A Three-Step Atomic Layer Deposition Process for SiN_<i>x</i> Using Si₂Cl₆, CH₃NH₂, and N₂ Plasma

Abstract

We report a novel three-step SiNx atomic layer deposition (ALD) process using Si2Cl6, CH3NH2, and N2 plasma. In a two-step process, nonhydrogenated chlorosilanes such as Si2Cl6 with N2 plasmas lead to poor-quality SiNx films that oxidize rapidly. The intermediate CH3NH2 step was therefore introduced in the ALD cycle to replace the NH3 plasma step with a N2 plasma, while using Si2Cl6 as the Si precursor. This three-step process lowers the atomic H content and improves the film conformality on high-aspect-ratio nanostructures as Si–N–Si bonds are formed during a thermal CH3NH2 step in addition to the N2 plasma step. During ALD, the reactive surface sites were monitored using in situ surface infrared spectroscopy. Our infrared spectra show that, on the post-N2 plasma-treated SiNx surface, Si2Cl6 reacts primarily with the surface −NH2 species to form surface −SiClx (x = 1, 2, or 3) bonds, which are the reactive sites during the CH3NH2 cycle. In the N2 plasma step, reactive −NH2 surface species are created because of the surface H available from the −CH3 groups. At 400 °C, the SiNx films have a growth per cycle of ∼0.9 Å with ∼12 atomic percent H. The films grown on high-aspect-ratio nanostructures have a conformality of ∼90%.