AVS 60th International Symposium and Exhibition
    Plasma Science and Technology Thursday Sessions
       Session PS-ThM

Paper PS-ThM2
MD Simulations of Pulsed Chlorine Plasmas Interaction with Ultrathin Silicon Films for Advanced Etch Processes

Thursday, October 31, 2013, 8:20 am, Room 104 C

Session: Plasma Modeling
Presenter: P.D. Brichon, Cnrs/ujf/ Cea - Ltm, France
Authors: P.D. Brichon, Cnrs/ujf/ Cea - Ltm, France
E. Despiau-Pujo, Cnrs/ujf/ Cea - Ltm, France
G. Cunge, Cnrs/ujf/ Cea - Ltm, France
M. Darnon, Cnrs/ujf/ Cea - Ltm, France
O. Joubert, Cnrs/ujf/ Cea - Ltm, France
Correspondent: Click to Email
Due to high ion bombardment energies and significant fragmentation rates, conventional continuous-wave plasma processes are not able to selectively etch ultrathin films without damaging the active layers of advanced nanoelectronic devices (e.g. FDSOIs, FinFETs). In order to achieve a uniform/smooth etching of sub-nm thick materials, one possible alternative is to use pulsed-plasma discharges which exhibit lower average ion energies, thus minimizing surface damage when necessary. Pulsing the plasma consists in switching on and off the RF power, which introduces two additional parameters, the pulsation frequency and the duty cycle, i.e. the ratio between the pulse on-time and the total pulse duration. This latter has been shown to control the dissociation rate of the plasma i.e. the proportion of atomic species (Cl, Cl+) relative to that of molecular species (Cl2, Cl2+). However, the interactions between reactive pulsed plasmas and surfaces are so complex that the efficient development of new processes requires numerical simulations. Therefore, we propose to develop Molecular Dynamics (MD) simulations to study the silicon-chlorine system under pulsed plasma conditions. These simulations can help to understand the precise role of the ion energy in plasma-surface interactions, as well as the relationship between the flux/energy of reactive species (ions, radicals) bombarding the surface and its structural/chemical modifications. To understand the impact of the dissociation rate in pulsed plasma processes, we first compare the effects of atomic (Cl, Cl+) versus molecular species (Cl2, Cl2+) bombardment on the silicon substrate. All simulations show an initial rapid chlorination of the surface followed by the formation of a stable SiClx mixed layer and a constant etch yield at steady state. Regarding the role of the ion energy, it appears that for most etch features (chlorine uptake, SiClx layer thickness, nature of etch products), bombarding the surface with X eV Cl+ is equivalent to bombarding it with 2X eV Cl2+. This mathematical relation does not hold for the etch rate, which is larger for atomic bombardment (Cl+) at low energy (5-10eV) but more important for molecular bombardment (Cl2+) at high energy (50-100eV). Comparisons with experiments and mechanisms responsible for these behaviors will be discussed during the presentation. The influence of both the ion-to-radical flux ratio and the duty cycle on the dynamics/characteristics of the etch (yield, products) and on the surface evolution (structure, chemical composition) will also be presented.