日本大学生産工学部　生産工学部研究報告A51-2

3/38

─ 1 ─1　IntroductionPlasma technology has been widely used by overcoming the drawbacks of wet-chemical methods with a much inu-ence in many elds1). Especially, plasma etching such as reac-tive ion etching (RIE) is a standard manufacturing technology for the fabrication of sub-micron2) and atomic-scale3) struc-tures on material surfaces in the semiconductor industry4). In plasma etching, kinetic energies of ions combined with high reactivity of various radical species generated in the plasma are used to cause non-thermal-equilibrium chemical reactions in a few-nanometer deep surface region of substrate materials. Anisotropic etching and high selectivity required in the fabri-cation processes result from such chemical reactions1, 4). Fol-lowing diminution of feature sizes of integrated circuits in semiconductor chips, the organic polymer materials is consid-ered as a candidate of low dielectric constant (low-k)5) inter-connect insulator. For organic polymer etching processes1), plasmas of hydrogen-nitrogen gases are often used6–14). In these experimental investigations, the authors have stated that a corbon-nitride (CN) layer is formed on the organic polymer surface after nitride ions/radicals beam irradiation, and (1) the ratio of the number of nitrogen atoms to that of carbon atoms tends to be unity10, 14), (2) major etching products such as CN, HCN, and C2N2 originate from such CN layers12, 14). In other words, the formation of CN layers which have almost same numbers of nitrogen and carbon atoms seems a necessary con-dition for higher sputtering yields to be achived in such plas-ma processes. And it has been also observed that (3) a CN layer formed on the surface has almost equal numbers of sp2 hybridized bonds (which consist of both σ and π bonds) and single bonds (which consist of only σ bonds) as carbon-nitro-gen bonds6–8, 10) and, for such CN layers, if a hydrogen plasma is exposed, the number of π bonds decreases whereas the number of σ bonds are unchanged without sputtering8).To clarify the atomic level mechanisms of the above experi-mental results, we have analyzed reaction dynamics of plasma Articles日本大学生産工学部研究報告Ａ2018年 12 月 第 51 巻 第 ２ 号Numerical Simulation Study of Surface Reactions on the Organic Polymer Etching by Hydrogen-Nitrogen Ion Beam InjectionsMasashi YAMASHIRO＊（Received June 6, 2018）Classical molecular dynamics (MD) simulations of surface reactions on the organic polymer etching by H2/N2 or H2/NH3 ion beam injections have been performed. In the simulations, we have examined the resulting surface modication, the sputtering yields, and the sputtered species. It is found that injected nitrogen atoms can form a thin carbon-nitride (CN) layer on the organic polymer surface whose carbon-to-nitrogen atomic density ratio is approximately unity. During the polymer etching process, this CN layer can be sputtered by incident energetic ions and the desorbed species are found to be mainly carbon-nitrogen clusters. It is also found that the CN layer impedes more etching of the substrate by incident low-energy hydrogens which form volatile hydrogen nitride radicals. These simulation results are consistent with the experimental observations that, in polymer etching by hydrogen-nitrogen plasmas, a CN layer promotes polymer etching by ion bombardment whereas it also acts as a passivation layer against side-wall etching by hydrogen ion bombardment.Keywords:Nitridation, CN layer, Etching products, Passivation layer＊Associate Professor, Department of Liberal Arts and Basic Sciences, College of Industrial Technology, Nihon University.