LAST POWER (Large Area silicon-carbide Substrates and heTeroepitaxial GaN for POWER device applications), the European Union-sponsored program aimed at developing a cost-effective and reliable technology for power electronics, has announced its three-year program achievements, targeted at placing Europe at the forefront of research and the commercialization of energy-efficient devices for industrial and automotive applications, consumer electronics, renewable-energy conversion systems, and telecoms.
Launched in April 2010 by the European Nanoelectronics Initiative Advisory Council (ENIAC) Joint Undertaking (JU), a public-private partnership in nanoelectronics, LAST POWER links private companies, universities and public research centers working in the field of wide-bandgap semiconductors based on silicon carbide (SiC) and gallium nitride (GaN). The consortium members are project coordinator STMicroelectronics (Italy), LPE/ETC (Italy), Institute for Microelectronics and Microsystems of the National Research Council –IMM-CNR (Italy), Foundation for Research & Technology-Hellas - FORTH (Greece), NOVASiC (France), Consorzio Catania Ricerche -CCR (Italy), Institute of High Pressure Physics - Unipress (Poland), Università della Calabria (Italy), SiCrystal (Germany), SEPS Technologies (Sweden), SenSiC (Sweden), Acreo (Sweden), Aristotle University of Thessaloniki - AUTH (Greece).
The main achievements in SiC-related efforts were based on the demonstration by SiCrystal of large-area 4H-SiC substrates, 150mm in diameter, with a cut-off angle of 2°-off-axis. The material quality, both in crystal structure and surface roughness, is comparable with the standard 100mm 4°-off-axis material available at the beginning of the project. At LPE/ETC, the substrates have been used for epitaxial growth of moderately doped epi-layers suitable for the fabrication of 600-1200V junction barrier Schottky (JBS) diodes and MOSFETs, owing to the development of a novel chemical vapor deposition (CVD) reactor for growth on large-area (150mm) 4H-SiC.
The epilayer quality enabled the fabrication of junction barrier Schottky diodes in the industrial production line at STMicroelectronics. Characterization of the first lots showed electrical performance comparable with state-of-the-art 4°-off-axis material. In this context, the fundamental technological step was the chemical mechanical polishing (CMP) process - StepSiC reclamation and planarization - implemented at NOVASiC, which is a key issue both for the preparation of the substrates before epi growth and for the sub-nanometric control of the surface roughness of the device’s active layers. Within the project, the same firm also developed epitaxial growth capability for both MOSFET and JFET devices.
Additional research activities on SiO2/SiC interfaces have been carried out in collaboration with ST and IMM-CNR to improve the channel mobility in 4H-SiC MOSFETs.
Finally, novel technological modules for high-temperature 4H-SiC JFETs and MOSFETs have been developed in collaboration between Acreo and FORTH, with the support of CCR for the study of molding compounds and ‘lead-free’ die-attach materials for reliable packaging solutions.
The LAST POWER project also researched the use of GaN-based devices in power-electronics applications. In particular, ST developed AlGaN/GaN HEMTs epi structures grown on 150mm silicon substrates, reaching a target of 3mm thickness and 200V breakdown voltage. LAST POWER worked with IMM-CNR, Unipress and ST to develop the technological steps for normally-off AlGaN/GaN HEMTs with a ‘gold-free’ approach. The process modules are fully compatible with the device fabrication flow-chart set in the ST production line and are being integrated for HEMT fabrication.
The interaction between the project partners working on material growth and device technology has enabled key steps towards the monolithic integration of GaN-based and SiC-based devices, it is reckoned, as both technologies have been proven on 2°-off-axis 4H-SiC substrates.
