Three-Layer SiGe Source Drain Structure for Leakage Control
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Solution Overview
Problem
High boron concentration in SiGe crystals for MOSFETs leads to crystal defects like stacking faults, increasing leakage current from source/drain layers to the semiconductor substrate, while reducing boron concentration increases parasitic resistance at junctions between source/drain and extension regions.
Innovation Solution
A semiconductor device with a Si mixed crystal layer structure comprising a first layer with a lower boron concentration, a second layer with a higher boron concentration, and a third layer with a lower boron concentration than the second layer, grown epitaxially in the trench portions of the source/drain regions to reduce parasitic resistance and prevent leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high boron concentration is used in SiGe crystals for MOSFETs, then parasitic resistance at junctions is reduced, but crystal defects like stacking faults increase causing leakage current
Solution Approach 1:
The SiGe crystal layer is divided into three distinct layers with different boron concentrations: a first layer with lower boron concentration to prevent stacking faults and leakage current, a second layer with higher boron concentration to reduce parasitic resistance, and a third layer with lower boron concentration to again prevent defects. This segmentation allows each layer to optimize for its specific function, resolving the contradiction between reducing parasitic resistance and preventing crystal defects.
Solution Approach 2:
Different regions of the SiGe crystal structure are assigned different boron concentrations based on their specific functional requirements. The intermediate layer has high boron concentration optimized for reducing parasitic resistance at junctions, while the outer layers have lower boron concentration optimized for preventing stacking faults and leakage current. This local quality differentiation allows simultaneous optimization of both contradictory requirements in different spatial locations.
2Object-affected harmful factors
If high boron concentration is used in SiGe crystals, then parasitic resistance decreases, but stacking faults and crystal defects increase
Solution Approach 1:
The SiGe crystal is segmented into three layers with progressively optimized boron concentrations. The first layer uses lower boron concentration to maintain crystal structure stability and prevent stacking faults. The second layer uses higher boron concentration to reduce parasitic resistance. The third layer returns to lower boron concentration to restore crystal stability. This segmentation strategy allows the system to temporarily tolerate higher defect risk in the intermediate layer while maintaining overall structural integrity through the protective outer layers.
Solution Approach 2:
The first and third layers with lower boron concentrations act as protective cushioning layers that prevent the propagation of crystal defects and stacking faults into the high-boron intermediate layer. These outer layers with stable crystal structures cushion against the formation and spread of defects, allowing the intermediate high-boron layer to effectively reduce parasitic resistance without compromising overall crystal structure stability.
3Stability of the object's composition
If boron concentration is reduced in SiGe crystals, then crystal defects decrease, but parasitic resistance at junctions increases
Solution Approach 1:
The invention applies local quality by concentrating high boron content specifically in the intermediate second layer where it is most needed for reducing parasitic resistance at junctions, while maintaining lower boron content in the first and third layers where crystal structure stability is the primary concern. This localized high-boron region optimizes electrical performance without sacrificing overall structural integrity.
Solution Approach 2:
The SiGe crystal structure is segmented into functional zones: outer layers with low boron concentration for structural stability, and an intermediate layer with high boron concentration for electrical performance. This segmentation allows the system to achieve both low defect density and low parasitic resistance by assigning different compositional characteristics to different spatial regions based on their functional requirements.
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
The three-layer Si mixed crystal structure effectively reduces parasitic resistance and minimizes leakage current by optimizing boron distribution, improving transistor performance with enhanced on-current and reduced off-current.
Implementation Method 1
a first Si mixed crystal layer 8, a second Si mixed crystal layer 9, and a third Si mixed crystal layer 10 are epitaxially grown
Data Source
AI summary
A semiconductor device includes, a gate insulating film, a gate electrode, a source/drain region, and a Si mixed crystal layer in the source/drain region. The Si mixed crystal layer includes a first Si mixed crystal layer that includes impurities with a first concentration, a second Si mixed crystal layer formed over the first Si mixed crystal layer and that includes the impurities with a second concentration higher than the first concentration, and a third Si mixed crystal layer formed over the second Si mixed crystal layer and that includes the impurities with a third concentration lower than the second concentration.