TVS Diode Breakdown Voltage via Trench Ion Implantation
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Solution Overview
Problem
Transient-voltage-suppression (TVS) diodes face challenges in reducing capacitance while maintaining low-cost and simple fabrication processes, which affects their performance in protecting integrated circuits from transient over-voltage events.
Innovation Solution
A semiconductor device and fabrication method involving a substrate with a first conductive type and active region, including epitaxial layers, buried layers, and trench isolation features, where a trench ion implantation process forms a connecting doped region between the buried and doped well regions, avoiding the formation of undesired silicon controlled rectifier structures and enhancing breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional fabrication processes are used for TVS diodes, then the manufacturing cost is low and process is simple, but the capacitance cannot be sufficiently reduced
Solution Approach 1:
The fabrication process is segmented into multiple discrete steps: forming the buried layer, performing first ion implantation to create the transition layer, performing second ion implantation to create the doped well region, and forming the isolation layer. This segmentation allows precise control of each layer's properties to reduce capacitance while maintaining manufacturability
Solution Approach 2:
Different regions of the semiconductor structure are given different dopant concentrations and conductive types. The buried layer has first conductive type, the transition layer has second conductive type with specific dopant concentration, and the doped well region has first conductive type with different dopant concentration. This local differentiation reduces capacitance by optimizing electrical properties in specific regions without requiring complete restructuring of the entire device
2Reliability
If ion implantation is performed without forming a transition layer first, then the process is simpler, but poor connection occurs between buried and doped well regions
Solution Approach 1:
The transition layer is formed through first ion implantation before the second ion implantation that creates the doped well region. This preliminary action establishes a proper conductive pathway between the buried layer and the upcoming doped well region, ensuring reliable electrical connection. The transition layer acts as an intermediate structure that facilitates subsequent doping steps
Solution Approach 2:
The transition layer serves as an intermediary between the buried layer and the doped well region. It has second conductive type that is opposite to the buried layer's first conductive type, creating a proper PN junction interface. This intermediary structure enables reliable electrical connection by providing a gradual transition in conductive properties, preventing direct contact between regions of the same conductive type which would cause poor connection
3Length of stationary object
If high ion implantation energy is used to form deep doped regions, then the doping depth is sufficient, but the fabrication cost increases
Solution Approach 1:
The first ion implantation process performs preliminary doping to create the transition layer at a moderate depth. This preliminary action allows the second ion implantation to achieve the required total doping depth through cumulative effect of multiple lower-energy implantation steps, rather than requiring a single high-energy implantation that would increase fabrication cost
Solution Approach 2:
The doping process is performed in periodic stages: first ion implantation to create the transition layer, then isolation layer formation, then second ion implantation to create the doped well region. This periodic action allows control of dopant distribution at different depths through separate process steps, achieving sufficient doping depth while maintaining lower fabrication costs by avoiding single high-energy implantation
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 method reduces fabrication costs and improves the breakdown voltage of TVS diodes by forming a connecting doped region with low ion implantation energy, preventing poor connections between buried and doped well regions, and simplifying the epitaxial growth process.
Implementation Method 1
performing a first ion implantation process to form a first conductive type buried layer in the second conductive type first epitaxial layer
Implementation Method 2
performing a first epitaxial growth process to form a second conductive type first epitaxial layer over the substrate
Data Source
AI summary
Semiconductor devices and methods of fabricating the same are provided. The semiconductor device includes a substrate having a first conductive type. A second conductive type first epitaxial layer is disposed over the substrate. A second conductive type second epitaxial layer is disposed over the second conductive type first epitaxial layer. An active region of the substrate includes a first conductive type buried layer in the second conductive type first and second epitaxial layers. A first conductive type doped well region is disposed in the second conductive type second epitaxial layer. A second conductive type heavily doped region is disposed over the first conductive type doped well region. A first trench isolation feature is disposed in the substrate. In addition, a first conductive type doped region is disposed between a bottom surface of the first trench isolation feature and the first conductive type buried layer.