Copper germanide schottky contacts to silicon and electrically active defects in n-type 6H-SiC and 4H-SiC epitaxial layers

Abstract: Metallization for contacts to silicon devices presents amajor challenge as the linewidths are further reduced into thesub-micron regime. Copper germanide due to its relatively lowroom temperature resistivity ( ~ 10 µ? - cm) has beenexamined as a potential contact metallixation. In addition, dueto the growing interest in silicon carbide as a potentialwide-bandgap semiconductor candidate for high voltage, power,and frequency devices, a characterization of electricallyactive deep levels was conducted on as-grown and electron andion irradiated layers as such defects can influence theelectrical behaviour of active devices. N-type 6H- and 4H-SiChave been characterized by deep level transient spectroscopy(DLTS) in conjunction with MeV electron beam irradiation andkeV hydrogen and deuterium implantation. Intrinsic levels havebeen identified in both polytypes through an examination ofas-grown and irradiated samples.It is demonstrated that silicon outdiffusion into the coppergermanide contact causes an increase in the electricalresistivity. Additionally, deviation from ideal behaviour isobserved in current-voltage (IV) measurements an indicationthat this outdiffusion of silicon produces recombinationcenters primarily in the upper part of the bandgap near to thecontact-semiconductor interface. Additionally, copper germanideis found to be morphologically unstable during theamorphous-to-crystalline transformation. The high diffusivityof copper in amorphous germanium at temperatures as low as 200°C coupled with the independence of the barrier height onthe germanium fraction used during contact formation indicatesthat the interface between copper germanide and silicon issimilar to that of copper silicide and silicon.A number of electrically active deep levels have beencharacterized in both the 4H- and 6H-SiC polytypes. In 6H-SIC,many of the defects are found to be intrinsic as they areobserved to grow as a function of increasing irradiation dose.In contrast, as-grown 4H-SiC epitaxial layers, exhibit only asingle acceptor-like level at 0.70 eV below the conduction bandedge (Ec). After irradiation the level is not observed toincrease in concentration, but two new levels are found. Theselevels are found to be unstable at room temperature in contrastto the 6H-SiC defects. In 6H-SiC, the defect concentration isfound to limit the average carrier lifetime. Through the use ofthermal annealing, SIMS, and electron irradiation, a model oftheir Origin is proposed.Keywords:Deep level transient spectroscopy (DLTS),secondary ion mass spectrometry (SIMS), amorphous germanium,electron irradiation, ion irradiation, wide-bandgap