Effect Of Different Annealing Treatment Methods On The Ni/SiC Contact Interface Properties

Silicon carbide (SiC) is one of the key materials of the third generation semiconductors. In order to exploit the potential of SiC in the fields of high temperature, high power, and high frequency electronic devices, one of the most important issues is the preparation of thermodynamically stable ohmic contacts with low specific contact resistance. Up to date, the preparation of ohmic contact remains one of the most important and most active research directions of SiC materials.In this paper, we deposited Ni on the Si-face of n-type4H-SiC by magnetron sputtering, and patterned the Ni film to form cathode pads via a metal mask. Then, one group of samples were annealed by traditional rapid thermal annealing (RTA) of850～1050℃, the other group of samples were processed with pulsed ultraviolet laser (LSA), of which the wavelength is248nm, the frequency is30Hz, the pulse width is2.5ns, and the single pulse energy varies from200mJ to300mJ. At last, all the samples were tested or analyzed via HMS, OM, XRD, Raman spectra, SEM, AFM, EDS, TEM, to get their information of Ⅰ-Ⅴ curves, macroscopic surface morphology, structure and chemical phase, microscopic surface morphology, element composition, and microscopic cross section morphology.The tests and analyses showed that both thermal treatments can help forming ohmic contacts. We also came to a conclusion as follows:the Ni film of RTA sample shrank badly thus formed tiny balls on the surface, while surface of LSA sample remained relatively smooth. The RMS values of surface roughness of the Ni films of as-deposited, RTA and LSA samples were8.65nm,91.3nm and17.5nm, respectively. The Ni/SiC interface of RTA sample was corroded badly, the RMS value of SiC wafer surface roughness at the interface was21nm; Si can be found in the whole Ni film, indicating an overall consumption of Ni to react with Si forming NiSi compounds; C, which do not react with Ni, clustered to the average size of40A, and gathered approximately as a layer located about20～30nm off the Ni/SiC interface. The Ni/SiC interface of LSA sample was relatively smooth, the RMS value of SiC wafer surface roughness at the interface was9.67nm; a small quantity of Ni diffused into the SiC wafer, forming lots of ternary phase diffusion zones of about tens of nanometers deep into the SiC wafer, in which C, Si, Ni had distributed uniformly; the average size of C clusters was12A and no obvious C enriched zone was found while no Si nor C was found diffused into the Ni film.Contrasted with RTA, ohmic contacts prepared by LSA have obvious advantages in many aspects, such as cathode surface morphology, interface morphology, uniformity of components in cathode films, et al. What’s more, the time consumed in LSA process is much shorter than that of RTA. All the issues mentioned above made LSA a promising method of thermal treatment in preparation of ohmic contacts.