The authors modeled SiN film etching with hydrofluorocarbon (CHxFy/Ar/O2) plasma considering physical (ion bombardment) and chemical reactions in detail, including the reactivity of radicals (C, F, O, N, and H), the area ratio of Si dangling bonds, the outflux of N and H, the dependence of the H/N ratio on the polymer layer, and generation of by-products (HCN, C2N2, NH, HF, OH, and CH, in addition to CO, CF2, SiF2, and SiF4) as ion assistance process parameters for the first time. The model was consistent with the measured C-F polymer layer thickness, etch rate, and selectivity dependence on process variation for SiN, SiO2, and Si film etching. To analyze the three-dimensional (3D) damage distribution affected by the etched profile, the authors developed an advanced 3D voxel model that can predict the time-evolution of the etched profile and damage distribution. The model includes some new concepts for gas transportation in the pattern using a fluid model and the property of voxels called “smart voxels,” which contain details of the history of the etching situation. Using this 3D model, the authors demonstrated metal–oxide–semiconductor field-effect transistor SiN side-wall etching that consisted of the main-etch step with CF4/Ar/O2 plasma and an over-etch step with CH3F/Ar/O2 plasma under the assumption of a realistic process and pattern size. A large amount of Si damage induced by irradiated hydrogen occurred in the source/drain region, a Si recess depth of 5 nm was generated, and the dislocated Si was distributed in a 10 nm deeper region than the Si recess, which was consistent with experimental data for a capacitively coupled plasma. An especially large amount of Si damage was also found at the bottom edge region of the metal–oxide–semiconductor field-effect transistors. Furthermore, our simulation results for bulk fin-type field-effect transistor side-wall etching showed that the Si fin (source/drain region) was directly damaged by high energy hydrogen and had local variations in the damage distribution, which may lead to a shift in the threshold voltage and the off-state leakage current. Therefore, side-wall etching and ion implantation processes must be carefully designed by considering the Si damage distribution to achieve low damage and high transistor performance for complementary metal–oxide–semiconductor devices.
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.
We developed a numerical simulation method for the depth profiles of plasma-induced physical damage to SiO2 and Si layers during fluorocarbon plasma etching. In the proposed method, the surface layer is assumed to consist of two layers: a C–F polymer layer and a reactive layer. Physical and chemical reactions in the reactive layer divided into several thin slabs and in the deposited C–F polymer layer, which depend on etching parameters, such as etching time, gas flow rate, gas pressure, and ion energy (V pp), are considered in detail. We used our simulation method to calculate the SiO2 etch rate, the thickness of the C–F polymer layer (T C–F), and the selectivity of SiO2 to Si during C4F8/O2/Ar plasma etching. We confirmed that the calculated absolute values and their behavior are consistent with experimental data. We also successfully predicted depth profiles of physical damage to the Si and SiO2 layers introducing our re-gridding method. We found that much Si damage is generated in the pre- and early stages of the overetching step of SiO2/Si layer etching despite the high selectivity. These simulation results suggest that the T C–F value and the overetching time must be carefully controlled by process parameters to reduce damage during fluorocarbon plasma etching. The results have also provided us with useful knowledge for controlling the etching process.
The fluctuations in etch rates caused by changes in chamber conditions were studied. Excess deposition of C-F polymer on the chamber wall increased CF x density while H was consumed by the polymer and/or was deactivated on the conductive surface of Si electrodes. The change in radical densities had a clear relationship with the SiN etch rate. The etch rate was accurately predicted by statistical analysis using equipment engineering system (EES) data and optical emission spectroscopy (OES) signals which were extracted by considering both the physical model and the results of statistical analysis.
Dramatic advances are being made in dry processing technologies. Atomic scale precision below 10 nm is now possible with fine patterning technologies for high-volume manufacturing of semiconductor devices. The isotropic and anisotropic nature of both film deposition and etching is versatile for nanoscale fabrication of three-dimensional features, such as high-aspect-ratio (HAR) features. Here we conduct a systematic review of the literature over the last 40 years to evaluate the history and progress of dry processes with regard to fine pattern transfer, HAR feature formation, and multiple patterning as lithographic techniques. Finally, we address the major challenges shared across the plasma science and technology community.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.