Non-uniform Composition Profiles in Inorganic Thin Films from Aqueous Solutions

Abstract

A variety of metal oxide films (InGaOx, AlOx, "HafSOx") prepared from aqueous solutions were found to have non-uniform electron density profiles using X-ray reflectivity. The inhomogeneity in HafSOx films (Hf(OH)4-2x-2y(O2)x(SO4)y·zH2O), which are currently under investigation as inorganic resists, were studied in more detail by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and medium-energy ion scattering (MEIS). The HAADF-STEM images show a greater concentration of heavy atoms near the surface of a single-layer film. MEIS data confirm the aggregation of Hf at the film surface. The denser "crust" layer in HafSOx films may directly impact patterning resolution. More generally, the phenomenon of surface-layer inhomogeneity in solution-deposited films likely influences film properties and may have consequences in other thin-film systems under investigation as resists, dielectrics, and thin-film transistor components.

High-κ Lanthanum Zirconium Oxide Thin Film Dielectrics from Aqueous Solution Precursors

“…68 Best fits were obtained using two-layer models comprised of a bulk layer and a ∼1−3 nm capping layer of different density (Figure 4, Table S1), consistent with XRR modeling performed on other aqueous solution-processed films. 76 Total film thickness decreases with increasing temperature, consistent with FTIR results, demonstrating the loss of H 2 O and NO x species as temperature increases. Overall film density (calculated from a weighted average of the densities derived from the two layer models) increases from 4.35 g cm −3 (300 °C) to 5.27 g cm −3 (600 °C), approximately 90% of the bulk density of the pyrochlore La 2 Zr 2 O 7 (6.05 g cm −3 ).…”

Inkjet‐Printed Ternary Oxide Dielectric and Doped Interface Layer for Metal‐Oxide Thin‐Film Transistors with Low Voltage Operation

“…[ 50 ] Another possible explanation for the observed effect of the plasma is that the bulk of Y x Al 2− x O 3 films annealed at T 1 remains partially uncured under an overlying crust of more thoroughly cured and densified material. Such high‐density top crust has been reported before for solution‐processed metal salt precursors both from aqueous [ 51 ] and from organic solvent routes (similarly using 2‐ME/ethylene glycol (EG) as here). [ 13 ] The formation of an interfacial crust is supported by X‐ray reflectivity (XRR) data for ALD films and Y x Al 2− x O 3 films annealed at T 1 and T 2 , as presented in Table S1 and Figures S4 and S5 (Supporting Information).…”

“…The crust then behaves as a diffusion barrier that prevents the formation of a uniform density gradient in the film. [ 51 ]…”

High Quality Magnetic Oxide Thin Films Prepared via Aqueous Solution Processing

“…This method, recently coined "Prompt Inorganic Condensation", or PIC, has been used to make high quality films of a number of oxides, including dielectrics, [53][54][55][56][57][58] transparent conducting oxides, 59,60 and high-resolution inorganic resists. 61,62 In these examples using PIC, dehydration and nitrate removal are shown to occur without negatively affecting film morphology, allowing the preparation of dense, smooth films at relatively low temperatures.…”

“…To overcome the limitations of previous wet-chemical approaches, we utilize a method to effectively prepare smooth thin films of metal oxides by spin coating them from aqueous precursor solutions with subsequent annealing. This method, recently coined “Prompt Inorganic Condensation”, or PIC, has been used to make high quality films of a number of oxides, including dielectrics, − transparent conducting oxides, , and high-resolution inorganic resists. , In these examples using PIC, dehydration and nitrate removal are shown to occur without negatively affecting film morphology, allowing the preparation of dense, smooth films at relatively low temperatures. We show that the electronic, optical, and magnetic properties of the nanocrystalline films prepared in this work are comparable to those achieved by vapor phase deposition techniques.…”