Atomic Layer Deposition of Ultrathin Tungsten Oxide Films from WH₂(Cp)₂ and Ozone

Abstract

This work reports the study of the initial stages of the atomic layer deposition growth of tungsten oxide aimed to reveal the opportunity of ultrathin continuous film obtainment. The suggested WH2(Cp)2-O3 ALD process demonstrated a clear saturate behavior on both reactants, reasonable uniformity and the opportunity to precisely tune the oxygen deficiency level within the saturation range. According to the X-ray diffraction and Raman spectroscopy measurements, the observed oxygen deficiency was found to strongly influence the film crystallinity. In situ XPS analysis demonstrated a visible film growth even from the first ALD cycles, however, the substrate material influenced the growth delay and film continuity moment. As a result, ≈1.5 nm thick continuous and smooth (RMS value of about 0.2–0.3 nm) WO3 films were successfully obtained both on sapphire and SiO2 substrates, requiring 20 and 30 ALD cycles, respectively. Overall, the suggested ALD process allows obtaining high-quality WO3 films, which may become a viable material for different electronic applications including electrochromic devices, transition metal dichalcogenide synthesis, and resistive switching memory technology.

Improvement of the Ferroelectric Response of La-Doped Hafnium Zirconium Oxide Employing Tungsten Oxide Interfacial Layer with Back-End-of-Line Compatibility

“…While tungsten oxide on bare Si showed a predominant W 6+ peak at ∼35.8 eV in W 4f 7/2 , the tungsten oxide as an interfacial layer showed various shoulders corresponding to W 5+ (∼34.1 eV) and W 4+ (∼32.5 eV), in addition to the main W 6+ peak (∼35.8 eV). 35,37,38 Although there would be peak overlaps from Ti 3p, Hf 5p, and Zr 4p XP spectra caused by TiN and the HZO layer, 39−42 the signal from the HZO layer would be insignificant. Also, a much decreased portion of the W 6+ peak at 4f 5/2 (∼37.8 eV) might be the reason for the reduction of WO 3 .…”

Low-Energy He+ Ions Induced Functionalization of the MoS2 Surface for ALD HfO2 Growth Enhancement

“…In particular, the first 50 ALD cycles resulted only in a small Hf4f signal appearance (Hf4f/Mo3d intensity ratio ≈ 0.08) on the pristine MoS 2 surface, corresponding to the island growth, while a much higher film signal can be detected for the same 50 ALD cycles on the irradiated surface (Hf4f/Mo3d intensity ratio ≈ 6.2) which is typical for continuous films. Additional analysis of the Hf4f and S2p spectra collected in the angle-resolved mode allowed to estimate the HfO 2 film thickness ( h ) and continuity factor ( f ) (see the Supporting Information for the model description) . In these experiments, the S2p substrate line was measured since the Mo3d and S2s lines are significantly overlapped by the Hf4d line from the growing film.…”

“…Additional analysis of the Hf4f and S2p spectra collected in the angle-resolved mode allowed to estimate the HfO 2 film thickness (h) and continuity factor (f) (see the Supporting Information for the model description). 43 In these experiments, the S2p substrate line was measured since the Mo3d and S2s lines are significantly overlapped by the Hf4d line from the growing film.…”

Thickness-Dependent Structural and Electrical Properties of WS2 Nanosheets Obtained via the ALD-Grown WO3 Sulfurization Technique as a Channel Material for Field-Effect Transistors

“…The other details of the utilized ALD process can be found elsewhere. 31 Sapphire pieces of 20 × 10 mm 2 in size were used as substrates. They were cleaned (piranha solution and deionized water) and subsequently annealed in a tube furnace in air for 1 h at 1000 °C prior to WO 3 growth.…”

“…The deposition temperature ( T dep ) was fixed at 300 °C. The other details of the utilized ALD process can be found elsewhere . Sapphire pieces of 20 × 10 mm 2 in size were used as substrates.…”