On Channel Shape Variation of 10-nm-Gate Gate-All-Around Silicon Nanowire MOSFETs

Recently, gate-all-around (GAA) nanowire field effect transistors (NWFETs) have attracted increasing attention due to their superior gate control and short channel effect immunity [1-4]. However, confined by the limitation of manufacturing process, the different aspect ratio (AR) results in different shapes of channel cross section, such as ellipse-shaped or rectangular-shaped instead of the ideal round-shaped and square-shaped, respectively [5-8]. In this study, we analyze the effects on 10-nm-gate singleand multi-channel GAA silicon NWFETs with different geometry of cross-section, including AR and radius variation by applying an experimentally validated three-dimension (3D) quantum correction simulation. We point out that an ellipse-shaped GAA NWFETs having relatively smaller AR of radius owns better electrical characteristics. As the technology nodes have channel length in nanoscale regime, therefore, it becomes necessary to include quantum mechanical effects when modeling any FET’s terminal property. To model the quantum mechanical effects, we adopt a computationally cost-effective simulation model which consists of drift-diffusion equations with doping-/field-dependent, channel orientation dependent, and surface roughness mobility for the carrier’s transport and density-gradient equations for various quantum mechanical effects [9]. The computational architecture of the 3D single-channel NWFET and cross-section views of channel are shown in Fig. 1(a). Figure 1(b) shows the achieved electrical characteristics of single-channel GAA NWFETs. In the case of AR = 0.5, the value of its subthredshold swing (SS) and drain induced barrier lowering (DIBL) is 66 mVdec and 68 mVV, respectively, and the order of magnitude of Ion/Ioff ratio reaches 6. However, for the case of AR = 2, has SS and DIBL are considerably larger at 116 mVdec and 113 mVV, respectively and the Ion/Ioff ratio is in the order of 4. It is obvious that when the AR decreases, the device shows better channel controllability. In addition, the device with a smaller AR demonstrates better operating characteristics and suffers from less short-channel effects. Figure 2 illustrates a transformation between ellipse to circle shaped cross-section of effective radius Reff and corresponding ID-VG characteristics. As can be seen, the device with the smallest Reff has the best Ion/Ioff ratio of all, but the case of the largest Reff (i.e. AR = 2) has the worst. This improvement is attributed to the effective gate control due to relatively smaller radius of the cross-section. For multichannel cases, we focus on the two-channel devices. Figure 3(a) is the 3D two-channel NWFET structure and its corresponding cross-section views respectively. The case of two-channel with AR equal to 0.5 has the best short-channel effect parameters (i.e. Ion/Ioff ratio, SS, and DIBL), which is shown in Fig. 3(b) among all the six cases. It also improves upon the values as compared with the single-channel case with AR = 0.5, while opposite is true for dual channels with AR = 2. Furthermore, it can be seen that two-channel case with both AR equal to 2 has the worst properties. The order of the Ion/Ioff ratio of it has degenerated to 3, and the DIBL is even worse. Consequently, the ability of suppressing short-channel effect of the structure with smaller AR is much better than that with the larger one. In summary, electrical characteristic of 10-nm-Gate silicon NWFET with various process variation of channel radius has been studied. We are currently studying NWFET with different channel materials. Acknowledgements: This work was supported in part by Ministry of Science and Technology, Taiwan Under Contract No. NSC-102-2221-E-009-161, and by tsmc, Hsinchu, Taiwan under a 2012-2013 grant.