devices ready in the next months. Automotive GaN applications include DC/DC high-voltage converters (650V/950V), DC/DC 48V/12V converters, onboard chargers, and LiDAR.

This article was originally published on EE Times Europe.

Maurizio Di Paolo Emilio holds a Ph.D. in Physics and is a telecommunication engineer and journalist. He has worked on various international projects in the field of gravitational wave research. He collaborates with research institutions to design data acquisition and control systems for space applications. He is the author of several books published by Springer, as well as numerous scientific and technical publications on electronics design.

 

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