Atomic Layer Etching - Flux Control
The approach that has gotten much attention of late is atomic layer etch by flux control, or layer by layer etch or cyclic etching. The difference to conventional etch approaches is depicted below for silicon oxide etch:
Whereas a constant background of Ar plasma is maintained throughout the process, precisely timed sections of adding a FC precursor and higher ion energy (by adding bias) are introduced in a repeating fashion.
The resulting process advantage is depicted nicely in the in-situ plot shown below:
Journal of Vacuum Science & Technology a 32(2), 2014
During the deposition step, deposition occurs (as expected). During the step where the ion energy is raised, removal occurs until the FC from the preceding step is exhausted. After this the removal saturates. One can very easily see the plateaus within each cycle that show the self-limiting behavior of this approach.
An investigation on the application of this approach to device patterning has also started. One of the main challenges of applying this approach to commercial reactors is the lack of in-situ measurement capabilities. As such timing of the etch step is critical as seen below:
After optimizing the etch step length and optimizing the precursor in the deposition step, significant overetch can be achieved in etching silicon oxide while being stopped on silicon nitride.
More detailled reports on the results can be seen here:
Advanced Etch Technology for Nanopatterning V, 2016
Journal of Vacuum Science & Technology A 34(1), 01B102, AVS: Science & Technology of Materials, Interfaces, and Processing, 2016