Atomic layer etching (ALE) is a multistep process used today in manufacturing for removing ultrathin layers of material. In this article, the authors report on ALE of Si, Ge, C, W, GaN, and SiO2 using a directional (anisotropic) plasma-enhanced approach. The authors analyze these systems by defining an “ALE synergy” parameter which quantifies the degree to which a process approaches the ideal ALE regime. This parameter is inspired by the ion-neutral synergy concept introduced in the 1979 paper by Coburn and Winters [J. Appl. Phys. 50, 5 (1979)]. ALE synergy is related to the energetics of underlying surface interactions and is understood in terms of energy criteria for the energy barriers involved in the reactions. Synergistic behavior is observed for all of the systems studied, with each exhibiting behavior unique to the reactant–material combination. By systematically studying atomic layer etching of a group of materials, the authors show that ALE synergy scales with the surface binding energy of the bulk material. This insight explains why some materials are more or less amenable to the directional ALE approach. They conclude that ALE is both simpler to understand than conventional plasma etch processing and is applicable to metals, semiconductors, and dielectrics.
The thermal chemistry of tetrakis[Cu(I)-N-secbutyl-iminopyrrolidinate] and bis[Cu(I)-N,N-dimethyl-N′,N″di-iso-propyl-guanidinate], promising precursor for atomic layer deposition (ALD) applications, was investigated on a Ni(110) single-crystal under ultrahigh vacuum (UHV) conditions by using X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). Both precursors, which exist as tetramers and dimers in the solid phase, respectively, undergo dissociative adsorption at temperatures below 200 K to produce adsorbed monomers on the surface. A β-hydride elimination step is then operative near 300 K that leads to the release of some of the ligands in dehydrogenated form. The remaining adsorbates obtained from either precursor undergo similar further decomposition between 350 K and 600 K as the Cu atoms are reduced from a Cu(I) oxidation state to metallic Cu(0). Hydrocarbons resulting from the elimination of the terminal moieties include ethene and acetonitrile from the Cu(I)-iminopyrrolidinate and propene from the Cu(I)-guanidinate, which are ejected at ∼420−490 K, and HCN in both cases at ∼570−580 K. These results shows several similarities with the surface chemistry previously reported for bis[Cu(I)-N,N′-di-sec-butyl-acetamidinate], and they suggest a common behavior in the surface reactions of these families of Cu(I)amidinate, Cu(I)-iminopyrrolidinate, and Cu(I)-guanidinate ALD precursors.
Surface oxidation states of transition (Fe and Co) and noble (Pd and Pt) metals were tailored by controlled exposure to O2 plasmas, thereby enabling their removal by specific organic chemistries. Of all organic chemistries studied, formic acid was found to be the most effective in selectively removing the metal oxide layer in both the solution and vapor phase. The etch rates of Fe, Co, Pd, and Pt films, through an alternating plasma oxidation and formic acid vapor reaction process, were determined to be 4.2, 2.8, 1.2, and 0.5 nm/cycle, respectively. Oxidation by atomic oxygen was an isotropic process, leading to an isotropic etch profile by organic vapor. Oxidation by low energy and directional oxygen ions was an anisotropic process and thus results in an anisotropic etch profile by organic vapor. This is successfully demonstrated in the patterning of Co with a high selectivity over the TiN hardmask, while preserving the desired static magnetic characteristic of Co.
Reaction mechanisms in the atomic layer deposition (ALD) of Li x Al y Si z O (LASO) using a LiOC(CH 3 ) 3 /H 2 O−Al(CH 3 ) 3 /H 2 O−Si-(OCH 2 CH 3 ) 4 /H 2 O chemistry were studied via in situ Fourier transform infrared spectroscopy (FTIR) at 225 °C. ALD deposition of Al 2 O 3 using an Al(CH 3 ) 3 /H 2 O chemistry and LiOH using a LiOC(CH 3 ) 3 /H 2 O chemistry demonstrated ideal ALD growth. ALD deposition of SiO 2 alone by Si(OCH 2 CH 3 ) 4 /H 2 O chemistry was unsuccessful; however, incorporation of the same Si(OCH 2 CH 3 ) 4 /H 2 O chemistry in between ALD processes of Al 2 O 3 and LiOH resulted in ALD deposition of Li x Al y Si z O. The as-deposited ALD LASO film with a composition of Li 0.40 Al 0.32 Si 0.28 O on a Si( 100) substrate was amorphous but crystallized into β-LiAlSiO 4 upon rapid thermal annealing (RTA) at 900 °C under N 2 . The ionic conductivity of as-deposited, amorphous ALD Li 0.40 Al 0.32 Si 0.28 O was as high as 1.62 × 10 −6 S/cm at 361 °C with an activation energy of E a = 0.70 eV.
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