AVS 49th International Symposium
    Plasma Science Tuesday Sessions
       Session PS-TuP

Paper PS-TuP21
Simulations of Topography Defects Development (Undercut and Bowing) for Deep Silicon Etching under a SF@sub 6@/O@sub 2@ Plasma Chemistry

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Plasma Applications
Presenter: G. Marcos, University of Orleans, France
Authors: G. Marcos, University of Orleans, France
A. Rhallabi, University of Nantes, France
P. Ranson, University of Orleans, France
Correspondent: Click to Email
New microelectronic applications such as MicroElectroMechanical Systems (MEMS) need very high aspect ratio trenches (deep/width>60) in semiconductors. Improvements in dry etching processes have been performed in obtaining deep silicon trenches by using a cryogenic method in an Inductive Coupled Plasma reactor with a SF@sub 6@/O@sub 2@ plasma discharge(see abstract of M. Boufnichel at al). The experimental research has shown that undercut and bowing formation is strongly correlated with plasma parameters, mask shape and time during processing. In order to understand the involved plasma-surface interaction mechanisms, we have developed a two dimensional etching model based on Monte-Carlo techniques. This etching model includes different surface processes due to neutral reactive species such as the fluorine and the atomic oxygen. Their flux is assumed to be isotropic. A transport model through the RF sheath is connected with the surface model to calculate angular and energetic ion function distribution. Monte-Carlo approach allows to introduce physical processes with probabilistic considerations, such as adsorption/desorption, spontaneous chemical etching, ion preferential sputtering, incident species reflexion, passivation layer formation and redeposition. Kinetic parameters are introduced as input data obtained by experimental measurements. The etched substrate is discretized by a series of uniform square cells which size defines a real number of silicon atoms. Local surface displacement is modelled by "full" cells dis/re-appearance when an etching or redeposition process occurs. This microscopic method gives an instantaneous picture of surface state during the process. In particular, it permits to follow the F/Si and O/Si surface coverage on the sidewalls versus depth and time. These information are useful to understand the transport of species in the trench. The model shows that undercut and bowing development depends on kinetic surface parameters.