HBT Base Dopant Profile Control Using Segmented Epitaxial Layers
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Solution Overview
Problem
Heterojunction bipolar transistors (HBTs) face challenges with phosphorus segregation diffusion and surface segregation during epitaxial growth, leading to unintended dopant profiles that can result in a PN junction outside the silicon germanium base sub-layer, affecting device performance.
Innovation Solution
A layered structure with sequentially epitaxially grown sub-layers is implemented, where the second sub-layer is in-situ doped with phosphorus, and the first and third sub-layers are not, to achieve a 'camelback' germanium profile, reducing segregation diffusion and surface segregation by performing epitaxial growth at lower temperatures and using selective epitaxial growth with an etchant gas, and doping with carbon to limit phosphorus diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If in-situ doping with phosphorus is performed during epitaxial growth of the base region, then dopant concentration can be controlled, but phosphorus segregation diffusion and surface segregation occur leading to unintended dopant profiles
Solution Approach 1:
The base region is divided into multiple sub-layers (first, second, third sub-layers) with different doping configurations. The second sub-layer is in-situ doped with phosphorus while the first and third sub-layers are not doped, creating a segmented structure that confines phosphorus within specific regions and prevents segregation diffusion from affecting the entire base region.
Solution Approach 2:
Different regions of the base region are assigned different doping qualities - the second sub-layer has high phosphorus concentration while the first and third sub-layers have no phosphorus doping. This local differentiation creates concentration gradients that control phosphorus distribution and prevent unwanted segregation by establishing clear boundaries between doped and undoped regions.
2Productivity
If epitaxial growth is performed at higher temperatures to improve growth rate, then productivity increases, but phosphorus surface segregation worsens
Solution Approach 1:
The first undoped sub-layer is grown before the phosphorus-doped second sub-layer to prepare the structure in advance. This preliminary layer acts as a buffer that reduces surface segregation effects during subsequent phosphorus doping, allowing the use of optimized growth conditions that balance productivity with reduced segregation.
Solution Approach 2:
The epitaxial growth process uses different temperature parameters for different sub-layers. By adjusting growth temperature and rate parameters specifically for each sub-layer, the process optimizes both growth productivity and phosphorus segregation control, allowing higher overall productivity while maintaining acceptable segregation levels through localized parameter optimization.
3Device complexity
If a single-layer base region is used to simplify structure, then device complexity decreases, but dopant profile control precision is insufficient
Solution Approach 1:
The base region is segmented into multiple sub-layers with distinct doping characteristics. This segmentation enables precise control of dopant concentration profiles by assigning different phosphorus doping levels to different sub-layers, achieving manufacturing precision that would be impossible with a single-layer structure while maintaining reasonable device complexity through systematic layering.
4Reliability
If phosphorus doping is applied throughout the entire base region to ensure sufficient dopant concentration, then electrical conductivity improves, but PN junction formation outside the silicon germanium base sub-layer occurs
Solution Approach 1:
Phosphorus doping is applied locally only to the second sub-layer rather than uniformly throughout the entire base region. This localized doping strategy maintains sufficient electrical conductivity in the doped region while preventing excessive phosphorus concentration that would cause PN junction formation outside the silicon germanium base sub-layer, thus preserving manufacturing precision for junction positioning.
Solution Approach 2:
The base region is segmented into doped and undoped sub-layers, with only the second sub-layer receiving phosphorus doping. This segmentation confines the phosphorus distribution to specific regions, ensuring adequate conductivity where needed while preventing unwanted electrical characteristics and PN junction formation in other regions, thereby maintaining precise junction positioning.
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 ensures a peak dopant concentration within the heteroepitaxial layer, reducing the likelihood of a PN junction being outside the intended layer, thereby enhancing HBT operating speed and performance.
Implementation Method 1
The base region is disposed on or over the collector region and includes a heteroepitaxial sub-layer
Implementation Method 2
A concentration gradient of the dopant increases from a region in a layer adjoining and overlying the heteroepitaxial sub-layer to a peak concentration in the heteroepitaxial sub-layer
Implementation Method 3
reducing segregation diffusion and surface segregation by performing epitaxial growth at lower temperatures and using selective epitaxial growth with an etchant gas, and doping with carbon to limit phosphorus diffusion
Data Source
AI summary
The present disclosure generally relates to dopant profile control in a heterojunction bipolar transistor (HBT). In an example, a semiconductor device structure includes a semiconductor substrate and an HBT. The HBT includes a collector region, a base region, and an emitter region. The base region is disposed on or over the collector region. The emitter region is disposed on or over the base region. The base region is disposed on or over the semiconductor substrate and includes a heteroepitaxial sub-layer. The heteroepitaxial sub-layer is doped with a dopant. A concentration gradient of the dopant increases from a region in a layer adjoining and overlying the heteroepitaxial sub-layer to a peak concentration in the heteroepitaxial sub-layer without decreasing between the region and the peak concentration.