Heterojunction Bipolar Transistor Lateral Base Contact
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Solution Overview
Problem
The fabrication of heterojunction bipolar transistors faces challenges such as complex process flows, reliability issues due to nitride remnants, difficulties at small processing nodes, and suboptimal emitter resistance, particularly concerning base contact region formation and stray capacitance.
Innovation Solution
A method involving a single-crystal silicon substrate with successive layers, including a sacrificial layer, where epitaxial growth forms collector, base, and emitter regions, and a base contact region, minimizing nitride presence and optimizing contact resistance and capacitance through selective etching and deposition techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a base contact region is formed to reduce access resistance, then the resistance of access to the base region decreases, but the stray capacitance between the base and collector increases
Solution Approach 1:
The base contact region is formed by growing semiconductor material laterally from the side wall of the base region in a horizontal direction, rather than vertically from the top surface. This lateral extension in another dimension allows the contact region to reach the base region without increasing vertical overlap with the collector, thus reducing access resistance while minimizing stray capacitance.
Solution Approach 2:
The sacrificial layer serves as an intermediary structure that enables the formation of the base contact region. By selectively removing the sacrificial layer from the side wall, the patent creates a template for lateral epitaxial growth of the base contact region, allowing precise control over the contact region's position and shape to optimize both resistance and capacitance.
2Manufacturing precision
If nitride layers are used in the stack, then the structural integrity and etch selectivity are improved, but reliability issues arise due to nitride remnants
Solution Approach 1:
The patent introduces a sacrificial layer that is selectively removed after serving its purpose as a mask and spacer during the formation of the base contact region. This discarding of the sacrificial layer eliminates nitride remnants that would otherwise remain in the final device structure and cause reliability issues, while the layer's temporary presence provides the necessary etch selectivity and structural integrity during manufacturing.
3Device complexity
If the process flow is simplified, then the manufacturing complexity decreases, but the robustness and reliability of the device may be compromised
Solution Approach 1:
The patent combines multiple functions into the sacrificial layer: it serves as an etch mask, a spacer for defining the base contact region geometry, and a temporary structural support. By merging these functions into a single layer that is selectively removed, the process flow is simplified compared to using separate layers for each function, while maintaining device robustness through the layer's temporary presence during critical manufacturing steps.
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 method simplifies the manufacturing process, enhances the robustness and reliability of heterojunction bipolar transistors by reducing access resistance and stray capacitance, while being compatible with standard CMOS methods.
Implementation Method 1
forming by selective epitaxy from the top surface of the substrate, to a level higher than a lower level of the stack, a collector region made of semiconductor material doped with a first conductivity type
Implementation Method 2
further forming by selective epitaxy from a top surface of the collector region, to a level at least as high as an upper level of the sacrificial layer, a base region made of semiconductor material doped with a second conductivity type
Implementation Method 3
further forming by deposition on a top surface of the base region, an emitter region made of semiconductor material doped with the first conductivity type
Data Source
AI summary
A bipolar transistor is supported by a single-crystal silicon substrate including a collector contact region. A first epitaxial region forms a collector region of a first conductivity type on the collector contact region. A second epitaxial region forms a base region of a second conductivity type. Deposited semiconductor material forms an emitter region of the first conductivity type. The collector region, base region and emitter region are located within an opening formed in a stack of insulating layers that includes a sacrificial layer. The sacrificial layer is selectively removed to expose a side wall of the base region. Epitaxial growth from the exposed sidewall forms a base contact region.