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

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 angstrom/cycle (4.94 +/- 0.1 ng/cm(2).cycle), which matches the range of maximum experimental values.