Iain Buchanan

Comparative study of ALD SiO2 thin films for optical applications

We have investigated the suitability of atomic layer deposition (ALD) for SiO2 optical coatings and applied it to broadband antireflective multilayers in combination with HfO2 as the high refractive index material. SiO2 thin films were successfully grown using tris[dimethylamino]silane (3DMAS), bis[diethylamino]silane (BDEAS) with plasma activated oxygen as precursors, and the AP-LTO330 precursor with ozone, respectively. The amorphous SiO2 films show very low optical losses within a spectral range of 200 nm to 1100 nm. Laser calorimetric measurements show absorption losses of 300 nm thick SiO2 films of about 1.5 parts per million at a wavelength of 1064 nm. The films are optically homogeneous and possess a good scalability of film thickness. The film surface porosity - which correlates to a shift in the transmittance spectra under vacuum and air conditions - has been suppressed by optimized plasma parameters or Al2O3 sealing layers.

New Volatile Strontium and Barium Imidazolate Complexes for the Deposition of Group 2 Metal Oxides

We report the synthesis, characterization, and experimental density function theory-derived properties of new volatile strontium and barium imidazolate complexes, which under atomic layer deposition conditions using ozone as a reagent can deposit crystalline strontium oxide at 375 °C.

Chemical interaction and ligand exchange between a [(CH3)3Si]3Sb precursor and atomic layer deposited Sb2Te3 films

The chemical interaction between the [(CH3)3Si]3Sb precursor and atomic layer deposited Sb2Te3 thin films was examined at temperatures ranging from 70 to 220 °C. The trimethylsilyl group [(CH3)3Si] displays greater affinity for Te than for Sb, and this drives replacement of Te in the film with Sb from the [(CH3)3Si]3Sb precursor, while eliminating volatile [(CH3)3Si]2Te, especially at elevated temperatures. The compositions of the resulting Sb–Te layers lie on the Sb2Te3–Sb tie line. The incorporation behavior of [(CH3)3Si]3Sb was explained in terms of a Lewis acid–base reaction. The exchange reactions occurred to relieve the unfavorable hard–soft Lewis acid–base pair between the trimethylsilyl group and Sb in [(CH3)3Si]3Sb. Such a reaction could be usefully adopted to control the chemical composition of ternary Ge–Sb–Te thin films.

Low-temperature atomic layer deposition of SiO2/Al2O3 multilayer structures constructed on self-standing films of cellulose nanofibrils

In this paper, we have optimized a low-temperature atomic layer deposition (ALD) of SiO2 using AP-LTO® 330 and ozone (O3) as precursors, and demonstrated its suitability to surface-modify temperature-sensitive bio-based films of cellulose nanofibrils (CNFs). The lowest temperature for the thermal ALD process was 80°C when the silicon precursor residence time was increased by the stop-flow mode. The SiO2 film deposition rate was dependent on the temperature varying within 1.5–2.2 Å cycle−1 in the temperature range of 80–350°C, respectively. The low-temperature SiO2 process that resulted was combined with the conventional trimethyl aluminium + H2O process in order to prepare thin multilayer nanolaminates on self-standing CNF films. One to six stacks of SiO2/Al2O3 were deposited on the CNF films, with individual layer thicknesses of 3.7 nm and 2.6 nm, respectively, combined with a 5 nm protective SiO2 layer as the top layer. The performance of the multilayer hybrid nanolaminate structures was evaluated with respect to the oxygen and water vapour transmission rates. Six stacks of SiO2/Al2O with a total thickness of approximately 35 nm efficiently prevented oxygen and water molecules from interacting with the CNF film. The oxygen transmission rates analysed at 80% RH decreased from the value for plain CNF film of 130 ml m−2 d−1 to 0.15 ml m−2 d−1, whereas the water transmission rates lowered from 630 ± 50 g m−2 d−1 down to 90 ± 40 g m−2 d−1. This article is part of a discussion meeting issue ‘New horizons for cellulose nanotechnology’.

Atomic Layer Deposition of Wet-Etch Resistant Silicon Nitride Using Di(sec-butylamino)silane and N2 Plasma on Planar and 3D Substrate Topographies

