Paper PS-FrM7
Atomistic Simulations of He Plasma Modification of SiO2 Thin Films for Advanced Etch Processes

Friday, October 26, 2018, 10:20 am, Room 104A

Due to high ion bombardment energies and significant fragmentation rates, conventional continuous wave (CW) plasma processes are not able to selectively etch ultra-thin films without damaging the underlying layers of advanced nano-devices. Used as dielectric film in Flash memory devices, inter-poly Oxide-Nitride-Oxide (ONO) stack layer is directly impacted by this issue. Its bottom SiO2 layer (40Å) etching is challenging as it must be performed with nanoscale-precision in order to avoid damaging the underlayer substrate, which would lead to device performance loss. To achieve this nanometric precision etching, one possible solution may be the use of a recently developed two-step etch technology, which has already proved its worth for nitride spacers etching in terms of both anisotropy and selectivity [1]. In the first step, the material to be etched is exposed to a hydrogen (H2) or helium (He) ICP or CCP plasma; in the second step, the modified material is chemically etched by wet cleaning (HF bath) or exposure to gaseous reactants only (NH3/NF3 downstream plasmas).

Due to the complexity of plasma-material interactions, the development of such a new etch approach requires a more detailed understanding of the fundamental mechanisms involved in the process. Therefore, we develop Molecular Dynamics (MD) simulations to study the implantation step in Si-O-N-He and Si-O-N-H systems and provide an overview of the reaction processes at the atomic scale. The objective is to understand precisely the role of the ion energy and ion dose in the implantation, and to determine the relationship between the flux/energy of plasma species (He+, Hx+, H) bombarding the surface and its structural/chemical modifications.

In this paper, we investigate specifically the interaction between low energy He+ ions and SiO2 thin films via MD simulations. We study in particular the influence of the ion energy (5-100eV) and ion dose on the substrate modification. Cumulative bombardment leads to a self-limited ion implantation followed by the formation of a modified He-implanted layer at steady state. The modified layer thickness is shown to increase with the incident ion energy, and only few sputtering of the SiO2 layer is observed in the ionic energy range considered here. Mechanisms of helium retention and desorption, as well as the detailed structure of the material at steady state, will be discussed during the presentation.