Atomic Layer Etching 

As the feature size shrinking to less than 10 nm, the conventional etching tool saturates. Atomic layer etching is a process taking advantage of ion bombardment through plasma (CCP/ICP reactor) for layer – by – layer removal of material at atomic scale. Atomic layer etching tool are vital in multi -layer pattern transfer essential for todays advanced microelectronic industry.

Figure 4 . Schematics of one cycle of fluorocarbon-based atomic layer etching (ALE) comprising a modification step and a removal step.(DOI: https://aip.scitation.org/doi/10.1063/5.0047811)

ICP is a promising plasma source for ALE because it has a low plasma potential and electron temperature. In addition, radio frequency (RF) capacitive bias can be applied to the electrode. This RF biased ICP allows independent control of the plasma density and ion energy, enabling plasma control during the modification and removal steps independently. The combination of ICP and bias can be used as an ALE cycle recipe with continuous or pulsed control and various possible cycle recipes for ALE using biased ICP are shown in figure below.

Figure 5 Schematics of possible ALE cycles using inductively coupled plasma (ICP): (a) Continuous ICP + pulsed bias; (b) pulsed ICP + pulsed bias; (c) continuous ICP + continuous bias (DOI: https://aip.scitation.org/doi/10.1063/5.0047811)

Figure 6 Schematic of the Oxford Instruments FlexAL system equipped with substrate biasing. During plasma exposure, a substrate placed on the substrate table can be grounded or biased using two configurations—either using RF sinusoidal waveform biasing or using low-frequency (LF: 100 kHz) tailored waveform biasing. (https://aip.scitation.org/doi/pdf/10.1063/5.0028033)

Overall, plasma etching is an important tool for product development and therefore, it is important to learn about the suitability of plasma in any fabrication process. Impedans sensors can help best, check the attached application notes.