Precursor-surface interactions revealed during plasma-enhanced atomic layer deposition of metal oxide thin films by in-situ spectroscopic ellipsometry

Abstract

We find that a five-phase (substrate, mixed native oxide and roughness interface layer, metal oxide thin film layer, surface ligand layer, ambient) model with two-dynamic (metal oxide thin film layer thickness and surface ligand layer void fraction) parameters (dynamic dual box model) is sufficient to explain in-situ spectroscopic ellipsometry data measured within and across multiple cycles during plasma-enhanced atomic layer deposition of metal oxide thin films. We demonstrate our dynamic dual box model for analysis of in-situ spectroscopic ellipsometry data in the photon energy range of 0.7-3.4 eV measured with time resolution of few seconds over large numbers of cycles during the growth of titanium oxide (TiO 2) and tungsten oxide (WO 3) thin films, as examples. We observe cyclic surface roughening with fast kinetics and subsequent roughness reduction with slow kinetics, upon cyclic exposure to precursor materials, leading to oscillations of the metal thin film thickness with small but positive growth per cycle. We explain the cyclic surface roughening by precursor-surface interactions leading to defect creation, and subsequent surface restructuring. Atomic force microscopic images before and after growth, x-ray photoelectron spectroscopy, and x-ray diffraction investigations confirm structural and chemical properties of our thin films. Our proposed dynamic dual box model may be generally applicable to monitor and control metal oxide growth in atomic layer deposition, and we include data for Sio 2 and Al 2 o 3 as further examples. Transition metal oxides (TMOs) are subject of contemporary interest for many applications. A wide range of interesting electrical, optical, electrochromic, and photocatalytic properties make TMOs attractive for device applications 1-6. TMOs are being exploited, for example, as efficient light absorber materials in photo-voltaic devices 7,8 , as ion-transport, and/or ion-storage materials in rechargeable batteries 9 , as active materials in switchable electrochromic optical windows 10-12 , in low-earth-orbit protective coatings for all-solid-state electrochromic surface heat radiation control devices 13,14 , in gas sensing devices 15,16 , and in photo-catalysis devices 6. TMOs are often fabricated as thin films, where fabrication conditions critically influence the resulting thin film properties 17-19. Various growth processes for the fabrication of TMO thin films have been developed by utilizing physical vapor deposition (PVD) such as magnetron sputtering 20-22 , thermal evaporation 23,24 , and chemical vapor deposition (CVD) 25-27. Thin films deposited by PVD processes are often affected by thickness and composition non-uniformity. Adhesion failure and non-homogeneous coverage across highly-faceted surfaces are often reported 28-30. CVD processes enable deposition of highly uniform thin films in the thickness range of nanometers to many micrometers 31-33. However, CVD growth processes critically depend on reaction conditions such as

Surface Modification of Nanoporous Anodic Alumina during Self-Catalytic Atomic Layer Deposition of Silicon Dioxide from (3-Aminopropyl)Triethoxysilane

“…On the other hand, ratio of refraction index and dielectric constant average values determined for both samples are practically independent of wavelength interval, being <n> Ox+SiO2/APTES /<n> Ox+SiO2/APTES/O 3 ~ 0.9 and <ε r > Ox+SiO2/APTES /<ε r > Ox+SiO2/APTES/O 3 ~ 0.8, proving evidence of surface effect difference associated to samples modification. Furthermore, the possibility of performing in - situ SE measurements during ALD deposition in both, custom-made and commercial devices, provides not only an accurate monitoring of the deposited film thickness and growth mechanisms, but also a powerful tool to determine film optical properties, including the possibility to tune at will some physical parameters of the samples such as the refraction index [ 64 , 65 , 66 ].…”

Chiroptical Second-Harmonic Tyndall Scattering from Silicon Nanohelices

“…Based on dynamic dual box model analysis of in situ spectroscopic ellipsometry data, an approximately 7 nm-thick ZnO ultrathin film was measured on the surface. 62 A custom-built, ultrahigh vacuum glancing angle deposition (GLAD) system was utilized in the fabrication of helical scatterers. The base pressure of the deposition system was measured at 1.0 × 10 −8 mbar, prior to the fabrication of the nanostructures.…”

“…Argon was employed as the purging gas source. Based on dynamic dual box model analysis of in situ spectroscopic ellipsometry data, an approximately 7 nm-thick ZnO ultrathin film was measured on the surface …”

Ferromagnetic resonators synthesized by metal-organic decomposition epitaxy

“…The change in structural and chemical order manifests in the optical, static and dynamic magnetic properties. Both real and imaginary parts of the dielectric function (figure 2(a)) were determined from spectroscopic ellipsometry [43] using multiple sample analysis [44,45] without the need for band structure calculation to model the dielectric function or guess the latter. The reflected intensity was recorded with a chargecoupled device based spectroscopic ellipsometer with synchronized dual rotating compensator (RC2 by J.A.…”