Real-Time Coherent X-Ray Scattering Studies of Plasma-Enhanced Atomic Layer Deposition Thin Film Growth

Real-time x-ray studies of surface growth processes using “low-coherence” x-ray sources have proven to be a powerful tool for studying average surface evolution during thin film growth processes. Enabled by the continued increase in accelerator-based x-ray source brightness, however, coherent x-ray scattering experiments are sensitive to fluctuations around the average, revealing dynamics information not accessible through “low-coherence” x-ray scattering or, typically, through any other means. We discuss recent studies utilizing the coherent scattering technique of X-ray Photon Correlation Spectroscopy (XPCS) to examine the epitaxial plasma-assisted atomic layer deposition (PEALD) of InN [1]. XPCS uses the evolution of the x-ray scattering speckle pattern in reciprocal space to obtain detailed information about the microscopic evolution of the sample. It shows that the plasma exposure component of the growth cycles does not simply freeze in a structure that is then built upon in subsequent cycles. Instead, there is significant surface evolution throughout all parts of the PEALD growth cycle, including gas purge periods.<br/><br/>[1] Peco Myint, Jeffrey Woodward, Jeffrey, Chenyu Wang, Xiaozhi Zhang, Lutz Wiegart, Andrei Fluerasu, Randall L. Headrick, Charles Eddy, and Karl Ludwig, <i>ACS Nano</i> <b>18</b>, 1982 (2024).<br/><br/>This work was partly supported by DOE DE-SC0017802 and by NSF DMR-1709380.