Modulating crack propagation in a multilayer stack with a super-layer
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Quantitative characterization of interface adhesion and fracture properties of thin film materials is of fundamental and technological interests in modern technologies. Sandwich beam specimens used in fracture mechanics techniques, such as four-point bending and double-cantilever beam have been widely adopted, including the semiconductor industry. In this work, we highlight some of the challenges that these techniques are facing in characterizing ever thinner films and tough interfaces, and propose a simple strategy to address these challenges by engineering the stack structure of the specimen. We show that crack propagation in a multilayer stack can be controlled using a super-layer (SL) structure, and the dependence of the cracking behavior on the thickness and mechanical properties of the SL is studied. The effectiveness of the SL strategy is demonstrated for a range of technologically important material systems used in the on-chip interconnects of modern microprocessors, which represents one promising path to extend the industry-standard techniques to meet future characterization needs.
I. INTRODUCTION
In relentless pursuit of Moore’s law, every new technology node has seen a continued downscaling of device dimensions accompanied by a drastic increase of the interface to volume ratio in the physical structures of microelectronics devices.1–3 Interface engineering and quality control have become increasingly critical with the adoption of more complicated architecture and new materials to improve performance, manufacture yield, and reliability. Quantitative characterization of the fracture resistance of critical component materials and their interfaces has become an integral part of technology development for the successful design and fabrication of robust integrated circuits to survive silicon processes, packaging and assembly, as well as reliability tests.4–9 In addition to their relevance on the mechanical reliability, interfacial adhesion properties are known to correlate well with important reliability parameters such as electromigration resistance of copper metallization.10,11 By characterizing the adhesion properties of copper interfaces using process-simulated film stack, valuable early learning can be inferred before fully integrated structures become available for direct electromigration test. Nevertheless, the introduction of new and extremely scaled material systems poses numerous challenges for characterizing their interface and fracture properties. Conventional techniques that were developed using relatively thick film stacks are becoming increasingly difficult to Contributing Editor: George M. Pharr a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.252 J. Mater. Res., Vol. 30, No. 20, Oct 28, 2015
apply as the film thickness continues to scale, as to be discussed later. From the perspective of process development, however, it is generally desirable that material properties be characterized at the relevant length scale instead of testing thicker version of the
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