Nanosheet FET Source/Drain Blocking Layers for Defect Control

The source/drain region is segmented into multiple blocking layers (first blocking layer, second blocking layer, third blocking layer) with different materials and positions. Each layer serves a specific function: the first blocking layer prevents facet formation at the interface, the second blocking layer provides lattice matching, and the third blocking layer offers additional protection. This segmentation allows the device to maintain high integration density while systematically addressing multiple failure modes that would otherwise occur during downscaled manufacturing.

The patent employs composite material structures in the source/drain region, combining different semiconductor materials (e.g., SiGe, SiC, diamond-like carbon) with varying germanium concentrations and crystalline properties. These composite materials are strategically layered to provide both mechanical support and electrical functionality, preventing process failures during downscaled fabrication while maintaining the high integration density required for modern IC devices.

The blocking layers are formed in advance during the epitaxial growth process, before the nanosheet FET structure is fully assembled and before operational stress is applied. The first blocking layer is deposited prior to nanosheet formation to prevent facet development at the interface. The second and third blocking layers are positioned to preemptively address lattice mismatch issues before they can manifest as defects during device operation, thereby maintaining both high operating speed and reliability.

The blocking layers act as intermediary structures between the substrate and the nanosheet active region. These intermediate layers mediate the interface between materials with different crystal structures and lattice constants, preventing direct interaction that would cause facet formation and lattice mismatch defects. The intermediaries maintain the high performance of nanosheet FETs while eliminating the reliability issues associated with direct interfaces.

The blocking layers are merged with the source/drain region formation process through continuous epitaxial growth, rather than being added as separate discrete structures. The first, second, and third blocking layers are integrated into the source/drain epitaxial growth sequence, allowing them to be formed in-situ with the surrounding semiconductor materials. This merging reduces structural complexity while maintaining the reliability benefits of multiple blocking layers.

Each blocking layer is designed to serve multiple functions simultaneously. For example, the first blocking layer not only prevents facet formation but also provides a transition interface for subsequent layers. The second blocking layer both matches lattice constants and provides mechanical support. The third blocking layer offers both protection and electrical isolation. This multi-functionality reduces the need for additional separate structures, thereby limiting the increase in device complexity while achieving high reliability.