Vertical MOSFET Well Gradient to Ease Electric 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 reduced conduction performance and altered electric field distribution, which affects device robustness and parasitic properties.
Innovation Solution
Implementing a lateral doping gradient with monotonic decreasing doping concentration in well regions, achieved through multiple masking steps during the manufacturing process, to reduce electric field crowding and enhance device robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cell size is reduced to increase channel density, then conduction performance is improved, but manufacturing precision and space between body implants are compromised
Solution Approach 1:
The patent applies local quality by creating a lateral doping gradient within the well regions, where the doping concentration varies laterally rather than being uniform. This allows different areas of the same well region to have optimized properties: higher doping near the current-accommodating region for better field control, and lower doping at the outer edges for reduced field crowding, thus resolving the contradiction between cell size reduction and manufacturing precision
Solution Approach 2:
The patent changes the doping concentration parameter spatially by implementing a lateral doping gradient. Instead of using a single doping concentration throughout the well region, the doping concentration is varied laterally to optimize both the electric field distribution and the device performance, enabling smaller cell sizes while maintaining manufacturing control
2Productivity
If cell size is reduced, then conduction performance is improved, but electric field distribution is altered affecting device robustness
Solution Approach 1:
The lateral doping gradient creates local quality variations within the well regions, with higher doping concentrations near the current-accommodating region to control the electric field, and lower concentrations at the edges to reduce field crowding. This local optimization maintains device robustness while enabling smaller cell sizes for better conduction performance
Solution Approach 2:
The patent converts the potentially harmful effect of reduced cell size (which causes electric field crowding and reduced robustness) into a benefit by using the lateral doping gradient to deliberately shape the electric field distribution. The varying doping concentration compensates for the geometric constraints of smaller cells, transforming the limitation into an opportunity for optimized field control
3Productivity
If cell size is reduced, then conduction performance is improved, but parasitic electric properties are impacted
Solution Approach 1:
The lateral doping gradient creates local quality variations that optimize the electric field distribution throughout the device structure. By having higher doping near the current-accommodating region and lower doping at the edges, the patent reduces parasitic effects like field crowding and unwanted charge accumulation, thereby improving conduction performance in smaller cells
Data Source
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AI summary
A vertical oriented semiconductor device, said semiconductor device 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 said first conductivity type, wherein at least one of said well regions has a lateral doping gradient with monotonic decreasing doping concentration, from a higher doping concentration at a first lateral end of said well regions towards a lower doping concentration at a second, opposite, lateral end thereof facing said current-accommodating region.