The advent of three-dimensional (3D) finFET transistors and emergence of novel memory technologies place stringent requirements on the processing of silicon nitride (SiNx) films used for a variety of applications in device manufacturing. In many cases, a low temperature (<400 °C) deposition process is desired that yields high quality SiNx films that are etch resistant and also conformal when grown on 3D substrate topographies. In this work, we developed a novel plasma-enhanced atomic layer deposition (PEALD) process for SiNx using a mono-aminosilane precursor, di(sec-butylamino)silane (DSBAS, SiH3N(sBu)2), and N2 plasma. Material properties have been analyzed over a wide stage temperature range (100-500 °C) and compared with those obtained in our previous work for SiNx deposited using a bis-aminosilane precursor, bis(tert-butylamino)silane (BTBAS, SiH2(NHtBu)2), and N2 plasma. Dense films (∼3.1 g/cm3) with low C, O, and H contents at low substrate temperatures (<400 °C) were obtained on planar substrates for this process when compared to other processes reported in the literature. The developed process was also used for depositing SiNx films on high aspect ratio (4.5:1) 3D trench nanostructures to investigate film conformality and wet-etch resistance (in dilute hydrofluoric acid, HF/H2O = 1:100) relevant for state-of-the-art device architectures. Film conformality was below the desired levels of >95% and attributed to the combined role played by nitrogen plasma soft saturation, radical species recombination, and ion directionality during SiNx deposition on 3D substrates. Yet, very low wet-etch rates (WER ≤ 2 nm/min) were observed at the top, sidewall, and bottom trench regions of the most conformal film deposited at low substrate temperature (<400 °C), which confirmed that the process is applicable for depositing high quality SiNx films on both planar and 3D substrate topographies.

Comparative study of ALD SiO_2 thin films for optical applications

We have investigated the suitability of atomic layer deposition (ALD) for SiO2 optical coatings and applied it to broadband antireflective multilayers in combination with HfO2 as the high refractive index material. SiO2 thin films were successfully grown using tris[dimethylamino]silane (3DMAS), bis[diethylamino]silane (BDEAS) with plasma activated oxygen as precursors, and the AP-LTO330 precursor with ozone, respectively. The amorphous SiO2 films show very low optical losses within a spectral range of 200 nm to 1100 nm. Laser calorimetric measurements show absorption losses of 300 nm thick SiO2 films of about 1.5 parts per million at a wavelength of 1064 nm. The films are optically homogeneous and possess a good scalability of film thickness. The film surface porosity - which correlates to a shift in the transmittance spectra under vacuum and air conditions - has been suppressed by optimized plasma parameters or Al2O3 sealing layers.

Comparative study of ALD SiO 2 thin films for optical applications

We have investigated the suitability of atomic layer deposition (ALD) for SiO2 optical coatings and applied it to broadband antireflective multilayers in combination with HfO2 as the high refractive index material. SiO2 thin films were successfully grown using tris[dimethylamino]silane (3DMAS), bis[diethylamino]silane (BDEAS) with plasma activated oxygen as precursors, and the AP-LTO330 precursor with ozone, respectively. The amorphous SiO2 films show very low optical losses within a spectral range of 200 nm to 1100 nm. Laser calorimetric measurements show absorption losses of 300 nm thick SiO2 films of about 1.5 parts per million at a wavelength of 1064 nm. The films are optically homogeneous and possess a good scalability of film thickness. The film surface porosity - which correlates to a shift in the transmittance spectra under vacuum and air conditions - has been suppressed by optimized plasma parameters or Al2O3 sealing layers.

Bis[O-methyl (S)-penicillaminato]-cis-dioxomolybdenum(VI), [MoO2{(S)-pen-OMe}2]; structure and spectroscopic studies

The complex [MoO2{(S)-pen-OMe}2] crystallises in the monoclinic space group P21, with a= 11.794(2), b= 12.519(3), c= 13.040(2)A, β= 106.32(2)°, and Z= 4. The structure was solved from 5 502 unique observed reflections, and refinement gave a final R of 0.039; anomalous dispersion was employed to verify the absolute configuration at molybdenum and at the chiral carbon of the ligands. The two crystallographically independent molecules have opposite absolute configurations (Λ and Δ) for the ligand chelate rings about the metal; the expected cis-dioxo-stereochemistry is confirmed, with normal bond lengths [average Mo–O 1.712(7), Mo–S 2.407(5), and Mo–N 2.362(26)A]. Proton, 13C, and 95Mo n.m.r. spectra are consistent with these two diastereoisomeric molecules persisting in solution, and together with c.d. data are taken to indicate that, for the (S)-ligand complex in (CD3)2SO at ca. 298 K, the Λ isomer is present in a ca. 2:1 excess over the Δ isomer, the reverse being the case for the (R)-ligand complex. The two diastereoisomers are in dynamic equilibrium and 1H n.m.r. data collected over the temperature range 297–385 K indicate that the activation parameters for the Λ→Δ interconversion are ΔH‡= 44 ± 6 kJ mol–1 and ΔS‡=–110 ± 17 J K–1 mol–1. The mechanism for the inversion of configuration at molybdenum is considered to proceed by an intramolecular process, involving Mo–N bond rupture followed by rotation of the ligand atoms of the subsequent intermediate and ring closure. C.d. spectra resolve each of the u.v.–visible absorption bands centred at ca. 264 and 352 nm into two components. The i.r. active ν(Mo–Ot) stretching vibrations of cis-[MoO2{(S)-pen-OMe}2] are manifest as a pair of doublets at 918/913 and 878/875 cm–1, presumably due to the Λ and Δ isomers having slightly different ν(Mo–Ot) values.