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

Abstract

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%.

Remote Plasma Atomic Layer Deposition of SiNx Using Cyclosilazane and H2/N2 Plasma

“…The PEALD of SiN x using aminosilane and NH 3 plasma leads to a reduced growth rate because the H-and NH x -terminated surface is not undercoordinated, which in turn inhibits precursor adsorption. In contrast, N 2 plasma is able to generate reactive undercoordinated bare surface sites; PEALD using aminosilane and N 2 plasma reveals quite sensible growth rates [21][22][23][24].…”

A Brief Review of Plasma Enhanced Atomic Layer Deposition of Si3N4

“…(Color online) Cross-sectional TEM image of post wet-etch SiNx deposited by a three-step PEALD process using Si2Cl6, CH3NH2, and N2 plasma at 400 °C. Reproduced with permission from [36], Copyright 2018, American Chemical Society.…”

“…Ovanesyan et al [36] reported SiN x thin films with ~95 % conformality on patterned structures (aspect ratio of ~5). Figure 9 is a TEM image for a ~25-nm-thick SiN x thin film deposited from Si 2 Cl 6 , CH 3 NH 2 , and N 2 plasma at 400 .…”

“…Figure 9 is a TEM image for a ~25-nm-thick SiN x thin film deposited from Si 2 Cl 6 , CH 3 NH 2 , and N 2 plasma at 400 . In this case, Ovanesyan et al [36] suggested a novel three-step PEALD process. By adding a CH 3 NH 2 exposure step in the PEALD cycle, conformality and growth rate per cycle (GPC) were increased compared to those with the PEALD method using aminosilanes and N 2 plasma.…”

“…Besides studies on the wet etch rate of SiN x thin films on planar surfaces, the wet etch rate has also been studied for high aspect ratio structures. However, most studies showed different wet etch rates for the sidewall, bottom, and top surface of 3D trench patterns [36]. The poor wet etch rate at the bottom sidewall is problematic in silicon nitride PEALD processes.…”