Microelectronics Reliability

Determination of the thermal conductivity of composite low-k dielectrics for advanced interconnect structures

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The increasing use of low-k dielectrics as inter/intralevel insulation materials and the aggressive scaling of advanced interconnects generate new challenges for thermal and electromigration (EM) solutions. Accurate specification of design rules and EM reliability modeling for interconnect systems require knowledge of the thermal behavior of the systems. A key parameter that characterizes thermal behavior is the thermal conductivity of the inter/intralevel dielectric (ILD). In practical, very large scale integration (VLSI) applications, the metal interconnects are fully embedded in a stacked, composite ILD media, which present challenges for the accurate determination of thermal conductivity. This article uses the "effective thermal conductivity" concept to model such complicated composite media, and to introduce a simple methodology that accurately measures effective and bulk thermal conductivities of various thin dielectric layers in integrated circuits (IC). We present measured effective conductivities of several composite media, including various Cu/low-k dielectric configurations: Cu/SiCOH, Cu/spin-on organic dielectric (SOD), Cu/fluorinated silicate glass (FSG), and a hybrid stack with Cu lines in SOD and Cu vias in undoped silicate glass (USG). Recorded temperature measurements ranged from 30 to 120 °C using a unique combination of fully embedded Cu lines as heater/thermometers, wafer-level temperature-voltage-power measurements, and the Harmon-Gill (H-G) quasi-analytical heat conduction model. We demonstrated optimal agreement between an experimental method and a finite element simulation, which suggests that this unique technique yields accurate and simple thermal conductivity measurements for complicated systems. Our observations show that thermal conductivities of all films in this study increased with rising substrate temperature. © 2005 Elsevier Ltd. All rights reserved.