Investigation of Electrical Characteristic Behavior Induced by Channel-Release Process in Stacked Nanosheet Gate-All-Around MOSFETs

In this brief, several issues attributed to the channel-release process in vertically stacked-gate-all-around MOSFETs (GAAFETs) having various nanosheet (NS) widths were rigorously investigated. Because of the finite selectivity of SiGe (sacrificial layer) etchant to Si (channel layer), Si channel is likely to be thinned during the channel-release step which is one of the key processes in stacked-GAA FET fabrication. Consequently, the thickness of channel and the interchannel space becomes variable depending on the NS width, since the etch time must be determined by the widest channel within a wafer. It results in a channel width dependence of gate work function, gate-to-drain capacitance, and channel interfacial property as well as the electrostatic gate controllability. The electrical characteristic behavior of stacked-GAAFETs induced by these effects was thoroughly investigated through process-based 3-D technology computer-aided design (TCAD) device simulation along with a transmission electron microscopy (TEM) and an energy-dispersive spectroscopy (EDS) analyses. The results confirm that width-dependent effects should be taken into account when fabricating and compact modeling the stacked-GAAFETs with various NS widths which are required for logic and static random access memory (SRAM) applications.