Silicon atomic layer etching by two-step plasma process consisting of oxidation and modification to form (NH4)2SiF6, and its sublimation

The process of precise silicon etching on the atomic scale was investigated by examining the formation of an (NH4)2SiF6 thin film as an intermediate phase followed by the removal of this layer by sublimation. An amorphous (NH4)2SiF6 thin film was formed on a Si substrate via a two-step plasma process consisting of an oxidation step involving an O2 plasma and a modification step to form an (NH4)2SiF6 thin film using an NH3/NF3 plasma, where the formed thin film was removed by a sublimation process. Because the thickness of the (NH4)2SiF6 thin film could be linearly controlled by altering the number of two-step plasma process cycles, the etching depth could be successfully controlled on the sub-nanometer scale.