The CORE Sequence: A Nanoscale Fluorocarbon-Free Silicon Plasma Etch Process Based on SF₆/O₂Cycles with Excellent 3D Profile Control at Room Temperature

Abstract

 Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

On the formation of black silicon in SF6-O2 plasma: The clear, oxidize, remove, and etch (CORE) sequence and black silicon on demand

“…In this study, we replace the conventional Bosch process by a recently developed plasma etch process named CORE (Clear, Oxidize, Remove, and Etch) in which the C 4 F 8 passivation cycle is replaced by an O 2 cycle. 33 The oxide thickness at the trench bottom is less dependent on the aspect ratio because the plasma oxidation is experimentally found to be self-limiting in our previous paper. 33 In short, during plasma oxidation, the growing oxide film will slow down the oxidation process logarithmically and effectively limit its thickness to about 3 nm or less.…”

“…33 The oxide thickness at the trench bottom is less dependent on the aspect ratio because the plasma oxidation is experimentally found to be self-limiting in our previous paper. 33 In short, during plasma oxidation, the growing oxide film will slow down the oxidation process logarithmically and effectively limit its thickness to about 3 nm or less. Consequently, all the horizontal surfaces will be cleared from the passivation in approximately the same R-time.…”

“…The CORE sequence has been shown to enable the etching of nanostructures having straight, smooth sidewalls with low (resist) mask erosion and undercutting. 33 Unlike the Bosch process, [34][35][36][37] the CORE sequence has no pileup of inhibitor deposits at the top of etching features. This is because the passivation layer originates from the silicon oxidation with a limited thickness as the growing silicon dioxide acts as a diffusion barrier.…”

“…This is because in this experiment, we only use 3 s for the O-step, which is not yet operational in the selflimiting regime as shown in our previous study. 33 Therefore, the open field areas will have a little more passivation and are more likely to develop grass when the R-time is restricted. Again, the formation of BSi in the open field will raise the fluorine pressure and, therefore, we observe a faster etch rate in the high aspect ratio features as these are virtually free of oxide residues.…”

“…More to the point, oxide growth slows down logarithmically once it is formed and becomes self-limiting when roughly 3 nm SiO x passivation has grown. 33 The latter means that at longer oxidation times, all surfaces tend to have exactly the same protective layer thickness independent of the aspect ratio. For the shorter O-step times, though, the limitation is not yet completed and the open areas will have more passivation than the high aspect ratio features and can result in BSi when the R-step is insufficient [as previously observed in Fig.…”