Plasma atomic layer etching

Summary form only given. The thinning of the dielectric in the metal (and non-metal) gate stacks and the need to resolve etching on an atomic layer basis present large technological challenges. Conventional plasma processes which utilize reactive ion etching typically do not have sufficient controllability to achieve atomic layer resolution and to avoid damage. To ensure atomic-level control it is desirable to use a self-limiting process which is independent of the process time. This self-limited etching can be described as layer-by-layer etching or atomic layer etching. Plasma atomic layer etching (PALE) is a methodology similar to plasma atomic layer deposition. In PALE, formation of a monolayer of reactants is followed by the removal of the layer that then self terminates the process. For example, deposition of a thin layer of polymer or passivation followed by etching in a non-polymerizing plasma with low energy ion energy could remove only a single layer or less of underlying material. The higher threshold energy required to remove the underlying material in the absence of the passivation would self-terminate the process. The challenge is to perform these processes in conventional plasma equipment as opposed to expensive and highly specialized beam equipment. In this paper, results from a computational investigation of PALE will be discussed with the goal of demonstrating the potential of using conventional plasma etching equipment. The hybrid plasma equipment model (HPEM) and the Monte Carlo feature profile model (MCFPM) were modified to have pulse periodic capability as required for PALE, and to kinetically resolve ion energy distributions to finely resolve threshold energies. Results will be discussed for at least two systems: 1) PALE of Si using steps of an Ar/Cl₂ plasma (passivation) followed by Ar plasma (etch) and 2) PALE of SiO₂ using steps of a fluorocarbon plasma (passivation) followed by an Ar plasma (etch)