Vertically Graded SiGe Channel Edges for Threshold Voltage Control
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Solution Overview
Problem
In integrated circuit devices, varying germanium concentration profiles within the device channel can increase fabrication costs and complexity, leading to defects such as erosion or agglomeration, which result in lower yields and unacceptable performance metrics.
Innovation Solution
The integration of vertically-graded silicon germanium (SiGe) regions adjacent to the channel in integrated circuit devices, which allows for modulation of the threshold voltage while minimizing additional processing steps and reducing defects, thereby enhancing device performance and yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If germanium concentration profiles are varied within the device channel to modulate threshold voltage, then threshold voltage modulation is achieved, but fabrication cost and complexity increase
Solution Approach 1:
The patent divides the SiGe structure into distinct regions: a channel region with uniform SiGe concentration and adjacent source/drain extension regions with vertically-graded SiGe concentration. This segmentation allows threshold voltage modulation through the graded regions while keeping the channel region simple and well-defined, thereby achieving voltage modulation without proportionally increasing overall fabrication complexity
Solution Approach 2:
The vertically-graded SiGe concentration is applied locally only in the source/drain extension regions adjacent to the channel, not throughout the entire device structure. This localized application provides the necessary threshold voltage modulation effect at the critical interface regions while minimizing the overall complexity and material usage compared to varying concentration throughout the whole channel
2Reliability
If germanium concentration profiles are varied within the device channel to modulate threshold voltage, then threshold voltage modulation is achieved, but defects such as erosion or agglomeration increase
Solution Approach 1:
By separating the channel region from the source/drain extension regions and applying different SiGe concentration profiles to each, the patent prevents defects from propagating through the entire device. The uniform channel region avoids the erosion and agglomeration issues that would result from varying concentrations, while the graded extension regions provide the necessary voltage modulation effect
Solution Approach 2:
The vertically-graded SiGe concentration is confined to the source/drain extension regions where it provides threshold voltage modulation without compromising the structural integrity of the channel. This localized grading prevents the formation of defects like erosion and agglomeration in the channel region while still achieving the desired electrical characteristics
3Ease of manufacture
If vertically-graded SiGe regions are formed adjacent to the channel, then threshold voltage modulation is achieved with minimal additional processing, but device structure complexity increases
Solution Approach 1:
The patent combines the threshold voltage modulation function with the existing source/drain extension regions of the transistor. By forming vertically-graded SiGe regions in these already-necessary structures, the patent achieves voltage modulation without adding separate dedicated components or structures, thereby minimizing additional processing steps while accepting increased structural complexity only where functionally required
Data Source
AI summary
An integrated circuit (IC) device is disclosed which includes a first transistor over a substrate. The first transistor includes a gate over the substrate and between a source region and a drain region. The transistor further includes a first region of vertically-graded silicon germanium (“SiGe”) adjacent a first side of a channel under the gate, and a second region of vertically-graded SiGe adjacent a second side of the channel. The channel includes substantially uniformly-graded SiGe.