Multigate Epitaxial Source/Drains for Contact Alignment

The patent applies local quality by differentiating the treatment of epitaxial source/drain regions based on their spatial location and functional requirements. Different epitaxial growth conditions, doping concentrations, and lateral dimensions are applied to different regions (e.g., first epitaxial source/drain versus second epitaxial source/drain) to optimize contact landing windows in specific locations while preventing merging in others. This localized optimization allows high device density while maintaining electrical isolation where needed.

The patent segments the epitaxial source/drain structure into distinct regions (first epitaxial source/drain, second epitaxial source/drain, and isolation regions) with different properties. By dividing the continuous epitaxial growth into separate, controlled segments, the patent prevents unintentional merging between adjacent devices while maintaining the benefits of scaled-down dimensions for high density. The segmentation is achieved through controlled epitaxial growth patterns and isolation barrier layers.

The patent applies preliminary action by forming mandrels and sacrificial structures before the final epitaxial source/drain regions. These preliminary structures serve as alignment references and define the precise locations for subsequent epitaxial growth. The mandrels are positioned and aligned in advance, providing a framework that guides the formation of accurately positioned epitaxial regions even at reduced feature sizes, thereby maintaining contact alignment precision during scaling.

The patent uses intermediary structures (such as mandrels, sacrificial layers, and isolation barriers) as mediators between the lithography patterning process and the final epitaxial source/drain formation. These intermediary elements translate the lithography patterns into precisely defined epitaxial growth regions, buffering the sensitivity to alignment errors. The intermediaries provide mechanical and chemical guidance that ensures accurate epitaxial placement even when feature sizes are reduced below the lithography resolution limit.

The patent applies local quality by optimizing epitaxial lateral extension differently in different spatial locations. In regions requiring large contact landing windows (e.g., under gate structures), the epitaxial growth is encouraged to extend laterally. In regions adjacent to other devices, the epitaxial growth is constrained or terminated to prevent merging. This spatially varying optimization is achieved through controlled epitaxial growth conditions, selective doping, and isolation barrier layers positioned at specific locations.

The patent uses isolation barrier layers and sacrificial structures as intermediaries to control epitaxial lateral extension. These intermediary layers act as growth barriers or selective etch stop layers that define where epitaxial material can and cannot extend. By strategically placing these intermediaries between adjacent device regions, the patent enables large contact landing windows in isolated regions while preventing epitaxial merging in proximity to other devices.