The effect of bias-temperature stress on N[a.sup.+] incorporation into thin insulating films

• Published in: Analytical and bioanalytical chemistry Vol. 400; no. 3; p. 649
• Main Authors: Krivec, Stefan, Buchmayr, Michael, Detzel, Thomas, Froemling, Till, Fleig, Juergen, Hutter, Herbert
• Format: Journal Article
• Language: English
• Published: Springer 01.05.2011
• Subjects: Dielectric films; Thin films
• ISSN: 1618-2642; 1618-2650
• DOI: 10.1007/s00216-011-4686-z

The action of N[a.sup.+] 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 N[a.sup.+], provided via sodium triflate. Combining BT stress and ToF-SIMS depth profiling enables the unambiguous detection of N[a.sup.+], incorporated into the insulating material. The insulators of interest vary in their nitride content: Si[O.sub.2], Si[O.sub.x][N.sub.y], and S[i.sub.2][N.sub.4]. For Si[O.sub.4], it is shown that once a threshold BT stress is exceeded, N[a.sup.+] gets quantitatively incorporated from PMMA into the underlying insulator, finally accumulating at the Si[O.sub.2]/Si interface. A quantitative assessment by combination of Butler-Volmer kinetics with hopping dynamics reveals activation energies of [E.sub.a] =1.55- 2.04 eV for N[a.sup.+] transport in SiO2 with varying thickness. On the other hand, Si[O.sub.x][N.sub.y] and S[i.sub.3][N.sub.4] films show a different N[a.sup.+] incorporation characteristic in this type of experiment, which can be explained by the higher coordination of nitrogen and hence the reduced N[a.sup.+] permeability within these insulators. Keywords Mobile ions * Bias-temperature stress ToF-SIMS * Barrier layers