Low-k dielectrics have been incorporated into advanced computer chip technologies as a part of the continuous effort to improve computer chip performance. One drawback associated with the implementation of low-k dielectrics is the large leakage current which conducts through the material, relative to silica. Another drawback is that the breakdown voltage of low-k dielectrics is low, relative to silica . This low breakdown voltage makes accurate reliability assessment of the failure mode time dependent dielectric breakdown (TDDB) in low-k dielectrics critical for the successful implementation of these materials. The accuracy with which one can assess this reliability is currently a topic of debate.
These material drawbacks have motivated the present work which aims both to contribute to the understanding of electronic conduction mechanisms in low-k dielectrics, and to improve the ability to experimentally characterize changes which occur within the material prior to TDDB failure. What follows is a study of the influence of an applied magnetic field on the conductivity of a low-k dielectric, or in other words, a study of the material’s magnetoresistance.
This study shows that low-k dielectrics used as intra-level dielectrics exhibit a relatively large negative magnetoresistance effect (∼2%) at room temperature and with modest applied magnetic fields (∼100 Oe). The magnetoresistance is attributed to the spin dependence of trapping electrons from the conduction band into localized electronic sites. Mixing of two-electron spin states via interactions between electron spins and the the spins of hydrogen nuclei is suppressed by an applied magnetic field. As a result, the rate of trapping is reduced, and the conductivity of the material increases.
This study further demonstrates that the magnitude of the magnetoresistance changes as a function of time subjected to electrical bias and temperature stress. The rate that the magnetoresistance changes correlates to the intensity with which the material was stressed. It is postulated that the change in magnetoresistance which occurs as a result of bias temperature stress could be used as an alias for measuring the degradation which contributes to TDDB.
Finally, it is shown that the magnetoresistance behavior is non-monotonic. That is, for small values of applied magnetic field (∼2 Oe) the conductivity initially decreases, while for further increase of the magnetic field the conductivity increases to a saturation. The non-monotonic behavior is consistently described in the context of competing spin mixing mechanisms.
|Advisor:||Lloyd, James R.|
|Commitee:||Dunn, Kathleen, LaBella, Vincent, Rosenberg, Robert, Witt, Christian|
|School:||State University of New York at Albany|
|Department:||Nanoscale Science and Engineering-Nanoscale Science|
|School Location:||United States -- New York|
|Source:||DAI-B 77/09(E), Dissertation Abstracts International|
|Subjects:||Nanoscience, Theoretical physics, Materials science|
|Keywords:||Low-k dielectrics, Magnetoresistance, Reliability, Time dependent dielectric breakdown|
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