Adsorption of Titanium Halides on Nitride and Oxide Surfaces during Atomic Layer Deposition: A DFT Study

Abstract

Various processes based on atomic layer deposition (ALD) have been reported for growing Ti-based thin films such as TiN and TiO2. To improve the uniformity and conformity of thin films grown via ALD, fundamental understanding of the precursor–substrate surface reactions is required. Herein, we present a density functional theory (DFT) study of the initial nucleation process of some titanium halide precursors (TiCl4, TiBr4, and TiI4) on Si surfaces having –OH or –NH2 functional groups. We consider the most favorable adsorption site in the reaction between the precursor and functional group of the surface, based on the thermodynamics and kinetics of the reaction. Sequential dissociation reaction mechanisms of halide ligands were systematically investigated. The exothermicity of the dissociative adsorption was found to be in the order of: TiI4 > TiBr4 > TiCl4. In addition, the precursors were observed to be more exothermic and show higher reaction rate constant when adsorbed on the –OH–terminated surface than on the –NH2–terminated surface. These observations reveal the selectivity of deposition by surface functional groups.

Inherently Area‐Selective Atomic Layer Deposition of SiO2 Thin Films to Confer Oxide Versus Nitride Selectivity

“…For deposition selectivity to be controlled by the adsorption chemistry of the precursor, lower process temperature is preferred. [ 19,37 ] Thus, another advantage of DIPAS for AS‐ALD is that thermal ALD of SiO 2 has been demonstrated at temperatures as low as 100 °C with O 3 . [ 38 ] Assuming simple Arrhenius kinetics for adsorption with the same pre‐exponential factor for both substrates, the kinetic selectivity (the ratio of the first‐order reaction rate constants) for adsorption of DIPAS was predicted to be as large as 1.3 × 10 13 at 100 °C and 2.3 × 10 10 at 200 °C.…”

The Effect of Surface Terminations on the Initial Stages of TiO2 Deposition on Functionalized Silicon

“…[19] The role of electronic and steric effects [20] and the role of promoting deposition by HOÀ or À NH x surface functional groups has been widely accepted. [21][22][23][24][25] However, to contrast these reactive surfaces (or growth surfaces), only H-termination has so far received some considerable attention as a surface functionalized to resist deposition. [6,22,23,26] The problem, however, is that the structure of H-terminated silicon surfaces depends drastically on the preparation methods and on the crystal face orientation.…”

“…Thermal ALD using TiCl 4 and water has been observed to yield thin films immediately on hydroxylated silicon surfaces (HOÀ Si), while hydrogenated silicon surfaces (HÀ Si) in general are less reactive [21] and do not form Ti oxide nuclei for several cycles. [22,23] While the selectivity of TiCl 4 between these surfaces has been established, the exact cause of selectivity loss is not fully understood, and quantitative differences between GS and NGS are only reported for specific surface preparation procedures and reaction conditions.…”

Role of Cyclopentadienyl Ligands of Group 4 Precursors toward High-Temperature Atomic Layer Deposition

“…The precursors for ALD must fulfill several requirements among which the combination of high reactivity and good thermal stability often sets major challenges. In the past decade, ALD precursor chemistry has primarily relied on homoleptic compounds including one type of ligand, such as halides, , alkylamides, , and alkoxides . These precursors, however, sometimes have drawbacks such as halide contamination and low stabilities in the case of the halide and alkoxides, respectively.…”