Simulation of Nano-Scale Multi-Fingered PD/SOI MOSFETs Using the Boltzmann Transport Equation

Abstract

This work uses a gray, a semi-gray, and a non-gray model based on the Boltzmann Transport Equation (BTE) in the relaxation time approximation to compute the temperature distribution in a nano-scale multi-finger, PD/SOI nMOSFET with copper interconnects. The BTE models were successfully incorporated in CFD software, Fluent 6.1. The BTE is used in the device layer, whereas in other regions of the device, such as the silicon substrate, buried oxide, gate oxide, poly-gate, and metal interconnects, the Fourier heat conduction equation is employed. The BTE is coupled with the heat conduction equation at the interfaces using the diffuse mismatch model (DMM). Heat dissipation in the channel region of the FET and in the metal lines of the device is specified based on circuit simulations for a clock buffer used in a microprocessor. The computed results for the temperature distribution in the multi-finger NFET using the different approaches are compared with simulations that employ the classical heat conduction equation in the entire domain. The comparisons demonstrate that the broad temperature fields in the transistor are primarily determined by the overall thermal resistances due to the various device structures; channel temperature, however, is determined in large part by sub-continuum effects. The need for direct measurements of channel temperature rather indirect gate temperature measurements is pointed out as well.