Influence of hydrogen in silicon nitride films on the surface reactions during hydrofluorocarbon plasma etching

Abstract

The influence of the amount of hydrogen (H) in hydrogenated silicon nitride films (SixNy:Hz) on the etching properties and etching mechanism are unclear for hydrofluorocarbon plasma etching. Therefore, the authors have investigated the effect of H in SixNy:Hz films on the surface reactions during CH2F2/Ar/O2 plasma etching by experimental and numerical simulation techniques. The experimental etch yield (EY) and polymer layer thickness (TC−F) values for SixNy:Hz films with different H concentrations of 2.6% (low-SiN), 16.8% (mod-SiN), and 21.9% (high-SiN) show different trends with the CH2F2/(CH2F2 + O2) flow rate ratio. To understand the mechanism of the different etching properties, the authors estimated the chemical reaction probabilities of the H outflux between F, O, N, C, and Si dangling bonds using first principles calculations and the results of Fourier transform infrared spectroscopy. Based on the estimated reaction probabilities, the authors modeled the surface reactions of SixNy:Hz films under the assumption that the H outflux mainly scavenges incident F radicals (the main etchant species). The authors also consider that the reaction between H and N from outfluxes decreases the desorption reactions of C2N2 and HCN, resulting in a larger TC−F value. Comparing the simulation results of the trends in the whole flow rate ratio range and the absolute values of EY and TC−F with experimental data, the surface model can successfully explain the mechanism. Furthermore, the authors demonstrated time-dependent etched profile and damage distribution for fin-type field-effect transistor SixNy:Hz side-wall etching using the three-dimensional voxel-slab model with the above surface reactions to obtain knowledge about the effect of H on the etched profile and damage distribution. The results show that the etched profile and damage distribution on the Si fin structure are very different for low-SiN and high-SiN because of the different EY and TC−F values induced by different H outfluxes. These results indicate that it is important to carefully control both the etching process and amount of H in the SixNy:Hz film to achieve high-performance advanced complementary metal oxide semiconductor devices.

Effects of hydrogen content in films on the etching of LPCVD and PECVD SiN films using CF4/H2 plasma at different substrate temperatures

“…These reactions presumably lead to a thinner CF polymer layer in the highly hydrogenated SiN films. [ 21,36 ] In this study, as illustrated in Figure 7, the CN violet system (B,0–X,0) with a bandhead of 388.34 nm was clearly observed in both kinds of films. More importantly, the emission intensity from the PE‐SiN during etching was much stronger than that of the LP‐SiN.…”

“…H outflux originated from the film being etched and its surface reaction has been reported to be essential factor for the etching of hydrogenated SiN by fluorocarbon plasmas. [ 21,22,32 ] The H atoms can scavenge the F atoms from the plasma to form HF molecules, which give high polymer deposition rates, especially for Si or SiO 2 etching, because of the fluorine‐poor condition. [ 33–35 ] Nevertheless, for SiN etching, H outflux also reacts with O and N atoms that react with C to form CO, C 2 N 2 , and FCN or HCN byproducts.…”

“…[ 20 ] However, how hydrogen content in the SiN prepared by LP‐ and PE‐CVD influence the etching behavior has not been addressed. The effect of hydrogen in the PE‐SiN films on etch behavior with the CH 2 F 2 /O 2 plasmas has been investigated, [ 21 ] suggesting that the hydrogen outflux from the films could affect the surface reactions on the films with the consequence of ER variation. Recently, we reported the dependence of ER on substrate temperature ( T s ) in two bonding types (Si−H bond rich or N−H bond rich) of the PE‐SiN.…”

Plasma etching of high aspect ratio features in SiO2 using Ar/C4F8/O2 mixtures: A computational investigation

“…These effects can be mitigated by carefully controlling the overlying polymer thickness through the gas flow rate and the over-etch time. 17,18 While being an etchant and providing activation energy, ions are also typically neutralized when striking surfaces on the top and inside of the feature. In doing so, positive charge is deposited on the surfaces.…”

The influence of hydrogen concentration in amorphous carbon films on mechanical properties and fluorine penetration: a density functional theory and ab initio molecular dynamics study

“…Therefore, the reason we only considered the "bulk" part is that during the real etch process, the "surface" part takes place in a very short time and most of the time is required for the "bulk" part. In fact, many other researchers in the elds of etch processes [44][45][46] have controlled the etch prole by tuning the "density" of thin lms, which is a very important "bulk" property that can be easily tuned by the etch chemistry ratio, temperature, and plasma power.…”