MOSFET Well Doping Gradients for Reduced Field Crowding
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Solution Overview
Problem
The reduction of cell size in vertical oriented semiconductor devices, such as MOSFETs, is limited by manufacturing accuracy and space between body implants, leading to challenges in achieving a balance between conduction performance, electric parasitics, and device robustness.
Innovation Solution
The implementation of at least two lateral doping gradients with monotonic decreasing doping concentrations at different depths in the well regions of semiconductor devices, which reduces electric field crowding and improves current distribution, thereby enhancing device robustness and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cell size is reduced to increase channel density, then conduction performance is improved, but manufacturing accuracy requirements increase and space between body implants decreases
Solution Approach 1:
The patent applies local quality by creating different doping concentrations at different lateral positions within the well region. The doping concentration varies from a first concentration at a first lateral position to a second concentration at a second lateral position, allowing optimized electrical characteristics in different areas of the device while maintaining compact cell dimensions.
Solution Approach 2:
The patent changes the doping concentration parameter spatially within the well region. By varying the doping concentration from one lateral position to another, the patent optimizes the balance between conduction performance and manufacturing tolerances, enabling reduced cell size without proportionally increasing manufacturing difficulty.
2Productivity
If body implants are placed closer together to reduce cell size, then channel density increases, but electric field crowding and parasitic effects increase
Solution Approach 1:
The patent addresses parasitic effects by creating local quality variations through spatially varying doping concentrations. The different doping concentrations at different lateral positions help control electric field distribution, reducing field crowding at implant boundaries while maintaining high channel density through closer implant spacing.
3Productivity
If doping variations are used to counter reduce cell size, then conduction performance is maintained, but electric field distribution changes and device robustness decreases
Solution Approach 1:
The patent carefully controls parameter changes in doping concentration to achieve the desired balance. By transitioning from a first doping concentration at a first lateral position to a second doping concentration at a second lateral position, the patent maintains conduction performance while managing electric field distribution to preserve device robustness.
Data Source
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AI summary
A vertical oriented semiconductor device, said comprising a semiconductor body having a first major surface, said semiconductor device comprising a current-accommodating region of a first conductivity type, well regions of a second conductivity type, at or near said first major surface, said second conductivity type opposite to said first conductivity type, said well regions laterally adjacent sides of said current-accommodating region, said well regions having a first depth into said semiconductor body, a substrate region, provided at a second major surface vertically opposite to said first major surface, said substrate region being of the first conductivity type, wherein at least one of said well regions has a first lateral doping gradient with monotonic decreasing doping concentration, from a first higher doping concentration at a first lateral end of said well region towards a first lower doping concentration at a second, opposite, lateral end thereof facing said current-accommodating region, and a second lateral doping gradient with monotonic decreasing doping concentration, from a second higher doping concentration at a first lateral end of said well region towards a second lower doping concentration at a second, opposite, lateral end thereof facing said current-accommodating region, wherein said second lateral doping gradient is deeper inside said semiconductor body compared to said first lateral doping gradient and wherein said first lateral doping gradient differs from said second lateral doping gradient.