Euro project seeks to solve SiC problems
European researchers have developed a breakthrough bulk-growth method for 3C-SiC - a cubic crystal polytype of SiC with higher electron mobility than existing dominant forms of SiC.
Currently hexagonal polytypes, called 4H and 6H, are the most widely-used forms of SiC. Because of this, Mikael Syväjärvi and colleagues from Linköping University in Sweden chose 6H as the seed crystal from which they produced high-purity 3C crystals, at a growth rate of 1 mm/hour.
Their work comes as part of an EU program called MANSiC that is hoping to ultimately make 3C-SiC electronic devices, avoiding a major drawback of hexagonal SiC polytypes.
That is: electron trapping at the interface with gate oxides, which presents a major obstacle to development of such important bipolar devices as MOSFETs.
The group reported a sublimation-epitaxy approach at ICSCRM in Otsu, Japan on October 17, in which they grew material up to 760 microns thick on 6H-on-axis substrates.
3C-SiC is inherently free of micropipes "“ crystal imperfections that plague the hexagonal polytypes "“ and according to Syväjärvi the photoluminescence of his material shows “striking purity”. However Gabriel Ferro, MANSiC s co-ordinator, emphasizes that the material is still to be fully characterized by other partners in the collaboration.
“This is very exciting, it demonstrates that really high quality 3C-SiC can be produced at high growth rate,” said Rositza Yakimova, who is leading Linköping's part of the program.
MANSiC is a €3.3 million ($4.7 million) four-year partnership between nine academic institutions and two companies.
Other than making devices based on the material, its commercial goals include providing good quality seed 3C-SiC, producing boules and slicing wafers from them. The higher the quality of these materials, the easier it should be to make the final devices.
“The idea is to develop a complete line of 3C-SiC from beginning to end,” said Ferro.
Growing a crystal network
Currently, nobody sells 3C-SiC, although in the past Hoya Corporation made an unsuccessful venture into the arena.
“They announced in 2001 that they were selling commercial wafers, but only a few, with bad quality,” explained Ferro. “Then they stopped. Presently there are no more providers of 3C.”
A large proportion of MANSiC s work is based upon the vapor-liquid-solid (VLS) 3C-SiC growth technique Ferro has developed at the University of Lyon. He suggests that Syväjärvi s crystal quality could be improved still further by using a VLS-grown 3C seed crystal.
Another bulk growth technique, continuous-feed physical vapor transport or CF-PVT, performed at Grenoble Institute of Technology, will also use Lyon s seeds.
All three growth methods must take place at relatively low temperatures, as 3C-SiC is only stable below 2000°C "“ whereas other forms of SiC growth are performed at over 2200°C.
French firm NovaSiC will apply its SiC polishing expertise on the resulting bulk crystals on both sides.
The Institute for Microelectronics and Microsystems in Italy and the Centro Nacional de Microelectronica in Spain will be responsible for this ultimate stage of the project - taking 3C-SiC wafers and using them to fabricate devices such as MESFETs and HEMTs.
