Effect of Trench Isolation on the Self-heating Phenomenon in Advanced Radio Frequency SiGe Heterojunction Bipolar Transistor

This work aims to determine the effect of the trench isolation on the self-heating and electrical performances of SiGe heterojunction bipolar transistor (HBT), the considered structure corresponds to BiCMOS7G 0.25 µm technology. Advanced SiGe technologies are essentially achieved with downscaling of the device dimensions and developing its architecture to improve the radio frequency capacity of the device. An interesting development is the introduction of the Shallow and Deep Trench isolation (STI, DTI). These make it possible to reduce considerably the parasitic capacitances and to provide a flat topography after SiGe base epitaxy. The drawback of this is the temperature rise in the device through the self-heating phenomenon. This corresponds to the internal heat dissipation at the transistor junctions. To optimize this effect, we consider the non-isothermal energy balance (NEB) model based on the finite element method and two-dimensional thermal simulations. This model takes into account, particularly, the temperature of the carriers and the overshoot effects which occur in the range of dimensions of the considered devices. Analysis of the effect of trench isolation (shallow and deep trench isolation) on electrical performances of radio frequency SiGe HBT is then carried out considering thermal transfer of the carriers. The software SILVACO-TCAD coupling Athena module (technological process) and Atlas module were used to achieve electro-thermal modeling. We simulated the static gain, the dynamic characteristics (fT, fmax) and analyzed the heat distribution with and without trench isolation. It is shown that in these modern SiGe HBT structures with trench isolation and for high power regimes, the lattice temperature can greatly exceed 300 K and so the electrical performances, fT, fmax are significantly degraded. The obtained results agree with some published experimental data.