Deposition profile of ammonium bromide in N₂/HBr plasmas for high-aspect-ratio multilayer etching

Abstract

The deposition profile of ammonium bromide in N2/HBr plasmas was evaluated as a function of depth in a macro-cavity structure for the high-aspect-ratio etching process. The macro cavity reproduces deep holes in 3D NAND structures. The profile was compared with the calculated results of that of fluorocarbon (FC) in CF2 radicals. The decay in the ammonium bromide deposition is smaller than that of FC over a depth of 50 mm in the cavity. The 50 mm depth corresponds to an aspect ratio of 60. To clarify the experiment, two models were investigated; ammonium bromide forms in the gas phase, and on a solid surface, respectively. It was found that the latter model reasonably clarifies the experiment when comparing the two models. These results imply that ammonium bromide sufficiently reaches the bottom of deep holes in 3D NAND high-aspect-ratio structures.