Allos Semiconductors has announced that its low leakage, doping-free 600V HEMT GaN-on-Si epiwafer technology is running in parallel on both Aixtron G5 and Veeco K465i reactors for a power electronics customer.
The project requirements included developing customised interlayer and superlattice based epi structures with up to 7 µm total thickness for 150 and 200mm wafer diameter. Additional project objectives were specified device-level parameters and establishing the epi process in the two different widely used reactors.
To have low leakage is seen as one of the prerequisites in the industry in order to enable mass-market adoption of GaN-on-Si for power electronic applications like power supplies and motor drives. Allos says its technology fulfills the required low vertical leakage current of less than 0.1 µA/mm2 at 600V and at the same time is using growth conditions optimised to reach Allos’ high crystal quality without using carbon or other dopants to isolate the GaN.
Carbon doping became popular in the GaN-on-Si industry in recent years as it can be easily employed to increase isolation. Unfortunately, commonly used techniques to increase carbon levels are resulting in degradations in crystal quality. Allos shares the increasing concerns of industry experts that insufficient crystal quality can have severe negative side-effects on crucial performance and quality characteristics.
Consequently, Allos has worked on novel ways to accomplish very low leakage without compromising the crystal quality. The core of these innovations is growing high quality epilayers without doping. This is based on Allos’ patented and proprietary growth techniques and epi structures.
“Another concern many deciders are sharing with us is possible conflicts with incumbents who own strong IP around using carbon doping,” says Allos’ CMO Alexander Loesing. “Avoiding such conflicts is another benefit of not using carbon,” he adds.
In the recent customer project, the same epi structures were successfully grown in both tools with very good and reproducible results, according to the company. These include crystal quality XRD FWHM values of 330 arcsec for (002) and 420 arcsec for (102), threading dislocation densities of 2x108 cm-2, no meltback and no cracks on the entire wafer, tightly controlled bow of less than 30 µm for SEMI-standard thick wafers, mobility of 2000 cm2/Vs and sheet resistance of 350 Ω/sq.
A sheet resistance uniformity of 1.5 to 3 percent (std. dev.) was achieved, depending on the platform. Furthermore, all device-level requirements were met, in particular low vertical leakage of < 0.1 µA/mm2. Beside these technical parameters the economic factors like consumption, yield, reliability, maintenance and throughput for each epi process have also been analysed.
“Allos’ vast experience in installing its technology on many different reactor platforms and the robustness of our technology were essential in achieving the excellent results on the two hardware platforms in this project,” says Atsushi Nishikawa, CTO of Allos. He adds: “However, for the first time the same epiwafer structures were grown in two alternative reactor types in parallel and the epiwafers were processed and characterised under equal conditions in the same facility. Based on hundreds of runs this provides a unique performance and cost comparison of MOCVD reactors to the customer. It also gives them all the information they need for choosing their future production platform.”
Allos says that these strong results demonstrate that the choice of the right hardware is important but not paramount. In both reactors superb crystal quality and very low leakage without carbon doping were achieved, and in both reactors this was possible for interlayer and superlattice structures. “We often hear that there are demands to purchase new reactors to allow developers to achieve the desired epiwafer quality. Certainly, there are such cases but often the truth is that you don’t need to wait and the grass can already today become green regardless on which side of the river you are,” adds Nishikawa.
“Allos remains neutral on reactor platform decisions and guided by our customers’ requirements,” clarifies Loesing. “We are proud that we can deliver our technology in any MOCVD reactor the customer might already have, while being able to provide fact-based advice on reactor purchasing decisions in other cases.”