Trench Field Effect Transistor Doping Layout for Low Channel Resistance

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Solution Overview

Problem

Field effect transistors face challenges in achieving a balance between high breakdown voltage and low channel resistance due to the narrow channel formation and high resistance issues caused by p-type deep layers with uniform impurity concentrations.

Innovation Solution

The design incorporates p-type deep layers with low and high concentration regions, where the low concentration region has a lower impurity concentration than the body layer, allowing for channel formation on both the side and bottom surfaces of trenches, thereby widening the channel and reducing resistance while maintaining high breakdown voltage through depletion layer extension from high concentration regions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If p-type deep layers with uniform high impurity concentration are used, then breakdown voltage is maintained, but channel resistance increases and channel formation is restricted

Engineering Contradiction:

Improvebreakdown voltageVSAvoidchannel resistance

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The p-type deep layer is divided into two regions with different impurity concentrations: a first region with lower p-type impurity concentration and a second region with higher p-type impurity concentration. This local differentiation allows the first region to support channel formation (reducing channel resistance) while the second region maintains the depletion layer and breakdown voltage characteristics.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The p-type deep layer is segmented into multiple regions along the depth direction. The first region (shallower) has lower impurity concentration to facilitate channel formation, while the second region (deeper) has higher impurity concentration to maintain breakdown voltage. This segmentation resolves the contradiction by assigning different functional properties to different segments of the same structure.

Inventive Principle:

Principle #1Segmentation

2Reliability

If p-type deep layers extend below trench bottom surface, then depletion layer extension is improved, but channel formation is restricted in uniform concentration structures

Engineering Contradiction:

Improvedepletion layer extensionVSAvoidchannel formation

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

By making the impurity concentration non-uniform in the p-type deep layer, the patent enables channel formation in the lower concentration first region while maintaining depletion layer extension capability in the higher concentration second region that extends below the trench bottom surface.

Inventive Principle:

Principle #3Local quality

3Reliability

If high p-type impurity concentration is used throughout, then breakdown voltage is maintained, but switching speed decreases due to slow depletion layer reduction

Engineering Contradiction:

Improvebreakdown voltageVSAvoidswitching speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The lower impurity concentration in the first region allows for faster carrier removal and quicker depletion layer reduction when the device turns off, improving switching speed. The higher impurity concentration in the second region maintains the breakdown voltage. This local quality differentiation resolves the contradiction between reliability and speed.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Segmenting the p-type deep layer into regions with different impurity concentrations allows the first region to facilitate fast switching (lower concentration) while the second region maintains high breakdown voltage (higher concentration), thus resolving the contradiction between switching speed and breakdown voltage.

Inventive Principle:

Principle #1Segmentation

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 effectively reduces channel resistance by up to 50% while maintaining equivalent breakdown voltage, enabling faster switching and improved performance by ensuring the high concentration regions do not float during off-states and quick depletion layer reduction upon turning on.

Implementation Method 1

allowing for channel formation on both the side and bottom surfaces of trenches, thereby widening the channel and reducing resistance while maintaining high breakdown voltage through depletion layer extension from high concentration regions

Methodology Applied

Scientific EffectDepletion layer extension:

Implementation Method 2

maintaining high breakdown voltage through depletion layer extension from high concentration regions

Methodology Applied

Scientific EffectDepletion layer extension:

Data Source

PatentUS20230369484A1Field effect transistor

Publication Date: 2023.11.16 DENSO CORP

AI summary

A field effect transistor includes a plurality of p-type deep layers. The p-type deep layers protrude downward from a body layer, extend so as to intersect a trench when a semiconductor substrate is viewed from above, and extend from the body layer to a position below a bottom surface of the trench. Each of the p-type deep layers includes a low concentration region and a high concentration region having a higher p-type impurity concentration than the low concentration region and the body layer. The low concentration region is in contact with the body layer from below, and is in contact with the gate insulating film on a side surface of the trench located below the body layer. The high concentration region is in contact with the low concentration region from below.