SiC Trench MOSFET Doping Sequence for Low On-Resistance Stability
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Solution Overview
Problem
Existing silicon carbide MOSFETs face challenges in reducing on-resistance and maintaining reliability due to issues with impurity diffusion and threshold voltage fluctuations during scaling-down processes.
Innovation Solution
A manufacturing method involving first and second ion implantations of carbon and aluminum, respectively, into the trench bottom and sidewalls of a silicon carbide layer, followed by high-temperature heat treatment, to form a trench gate structure with optimized electric field relaxation regions, thereby reducing on-resistance and enhancing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the trench gate type vertical MOSFET is scaled down to reduce on-resistance, then the on-resistance decreases, but impurity diffusion increases causing threshold voltage fluctuations and reliability degradation
Solution Approach 1:
Carbon ions are implanted into the silicon carbide layer before the main aluminum impurity implantation. This preliminary carbon implantation creates a diffusion barrier that prevents subsequent aluminum impurity diffusion, thereby maintaining threshold voltage stability while allowing the device to be scaled down for lower on-resistance
Solution Approach 2:
Carbon ions serve as an intermediary substance between the mask and the aluminum impurity source. The carbon layer acts as a mediator that blocks aluminum diffusion without directly participating in the electrical operation of the device, thus protecting the channel region from impurity contamination
2Stability of the object's composition
If high-temperature heat treatment is performed to form the trench gate structure, then the crystallinity is improved, but impurity diffusion is accelerated
Solution Approach 1:
Carbon ions are implanted into the silicon carbide layer before the main aluminum impurity implantation. This preliminary carbon implantation creates a diffusion barrier that prevents subsequent aluminum impurity diffusion, thereby maintaining threshold voltage stability while allowing the device to be scaled down for lower on-resistance
Solution Approach 2:
Carbon ions serve as an intermediary substance between the mask and the aluminum impurity source. The carbon layer acts as a mediator that blocks aluminum diffusion without directly participating in the electrical operation of the device, thus protecting the channel region from impurity contamination
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
The method effectively suppresses impurity diffusion, increases the channel area, and improves the reliability of the gate insulating layer by maintaining high crystallinity and reducing on-resistance and switching losses in the MOSFET.
Implementation Method 1
performing first ion implantation for implanting carbon (C) into a bottom face of the trench
Implementation Method 2
performing second ion implantation for implanting a p-type first impurity into the bottom face of the trench
Implementation Method 3
performing heat treatment at 1600° C. or more
Data Source
AI summary
A method of manufacturing a semiconductor device according to an embodiment includes: forming a mask material having an opening on a surface of a silicon carbide layer; forming a trench in the silicon carbide layer using the mask material as a mask; performing first ion implantation for implanting carbon (C) into a bottom face of the trench using the mask material as a mask; forming a sidewall material on a side face of the trench; performing second ion implantation for implanting a p-type first impurity into the bottom face of the trench using the sidewall material as a mask; and performing heat treatment at 1600° C. or more.