SiC Trench Gate Depletion Suppression for ON-Resistance
Solution Overview
Problem
Trench gate type silicon carbide semiconductor devices face challenges in maintaining breakdown voltage while reducing ON-resistance due to the concentration of electric fields at the trench bottom, leading to potential gate insulating film breakdown and increased JFET resistance.
Innovation Solution
A silicon carbide semiconductor device with a drift layer, body region, source region, gate insulating film, trench bottom protective layer, and depletion suppressing layer is designed, where the depletion suppressing layer is formed between the gate trench and drift layer with a higher impurity concentration that decreases as distance from the trench increases, reducing electric field strength and ON-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a trench gate structure is used to increase channel width density, then device performance is improved, but electric field concentration at the trench bottom increases leading to gate insulating film breakdown risk
Solution Approach 1:
An n-type depletion suppressing layer is introduced as an intermediary between the p-type protective layer and the n-type drift layer. This intermediate layer prevents direct contact between opposite polarity layers, suppressing depletion layer extension and reducing electric field concentration at the trench bottom, thereby protecting the gate insulating film while maintaining the trench gate structure's performance benefits
Solution Approach 2:
The invention changes the impurity concentration parameter by forming a depletion suppressing layer with higher impurity concentration than the drift layer. This parameter change suppresses the formation and extension of depletion layers, effectively reducing electric field concentration at the trench bottom and preventing gate insulating film breakdown
2Reliability
If a p-type protective layer is formed on the trench bottom to reduce electric field strength, then gate insulating film reliability is improved, but JFET resistance increases leading to higher ON-resistance
Solution Approach 1:
The invention applies local quality by creating an n-type depletion suppressing layer with higher impurity concentration in the specific region between the protective layer and drift layer. This localized high impurity concentration region suppresses depletion layer extension only where needed, reducing JFET resistance in the channel region while maintaining electric field reduction at the trench bottom
Solution Approach 2:
By changing the impurity concentration parameter to create a higher doped n-type layer, the invention suppresses depletion layer formation and extension, thereby reducing JFET resistance and lowering ON-resistance while the protective layer continues to reduce electric field strength at the trench bottom
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 suppresses the extension of the depletion layer, reducing ON-resistance and maintaining breakdown voltage, thereby enhancing the reliability and power efficiency of the semiconductor device.
Implementation Method 1
the depletion layer extends largely from these p-type regions, and even when the MOSFET is conducting, the depletion layer expands to some degree from the protective layer into the drift layer
Implementation Method 2
the electric field is easily concentrated. From the above, there is an apprehension that the reliability of the gate insulating film on the bottom portion of the trench may be reduced
Data Source
AI summary
A drift layer is formed of silicon carbide and has a first conductivity type. A trench bottom protective layer is provided on a bottom portion of a gate trench and has a second conductivity type. A depletion suppressing layer is provided between a side surface of the gate trench and the drift layer, extends from a lower portion of a body region up to a position deeper than the bottom portion of the gate trench, has the first conductivity type, and has an impurity concentration of the first conductivity type higher than that of the drift layer. The impurity concentration of the first conductivity type of the depletion suppressing layer is reduced as the distance from the side surface of the gate trench becomes larger.