Origin of Instability of Titanicone Grown by Molecular Layer Deposition Using TiCl₄ and Ethylene Glycol

Abstract

Titanicone, obtained through molecular layer deposition (MLD) using TiCl 4 and ethylene glycol (EG), is often regarded as a thin film of titanium ethylene glycolate [Ti(OCH 2 CH 2 O) 2 ]. Nevertheless, titanicone exhibits a distinct vulnerability to moisture, while single crystals of Ti(OCH 2 CH 2 O) 2 remain stable, even in the presence of water. To elucidate the origin of instability, we investigated the pathway of chemical degradation for titanicone using in situ and ex situ analytical methods such as Fourier transform infrared spectrometry, quartz crystal microbalance, quadrupole mass spectrometry, and X-ray photoelectron spectroscopy. Our analyses unveiled that the instability of the MLD-grown titanicone film in the presence of water can be primarily attributed to the high chlorine content present as Ti−Cl species and the coexistence of single-reacted EG species as well as double-reacted EG species, unlike in Ti(OCH 2 CH 2 O) 2 crystals. Water molecules react with the Ti−Cl species, leading to the formation of Ti−OH species and the release of HCl gas. Furthermore, the single-reacted EG species undergo an intramolecular cyclization reaction catalyzed by HCl, resulting in the formation of Ti−OH and the liberation of ethylene oxide. Consequently, when exposed to water, the MLD-grown titanicone turns into a water-stable mixed film composed of TiO 2 and Ti(OCH 2 CH 2 O) 2 .

Chemical, Structural, and Electrical Changes in Molecular Layer-Deposited Hafnicone Thin Films after Thermal Processing

“…Molecular layer deposition (MLD) is an analogue of ALD where molecular fragments are included in the resulting films and may be a route to porous and/or low- k materials. , In prior studies, chemical changes in MLD metalcone films were observed with UV, thermal, and/or ambient exposure, indicating the removal of organics and changes in physical properties. − Previously, aluminum oxide-based materials were developed for low- k etch stop applications motivating us to explore the applicability of hafnium-based MLD films for the low- k applications and to better understand the synthesis–structure–composition–property relationships in these materials. ,, In this work, we deposit hafnicone, which is a hybrid hafnium alkoxide film, using MLD and report the thermally induced removal of the organic components and the ability to create low density and low k films relative to HfO 2 . We examine the evolution of chemical, structural, and electrical properties of the as-deposited and annealed hafnicone films in comparison to those of ALD hafnia films.…”

“… 31 , 32 In prior studies, chemical changes in MLD metalcone films were observed with UV, thermal, and/or ambient exposure, indicating the removal of organics and changes in physical properties. 33 − 38 Previously, aluminum oxide-based materials were developed for low- k etch stop applications motivating us to explore the applicability of hafnium-based MLD films for the low- k applications and to better understand the synthesis–structure–composition–property relationships in these materials. 32 , 39 , 40 In this work, we deposit hafnicone, which is a hybrid hafnium alkoxide film, 41 using MLD and report the thermally induced removal of the organic components and the ability to create low density and low k films relative to HfO 2 .…”