Interfacial reaction pathways and kinetics during annealing of 111-textured Al-TiN bilayers: A synchrotron x-ray diffraction and transmission electron microscopy study

Growth of TiN layers in most diffusion-barrier applications is limited to d eposition temperatures T-s less than or similar to 500 degreesC. We have gr own polycrystalline. TiN layers, 160 nm thick with a N/Ti ratio of 1.02 +/- 0.03 and a 111 texture, at T-s = 450 degreesC on SiO2 by ultrahigh vacuum reactive magnetron sputter deposition in pure N-2. Al overlayers, 160 nm th ick with inherited 111 preferred orientation, were then deposited at T-s = 1OO degreesC without breaking vacuum. The as-deposited TiN layer is underde nse due to the low deposition temperature (T-s / T-m similar or equal to 0. 23 in which T-m is the melting point) resulting, in kinetically limited ada tom mobilities leading to atomic shadowing which, in turn, results in a col umnar microstructure with both inter- and intracolumnar voids. The Al overl ayer is fully dense. Synchrotron x-ray diffraction was used to follow inter facial reaction kinetics during postdeposition annealing of the 111-texture d AI/TiN bilayers as a function of time (t(a) = 12-1200s) and temperature ( T-a = 440-550 degreesC). Changes in-bilayer microstructure and microchemist ry were investigated using transmission electron microscopy (TEM) and scann ing TEM to obtain compositional maps of plan-view and cross-sectional speci mens. Interfacial reaction during annealing is initiated at the Al/TiN inte rface. Al diffuses rapidly into TiN voids during anneals at temperatures eq ual to or less than 480 degreesC. In contrast, anneals at higher temperatur es lead to the formation of a continuous nanocrystalline AIN layer which bl ocks Al penetration into TiN. At all annealing temperatures, Ti atoms relea sed during AIN formation react with Al to form tetragonal Al3Ti at the inte rface. Al3Ti exhibits a relatively planar growth front extending toward the Al free surface. Analyses of time-dependent x-ray diffraction peak intensi ties during isothermal annealing as a function of temperature show that Al3 Ti growth kinetics are, for the entire temperature range investigated, diff usion limited with an activation energy of 1.5 +/- 0.2 eV. (C) 2001 America n Vacuum Society.