Multigate Epitaxial Source/Drain Structures on Dielectric Substrates

The patent introduces a dielectric substrate as an intermediary between the epitaxial source/drain structures and the underlying substrate. This dielectric layer prevents direct contact that would form parasitic transistors, while still allowing the epitaxial structures to be formed using standard processes. The dielectric substrate acts as a mediator that eliminates the harmful parasitic effects without complicating the overall fabrication flow.

The patent extracts the problematic semiconductor substrate interface and replaces it with a dielectric substrate. By removing the semiconductor-substrate contact, the source of parasitic transistor formation is eliminated. The epitaxial source/drain structures are now grown on a dielectric surface rather than a semiconductor surface, which prevents the formation of unwanted parasitic devices while maintaining the desired electrical functionality.

The patent changes the fundamental parameter of the substrate material from semiconductor to dielectric. This parameter change fundamentally alters the electrical characteristics at the source/drain interface, preventing parasitic transistor formation that would otherwise become increasingly problematic as devices scale. The dielectric substrate provides a non-conductive foundation that maintains gate control even as device dimensions shrink and density increases.

The patent applies preliminary anti-action by pre-establishing a dielectric substrate before forming the epitaxial source/drain structures. This preliminary measure prevents the formation of parasitic transistors before they can occur, countering the scaling-induced increase in parasitic effects. By acting in advance with the dielectric substrate, the patent prevents reliability degradation as devices continue to scale down for higher density.