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FinFETs have demonstrated significant performance improvement compared to planar devices, because of its superior short channel control and higher driving capability at a much smaller footprint. It has become the mainstream technology in CMOS industry since N20 node onward. Contact Poly Pitch (CPP) scaling used to be the main driving force in extending Moore’s law. However, severe limitations are foreseen from N3 node in terms of electrical performance, process requirements and manufacturing complexity. At N3 node, both fin and gate pitches are expected to reach their ultimate values, respectively 21 nm and 42 nm. Therefore, complex plasma etching processes using advanced plasma pulsing modes or atomic layer etching (ALE) are deployed to achieve high aspect ratio patterning capability with a detrimental effect on both process control and throughput. As an alternative, device architecture innovation will become the main scaling driving force for N3 node and beyond. 2D scaling like horizontal Gate-All-Around (GAA) devices, such as nanosheet (NS) and forksheet (FS) have demonstrated the potential for further device performance improvement [1,2]. The major NS patterning challenges are the SiGe lateral etch in the Si/SiGe superlattice stack and severe depth micro-loading due to the etch rate difference of SiGe and Si. In addition, 3D hybrid device architectures like Complementary FET (CFET) and Surrounding-Gate-Transistors (SGT) are proposed as revolutionary innovations to scale the devices in the vertical direction. For CFET devices, the N/P separation is moved to the vertical direction by stacking nMOS on top of pMOS or vice versa to achieve aggressive device scaling. This requires extremely high aspect ratio fin and gate patterning compared to horizontal-GAA NS devices. For SGT device, the channel is switched to the vertical direction, which can decouple the Gate length (Lg) from CPP scaling and eliminate the diffusion break to deeply scale the cell size. High aspect ratio vertical nanowire (NW) and direct metal gate etching with tight pitch are the new FEOL patterning challenges for the fabrication of SGT vertical devices.
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