Epitaxial Blocking Layer for Uniform GAA Channel Lengths
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Solution Overview
Problem
Conventional gate-all-around (GAA) transistor fabrication processes face challenges with lattice dislocation and inner spacer misalignment due to dopant diffusion, leading to non-uniform channel lengths and performance degradation.
Innovation Solution
The introduction of an undoped blocking layer to replace the anti-punch-through implantation region, which blocks dopant diffusion and allows for the epitaxial growth of high-quality epitaxial stacks with controlled dimensions, thereby improving channel length uniformity across nanosheets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If anti-punch-through (APT) implantation is performed in the substrate before epitaxial stack formation, then punch-through protection is improved, but lattice dislocation occurs due to dopant diffusion during epitaxial growth
Solution Approach 1:
An undoped blocking layer is introduced as an intermediary between the APT implantation region and the epitaxial stack. This blocking layer prevents dopant diffusion into the epitaxial structure while maintaining the punch-through protection function, thereby resolving the contradiction between reliability and manufacturing precision
Solution Approach 2:
The structure is segmented into distinct functional layers: the APT implantation region, the undoped blocking layer, and the epitaxial stack. This segmentation isolates the dopant-containing region from the epitaxial growth region, preventing lattice dislocation while preserving punch-through protection
2Reliability
If APT implantation is performed before inner-spacer formation, then punch-through protection is achieved, but inner-spacer misalignment occurs due to uneven dopant diffusion
Solution Approach 1:
The undoped blocking layer serves as a mediator that prevents uneven dopant diffusion into regions where inner-spacers will be formed. This ensures uniform dopant distribution and prevents inner-spacer misalignment while maintaining punch-through protection
Solution Approach 2:
The undoped blocking layer is formed preliminarily before inner-spacer formation to establish a uniform dopant barrier. This preliminary action ensures that subsequent inner-spacer formation processes occur on a uniformly doped surface, preventing alignment issues
3Reliability
If dopant diffusion is allowed during epitaxial growth, then APT function is maintained, but channel length uniformity degrades due to lattice dislocation
Solution Approach 1:
The undoped blocking layer acts as an intermediary barrier that decouples the APT function from the epitaxial growth process. It allows the APT region to maintain its dopant profile for punch-through protection while preventing dopant diffusion into the epitaxial stack, thereby preserving channel length uniformity
Solution Approach 2:
Different regions are assigned different doping qualities: the APT region maintains high dopant concentration for punch-through protection, while the blocking layer and epitaxial stack regions maintain low or zero dopant concentration for lattice uniformity and channel length control
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 approach reduces lattice dislocation and achieves uniform inner spacer dimensions, enhancing the performance and reliability of GAA devices by preventing dopant-induced variations during the fabrication process.
Implementation Method 1
unwanted diffusion of the impurity dopants from the APT layer during the epitaxial growing of semiconductor fins may cause lattice dislocation
Implementation Method 2
epitaxially growing a blocking layer from a top surface of the semiconductor substrate
Data Source
AI summary
A semiconductor device includes a semiconductor substrate having a first lattice constant, a dopant blocking layer disposed over the semiconductor substrate, the dopant blocking layer having a second lattice constant different from the first lattice constant, and a buffer layer disposed over the dopant blocking layer, the buffer layer having a third lattice constant different from the second lattice constant. The semiconductor device also includes a plurality of channel members suspended over the buffer layer, an epitaxial feature abutting the channel members, and a gate structure wrapping each of the channel members.