Vertical MOSFET Well Doping Gradients for Electric Field Control
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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, particularly due to doping variations that affect electric field distribution and parasitic properties.
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, enhancing device robustness and performance by controlling the pinch-off effect and capacitance.
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 and space between body implants become limiting factors
Solution Approach 1:
The patent applies local quality by implementing different doping concentrations at different lateral positions within the well regions. The doping concentration varies from a first concentration at a first lateral end to a second concentration at a second lateral end, allowing optimized electrical properties in different local areas while maintaining manufacturable cell sizes
Solution Approach 2:
The patent transitions from uniform doping to graded doping by adding a lateral dimension to the doping profile. The doping concentration changes laterally across the well region, creating a gradient that improves electric field distribution and allows smaller cell sizes without compromising manufacturing accuracy
2Productivity
If body implants are placed closer together to reduce cell size, then channel density increases, but pinch-off avoidance becomes more difficult
Solution Approach 1:
The graded doping profile creates different local electrical properties within the well region. By having higher doping concentration at one lateral end and lower at the other, the patent optimizes the balance between preventing pinch-off near the body implant while maintaining high channel density
Solution Approach 2:
The patent changes the doping concentration parameter laterally across the well region, transitioning from a first doping concentration to a second doping concentration. This parameter variation allows closer spacing of body implants while maintaining reliability by controlling the electric field distribution to prevent pinch-off
3Productivity
If doping variations are used to counter reduction in conduction performance, then conduction performance is maintained, but parasitic electric properties and electric field distribution are impacted
Solution Approach 1:
The patent uses controlled parameter changes in the doping concentration to maintain conduction performance. By implementing a gradual lateral gradient rather than abrupt variations, the patent maintains good conduction while minimizing negative impacts on parasitic properties
Solution Approach 2:
The localized graded doping creates optimal electrical properties in specific regions. The first doping concentration region and second doping concentration region serve different functional purposes, balancing conduction performance with reduced parasitic effects
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 increases semiconductor device robustness, reduces electric field crowding, and improves current distribution, leading to better conduction performance and reduced parasitic effects, thereby optimizing the device's operational efficiency and reliability.
Implementation Method 1
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
Implementation Method 2
These doping variations may also impact the parasitic electric properties of the device and thereby also the dynamic device performance. In addition to the parasitics, the electric field distribution may be strongly changed by doping variations
Data Source
AI summary
A vertical oriented semiconductor device is provided. The present disclosure further provides that at least one of the well regions of the device have at least two lateral doping gradients, at different depths in the semiconductor material, and each doping gradient has a monotonic decreasing doping concentration, from a higher doping concentration at a first lateral end of the well regions towards a lower doping concentration at a second, opposite lateral end thereof facing the current-accommodating region. These two doping gradients, at different depths, differ from each other, with one of the advantages being that the semiconductor device is made more robust. Multiple ways of implementing the two different lateral doping gradients are provided. Some of the advantages are that the electric field crowding at the corners of the well regions is gradually reduced, and the current distribution can be improved.