Lateral DMOS Transistor Source-Side Blocking via Segmented Implant
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Solution Overview
Problem
In integrated circuits, forming low resistance drain connections and electrical isolation links between buried drift regions and substrates while minimizing photolithographic and ion implant operations is challenging, particularly in achieving desired breakdown voltages and series resistances.
Innovation Solution
Concurrently forming drain, channel, and isolation links in MOS transistors by ion implanting dopants and subsequent annealing, with segmented ion implant areas to achieve diluted dopant distributions and specific doping densities, allowing for electrical isolation and optimized performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate ion implant operations are used to form drain links, channel links, and isolation links, then each link can be precisely controlled, but the number of fabrication steps increases
Solution Approach 1:
The patent combines the formation of drain links, channel links, and isolation links into a single ion implant operation. By using a unified implant process with strategically placed openings in the dielectric layer, all three link types are created simultaneously, reducing the number of fabrication steps while maintaining precise doping control through the use of different dopant species (e.g., phosphorus for drain links, boron for isolation links) and controlled diffusion conditions.
2Reliability
If high doping density is used in isolation links, then electrical isolation is improved, but breakdown voltage decreases
Solution Approach 1:
The patent applies local quality by creating spatially varying doping densities within the isolation link structure. The isolation link has higher doping density near the source/body regions to ensure effective electrical isolation, while the doping density gradually decreases toward the drift region. This graded doping profile maintains strong isolation capability while preserving the high breakdown voltage required for power device operation.
3Strength
If low doping density is used in drain links, then breakdown voltage is improved, but series resistance increases
Solution Approach 1:
The patent employs parameter changes by optimizing the doping density, dopant type, and diffusion depth parameters of the drain link. By selecting appropriate dopant species (such as phosphorus or arsenic) and controlling the implantation energy and annealing conditions, the drain link achieves a doping profile that provides low series resistance for efficient current conduction while maintaining sufficient breakdown voltage through controlled junction depth and lateral doping distribution.
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 reduces the number of fabrication steps, achieves efficient electrical isolation, and allows for customizable breakdown voltages and series resistances in MOS transistors, enhancing the operational performance of integrated circuits.
Implementation Method 1
an anneal operation which diffuses the implanted dopants to make an electrical connection with the buried drift region
Implementation Method 2
ion implanting dopants
Data Source
AI summary
An integrated circuit and method having an extended drain MOS transistor with a buried drift region, a drain diffused link, a channel diffused link, and an isolation link which electrically isolated the source, where the isolation diffused link is formed by implanting through segmented areas to dilute the doping to less than two-thirds the doping in the drain diffused link.