Insights into different etching properties of continuous wave and atomic layer etching processes for SiO2 and Si3N4 films using voxel-slab model

Abstract

This work describes the modeling of the surface reactions involved in atomic layer etching (ALE) of SiO2 and Si3N4 with a deposition step using C4F8/O2/Ar plasma and an Ar plasma etch step. In the etching step, the surface was assumed to consist of two layers: a C-F polymer layer and a reactive layer. The effects of residual F from the deposition step and F originating from the C-F polymer layer during the etch step and the influences of the O and N outfluxes generated from the reactive layer were considered, in terms of their effects on the etch rates of the SiO2 and Si3N4 films. Using a three-dimensional voxel-slab model that included the surface reactions described above, an analysis was performed based on the differences between the etching properties of continuous wave (CW) etching and ALE in the cases of blanket wafers and self-aligned contact layers from the viewpoints of numerical simulations. As a result of these analyses, it was found that the use of monoenergetic ion energy improves surface layer thickness controllability for both the polymer layer and the reactive layer and that quantitative control of time variations in both the C-F polymer layer thickness and the ion penetration depth is necessary for high selectivity of SiO2 over Si3N4 (SiO2/Si3N4) and for low plasma-induced damage on the Si3N4 film. Furthermore, in the authors’ simulations, a relatively high SiO2 etch rate was obtained for a modified quasi-ALE (43 nm/min) while maintaining high SiO2/Si3N4 selectivity (more than 100) after optimization of the C-F polymer layer thickness, the ion energy, and the ALE cycle time; this represents a solution in terms of the important issue of the very low etch rate of ALE. These simulation results indicate that accurate prediction of the surface reaction, further quantitative control of the plasma parameters, and optimization of the pattern layout design are necessary to realize higher ALE process performance for practical use in mass production.

In Situ Monitoring of Etching Characteristic and Surface Reactions in Atomic Layer Etching of SiN Using Cyclic CF4/H2 and H2 Plasmas

“…These advancements necessitate atomic-scale precision in manufacturing trillions of devices per day while controlling process variability . To meet these requirements, atomic layer etching (ALE) has garnered significant attention as an alternative to conventional etching techniques. − …”

Review and future perspective of feature scale profile modeling for high-performance semiconductor devices

“…To reproduce a realistic ALE and investigate optimum control of the ALE process with low damage, Kuboi et al 71 . also reported an ALE model of the dielectric films (SiO2 and SiN) in which the etching effects due to fluorine (F) in the polymer layer, residual F from the previous step, and the outflux of oxygen (O), and the deposition effect due to outflux of nitride (N), as shown in Fig.…”

“…Surface reaction model of the ALE process (cycles of deposition and Ar+ etch steps) for SiO2 and SiN films using normalC4normalF8/normalO2/Ar plasma 71 …”

“…Fig. 26 Simulated feature profiles for SAC etching in the cases of (a) CW, (b) realistic ALE, and (c) ideal ALE after performing CW etching of 70 s. The depth and diameter of the SAC structure were 400 and 100 nm, respectively 71. …”

“…Fig. 25 Simulated etching amounts and damage distributions for (a) CW, (b) realistic ALE, and (c) ideal ALE (mALE) for SiN film 71. …”