16 February 2017

ALLOS' doping-free 600V HEMT epi technology running on both Aixtron G5 and Veeco K465i at customer

Technology engineering & licensing firm ALLOS Semiconductors GmbH of Dresden, Germany says the latest generation of its gallium nitride on silicon (GaN-on-Si) process has achieved excellent isolation without doping. Applying this technology, ALLOS recently concluded the development of customized epitaxial structures with very low leakage for a power electronics customer. The epiwafer growth processes were established in the customer's Aixtron G5 and Veeco K465i metal-organic chemical vapor deposition (MOCVD) reactors so, besides providing the desired epiwafer and device performance, the project has also allowed a unique performance and cost comparison of the two major reactor platforms used in the GaN-on-Si industry.

ALLOS says that, since starting its GaN-on-Si epi technology business in 2014, it has invested heavily in technology development and has achieved several breakthroughs. Key elements are very low leakage currents, superior crystal quality, and a focus on manufacturability.

Low leakage is seen as a prerequisite for mass-market adoption of GaN-on-Si for power electronic applications (such as power supplies and motor drives). ALLOS says that its technology fulfills the required low vertical leakage current of less than 0.1µA/mm2 at 600V, while using growth conditions optimized to achieve ALLOS' 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 result in degradation in crystal quality, which can have severe negative side-effects on crucial performance and quality characteristics, notes ALLOS. Consequently, the firm has worked on novel ways to accomplish very low leakage without compromising crystal quality. The core of these innovations is growing extremely high-quality epilayers without doping, 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 chief marketing officer Alexander Loesing. "Avoiding such conflicts is another benefit of not using carbon."

In parallel, ALLOS continues to implement its 'design for manufacturability' strategy. Features relevant for the epiwafer making process and for using these epiwafers for device production in existing silicon-based processing lines are taken into account and are optimized according to market requirements. ALLOS claims that, using this technology, its customers can produce cost-efficient GaN-on-Si epiwafers of up to 200mm diameter that meet the SEMI-standard specification for thickness and bow, are very reliable in device making, and show excellent electrical performance.

ALLOS' latest technology generation was recently transferred to and adapted for a power electronics customer. The project requirements included developing customized interlayer and superlattice-based epi structures with up to 7µm total thickness for 150mm and 200mm wafer diameters. Additional project objectives included specified device-level parameters and establishing the epi process in both the Aixtron G5 and Veeco K465i reactors used for GaN-on-Si by the customer (these two most widely used reactors types in the industry). The same epi structures were grown in both tools, with good, reproducible results, says ALLOS. Differences between results in the two reactors in terms of epiwafer characteristics and device performance were small, and each reactor type showed merits and demerits, the firm comments.

Regardless of hardware and handling differences, ALLOS achieved what are claimed to be industry-leading results in both reactor types. These include crystal quality x-ray diffraction (XRD) full width at half maximum (FWHM) values of 330 arcsec for (002) and 420 arcsec for (102), threading dislocation densities of 2x108cm-2, no meltback and no cracks on the entire wafer, tightly controlled bow of less than 30µm for SEMI-standard thick wafers, mobility of 2000cm2/Vs and sheet resistance of 350Ω/sq. A sheet resistance uniformity of 1.5-3% (standard deviation) was achieved, depending on the platform. All device-level requirements were met, in particular low vertical leakage of <0.1µA/mm2. Beside these technical parameters, economic factors such as 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 chief technology officer Dr Atsushi Nishikawa. "However, for the first time the same epiwafer structures were grown in two alternative reactor types in parallel, and the epiwafers were processed and characterized 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," he adds.

The results demonstrate that the choice of the right hardware is important but not paramount, says ALLOS. In both reactors, superb crystal quality and very low leakage without carbon doping were achieved, and this was possible for both interlayer and superlattice structures. "We often hear that there are demands to purchase new reactors to allow developers to achieve the desired epiwafer quality," says Nishikawa. "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 of which side of the river you are on," he adds.

"ALLOS remains neutral on reactor platform decisions and guided by our customers' requirements," states Loesing. "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," he adds.

See related items:

ALLOS transfers GaN-on-Si power semiconductor epi technology to customer

Transfer of ALLOS' 150 and 200mm GaN-on-Si epi technology to Epistar concluded in under 6 months

Tags: Azzurro GaN-on-Si

Visit: www.allos-semiconductors.com