Double-Diffused Channel Epitaxy for Uniform Fin-and-Trench Doping
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Solution Overview
Problem
In semiconductor device fabrication, particularly for folded transistors with corrugated fin-and-trench structures, uniform doping of dopants across the surfaces of fins and trenches is challenging due to the varying curvature and shadowing effects, leading to non-uniform concentrations of faster- and slower-diffusing dopants, which can result in inoperatively uniform double-diffused channels.
Innovation Solution
The method employs selective epitaxy to grow differentially doped semiconductor materials within recesses formed by isotropic etching, ensuring uniform doping by filling the recesses with silicon doped with specific concentrations of boron and arsenic, thereby forming a double-diffused channel that conforms to the transistor's topography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional doping methods are used on corrugated fin-and-trench structures, then the doping process can be completed, but uniform doping across surfaces of fins and trenches cannot be achieved due to varying curvature and shadowing effects
Solution Approach 1:
The patent applies local quality by creating recesses at specific locations (fin tops and trench bottoms) where doping is needed, then filling these recesses with dopant-containing material. This localized approach ensures uniform doping concentrations in the channel regions while avoiding the shadowing effects that plague conventional blanket doping methods on corrugated structures.
Solution Approach 2:
The patent employs preliminary action by forming the recesses and depositing the dopant-containing semiconductor material before the actual doping diffusion process. This preliminary preparation ensures that the dopant is already positioned and concentrated in the correct locations, leading to uniform doping when diffusion occurs, without requiring complex real-time control during doping.
2Power
If shorter channel lengths are used to increase transconductance, then voltage gain and power gain improve, but fabrication variation increases due to quantization effects of atomic layers
Solution Approach 1:
The patent changes the parameter of channel length to be defined by dopant diffusion distance rather than physical lithographic dimensions. By using the difference in lateral diffusion extents of fast- and slow-diffusing dopants, the effective channel length is determined by thermal diffusion parameters rather than atomic layer thickness, thereby reducing sensitivity to quantization effects and fabrication variation.
3Length of moving object
If double-diffused channels are formed using conventional methods, then short channel length is achieved, but fabrication cost increases and process complexity increases
Solution Approach 1:
The patent merges multiple functions into a single integrated process: the recess formation, dopant incorporation, and channel length definition are all achieved through the epitaxial growth process rather than requiring separate lithography, implantation, and diffusion steps. This consolidation reduces fabrication cost and process complexity while maintaining the short channel length benefit.
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 achieves uniform doping across the surfaces of fins and trenches, enabling the creation of highly uniform and effective double-diffused channels with improved conductivity and reduced fabrication complexity, even in complex geometries like folded transistors, by using selective epitaxial growth to fill recesses with specific dopant concentrations.
Implementation Method 1
A first selective epitaxial growth of a first semiconductor material doped with a first dopant is performed on the semiconductor layer in the recess. A second selective epitaxial growth of a second semiconductor material doped with a second dopant is performed on the first semiconductor material in the recess.
Implementation Method 2
a faster-diffusing p-type dopant (e.g., boron, gallium, or indium) and a slower-diffusing n-type dopant (e.g., phosphorus, arsenic, or antimony) implanted and subsequently diffused (e.g., upon anneal) into a silicon transistor body
Implementation Method 3
The exposed portion of the semiconductor layer is isotropically etched away to form a recess having a depth
Data Source
AI summary
A method includes forming a gate on a semiconductor layer of a substrate. A hard mask is formed over the gate and the semiconductor layer to expose a portion of the semiconductor layer. The exposed portion of the semiconductor layer is isotropically etched away to form a recess having a depth. A first selective epitaxial growth of a first semiconductor material doped with a first dopant is performed on the semiconductor layer in the recess. A second selective epitaxial growth of a second semiconductor material doped with a second dopant is performed on the first semiconductor material in the recess. The hard mask is then removed.