Date of Award
Program or Major
Doctor of Philosophy
The effects of off-normal ionized vapor bombardment on the orientation and structure of off-normal sputter deposited TiAlN thin films has been investigated with the goal of better understanding the mechanistic pathways in ion beam assisted thin film growth for better control of film properties during deposition. The effects of incident angle for ion bombardment has been investigated as a potential variable during deposition and a comprehensive comparison to current theories of thin film orientation development has been made.
It is shown that for low levels of ion energies and rates, films develop (220) orientation with a near amorphous zone 1 (Z1) morphology for low ion incident angles. As the rates and energies of ions increases, (111) orientation and fibrous transition zone (ZT) morphology develops. It is also seen that as the angle of ion bombardment increases the threshold level for rates and energies of ions to cause (111) orientation and ZT morphologies is reduced. This change in orientation and morphology has been shown to change in-situ according to the level of ion bombardment making this transition a potential tool for developing microstructures within thin films.
Commonly accepted theories of thin film orientation have been investigated with respect to the development of (111) orientation for low energy ion beam assisted deposition including surface energy reduction, thermal influences, strain energy reduction, ion channeling, and ion damage anisotropy though such mechanisms were not successful in describing the development of (111) orientation. Atomic subplantation, generally regarded as a mechanism for bond formation in diamond-like carbon films, has also been investigated as a potential mechanism for orientation development. By treating the interaction of ions with the depositing film as a collision between ion and surface atom, the transition from (220) to (111) orientation is found to occur when the average energy transferred per atom normal to the surface in such a collision is ~ 12.5 eV/atom. Comparisons to simulations made using the SRIM/TRIM 2013 package show that though the subplantation threshold for Ti is ~ 7.5eV, the threshold for Al is ~ 12.5eV. Given such an agreement is is concluded that surface metal species subplantation is the mechanism for (111) development during the low energy ion beam assisted deposition of thin film.
Structure development has also been investigated and it has been shown that ion bombardment during thin film growth can be used to control columnar tilt in off-normal sputter deposition. The level of tilt is shown to be dependent on ion incidence angle and it was found that the average energy transferred normal to the substrate determined the level of tilt reduction for all angles. The mechanism for tilt reduction is attributed not to subplantation, but to the forward sputtering mechanism allowing for collision cascades to fill voids within the film during growth.
Better understanding the ability of ion bombardment during thin film growth to influence morphologies and microstructures will expand the current range and applicability of techniques for developing microstructures within thin films for application. Additionally, understanding mechanisms for orientation development during thin film growth will allow for a wider range of film properties to be developed for use in future applications.
Aliotta, Paul Vincent, "Mechanisms for Orientation in Low Energy Ion Beam Assisted TiAlN Thin Film Growth" (2016). Doctoral Dissertations. 1360.