A Three-Step Atomic Layer Deposition Process for SiN _x Using Si₂Cl₆, CH₃NH₂, and N₂ Plasma

We report a novel three-step SiN _x 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 SiN _x 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 SiN _x surface, Si₂Cl₆ reacts primarily with the surface -NH₂ species to form surface -SiCl _x ( 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 SiN _x 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%.