Broadband Dielectric Spectroscopic Characterization of Thermal Stability of Low-k Dielectric Thin Films for Micro- and Nanoelectronic Applications

Abstract

In this paper, we discuss the use of broadband microwaves (MW) to characterize the thermal stability of organic and hybrid silicon-organic thin films meant for insulation applications in micro-and nanoelectronic devices. We take advantage of MW propagation characteristics to extract and examine the relationships between electrical properties and the chemistry of prototypical low-k materials. The impact of thermal anneal at modest temperatures is examined to shed light on the thermal-induced performance and reliability changes within the dielectric films. These changes are then correlated with the chemical changes in the films, and could provide basis for rational selection of organic dielectrics for integrated devices.Semiconductor manufacturers have been shrinking transistor size in integrated circuits (IC) to improve chip performance and energy efficiency. Consequently, interconnect delay has become a bottle neck for advanced very-large-scale integration (VLSI) systems, and new materials are needed for technology nodes beyond 22 nm to address this problem. 1 The introduction of emerging materials comes with a myriad of reliability issues arising primarily from the thermomechanical properties of the new materials. In contrast with conventional silicon oxides, low-and ultra-low dielectric constant (i.e., low-k and ULK) materials, with tunable dielectric constants, tend to have decreased thermal performance and diminished mechanical properties. [2][3][4] Due to the differences in the thermal, chemical and mechanical properties of these materials, stress can build up within the integrated systems that use these new materials, and may cause mechanical damage. The low-k dielectric materials have different coefficients of thermal expansion from the metals they clad, which leads to the formation of strong local tensile stresses and thermal issues, particularly if the device is thermally cycled in the broad processing temperature range of 25°C to 450°C. With many of the emerging dielectric materials, repeated thermal cycling results in molecular and structural changes, such that the lowest-lying dielectric layer may not have the same properties as the back-end-of line dielectrics of the same composition which have beenThis is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http:// creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. * Electrochemical Society Member. z yaw.obeng@nist.gov