Effects of BEOL on self-heating and thermal coupling in SiGe multi-finger HBTs under real operating condition

• Effects of back-end-of-line on the self-heating and thermal coupling are estimated.
• A method to estimate the coupling under a real operating condition is proposed.
• Coupling factors are found to slightly increase with dissipated power.
• A closed-form formulation is proposed for the coupling factors in a multi-finger HBT.

Effects of the back-end-of-line layers up to metal-1 on the self-heating and thermal coupling in a multi-finger silicon germanium heterojunction bipolar transistor (SiGe MFT) are investigated. It is observed that the rise in junction temperature is overestimated if the BEOL effects are not considered. A new method for estimating the thermal coupling coefficients is proposed emulating the real operating condition. The proposed methodology demonstrates that the thermal coupling is increased in real operating condition and the estimated coupling coefficients are almost independent of the dissipated power. Further an empirical closed-form formulation is proposed for estimating the coupling coefficients analytically and for subsequently using in compact model simulation. The formulation is found to predict the coefficients quite accurately. Compact model simulations using the analytically obtained coupling coefficients show excellent model agreement with the static and dynamic 3D TCAD simulation data for junction temperature. Finally the model is validated against the measured data corresponding to an SiGe MFT fabricated using B55 technology from ST microelectronics.