Amorphous silicon carbide nitride layer as an alternative to a disordered silicon surface to suppress RF/microwave losses

•An alternative thermally-stable RF passivation method is presented.•The method relies on placing the surface currents in a high resistive region.•The lowest RF losses are achieved for the thin nitrated amorphous SiC layers.•The nitridation changed the SiC surface from an insulating to a conductive layer.•The presence of 10% SiCN and 90% SiC compounds suggests n-type doping by nitrogen.

A large number of dielectric layer stacks of different combinations of SiC, SiN and SiO2 are studied with respect to their ability to suppress surface-channel currents that give radio-frequency (RF) and microwave losses in coplanar waveguides (CPWs), integrated on high-resistivity silicon (HRS) substrates. Measurements are performed of the Space Charge Layer sheet resistances (SCL-RSH) and the RF losses in CPWs. The lowest, bias-independent losses of 1.6 dB/cm are achieved on thin Low-Pressure Chemical Vapor Deposition (LPCVD)-nitrated Plasma-Enhanced Chemical Vapor Deposition (PECVD) amorphous (αα-) SiC layers, for which the surface currents are conducted away from the crystalline HRS into the αα-SiC:N. The nitridation appears to have changed the surface of the SiC from an insulating to a highly resistive layer, where the presence of SiC:N compounds suggests a possible n-doping by nitrogen. The αα-SiC/SiC:N layer is known to remain stable during high-temperature thermal treatments typically used for dopant activation as indicated previously.

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