Split-gate trench MOSFET poly-to-poly isolation
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Solution Overview
Problem
Existing split-gate trench power MOSFET devices face challenges in reducing threshold voltage while maintaining adequate gate-to-source leakage current control, as thinning the gate oxide to achieve lower threshold voltage leads to weak poly-to-poly isolation and increased leakage current.
Innovation Solution
The method involves forming a trench in a semiconductor substrate, lining it with insulating layers, and filling it with conductive materials to create a field plate and gate electrode structure, where the gate oxide thickness is controlled to be thin (450-500Å) and the third insulating layer's position and thickness are optimized for strong poly-to-poly isolation, using a resist material as a mask for precise etching to ensure adequate insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the gate oxide thickness is thinned to reduce threshold voltage, then the threshold voltage is reduced, but the poly-to-poly isolation becomes weak and gate-to-source leakage current increases
Solution Approach 1:
The gate structure is segmented into two separate polysilicon regions: a first polysilicon region forming the field plate electrode and a second polysilicon region forming the gate electrode. These regions are electrically isolated by a third insulating layer, allowing independent optimization of each region's function while maintaining proper isolation even with thin gate oxide (450-500Å).
Solution Approach 2:
A third insulating layer is introduced as an intermediary between the first polysilicon region (field plate) and the second polysilicon region (gate). This intermediate layer provides the necessary poly-to-poly isolation to prevent leakage current while allowing the gate oxide to be sufficiently thin for low threshold voltage operation.
2Manufacturing precision
If the gate oxide is thinned to achieve lower threshold voltage, then the threshold voltage decreases, but the insulation between gate and field plate becomes insufficient
Solution Approach 1:
The gate structure is segmented into two separate polysilicon regions: a first polysilicon region forming the field plate electrode and a second polysilicon region forming the gate electrode. These regions are electrically isolated by a third insulating layer, allowing independent optimization of each region's function while maintaining proper isolation even with thin gate oxide (450-500Å).
Solution Approach 2:
A third insulating layer is introduced as an intermediary between the first polysilicon region (field plate) and the second polysilicon region (gate). This intermediate layer provides the necessary poly-to-poly isolation to prevent leakage current while allowing the gate oxide to be sufficiently thin for low threshold voltage operation.
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 allows for a lower threshold voltage while maintaining acceptable gate-to-source leakage current levels by ensuring sufficient insulation between the gate and field plate electrodes, thus enhancing the transistor's performance.
Implementation Method 1
The side walls and bottom of each trench 18 are lined with a first insulating layer 20... Each trench 18 is filled by a first polysilicon material 22, with the first insulating layer 20 insulating the first polysilicon material 22 from the substrate 12
Implementation Method 2
The second insulating layer 30a forms the gate oxide layer
Implementation Method 3
the third insulating layer 30b insulating the polysilicon material 32 from the upper portion 22a
Data Source
Figure 1~2
Figure 3~4
Figure 5A~5D
AI summary
A semiconductor substrate (12) has a trench (18) extending from a front surface (14) and including a lower part and an upper part. A first insulation layer (20) lines the lower part of the trench, and a first conductive material (22) in the lower part is insulated from the semiconductor substrate by the first insulating layer to form a field plate electrode of a transistor. A second insulating layer (130) lines sidewalls of the upper part of said trench. A third insulating layer (132) lines a top surface of the first conductive material at a bottom of the upper part of the trench. A second conductive material (32) fills the upper part of the trench. The second conductive material forms a gate electrode of the transistor (100) that is insulated from the semiconductor substrate by the second insulating layer and further insulated from the first conductive material by the third insulating layer.