Advanced thermal resistance simulation of SiGe HBTs including backend cooling effect

3-D thermal analyses of state-of-the-art silicon-germanium heterojunction bipolar transistors are performed with the aim of improving the simulation accuracy with respect to conventional approaches. Toward this goal, a nonuniform heat source obtained from calibrated electrical simulation results is considered, and thermal conductivity variations due to germanium mole fraction, doping profile, and thin-layer effects are accounted for. The cooling action of the backend metallization due to the upward heat flow, which is commonly disregarded, is then quantified for each layer.