Aluminum/titanium nitride metal/diffusion-barrier systems: Interfacial reaction paths and kinetics as a function of microstructure and texture

Under “standard” industrial growth conditions, TiN layers have an underdense weak 111 texture containing a network of both inter- and intracolumnar porosity. Obtaining a dense TiN layer with complete 111 texture at low growth temperatures, as required for diffusion-barrier and many hard-coating applications, is a challenging growth kinetics problem. Moving toward a higher growth temperature favors the development of the 002 texture, rather than 111, since (002) is the low-energy surface for TiN. In addition, the use of ion irradiation to promote densification of 111-textured TiN leads to either 002 preferred orientation for low ion energies with high ion-to neutral ratios or very high in-plane compressive stress and mixed texture with higher energies and low ion-to-neutral ratios.; I have demonstrated, for the first time, the low-temperature growth of fully-dense polycrystalline TiN with complete 111 preferred orientation. This was achieved using a combination of highly-oriented thin 0002 Ti underlayers to provide orientation through texture inheritance (local epitaxy) and high-flux, low-energy, $N+2$ ion irradiation ($JN+2/JTi=14$, $EN+2\simeq 20$ eV) to provide enhanced adatom diffusion leading to densification. The preferred orientation of Al overlayers grown on dense fully-111-oriented TiN was also greatly enhanced due to texture inheritance. Al/TiN bilayers were then annealed at a constant ramp rate of 3°C-s−1 to 650°C and the interfacial reaction between Al and TiN was monitored by in-situ synchrotron x-ray diffraction measurements. As a reference point, Al₃Ti formation is not observed during 3°C-s −1 temperature-ramp annealing experiments until $T*a$ > 560°C for fully-dense completely-002-textured bilayers, compared with 450°C for 111-textured Al/underdense-TiN bilayers, deposited by conventional reactive sputter deposition and 610°C in bilayers with fully dense TiN exhibiting complete 111 preferred orientation. The Al overlayers are fully dense in all cases.; Based upon overall results, this research establishes that dense 111-textured Al/TiN bilayers exhibit much higher thermal stability than dense 002-textured A/TiN bilayers which are, in turn, more stable than the underdense Al/TiN bilayers currently used in industry. I have demonstrated that the primary reason for the enhancement in thermal stability is the higher structural quality of the interfacial reaction product AlN which serves as a blocking layer for further reactions. Therefore, optimizing the quality and structural integrity of the AlN layer through texture and microstructure control of the TiN diffusion barrier is key to enhancing the thermal stability of the Al/TiN interface.