Physics of defect generation in high-k and ferroelectric materials and their reliability implications for advanced electronic devices

Muhammad Masuduzzaman, Purdue University

Abstract

As the SiO2-based classical transistor reaches its scaling limit, a broad range of alternate dielectric materials are being explored for classical CMOS as well as other emerging technologies. These include high-k materials for gate dielectrics; low-k materials for interlayers; extreme high-k, ferroelectric materials for memory, embedded capacitor, and transistor applications; transparent conducting oxides for solar cells; metal-oxide phase changing materials for high speed transistor applications, etc. Despite their attractive features, poor reliability has been a persistent concern and threatens the commercial adoption of these dielectrics. The purpose of the thesis is to develop a fundamental (microscopic) understanding of these macroscopic reliability phenomena in a systematic way. In this regard, our extensive experimental approach and a critical analysis revealed many of the underlying physics of damage mechanisms of such new materials and structures. For example, we found a novel hot atom induced defect generation mechanism in ferroelectrics, analogous to the electronic hot carrier damage. We also showed how the defect kinetics at the grain boundaries in polycrystalline oxides is responsible for the anomalous large distributions of breakdown times. For the first time, we observed a push-pull oscillation of soft breakdown within series capacitors, and interpreted its role in improving system reliability by appropriately modifying the classical theories. We also developed a set of characterization tools for high-k dielectrics to explore the kinetics of defect generation as a primary cause of dielectric degradation. Among the tools developed, our generalized charge pumping can probe energy location of bulk defects, the SILC transient can isolate defect generation from pre-existing defects, etc. Using the above tools, we not only located the defect regions, but also identified a surprising universality in the defect generation dynamics in high-k dielectrics from diverse sources. Finally, we provided specific guidelines to improve reliability in many cases, including the soft-switching approach to reduce hot-atom damage in ferroelectrics for reliable future device applications. The fundamental understanding of defect dynamics made possible by this thesis research opens up opportunities to improve reliability dramatically for a broad class of dielectric films relevant for classical and emerging technologies.

Degree

Ph.D.

Advisors

Alam, Purdue University.

Subject Area

Electrical engineering|Nanotechnology

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