Backside Source/Drain Via Structure for Lower Contact Resistance

The patent introduces backside power rails and vias, utilizing the third dimension (vertical depth from backside to frontside) to create additional current paths. By forming via holes through the substrate and filling them with conductive material, the invention adds vertical conductive pathways that complement the lateral power rails, effectively distributing current in 3D space rather than being constrained to 2D planes, thereby reducing resistance and power consumption while maintaining integration density.

The invention changes the geometric parameters of the via structure by laterally expanding the via holes beyond the original fin width. This expansion increases the cross-sectional area and interfacial contact area between the conductive fill material and the surrounding structures, thereby reducing contact resistance. The lateral expansion is achieved through selective etching and filling processes that modify the via dimensions while maintaining manufacturing feasibility.

The invention performs preliminary actions by forming mandrels and applying sacrificial layers before creating the final via structure. The mandrels are formed with controlled dimensions, and sacrificial layers are deposited to define the final via geometry. These preliminary structures serve as templates that guide subsequent etching and filling processes, ensuring that the final via holes achieve the desired expanded dimensions with appropriate precision without requiring direct high-precision formation of the final via structure.