The SaSHa Project: A list of achievements:
WP2. Simulation.
• First of a kind Si/SiC power MOSFET and IGBT devices have been designed and optimised using simulations and newly developed TCAD models for Si on SiC bonded substrates. This was refined using the feedback from the first MOSFET process and test devices. Their proof of concept and a publication detailing their full characteristics will be forthcoming in 2018.
• One of the key objectives was to develop an immunity to single event effects up to a very challenging LET of 90 MeV. The device design realised by the project team involved a novel device structure with p-type shorts surrounding the n-channel, such that in the event of a heavy ion strike, the charge accumulated could be efficiently dissipated, avoiding latch up and permanent device destruction. This work was the subject of conference publication.
WP3. Materials.
• A novel radical activated Si-to-SiC wafer-bonding process was developed. Anneals performed to produce a permanent bond are performed at low-temperature, meaning that little strain is induced into the interface, reducing the density of interface charge. The final wafers produced by this method with material from a second SOI supplier proved the material to be of excellent quality, free of doping issues that were present earlier in the project. This has resulted in a patent, with publications to follow in 2018.
• The Si/SiC process is now scalable for future production.
WP4. Fabrication.
• A distinct challenge of this project was learning how to process the Si/SiC material for the first time. In particular, the combination of the unique material and the analysis of the Si device layer, which flipped from n-type to p-type, was the feature of an invited journal publication in the Materials Science in Semiconductor Processing journal.
• A Si/SiC LDMOSFET and LIGBT process was established. In each of the development cycles, this would have produced successfully working devices, but for the materials problems. As such, with a significant breakthrough in the Si/SiC material development having occured at the end of the project, these devices will be produced in 2018, with further publications to follow.
WP5. Reliability.
• Introduction of NO2 treatment into thick field oxide fabrication process provided very encouraging results in terms of radiation hardness. Radiation induced oxide charge values were extracted to be lower than values included in TCAD simulations to assure invariance of breakdown voltage under TID effect.
• First SEB tests on second generation devices were encouraging, revealing a device successfully operated at Vd=390 V under Xe ions (LET=62.5 MeV/cm2/s). This suggests that Si/SiC LDMOS devices merit further studies for rad-hard applications.
WP6. Dissemination
• In the second six months, a promotional video was produced and launched on the website, introducing the project and the concepts involved.
• Academic output from the project currently stands at one invited journal paper, two other journal publications and 6 conference publications, involving talks at ESA’s European Space Power Conference (ESPC), the European Silicon Carbide Conference (ECSCRM), Solid State Materials and Devices (SSDM) and High Temperature Electronics Network (HiTEN).
• The most significant results and papers are still to come, and several more conference and journal papers acknowledging the SaSHa project will be published in 2018 and 2019.
