SiC Bipolar Junction Transistor Base Region Spacer Layer Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High power silicon carbide bipolar junction transistors (BJTs) face challenges in achieving simultaneous high blocking voltage, low on-state voltage drop, and high emitter current gain due to limitations in manufacturing processes, particularly in reproducibility and dopant diffusion rates, which are exacerbated by ion implantation damage and non-uniform epitaxial designs.
Innovation Solution
A silicon carbide BJT design featuring a base region with a low-high doping profile, where a lower-doped portion acts as a spacer next to the emitter region and a higher-doped portion is adjacent to the drift region, improving current gain and stability while allowing for more reproducible manufacturing through epitaxial growth and reduced dopant loss during mesa formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional epitaxial designs with uniform doping are used, then manufacturing simplicity is maintained, but manufacturing precision and reproducibility deteriorate due to dopant loss during mesa formation
Solution Approach 1:
The base region is segmented into two distinct portions: a first portion with a first doping concentration and a second portion with a second doping concentration. This segmentation allows the patent to address dopant loss during mesa formation by having a lower-doped region that is less susceptible to such losses, thereby improving manufacturing precision without excessive complexity
Solution Approach 2:
Different regions of the base are assigned different doping concentrations tailored to their specific functions. The first portion has higher doping to provide stability and reduce dopant loss effects, while the second portion has lower doping to optimize carrier transport. This local quality differentiation resolves the contradiction by optimizing each region independently
2Ease of manufacture
If ion implantation is used to form doped regions, then doping can be achieved, but manufacturing precision deteriorates due to ion implantation damage that cannot be entirely removed
Solution Approach 1:
The patent extracts the problematic ion implantation step from the manufacturing process and replaces it with epitaxial growth methods. By taking out the damaging ion implantation process and substituting it with a growth-based doping approach, the patent eliminates the source of implantation damage while maintaining doping capability, thus improving manufacturing precision
Solution Approach 2:
The mechanical/physical process of ion implantation is substituted with a chemical growth process (epitaxy). This substitution replaces the high-energy ion bombardment that causes damage with a controlled atomic-layer deposition process that achieves doping without the harmful mechanical effects, resolving the contradiction between ease of manufacture and manufacturing precision
3Stability of the object's composition
If the base region has high doping concentration throughout, then stability is improved, but current gain deteriorates due to increased recombination
Solution Approach 1:
The base region is divided into two portions with different doping concentrations. The first portion has higher doping to provide stability and reduce dopant loss during manufacturing, while the second portion has lower doping to minimize recombination and enhance current gain. This segmentation resolves the contradiction by allowing each portion to optimize for its primary function
Solution Approach 2:
Different doping concentrations are applied to different regions of the base based on their functional requirements. The region closer to the emitter has lower doping to maximize current gain, while the region farther away has higher doping to provide stability. This local quality approach resolves the contradiction by optimizing performance locally rather than uniformly
4Shape
If mesa formation with etching is used to define emitter and base, then vertical topology is achieved, but manufacturing precision deteriorates due to overetching and dopant loss
Solution Approach 1:
The patent incorporates a doping concentration gradient in the base region before mesa formation, with the first portion having higher doping that acts as a buffer or cushion against the effects of overetching and dopant loss. This beforehand cushioning ensures that even if etching removes some material, the critical doping levels are maintained, thus preserving manufacturing precision while achieving the required vertical structure
Solution Approach 2:
The patent changes the doping concentration parameter across the base region, creating a gradient from the first portion to the second portion. This parameter change creates a more robust structure that is less sensitive to variations in etching depth and dopant loss, thereby maintaining manufacturing precision while enabling successful mesa formation
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 design enhances current gain, maintains sufficient blocking voltage, and improves manufacturing reproducibility by minimizing dopant loss during etching, resulting in a more stable and efficient high-power BJT with increased tolerance to overetching.
Implementation Method 1
Consequently, SiC BJTs are usually based on epitaxial designs, at least for the most critical regions of the BJT, such as the emitter and the intrinsic base
Data Source
Figure 1~3
Figure 4~6
Figure 7~8
AI summary
New designs for silicon carbide (SiC) bipolar junction transistors (BJTs) and new methods of manufacturing such SiC BJTs are provided. The SiC BJT comprises a collector region (220), a base region (240) and an emitter region (260) arranged as a stack, the emitter region and part of the base region forming a mesa. The intrinsic part of the base region includes a first portion having a first doping concentration and a second portion having a second doping concentration lower than the first doping concentration. Further, the second portion is vertically arranged between the first portion and the emitter region in the stack.