In Situ Synchrotron X‐Ray Diffraction Analysis of Phase Transformation in Epitaxial Metastable hcp Nickel Thin Films, Prepared via Plasma‐Enhanced Atomic Layer Deposition.

Ultrathin metal films have a wide variety of applications, especially in microelectronics. A key method to deposit these films is plasma‐enhanced atomic layer deposition (PEALD), which is known for its ability to deposit thin films conformally and at relatively low temperatures. Building on the recent work, an improved recipe is reported on for the development of nickel PEALD technology, through which fully epitaxial nickel thin films are deposited. The effect of continuous heating on the phase structure and agglomeration in the metastable thin films is investigated in this paper. The variations of the phase structure are monitored via in situ synchrotron X‐ray diffraction, as well as optical roughness analysis. The temperature windows for phase transformation and particle formation are determined. It is noted that, after the hcp‐to‐fcc transformation and particle coalescence processes are complete, the particles reshape to acquire the thermodynamically stable shapes dictated by the Wulff theorem. Additionally, a crystallographic orientation relationship between the fcc particles and the sapphire substrate is observed, i.e., Ni (111)||Sapphire(002). Epitaxial nickel thin films are prepared via atomic layer deposition. These films have a hexagonal crystal structure, as dictated by the sapphire substrate. The nickel hexagonal phase is metastable at lower temperatures. The effect of continuous heating of the films to various temperatures is investigated, and the nature of phenomena such as phase transformation and particle formation is discussed. [ABSTRACT FROM AUTHOR]