Investigation Of The Relationship Between Hydrogen-Nitrogen Mixed Plasma Treatment And TiC/n-type 4H-SiC Ohmic Contacts

As a third generation of semiconductor,SiC has been known to be an ideal material in fabrication of high temperature, high voltage, high frequency high power electronic devices because of its properties such as wide band gap, high critical electric field, high carrier saturation drift velocity and high thermal conductivity, Low resistance and thermal stable ohmic contact is the key to the use of SiC devices. Ohmic contact is related to both the type of the electrode and semiconductor surface states. Combined with ECR nitrogen-hydrogen surface treatment technology, this paper chose TiC as the electrode material and research the relationship between surface treatment and the quality of ohmic contact.TiC has low resistance and stable chemical properties, and its work function is 3.94 eV, lower than 4H-SiC,so it’s the ideal material of ohmic contacts electrode. This work uses different ratios of nitrogen-hydrogen plasma and treat the surface of SiC, sputter TiC on the surface and lift-off the redundant metal. Annealing was performed at different temperatures and the electric test was done afterwards, dot circle transmission line model was used to calculate the specific contact resistivity. The lowest contact resistivity is obtained after 400 ℃ annealing 。 This phenomenon proved TiC/SiC ohmic contacts don’t need high temperature annealing.The specific contact resistivity of the sample treated after NHPT(Hydrogen-Nitrogen Plasma treatment) is much lower than the one didn’t, as the increase of N2 flow, the resistivity decreased, the lowest resistivity is obtained when the rate of H2 and N2 flow is 60 sccm and 12 sccm,and the value is 1.34×10-5 Ω·cm2.At the same time, the increase of N2 flow rate helps reduce surface treatment’s sensitiveness to the treat time and optimize the structure of the surface,the addition of N makes the experiment more controllable and relieable.This experiment used NHPT on the SiC surface and fabricated TiC/SiC ohmic contacts, and the advantage of this method is obvious:avoiding high temperature annealing, ohmic behavior of the contact improved, this experiment makes great sense in improving thermal stability and avoiding high temperature degradation.