Crystal clear semi-conductor research
The importance of silicon carbide in the electronics industry cannot be overstated. Silicon carbide (SiC) offers the potential for dramatic improvements in the efficiency and range of applications for power electronics and electronic sensor technologies. It occurs naturally but since its manufacture over one hundred years ago, it has rocketed in importance to play a crucial role in energy and transport technologies set to continue this century. There are several different crystalline forms. The polymorph most used today is the hexagonal crystal but major leaps in realising the full potential of SiC could be made if the cubic or beta form were used. The main aim of the SOLSIC project then was to develop bulk cubic crystals and wafers to avail of the potential in metal-oxide semiconductor (MOS) technology. Researchers at CEA, Grenoble in France examined protocols to manufacture the beta form of the semiconductor material. Based on an industrial set-up from a partner Cyberstar, crystals were grown in a silicon float zone. This is a high-purity alternative because there is a molten zone where impurities are more soluble than in the crystal. The variables in the crystal growth environment were compute controlled and included solid and liquid density, crystal shape, growth speed, rotation speed, cooling duration and atmosphere. The system was heated in the two megahertz range. An innovation was that there was access to the core zone where crystallisation takes place. Upper and lower units can rotate separately at a very low rate and rotation strategies can be varied to control the forced convection in the silicon. One extra benefit is that the system can be used for other crystals where a solvent is necessary. These include titanium carbide, important for its resistant industrial cutting ability, and zirconium carbide used for the same purpose as well as a coating for uranium fuel in the nuclear industry. Silicon carbide has revolutionised the way we live. With advances in crystal production, it appears that this progression is set to continue.
