UMD Graduate Student Kang-Yi Lin Receives 2019 ALD/ALE Award

Kang-Yi Lin - a graduate student in the University of Maryland (UMD) Department of Materials Science and Engineering (MSE) - received the best presentation award at the 2019 AVS International Conference on Atomic Layer Deposition (ALD)/Atomic Layer Etching (ALE) for his talk entitled, Atomic Layer Etching of HfO2 with Selectivity to Si by Utilizing Material-Selective Deposition Phenomena.

Lin provided the following abstract: "Atomic layer etching (ALE) applies sequential deposition, reactant purge and etching steps with a short processing step length to establish self-limited material removal and atomic scale precision. The reactants during the ALE deposition steps may exhibit material-selective deposition based on the chemical affinity of precursor gases to the substrate material and nature of interfacial bonding. Integrating the feature of material-selective deposition with an etching step opens a new processing window for selective ALE. In this study, we evaluated the deposition behaviors of different hydrofluorocarbon (HFC) precursors, i.e. mixtures of methane (CH₄) with trifluoromethane (CHF₃) and mixtures of methane with octafluorocyclobutane (C₄F₈), on Si and HfO₂ surfaces, respectively. This is followed by the investigation of substrate-dependent selective deposition using a mixture of HFC precursors to achieve HfO₂ etching and etching selectivity relative to Si. Our results show that during the purge step of ALE sequences using CH₄/CHF₃ selectively deposit a fraction of a nm thick FC layers on Si surface while self-desorption is observed on the HfO₂ surface. In contrast, mixtures of CH₄ with C₄F₈etchant do not show this self-desorption behavior for HfO₂. By utilizing the selective deposition behavior seen for CH₄/CHF₃-based ALE in conjunction with low energy Ar ion bombardment we were able to remove the top HfO₂ layer while simultaneously forming a FC passivation layer on the underlying Si surface. In order to confirm the etching performance of CH₄/CHF₃-based ALE of HfO₂, X-ray photoelectron spectroscopy (XPS) was used to study whether any HfO₂remains on the sample at the end of the processing cycle where the in-situ ellipsometry indicated a depletion of the HfO₂ layer. The XPS results show that after the ALE processing the Hf-O peaks no longer exist in the Hf4f and O1s spectra. Instead, a weak intensity of the fluorinated Hf peaks are observed, suggesting the HfO₂ layer with an initial thickness of 2.9 nm was removed and a few hafnium etching byproducts were left on the substrate. These results support the concept that gas pulsing of complex HFC precursors during ALE sequences provides the opportunity to achieve material-selective deposition and enable ALE selectivity of HfO₂ relative to Si. "

Lin, advised by MSE Professor Gottlieb Oehrlein, was also the runner-up for overall winner. This year's workshop was held July 21-24 in Bellevue, Washington.

For additional information, visit https://ald2019.avs.org/awards/.

Published September 11, 2019