Implementation of atomic layer etching of silicon: Scaling parameters, feasibility, and profile control

Abstract

Atomic or layer by layer etching of silicon exploits temporally segregated self-limiting adsorption and material removal steps to mitigate the problems associated with continuous or quasicontinuous (pulsed) plasma processes: selectivity loss, damage, and profile control. Successful implementation of atomic layer etching requires careful choice of the plasma parameters for adsorption and desorption steps. This paper illustrates how process parameters can be arrived at through basic scaling exercises, modeling and simulation, and fundamental experimental tests of their predictions. Using chlorine and argon plasma in a radial line slot antenna plasma source as a platform, the authors illustrate how cycle time, ion energy, and radical to ion ratio can be manipulated to manage the deviation from ideality when cycle times are shortened or purges are incomplete. Cell based Monte Carlo feature scale modeling is used to illustrate profile outcomes. Experimental results of atomic layer etching processes are illustrated on silicon line and space structures such that iso-dense bias and aspect ratio dependent free profiles are produced. Experimental results also illustrate the profile control margin as processes move from atomic layer to multilayer by layer etching. The consequence of not controlling contamination (e.g., oxygen) is shown to result in deposition and roughness generation.

Atomic layer etching of 3D structures in silicon: Self-limiting and nonideal reactions

“…After the initial transient the surface quickly establishes a steady state coverage of 1% SiCl, 21% SiCl 2 , and 78% SiCl 3 , making an average chlorination per surface site, hCli, of 2.77. The predicted time to saturation for both the chlorination and ion bombardment phases are similar to those observed by Ranjan et al, 20 as well as Goodyear and Cooke. 34 The same etching conditions were used on the AR ¼ 10 feature as for the AR ¼ 2 feature.…”

“…This system is capable of producing ALE behavior in experiments, and previous modeling efforts. 14,[19][20][21] Starting from an idealized process, where only completely self-limited reactions occur, individual nonidealities are introduced to examine their effect on ALE performance. Once these dependencies are established, realistic nonidealities are introduced by coupling the feature scale model to a reactor scale model of an inductively coupled plasma (ICP).…”

The 2017 Plasma Roadmap: Low temperature plasma science and technology

“…The large dynamic range of time/ spatial scales and physical phenomena continues to challenge the field. Integrating low pressure simulations with the formation of micro-and nano-structures for semiconductor processing still hold challenges [170] that extend to atmospheric plasmas interacting with microstructures, such as catalysts and porous materials. Progress continues in multiscale simulations.…”

Utilizing surface modification in plasma‐enhanced cyclic etching of tantalum nitride to surpass lithographic limits

“…While the effects of varying plasma parameters such as power and pressure are well known for CW plasmas, the delineation of the ALE process facilitates a greater degree of control, as factors such as neutral to ion ratio can be partially tailored by adjusting the pressure in each discrete step . We investigated the effect of pressure on the cyclic etching of TaN and observed its impact on mask retention, sidewall profile, and redeposition.…”