Nanosheet

**Nanosheet FET (Gate-All-Around) Fabrication** is **an advanced semiconductor manufacturing process that creates thin silicon or silicon-germanium channel layers stacked vertically with gate structures wrapped around multiple sides of each nanowire channel — enabling superior electrostatic control and performance compared to traditional FinFET architectures**. The nanosheet FET fabrication process begins with epitaxial growth of alternating silicon and silicon-germanium layers on a silicon substrate, creating a superlattice structure with precisely controlled layer thicknesses in the range of 5-15 nanometers to define the channel dimensions. The vertical stacking of multiple nanosheet channels enables the effective gate length to be defined independently of lithographic resolution through the thickness of deposited layers rather than relying on minimum patterned feature size, allowing excellent gate length control even as patterning becomes more challenging. Selective etching processes remove the silicon-germanium sacrificial layers while preserving the silicon channel layers, creating free-standing silicon nanowires suspended above the substrate that subsequently form the conduction channels when the gate stack is deposited. The gate stack deposition involves careful conformal coating of the suspended nanosheet channels with a dielectric layer (typically silicon dioxide with thickness 2-5 nanometers), followed by deposition of work function metals and a polysilicon gate conductor that completely surrounds each nanosheet channel. The nanowire suspension and gate wrap-around geometry requires sophisticated processing including careful control of etch chemistries to avoid unintended damage to channel materials, precise control of dielectric thickness to achieve target threshold voltages, and reliable work function metal selection to minimize threshold voltage variation. Source and drain engineering for nanosheet transistors requires selective epitaxial growth of heavily doped silicon or silicon-germanium layers at the nanosheet extremities, creating low-resistance contacts while maintaining isolation between adjacent devices. **Nanosheet FET fabrication represents a critical advancement in gate-all-around transistor technology, enabling superior electrostatic control through multi-layer vertical channel stacking.**