Bipolar Transistor Collector Doping via Epitaxial Diffusion
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Solution Overview
Problem
Existing methods for doping collector regions in bipolar transistors, such as in situ doping during epitaxy or post-epitaxy implantation, face challenges in cost, complexity, and the co-integration of high-speed and high-breakdown voltage transistors within the same integrated circuit, as they require different doping processes and mask usage.
Innovation Solution
A method involving the diffusion of dopants from an underlying reservoir during epitaxy, activated by the epitaxial process, which forms a doped collector region with controlled doping profiles, allowing for the co-integration of high-speed and high-breakdown voltage transistors using a single epitaxy process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If in situ doping during epitaxy is used, then doping is achieved, but method constraints such as duration, cost, type of dopant, and selectivity are difficult to satisfy
Solution Approach 1:
The collector region is divided into two distinct doped portions: a first doped portion formed by implantation in the semiconductor substrate, and a second doped portion formed by diffusion from the first portion into epitaxiated material. This segmentation allows each portion to be optimized for different requirements, satisfying both ease of manufacture and process constraints.
Solution Approach 2:
The first doped portion is formed by implantation before the epitaxial growth of the second portion. This preliminary action creates a dopant reservoir that will subsequently diffuse during epitaxy, allowing control over the doping profile while simplifying the overall manufacturing process.
2Adaptability or versatility
If different epitaxies are performed for different doping requirements, then high-speed and high-breakdown voltage transistors can be manufactured, but co-integration in the same integrated circuit becomes complicated
Solution Approach 1:
Different doping profiles are achieved locally within the same integrated circuit by controlling the diffusion characteristics in different regions. The first and second doped portions can have different dopant concentrations and distributions, allowing customization for high-speed versus high-breakdown voltage transistors while using a single epitaxial process.
Solution Approach 2:
A single epitaxial process serves multiple functions: it grows the semiconductor material for the collector region and simultaneously activates diffusion from the implanted dopants to create the desired doping profiles. This universal approach enables co-integration of different transistor types without requiring separate epitaxial processes.
3Manufacturing precision
If implantation after epitaxy is used, then doping is achieved, but mask usage is required increasing process complexity
Solution Approach 1:
The implantation step and the epitaxial growth step are merged in their temporal and functional relationship. The implantation creates the dopant reservoir, and the subsequent epitaxial growth automatically activates diffusion from this reservoir. This combination eliminates the need for separate mask processes that would be required if implantation were performed after epitaxy.
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 simplifies the manufacturing process, reduces costs, and enables the co-integration of different transistor types by controlling dopant diffusion, resulting in a doping profile that distinguishes between high-speed and high-breakdown voltage transistors based on their specific performance requirements.
Implementation Method 1
a diffusion of dopants in the epitaxiated material, from the first doped portion, said diffusion being activated at least by said epitaxy
Data Source
AI summary
A bipolar transistor includes a collector region having a first doped portion located in a substrate and a second doped portion covering and in contact with an area of the first doped portion. The collector region has a doping profile having a peak in the first portion and a decrease from this peak up to in the second portion.