Molecular Mechanism of Thermal Dry Etching of Iron in a Two-Step Atomic Layer Etching Process: Chlorination Followed by Exposure to Acetylacetone

Abstract

Controlling thickness and morphology of transition-metal thin films used in magnetic random-access memory fabrication is a major challenge. Thermal dry etching has emerged as a method of choice for preparing the desired films; however, the mechanisms of the underlying surface processes are very difficult to assess. In this work, thermal dry etching of metallic iron by using sequential exposure to chlorine gas and 2,4-pentanedione (acetylacetone, acacH) was investigated. The mechanism of reacting acacH with chlorine-modified iron surface was studied by following the fragments desorbing from the surface in temperature-programmed desorption experiments in half-cycle processes that compared the chlorinated, oxidized, mixed (Cl and O), and clean (sputtered) iron films. In situ Auger electron spectroscopy and ex situ X-ray photoelectron spectroscopy of each sample after each etching step confirmed that the surface is activated by chlorine and then the chlorine-containing iron species are removed from the top layer of the sample, resulting in a metallic iron surface. No etching of clean (sputtered) surface was observed with acacH. The complete mechanism of acacH reaction with chlorinated iron samples is complicated, and etch products can contain both Fe2+ and Fe3+. However, a number of major conclusions, including the formation of surface intermediates and the final products of etching, primarily removal of Fe­(acac) x Cl y , are inferred by comparing the results of these experiments with the computational investigation of selected surface processes using density functional theory calculations.

Recent Progress of Atomic Layer Technology in Spintronics: Mechanism, Materials and Prospects

“…If ALE's study overcomes these obstacles, it will have a huge impact on how metals are used in integrated circuits. Currently, the majority of ALE approaches for metal films are also two-step processes [141]. The first stage is to change the metal film into the aforementioned metal oxide, nitride, or chloride.…”

Thermal Atomic Layer Etching Process for 2D van der Waals Material CrPS4

“…However, mixedligand compounds were formed for both light (B), and heavy (Co, Fe) elements in the form of M(acac) x Cl y as shown by temperature-programmed desorption (TPD) measurements. 29,30 In fact, the formation of volatile acetylacetonates of Co and Fe does occur, but at much higher temperatures compared to the ones used in ALE. 29,31−33 In a similar approach, one could start considering Cr(acac) 3 and H 3 PS 4 as potential products of the ALE of CrPS 4 .…”

Fluorination of TiN, TiO2, and SiO2 Surfaces by HF toward Selective Atomic Layer Etching (ALE)

“…Using atomistic computational chemistry simulations, the pathways of each reaction in the etching processes can be explored, and volatile byproducts can be inferred [23,24]. However, since the thermal ALE processes present various theoretical challenges, such as self-limiting reactions and the generation of volatile reaction products, only limited studies have been conducted to identify the reaction mechanisms [25][26][27][28][29][30][31][32]. In particular, while the process conditions for fluorination and removal of Ti atoms from TiO 2 by HF were previously molecularly elucidated [33,34], its selectivity against TiN or SiO 2 substrates is yet to be known.…”