[en] Growth of TiN layers in most diffusion-barrier applications is limited to deposition temperatures T_s < or approx. 500 deg. C. We have grown polycrystalline TiN layers, 160 nm thick with a N/Ti ratio of 1.02±0.03 and a 111 texture, at T_s=450 deg. C on SiO₂ by ultrahigh vacuum reactive magnetron sputter deposition in pure N₂. Al overlayers, 160 nm thick with inherited 111 preferred orientation, were then deposited at T_s=100 deg. C without breaking vacuum. The as-deposited TiN layer is underdense due to the low deposition temperature (T_s/T_m≅0.23 in which T_m is the melting point) resulting in kinetically limited adatom mobilities leading to atomic shadowing which, in turn, results in a columnar microstructure with both inter- and intracolumnar voids. The Al overlayer is fully dense. Synchrotron x-ray diffraction was used to follow interfacial reaction kinetics during postdeposition annealing of the 111-textured Al/TiN bilayers as a function of time (t_a=12-1200 s) and temperature (T_a=440-550 deg. C). Changes in bilayer microstructure and microchemistry were investigated using transmission electron microscopy (TEM) and scanning TEM to obtain compositional maps of plan-view and cross-sectional specimens. Interfacial reaction during annealing is initiated at the Al/TiN interface. Al diffuses rapidly into TiN voids during anneals at temperatures ∼<480 deg. C. In contrast, anneals at higher temperatures lead to the formation of a continuous nanocrystalline AlN layer which blocks Al penetration into TiN. At all annealing temperatures, Ti atoms released during AlN formation react with Al to form tetragonal Al₃Ti at the interface. Al₃Ti exhibits a relatively planar growth front extending toward the Al free surface. Analyses of time-dependent x-ray diffraction peak intensities during isothermal annealing as a function of temperature show that Al₃Ti growth kinetics are, for the entire temperature range investigated, diffusion limited with an activation energy of 1.5±0.2 eV