Trench-Gated Turn-Off Structure for Stable Turn-On Voltage
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Solution Overview
Problem
Existing vertical, insulated-gate controlled semiconductor devices, such as IGBTs and IGTOs, are sensitive to process-inherent variations in trench depth and p-body depth, leading to inconsistent turn-on voltages from lot to lot.
Innovation Solution
The effective distance between the bottom of the gate trench and the p-well is made more consistent by forming a p-epitaxial layer within the trench, which is precisely controlled in thickness and dopant concentration, thereby reducing the dependence on the original p-body and trench depth variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional trench-gated structures are used, then device fabrication is simpler, but turn-on voltage becomes sensitive to process variations in trench depth and p-body depth
Solution Approach 1:
The patent applies preliminary action by forming the p-type epitaxial layer within the trench before finalizing the gate structure. This preliminary layer is precisely controlled in thickness and dopant concentration, establishing a reference point that compensates for subsequent variations in trench depth and p-body depth during fabrication processes.
Solution Approach 2:
The patent changes the physical parameters of the semiconductor structure by introducing a p-type epitaxial layer with specifically controlled thickness and dopant concentration. This parameter control creates a standardized reference level within the trench, making the turn-on voltage dependent on precisely controllable parameters rather than on the variable depths of the trench or p-body.
2Reliability
If precise control of trench depth and p-body depth is implemented, then turn-on voltage consistency improves, but fabrication complexity and cost increase
Solution Approach 1:
The patent introduces a p-type epitaxial layer as an intermediary element within the trench structure. This intermediary layer serves as a mediator that decouples the turn-on voltage characteristic from the variable depths of the trench and p-body, allowing precise voltage control without requiring precise control of the underlying structural depths.
Solution Approach 2:
By changing the approach from controlling geometric parameters (trench depth, p-body depth) to controlling material parameters (epitaxial layer thickness and dopant concentration), the patent achieves turn-on voltage consistency through a fabrication process that is precisely controllable through well-established epitaxial growth techniques.
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 results in more consistent turn-on voltage and device characteristics across lots, as the npn transistor's beta and turn-on voltage are less affected by imprecise trench and p-body depths.
Implementation Method 1
forming a p-epitaxial layer within the trench, which is precisely controlled in thickness and dopant concentration
Data Source
AI summary
In a trench-gated device, the effective depth of a gate-induced inversion layer into a p-body is made more consistent to make the operating characteristics of the device more consistent. In one example, the p-body is formed over an n-drift layer, and an n+ source layer is formed over the p-body. Trenches are then etched that extend through the p-body and into the n-drift layer. Next, a p-doped layer is grown or deposited in the trenches. In one embodiment, the p-doped layer remains in the trench. In another embodiment, the p-dopants in the layer are diffused into the trench walls, and the layer is removed. This added p-type layer in or around the trenches contacts the side of the p-body to effectively form a very controllable deeper portion of the p-body. A gate oxide is formed, and the insulated trenches are filled with a conductor, such as doped polysilicon.