Controlling the Atomic Layer Deposition of Titanium Dioxide on Silicon: Dependence on Surface Termination

Abstract

Patterned fabrication depends on selective deposition that can be best achieved with atomic layer deposition (ALD). For the growth of TiO2 by ALD using TiCl4 and H2O, X-ray photoelectron spectroscopy reveals a marked difference in growth on oxidized and hydrogen-terminated silicon surfaces, characterized by typical and predictable deposition rates observed on SiO2 surfaces that can be 185 times greater than the deposition rates on hydrogen-terminated Si(100) and Si(111) surfaces. Large-scale patterning is demonstrated using wet chemistry, and nanometer-scale patterned TiO2 growth is achieved through scanning tunneling microscopy (STM) tip-based lithography and ALD. The initial adsorption mechanisms of TiCl4 on clean, hydrogen-terminated, and OH-terminated Si(100)-(2 × 1) surfaces are investigated in detail through density functional theory calculations. Varying the reactive groups on the substrate is found to strongly affect the probability of precursor nucleation on the surface during the ALD process. Theoretical studies provide quantitative understanding of the experimental differences obtained for the SiO2, hydrogen-terminated, and clean Si(100) and Si(111) surfaces.

Atomic layer deposition of nano-TiO_2 thin films with enhanced biocompatibility and antimicrobial activity for orthopedic implants

“…In addition, the surface morphology of the ALD-grown TiO 2 films can be well controlled to achieve favorable nanoroughness and crystallinity. 31,42 In this study, TiO 2 coatings were deposited onto the Ti substrates by adjusting the reactor temperatures from 120°C and 160°C to 190°C. Morphological observations by SEM ( Figure 1A-D) indicated that all TiO 2 coatings were composed of grains with sizes ,200 nm and exhibited remarkable nanorough surfaces that were obviously different from Ti controls.…”

Spurious dangling bond formation during atomically precise hydrogen depassivation lithography on Si(100): The role of liberated hydrogen

“…Some metals such as gallium 20 or organic molecules such as styrene 21 have shown an affinity for single DB deposition. Fortunately, for applications such as phosphorus incorporation, 3 patterned atomic layer deposition, 22 or even molecular deposition of disilane for patterned epitaxy, 2,23,24 multiple DBs are required to open up energetically favorable pathways for deposition. Also, since tip dependence [ Fig.…”

Pattern transfer of hydrogen depassivation lithography patterns into silicon with atomically traceable placement and size control

“…30 Upon exposure to atmosphere, the depassivated areas spontaneously oxidize while the hydrogen passivation layer does not. As described previously, 28 the ALD is performed using an unmodified commercial ex-situ ALD system (Savannah 100, Cambridge NanoTech Inc.). To avoid damaging the surface during transport and storage, the sample is stored in approximately one atmosphere pressure of ultrapure argon.…”

“…24 Scale-up pathways similar to IBM's "millipede" 25 or hybrid HDL/ e-beam lithography 26 systems remain a possibility. 28 The metal oxide-TiO 2 in this case-resists RIE ultimately leading to the transfer of the HDL patterns into the silicon substrate [supplementary material 1], 29 with down to 13 nm full-pitch structures demonstrated here. Figure 1 summarizes the process used in this work to fabricate 17 nm tall silicon structures with pattern traceability to the silicon atomic lattice.…”