Graduate Thesis Or Dissertation


Thermal Atomic Layer Etching of Crystalline Metal Oxides and Metals Public Deposited

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  • Thermal atomic layer etching (ALE) is used to remove thin films with Ångstrom-level precision and is achieved using sequential, self-limiting reactions. ALE processes typically consist of two reactions: surface modification and removal. The modification reactions used in this work are fluorination or chlorination. The two removal reactions explored are ligandexchange or ligand-addition. Both removal reactions result in volatilization of the modified surface. During the ALE process, these two reactions are repeated until the desired amount of material is removed. ALE has applications in the semiconductor industry because smaller scale devices require precise removal of various types of material. 

    The first two studies investigated the differences in ALE etch per cycle for an amorphous versus crystalline metal oxides. The first study examined the difference in ALE of amorphous and crystalline HfO2, ZrO2, and HfZrO4. The second study examined amorphous and crystalline Al2O3 thin films. The amorphous metal oxides had a higher etch per cycle compared to their crystalline counterparts. 

    The last two studies focused on developing ALE processes for nickel and cobalt. Metals are particularly difficult to etch using ALE because they have an oxidation state of zero. Usually volatile products contain oxidized metals. During the ALE process, the metal must be oxidized to successfully create volatile etch products. This study used chlorination, using sulfuryl chloride (SO2Cl2), as the modification step for both nickel and cobalt. Then a ligand-addition step exposed the metal chloride surface to an L ligand. The L ligands contain a lone pair of electrons that can donate to the metal center. The L ligand used for nickel was trimethyl phosphine (PMe3). The L ligands used for cobalt ALE were PMe3 or tetramethyl ethylenediamine (TMEDA), which can act as a bidentate L ligand. The TMEDA ligand was more efficient than PMe3 for ALE of cobalt. 

Date Issued
  • 2022-10-31
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  • 2024-01-08
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