Study of line edge roughness on various types of gate-all-around field effect transistor

The impact of line edge roughness (LER) on gate-all-around FETs (GAAFETs) with various channel types is investigated. Among various channel types of GAAFET, (i) nanowire (NW), (ii) nanosheet (NS), and (iii) stacked channel are investigated. Considering the Si/SiGe stacking and selective etching process (which is commonly used to release the channel of GAAFET), we modeled the LER profile for channels. Moreover, 3D LER modeling is adopted to represent the LER profile in non-planar device structure. It turned out that the NS channel GAAFET has not only higher on-state drive current but also better performance variation immunity than the NW channel GAAFET. This is because the aspect ratio of channel affects the LER profile. Compared against single-channel GAAFET, the stacked channel GAAFET has better variation immunity because of its complementary effect in-between stacked channels. To investigate the impact of complementary effect, we simulated two different stacked channels, one of which has no correlation between stacked channels, and the other of which has the correlation induced from the channel-releasing processing step. It turned out that the stacked channel GAAFET with no correlation in-between the channels can have better variation-robustness.