The effect of bias-temperature stress on Na+ incorporation into thin insulating films

• Published in: Analytical and bioanalytical chemistry Vol. 400; no. 3; pp. 649 - 657
• Main Authors: Krivec, Stefan, Buchmayr, Michael, Detzel, Thomas, Froemling, Till, Fleig, Juergen, Hutter, Herbert
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.05.2011
• Subjects: Analytical Chemistry; Biochemistry; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Food Science; Insulators; Laboratory Medicine; Monitoring/Environmental Analysis; Original Paper; Polymethyl methacrylates; Silicon; Silicon dioxide; Silicon nitride; Stresses; Thin films; Transport; Bias-temperature stress; ToF-SIMS; Barrier layers; Mobile ions
• ISSN: 1618-2642; 1618-2650
• DOI: 10.1007/s00216-011-4686-z

The action of Na + incorporation into thin insulating films and transport therein under influence of a bias voltage and temperature (BT stress) is the subject of this work. Deposited onto highly n -doped Si wafers, the insulators get BT stressed and subsequently investigated by means of time-of-flight–secondary ion mass spectrometry (ToF-SIMS). A thin PMMA film, spin-coated onto the insulator, serves as host matrix for a defined amount of Na + , provided via sodium triflate. Combining BT stress and ToF-SIMS depth profiling enables the unambiguous detection of Na + , incorporated into the insulating material. The insulators of interest vary in their nitride content: SiO 2 , SiO x N y , and Si 3 N 4 . For SiO 2 , it is shown that once a threshold BT stress is exceeded, Na + gets quantitatively incorporated from PMMA into the underlying insulator, finally accumulating at the SiO 2 /Si interface. A quantitative assessment by combination of Butler–Volmer kinetics with hopping dynamics reveals activation energies of E a  = 1.55 − 2.04 eV for Na + transport in SiO 2 with varying thickness. On the other hand, SiO x N y and Si 3 N 4 films show a different Na + incorporation characteristic in this type of experiment, which can be explained by the higher coordination of nitrogen and hence the reduced Na + permeability within these insulators.