Superjunction Power MOSFET Shield Electrode Corner Rounding
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Solution Overview
Problem
Current superjunction power semiconductor devices experience high electrical leakage and low breakdown due to sharp corners formed in the gate and shield electrodes, degrading performance and long-term reliability, primarily attributed to the thicker inter-poly dielectric (IPD) oxide layer.
Innovation Solution
A method is developed to form a superjunction power MOSFET by creating trenches in a semiconductor substrate, filling them with polysilicon, and then recessing the polysilicon to form shield electrodes, followed by depositing an oxide layer and forming gate dielectrics, which reduces or eliminates sharp corners in the electrodes, thereby improving the IPD quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the IPD oxide layer is made thicker to provide better insulation, then the breakdown voltage increases, but sharp corners are formed in the gate and shield electrodes resulting in high electrical field and high leakage
Solution Approach 1:
The patent applies preliminary action by forming a mandrel structure with rounded corners before depositing the IPD oxide layer. This pre-formed rounded geometry prevents sharp corner formation during subsequent processing steps, thereby eliminating the root cause of high electrical field concentration while maintaining the required oxide thickness for breakdown voltage.
Solution Approach 2:
The patent introduces a mandrel structure as an intermediary element that serves as a template for forming the gate and shield electrodes with rounded corners. This intermediary structure enables the transfer of rounded geometry to the final electrode configuration, resolving the contradiction between thick oxide insulation and sharp corner elimination.
2Reliability
If the IPD oxide layer is grown thicker, then insulation performance improves, but manufacturing complexity increases due to additional process steps required to eliminate sharp corners
Solution Approach 1:
The patent merges the formation of the gate/shield electrode structure with the IPD oxide deposition process by using the mandrel as a combined template. The rounded corners are formed in the mandrel itself, and this geometry is transferred to the electrodes during a single deposition and etch sequence, eliminating the need for separate corner-rounding process steps.
Solution Approach 2:
The mandrel structure with pre-formed rounded corners is created before IPD oxide deposition, allowing the subsequent processing to directly inherit the rounded geometry. This preliminary action simplifies the overall manufacturing process by eliminating the need for additional steps to modify electrode corners after oxide formation.
3Ease of manufacture
If conventional oxide growth processes are used, then processing simplicity is maintained, but sharp corners are formed degrading device performance and long-term reliability
Solution Approach 1:
The mandrel structure serves as an intermediary that enables conventional oxide growth processes to produce rounded-corner electrodes. By forming the rounded geometry in the mandrel before oxide deposition, the patent allows standard processing techniques to be used while achieving the reliability benefits of sharp corner elimination.
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 enhances the performance and long-term reliability of superjunction power devices by reducing leakage and increasing breakdown voltage through the elimination of sharp corners in the gate and shield electrodes.
Implementation Method 1
forming a first oxide layer over the semiconductor substrate and in the first trench
Implementation Method 2
depositing electrically conductive material in the first trench to form a first shield electrode
Implementation Method 3
forming a gate dielectric along exposed sidewalls of the first trench
Data Source
Figure 1~2
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Figure 5~6
AI summary
A method for manufacturing a power MOSFET includes forming a first trench in a substrate, forming a first oxide layer over the substrate and in the bottom and along sidewalls of the trench, depositing electrically conductive material in the trench, masking a first portion of the electrically conductive material at the end portion of the sidewalls of the trench along a certain direction, forming a recessed portion of the electrically conductive material, forming an oxide portion over and in contact with the recessed portion of the electrically conductive material, removing a part of the oxide portion by masking, removing the first oxide layer on the sidewalls while another part of the oxide portion remains in contact with the recessed portion of the electrically conductive material, forming a gate dielectric along exposed sidewalls of the trench, and depositing additional electrically conductive material over the other part of the oxide portion in the trench.