Trench MOSFET Source Contact with Copper Wire Bonding
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Solution Overview
Problem
Trench MOSFETs face challenges in achieving low spreading resistance while maintaining small size and low fabrication cost, as existing solutions with thick Ni and Au deposition are costly and inefficient due to low cell density and increased area waste.
Innovation Solution
The implementation of a trench source contact structure with vertical and slope sidewalls, high cell density, and copper wire bonding replaces Au wire, reducing spreading resistance and die size without additional expensive metal layers, and enhancing avalanche capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick Ni and Au metal layers are deposited to reduce spreading resistance, then spreading resistance is reduced, but fabrication cost increases significantly
Solution Approach 1:
The patent replaces expensive Au wire and thick Ni/Au metal layers with copper wire and thin AlCu alloy layers. Copper is significantly cheaper than gold, and the thin alloy layer reduces material costs while maintaining electrical performance. This directly addresses the contradiction by using cheaper materials to achieve the same low spreading resistance without the high fabrication cost of traditional thick Ni/Au deposition.
Solution Approach 2:
The patent changes the material parameters from traditional Au/Ni to Cu/AlCu alloy, and adjusts the thickness parameters of metal layers. By optimizing the thickness of AlCu alloy layer (3-5 μm) and using copper wire bonding, the system achieves low spreading resistance with reduced material costs, resolving the contradiction between reliability and manufacturing cost.
2Reliability
If planar source contact with thick metal layer is used to reduce spreading resistance, then spreading resistance is reduced, but device area increases due to low cell density
Solution Approach 1:
The patent transitions from planar source contact to trench source contact structure, moving the contact interface into the vertical dimension. The trench contact allows current to flow vertically through the AlCu alloy layer filling the trench, enabling higher cell density without increasing device area, while maintaining low spreading resistance through the conductive alloy material.
Solution Approach 2:
The patent applies different material properties to different regions: AlCu alloy with specific electrical properties is placed in the trench contact region to reduce spreading resistance, while the overall device structure achieves high cell density. This localized optimization allows simultaneous achievement of low resistance and compact area.
3Ease of manufacture
If copper wire bonding is used to replace Au wire, then fabrication cost is reduced, but the underlying metal layer must be sufficiently thick to prevent damage
Solution Approach 1:
The patent changes the material from traditional Au wire to copper wire, and simultaneously optimizes the thickness parameter of the AlCu alloy layer to 3-5 μm. This parameter optimization ensures the metal layer is thick enough to support copper wire bonding without damage, while being thin enough to reduce overall device area and cost, resolving the contradiction between cost reduction and manufacturing precision requirements.
Data Source
AI summary
A trench MOSFET with trench source contact structure having copper wire bonding is disclosed. By employing the proposed structure, die size can be shrunk into 30%˜70% with high cell density, and the spreading resistance is significantly reduce without adding expensive thick metal layer as prior art. To further reduce fabricating cost, copper wire bonding is used with requirement of thick Al alloys.