Effect of reactant transport on the trench profile evolution for silicon etching in chlorine plasmas

• A multi-scale model is applied to consider the trench profile evolution in silicon etching.
• The micro-trenching is mainly decided by pressure, local charging and ion reflection.
• Surface neutral coverage is crucial for profile shape with synergic role of ions.
• Discharge condition and micro-mechanisms in trench decide the pattern transfer fidelity.

A sheath is generated over the rf biased substrate in etching processes, its properties play an important role in determining the transport of reactant species including ions and neutrals toward the substrate, as well as the surface reactions, and as a consequence the evolution of the etching profile. In this work, a multi scale model including the global, sheath and trench model is applied to simulate dry etching processes in nano-patterned samples. First, the global model gives the discharge parameters in chamber. Sheath properties in terms of external discharge parameters are decided using the sheath model, the reactant transports in sheath to trench surface are then obtained. At last, based on the surface reaction model and cellular removal algorithm, the evolution of trench profile is simulated. Influences of different discharge parameters like pressure and bias voltage on microscopic non-uniformity generation during etching are studied for better understanding of etching mechanism. Results show that the profiles have different evolution processes under various discharge conditions. Specially, the directionality, charging induced distortion and reflection for ions determine the profile of micro-trenching. Besides, neutral coverage associated with pressure and pattern geometry can influence the local etch rate, further decide the formation of RIE lag, undercut and bowing.