Thermal conductivity of doped polysilicon layers

The thermal conductivities of doped polysilicon layers depend on grain size and on the concentration and type of dopant atoms. Previous studies showed that layer processing conditions strongly influence the thermal conductivi ty, but the effects of grain size and dopant concentration were not investi gated in detail. The current study provides thermal conductivity measuremen ts for low-pressure chemical-vapor deposition (LPCVD) polysilicon layers of thickness near 1 mum doped with boron and phosphorus at concentrations bet ween 2.0 x 10(18) cm(-3) and 4.1 x 10(19) cm(-3) for temperatures from 20 K to 320 K. The data show strongly reduced thermal conductivity values at al l temperatures compared to similarly doped single-crystal silicon layers, w hich indicates that grain boundary scattering dominates the thermal resista nce. A thermal conductivity model based on the Boltzmann transport equation reveals that phonon transmission through the grains is high, which account s for the large phonon mean free paths at low temperatures. Algebraic expre ssions relating thermal conductivity to grain size and dopant concentration are provided for room temperature. The present results are important for t he design of MEMS devices in which heat transfer in polysilicon is importan t.