GAAFET Source/Drain Diffusion Barrier for Channel Integrity
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Solution Overview
Problem
In gate-all-around (GAA) nanostructure transistors, the diffusion of dopants from source/drain epitaxial structures into the nano-sheet or nano-wire channel layers leads to integrity issues and current crowding effects, degrading the performance of the transistors.
Innovation Solution
The integration of low doping regions as diffusion barrier structures in the source/drain epitaxial structures, which cover not only the interfaces with the channel layers but also the side surfaces of the inner spacer structures, to prevent dopant diffusion and maintain channel integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If source/drain epitaxial structures are formed with high doping regions to improve electrical conductivity, then drive current is enhanced, but dopant diffusion into channel layers occurs causing integrity issues and current crowding
Solution Approach 1:
The source/drain epitaxial structure is segmented into distinct doping regions: a first doping region with lower dopant concentration adjacent to the channel layer, and a second doping region with higher dopant concentration away from the channel. This segmentation prevents direct contact between high doping regions and the channel, eliminating dopant diffusion while maintaining electrical conductivity through the higher-doped region.
Solution Approach 2:
Different regions of the source/drain epitaxial structure are assigned different doping concentrations based on their functional requirements. The region adjacent to the channel (first doping region) has lower doping to prevent diffusion and maintain channel integrity, while the region away from the channel (second doping region) has higher doping to provide low resistance and high drive current. This local differentiation resolves the contradiction between conductivity and reliability.
2Reliability
If dopant concentration in source/drain regions is increased to reduce resistance, then electrical conductivity improves, but current crowding effects occur at the channel interface
Solution Approach 1:
The source/drain structure is divided into a first doping region with lower concentration adjacent to the channel and a second doping region with higher concentration away from the channel. This segmentation creates a gradual transition zone that distributes current flow more evenly, preventing the concentration of current at a single interface and thereby reducing current crowding effects while maintaining overall conductivity.
Solution Approach 2:
The dopant concentration parameter is varied spatially within the source/drain epitaxial structure. By creating a gradient or stepped profile where concentration increases with distance from the channel, the structure achieves low resistance through the high-concentration region while the lower-concentration region at the interface prevents current crowding and maintains uniform current distribution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively mitigates dopant diffusion, preserves the purity and mobility of charge carriers in the channel layers, and reduces current crowding effects, thereby enhancing the performance and reliability of GAA nanostructure transistors.
Implementation Method 1
The diffusion barrier structure separates the high doping region of the source/drain epitaxial structure from the nanostructure channel layers and prevents dopants in the high doping region from diffusing into the nanostructure channel layers and the inner spacer structure
Data Source
AI summary
The present disclosure is directed to a structure of a gate-all-around field effect transistors (GAAFET) and a method of forming the structure. The structure includes a diffusion barrier structure in an S/D epitaxial structure of the GAAFET. The diffusion barrier structure is in contact with an NS layer of the GAAFET and extends over side surfaces of inner spacer structures adjacent to the NS layer. The diffusion barrier structure separates a high doping region of the S/D epitaxial structure from the NS layer and regions of the inner spacer structures close to the NS layer. The diffusion barrier structure prevents (or mitigates) dopants in the high doping region from diffusing into the NS layer and the inner spacer structures, preserving the integrity of the NS layer as a semiconducting channel of the GAAFET and avoiding a current crowding effect.