Experimental Cross-Plane Thermal Transport Characterization of BEOL Materials and Sensitivity to In-Plane Thermal Transport

This work reports the experimental measurements of cross-plane thermal conductivities of individual BEOL films, using 3ω technique with a central heater. Each thermal measurement requires two steps viz., the calibration of temperature coefficient of resistance (TCR) of the metallic thermistors followed by measurements of the AC temperature amplitude of the central heater as a function of the applied AC frequency. The collected thermal signals are then fitted against a 2D heat conduction model to determine the anisotropic thermal conductivities of the thin film. This work presents the effective cross-plane thermal conductivities of different thicknesses of isotropic silicon nitride (SiN) and tetraethyl orthosilicate (TEOS) samples and compares them with that reported in the literature. Moreover, this work presents an analytical sensitivity study to the in-plane thermal transport in both individual BEOL films and sandwiched layers of copper and BEOL dielectrics. In the analytical sensitivity study, the in-plane thermal conductivity of both individual dielectric film and metal layer sandwiched between two dielectric films, is changed by 10% and the corresponding percentage change in temperature amplitude is captured as a function of applied AC frequency, heater width, and cross-plane thermal conductivity of the dielectric film(s). Temperature amplitude sensitivity is shown to increase with increasing AC frequency, decreasing heater width, and decreasing cross-plane thermal conductivity of the dielectric layer for both single layer of dielectric film and sandwiched layers of metal and dielectric films. However, an understanding of both signal sensitivity and signal strength is required to position the in-plane thermistor optimally.