A Three-Step Atomic Layer Deposition Process for SiN Using SiCl, CHNH, and N Plasma.

We report a novel three-step SiN atomic layer deposition (ALD) process using SiCl, CHNH, and N plasma. In a two-step process, nonhydrogenated chlorosilanes such as SiCl with N plasmas lead to poor-quality SiN films that oxidize rapidly. The intermediate CHNH step was therefore introduced in the ALD cycle to replace the NH plasma step with a N plasma, while using SiCl 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 CHNH step in addition to the N plasma step. During ALD, the reactive surface sites were monitored using in situ surface infrared spectroscopy. Our infrared spectra show that, on the post-N plasma-treated SiN surface, SiCl reacts primarily with the surface -NH species to form surface -SiCl ( x = 1, 2, or 3) bonds, which are the reactive sites during the CHNH cycle. In the N plasma step, reactive -NH surface species are created because of the surface H available from the -CH groups. At 400 °C, the SiN 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%.