High-resolution scanning electron microscopy study of sputtered nanolaminated Ti/TiN multilayers

This work presents the morphologic and structural study of nanolaminated Ti/TiN multilayers using high-resolution scanning electron microscopy (HR-SEM), coupled to x-ray reflectometry (XRR). The multilayers have been deposited by reactive rf-sputtering on silicon substrates. For large period thickness (lambda=40 nm, 10 periods), in XRR, the low number of interfaces makes the interference less structured. An experimental pattern with broad and weakly intense Braggs peaks is obtained, but is difficult to simulate. On the other hand, HR-SEM observation of cross sections gives excellent pictures of the multilayer, so that precise measurements of the thickness can be achieved: a 42 nm thick period is observed, formed with 17 nm of Ti and with 25 nm of TiN. For small (Ti+TiN) period thickness (lambda=2.5 nm, 120 periods), the XRR pattern exhibits intense and narrow Bragg peaks: the number of interfaces is sufficient to structure the interference and an intense signal is obtained. The best fit of simulation is obtained for a 2.6 nm thin period, made of 0.9 nm of Ti and 1.7 nm of TiN. No laminated structure has been observed by cross-section HR-SEM observation because its resolution (around 2 nm at 10 kV) is larger than the layer thickness in a period. High-resolution SEM and XRR are thus two complementary techniques for the routine characterization of multilayers.