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6 April 2018

Imec and Qromis present p-GaN HEMTs on 200mm CTE-matched substrates

© Semiconductor Today Magazine / Juno PublishiPicture: Disco’s DAL7440 KABRA laser saw.

Nanoelectronics and photovoltaics research centre imec of Leuven, Belgium and fabless firm Qromis Inc of Santa Clara, CA, USA (spun off from Micron Technology in March 2015) have developed high-performance enhancement-mode p-GaN power devices on 200mm engineered coefficient of thermal expansion (CTE)-matched substrates, processed on imec’s silicon pilot line. The substrates are offered by Qromis as commercial 200mm QST substrates as part of its patented product portfolio. The results are being presented at the CS International conference in Brussels, Belgium (10-11 April).

Gallium nitride on silicon (GaN-on-Si) technology is currently the industry-standard platform for commercial GaN power switching devices for wafer diameters up to 150mm/6-inches. Imec has developed GaN-on-Si power technology for 200mm/8-inch wafers and qualified enhancement-mode high-electron-mobility transistor (HEMT) and Schottky diode power devices for 100V, 200V and 650V operating voltage ranges, paving the way to high-volume manufacturing applications. However, for applications beyond 650V such as electric cars and renewable energy, it has become difficult to further increase the buffer thickness on 200mm wafers to the levels required for higher breakdown and low leakage levels, because of the mismatch in CTE between the GaN/AlGaN epitaxial layers and the silicon substrate. One can envisage using thicker silicon substrates to keep wafer warp and bow under control for 900V and 1200V applications, but practice has shown that, for these higher voltage ranges, mechanical strength is a concern in high-volume manufacturing, and the ever thicker wafers can cause compatibility issues in wafer handling in some processing tools.

Carefully engineered and CMOS-fab-friendly QST substrates with a CTE-matched core (with a thermal expansion that very closely matches the thermal expansion of the GaN/AlGaN epitaxial layers) are paving the way to 900-1200V buffers and beyond, on a standard semi-spec thickness 200mm substrate. Moreover, QST substrates open perspectives for very thick GaN buffers, including the realization of free-standing and very low-dislocation-density GaN substrates by >100┬Ám-thick fast-growth epitaxial layers. These unique features enable the long-awaited commercial vertical GaN power switches and rectifiers, suitable for high-voltage and high-current applications presently dominated by silicon IGBTs and silicon carbide (SiC) power FETs and diodes.

“QST is revolutionizing GaN technologies and businesses for 200mm and 300mm platforms,” claims Qromis’ president & CEO Cem Basceri. “I am very pleased to see the successful demonstration of high-performance GaN power devices by stacking leading-edge technologies from Qromis, imec and Aixtron,” he adds.

In this specific collaboration, imec and Qromis developed enhancement-mode p-GaN power-device-specific GaN epitaxial layers on 200mm QST substrates, with buffers grown in Aixtron’s G5+ C 200mm high-volume manufacturing metal-organic chemical vapor deposition (MOCVD) system. Imec then ported its p-GaN enhancement-mode power device technology to the 200mm GaN-on-QST substrates in their silicon pilot line and demonstrated high-performance power devices with a threshold voltage of 2.8V.

“The engineered QST substrates from Qromis facilitated a seamless porting of our process of reference from thick GaN-on-Si substrates to standard-thickness GaN-on-QST substrates using the AIX G5+ C system, in a joint effort of imec, Qromis and Aixtron,” says Stefaan Decoutere, program director for GaN power technology at imec. The careful selection of the material for the core of the substrates, and the development of the light-blocking wrapping layers resulted in fab-compatible standard-thickness substrates and first-time-right processing of the power devices.

Imec acknowledges funding from the Electronic Component Systems for European Leadership Joint Undertaking under grant agreement No 662133, designated as PowerBase.

See related items:

Kyma demos 200mm GaN HVPE on QROMIS’ MOCVD GaN-on-QST wafers

Kyma and Quora partner on GaN substrate materials

Tags: GaN-on-Si Imec

Visit: www.imec.be

Visit: www.qromis.com

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