Density Functional Theory Study of Oxygen Adsorption on Polymer Surfaces for Atomic-Layer Etching: Implications for Semiconductor Device Fabrication

Abstract

Atomic-layer etching (ALE) is a technique that removes thin layers of material using sequential self-limiting reactions and is considered to be one of the most promising techniques for achieving the low-process variability necessary in the imminent atomic-scale era of semiconductor device fabrication. Here, a theoretical investigation of the ALE of organic polymer surfaces using oxygen pulses has been performed, by means of density functional theory calculations. Experimental evidence shows that ion bombardment of polymer surfaces results in carbon-abundant layers, which are formed as a competition between two opposite effects, the breaking of C–H and C–C bonds, which leads to either structural evolution or sputtering of the polymer surface. Cognizant of that, we develop appropriate polymer surface models, first, to investigate whether the adsorption of oxygen on organic surfaces can be rendered self-limiting, as required in ALE and, second, to establish the conditions for obtaining controlled, self-limiting etching of surface carbon atoms. Our results show that, indeed, for large oxygen flux densities, atomically controlled etching can be obtained in the form of desorption of different carbonate species. We quantify the etching process through both the oxygen flux density and the initial kinetic energy of the impacting oxygen atoms. On the basis of a saturated carbon surface model, the theoretical maximum etch rate was estimated to be 0.51 ± 0.05 Å/cycle (4.94 ± 0.1 ng/cm2·cycle), which matches the range of maximum experimental values.

Non-Equilibrium Plasma Methods for Tailoring Surface Properties of Polyvinylidene Fluoride: Review and Challenges

“…In contrast, the incomplete dehydrogenation of the surface film favored oxidation upon exposure to air. As recently predicted by theory [ 11 ] and confirmed by experiments [ 12 ], the C–H bond is replaced by C–OH even after receiving a very small fluence of O atoms. The discrepancy between the wettability and the oxygen concentration between the results reported by Duca et al [ 6 ] and Park et al [ 10 ] reveals a non-trivial relationship between these two properties of argon plasma-modified fluorine-containing polymers.…”

“…According to theoretical predictions [ 11 ], the substitution of hydrogen with the hydroxyl group is highly probable and exothermic. The initial stage in oxygen-plasma treatment of the PVDF materials should be the partial substitution of the surface C–H bonds with the C–OH functional groups.…”

Precise Control of Nanoscale Cu Etching via Gas-Phase Oxidation and Chemical Complexation

“…34,35 More recently, DFT has provided understanding of surface reactions during ALE of aluminum oxide and polymers. 36,37 While ALE of copper has been reported recently experimentally, 38−40 quantification of the volatile reaction products has been challenging due to their low concentrations. It is therefore the goal of this work to combine experimental studies and theoretical insight to delineate the most probable reaction mechanism leading to selective ALE of copper.…”

“…Computational methods based on density functional theory (DFT), with at least gradient-corrected exchange-correlation functionals, now routinely provide atomic-scale understanding of many ground-state chemical reactions and materials properties. − DFT-based simulations have been instrumental to innovations in the fields of photovoltaics, − (photo)­electrocatalysis, − energy storage devices, , and materials (bulk and surface) processing − to name a few. It has become an enabling approach for functional material design and chemical process development and has been used to evaluate gas-phase chemical processes relevant to the semiconductor industry, including chemical vapor deposition (CVD) and ALD of copper. , More recently, DFT has provided understanding of surface reactions during ALE of aluminum oxide and polymers. , While ALE of copper has been reported recently experimentally, − quantification of the volatile reaction products has been challenging due to their low concentrations. It is therefore the goal of this work to combine experimental studies and theoretical insight to delineate the most probable reaction mechanism leading to selective ALE of copper.…”

In silico design of a thermal atomic layer etch process of cobalt

“…However, very few rigorous computational studies of thermal ALE processes using quantum chemical calculations have been reported so far. Of note is the work of Ventzek and co-workers 53 who presented a DFT study focusing on the ALE of polymer surfaces using an oxygen flux and Hamaguchi and co-workers 54,55 who investigated the self-limiting behavior of hexafluoroacetylacetone (hfacH) on Ni and NiO. However, the above computational studies were based on known ALE processes.…”