Trench MOSFET Source Region Doping for Avalanche Capability
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Solution Overview
Problem
Conventional N-channel trench MOSFETs experience UIS failure at trench corners due to uniform doping concentration and junction depth of N+ source regions, leading to poor avalanche capability.
Innovation Solution
The source region is implanted through the open region of a thick contact interlayer, resulting in a Gaussian-distribution of doping concentration and shallower junction depth, reducing base resistance and enhancing avalanche capability by diffusing dopants to just reach the cell edge and optimizing the trade-off between Rds and avalanche performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform doping concentration and junction depth are used for N+ source regions, then manufacturing simplicity is maintained, but UIS failure occurs at trench corners due to poor avalanche capability
Solution Approach 1:
The patent applies local quality by creating non-uniform doping concentration and junction depth in the N+ source region. Specifically, the doping concentration varies from the trench contact region to the channel region, and the junction depth is shallower near the trench corner. This local variation improves avalanche capability at critical corners while maintaining overall device functionality.
Solution Approach 2:
The patent changes the doping parameters (concentration and junction depth) as functions of position. The doping concentration gradient and varying junction depth are achieved through controlled ion implantation and diffusion processes, transforming the uniform parameters into spatially-dependent parameters that improve reliability without excessive manufacturing complexity.
2Manufacturing precision
If source Ion Implantation is performed through source mask, then uniform doping concentration is achieved, but base resistance becomes high due to longer current path at cell corners
Solution Approach 1:
Instead of uniform doping, the patent creates local quality variations where doping concentration and junction depth depend on the spatial position. The N+ source region has higher doping concentration and shallower junction depth near the trench contact, transitioning to lower concentration and deeper junction toward the channel, optimizing both resistance and reliability.
Solution Approach 2:
The patent inverts the conventional approach by making the doping profile non-uniform rather than uniform. The conventional method achieves uniformity through masking, while this patent achieves optimization through controlled non-uniformity, inverting the design philosophy from uniformity to functional variation.
3Device complexity
If N+ source region has same junction depth along epitaxial surface, then fabrication process is simplified, but parasitic NPN bipolar transistor turns on easily at trench corners
Solution Approach 1:
The patent applies local quality by making the junction depth vary spatially across the epitaxial surface. The junction depth is shallower at the trench corner region and deeper toward the channel region. This local variation prevents easy turn-on of parasitic NPN transistors at corners while maintaining a relatively simple fabrication process using controlled ion implantation and diffusion.
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 configuration reduces the risk of UIS failure and improves avalanche capability by minimizing the Emitter injection efficiency of the parasitic NPN bipolar transistor, while also reducing contact resistance through the use of BPSG or PSG layers and vertical trenched source-body contacts.
Implementation Method 1
the source region is formed by performing source Ion Implantation through open region of a thick contact interlayer covering the epitaxial layer
Implementation Method 2
the dopant of source region is diffused to just reach cell edge
Data Source
AI summary
A trench MOSFET structure having improved avalanche capability is disclosed, wherein the source region is formed by performing source Ion Implantation through contact open region of a thick contact interlayer, and further diffused to optimize a trade-off between Rds and the avalanche capability. Thus, only three masks are needed in fabrication process, which are trench mask, contact mask and metal mask. Furthermore, said source region has a doping concentration along channel region lower than along contact trench region, and source junction depth along channel region shallower than along contact trench, and source doping profile along surface of epitaxial layer has Gaussian-distribution from trenched source-body contact to channel region.