AVS 62nd International Symposium & Exhibition
    Plasma Science and Technology Friday Sessions
       Session PS+SS+TF-FrM

Paper PS+SS+TF-FrM11
Towards a Nanoscale Plasma Etching Precision: Molecular Dynamics Simulations of Si-Cl Interactions

Friday, October 23, 2015, 11:40 am, Room 210B

Session: Atomic Layer Etching (ALE) and Low-Damage Processes II
Presenter: Paulin Brichon, Univ. Grenoble Alpes-CNRS-CEA/Minatec-LTM,38000 Grenoble-France
Authors: P. Brichon, Univ. Grenoble Alpes-CNRS-CEA/Minatec-LTM,38000 Grenoble-France
E. Despiau-Pujo, LTM, France
O. Mourey, Univ. Grenoble Alpes-CNRS-CEA/Minatec-LTM,38000 Grenoble-France
G. Cunge, LTM - CEA/LETI, France
O. Joubert, Univ. Grenoble Alpes-CNRS-CEA, France
Correspondent: Click to Email
Due to high ion bombardment energies and significant fragmentation rates, conventional CW plasma processes are not able to selectively etch ultrathin films without damaging the active layers of advanced nanoelectronic devices (FDSOI, FinFET). In order to achieve uniform and damage-free etching of sub-nm-thick materials, one alternative is to lower the electron temperature (Te) of the plasma. This can be achieved temporally by pulsing the plasma (i.e. switching on and off the RF source power), which introduces two additional parameters to tune an etching process, the pulsation frequency and the duty cycle (DC). Pulsed-plasma discharges exhibit lower average ion energies (Ei~5-10eV); their chemical reactivity (or dissociation rate) can also be controlled by varying the DC. Another alternative is to lower Te spatially, by segregating the electron heating region far from the wafer. These low-Te plasmas are characterized by very low Ei (Ei<5eV) and high radical densities.

With lower Ei and controllable reactivity, these plasmas are promising to etch sub-nm-thick stacked materials. However, the interactions between reactive plasmas and surfaces are so complex that the efficient development of new processes can require numerical simulations. Therefore, we develop Molecular Dynamics (MD) simulations to understand the impact of various plasma technologies on the interactions between ultrathin Si films and Cl2 plasmas under a wide range of plasma conditions. They help to understand the precise role of Ei in plasma-surface interactions, the relationship between the flux/energy of reactive species bombarding the surface and its structural/chemical modifications.

In this study, MD simulations - coupled with experiments - are performed to quantify modifications (plasma-induced damage, etch rate) of Si films after exposition to various Cl2 plasma conditions, simulated by bombarding the substrate with both ion and neutral species. All simulations show the formation of a stable SiClx reactive layer and a constant etch yield (EY) at steady state. The key plasma parameter to control the etching of ultrathin Si layers is Ei, which lowers both the damaged layer thickness and EY when it is decreased. The neutral-to-ion flux ratio (Γ) is the 2nd key parameter: its increase reduces the damaged layer thickness while the etch rate grows. While maintaining Γ constant, the neutral dissociation rate and the ion composition do not influence significantly the etching process. Etching simulations of a simple Si pattern are then compared to the etching of blanket silicon, focusing on phenomena such as ion channeling, passivation/damage of pattern sidewalls and top pattern erosion.