Shield Gate MOSFET Trench Doping for Higher Breakdown Voltage
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Solution Overview
Problem
As semiconductor components shrink and operating voltage increases, there is a need to enhance the breakdown voltage of shield gate MOSFETs to improve their performance and reliability.
Innovation Solution
A method for fabricating a shield gate MOSFET involves forming epitaxial layers with doped regions of different conductivity types within trenches, where the second doped region has the same conductivity type as the epitaxial layer to reduce leakage paths and improve breakdown voltage, and an insulating layer is used to enhance the breakdown voltage further.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If component size is reduced and operating voltage is increased, then device performance and switching loss are improved, but breakdown voltage decreases
Solution Approach 1:
The patent introduces a shield gate structure with specific doped regions (first doped region with conductivity type opposite to epitaxial layer, and second doped region with same conductivity type as epitaxial layer) at the trench bottom to create localized field control. This local structural modification enables uniform electric field distribution in the critical breakdown region while maintaining overall device performance
Solution Approach 2:
The patent adds a vertical dimension to field control by forming doped regions at the trench bottom and using an insulating layer between the shield gate and epitaxial layer. This three-dimensional structure creates additional field control zones that prevent breakdown without increasing lateral device size
2Loss of energy
If shield gate structure is implemented to reduce gate-to-drain capacitance, then switching loss is improved, but breakdown voltage control becomes challenging
Solution Approach 1:
The patent introduces an insulating layer as an intermediary between the shield gate and the epitaxial layer. This insulating layer mediates the electric field interaction, preventing direct field concentration at the gate-semiconductor interface while maintaining the capacitance reduction benefit of the shield gate structure
Solution Approach 2:
The patent modifies the electrical parameters by introducing doped regions with specific conductivity types and controlled doping concentrations. The first doped region (opposite conductivity type) and second doped region (same conductivity type as epitaxial layer) create specific field distribution characteristics that control breakdown voltage independently of the shield gate capacitance effect
Data Source
AI summary
A method for fabricating a shield gate MOSFET includes forming an epitaxial layer having a first conductivity type, forming a plurality of trenches in the epitaxial layer, forming a first and a second doped regions in the epitaxial layer at a bottom of each of the trenches, wherein the first doped region has a second conductivity type, and the second doped region has the first conductivity type. An insulating layer and a conductive layer as a shield gate are orderly formed in each of the trenches, and a portion of the conductive layer and the insulating layer are removed to expose a portion of the epitaxial layer in the trenches. An inter-gate oxide layer and a gate oxide layer are formed in the trenches, and a control gate is formed on the inter-gate oxide layer in the plurality of trenches.