Measurements of effective thermal conductivity for advanced interconnect structures with various composite low-k dielectrics

Accurate specification of design groundrules for interconnect systems requires knowledge of the thermal behavior of the systems. A key parameter that characterizes the thermal behavior is the thermal conductivity of the inter-level dielectric (ILD). In practical VLSI applications, the metal interconnects are fully embedded in a stacked, composite ILD media, which presents difficult challenges for the accurate determination of thermal conductivity. In this paper, we propose the concept of an "effective thermal conductivity" to model such complicated, composite media, and introduce a simple methodology to accurately measure effective and bulk thermal conductivities of various thin dielectric layers in integrated circuits. We present measured effective conductivities of several composite media, including various Cu/low-k dielectric configurations such as Cu/SiCOH, Cu/SiLK^®, Cu/fluorinated silicate glass (FSG), and a hybrid stack with Cu lines in SiLK^® and Cu vias in un-doped silicate glass (USG). Measurements were recorded in the temperature range from 30°C to 120°C using a unique combination of fully embedded Cu lines as heater/thermometers, wafer-level temperature vs. power (TVP) measurements, and the Harmon-Gill (H-G) quasi-analytical heat conduction model. The thermal conductivities of all the films studied here were observed to increase with rising substrate temperature.