Plasma atomic layer etching using conventional plasma equipment

Abstract

The decrease in feature sizes in microelectronics fabrication will soon require plasma etching processes having atomic layer resolution. The basis of plasma atomic layer etching ͑PALE͒ is forming a layer of passivation that allows the underlying substrate material to be etched with lower activation energy than in the absence of the passivation. The subsequent removal of the passivation with carefully tailored activation energy then removes a single layer of the underlying material. If these goals are met, the process is self-limiting. A challenge of PALE is the high cost of specialized equipment and slow processing speed. In this work, results from a computational investigation of PALE will be discussed with the goal of demonstrating the potential of using conventional plasma etching equipment having acceptable processing speeds. Results will be discussed using inductively coupled and magnetically enhanced capacitively coupled plasmas in which nonsinusoidal waveforms are used to regulate ion energies to optimize the passivation and etch steps. This strategy may also enable the use of a single gas mixture, as opposed to changing gas mixtures between steps.

Atomic Layer Etching at the Tipping Point: An Overview

“…By working close to the energy threshold for physical sputtering of one material, and exploiting energy threshold differences among different materials, etching selectivity can be optimized. 9 The threshold energy for physical sputtering E psth depends on the nature of the material and is higher in the case of SiO 2 than for Si, E psth (SiO 2 )>E psth (Si). By supplying chemical reactant to the substrate surface, chemically enhanced etching is possible, with an energy threshold E ceth (SiO 2 ) that is lower than for physical sputtering E psth (Si), which may enable selective etching of SiO 2 over Si.…”

“…While average ion energy has been shown to be useful, 9 careful studies of the impact of ion energy distributions on ALE performance are required to answer the question how closely ion energies must be controlled to enable optimal exploitation of the ALE window. Shin et al 46 investigated nearly mono-energetic ion energy distributions (IEDs) and observed novel phenomena (see below).…”

“…The modification of the surface by the precursor allows the material to be etched with lower activation energy as compared to the underlying material without modification. 9 The presence of chemical reactants at the substrate surface along with ion bombardment induce a chemical reaction between the surface atoms and the precursor which causes etch products to boil off or sputter from the surface. This process enables directional etching of the material at ion energies above the chemically enhanced etching energy threshold E ceth and below the physical sputtering energy threshold E psth , respectively.…”

“…In a second surface reaction step, bombardment of the surface with energetic species, typically a beam of low energy ions, 9 provides the necessary energy to induce chemical reactions between the adsorbed (d)) may include self-limited adsorption, short deposition, etc, followed by pump-out. Low energy Ar ion bombardment is often used for selective removal of reacted region ((e),(f)).…”

“…Key challenges for these approaches have been specialized equipment, long process times and low throughput. 9,10 However, a recent demonstration using a commercial plasma etch tool 10 and activities within the dry etching community 11 provide indications that the situation has changed, and that we may have reached for ALE the Tipping Point which Gladwell defined as the "the moment of critical mass, the threshold, the boiling point" when "ideas and products and messages and behaviors spread like viruses do".…”