Superjunction Semiconductor Device With Inverted Fabrication Sequence
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Solution Overview
Problem
In semiconductor devices, particularly superjunction semiconductor elements, it is challenging to form a good superjunction structure with fine pitch due to impurity diffusion during thermal history, which affects the trade-off between breakdown voltage and on-resistance.
Innovation Solution
A semiconductor device design that includes a semiconductor substrate with specific conductivity-type regions and trenches, where a protruding portion is formed with controlled carrier concentration and depth to balance carrier quantities, reducing on-resistance while maintaining breakdown voltage, by satisfying the equation 0.9≦Wc-Wt×Nd/Na≦1.1, and incorporating a contact trench and gate trenches with a gate insulating film and conductive section.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a superjunction structure is formed and then an MOS structure is formed, then the device can achieve low on-resistance while securing breakdown voltage, but impurities in the superjunction structure diffuse due to thermal history during MOS structure formation, making it difficult to form a good superjunction structure
Solution Approach 1:
The patent forms the MOS structure (gate trench, gate insulating film, gate electrode) before forming the superjunction structure. This preliminary action prevents thermal diffusion damage to the superjunction impurities, as the high-temperature MOS formation process occurs before the superjunction is created. The gate structure is established first, then the superjunction p-n alternating columns are formed through ion implantation or epitaxial growth without subsequent high-temperature processing that would cause impurity diffusion.
Solution Approach 2:
The patent inverts the conventional fabrication sequence by forming the MOS structure first and then forming the superjunction structure. Normally, the superjunction is formed first followed by MOS structure formation, but this patent reverses the order to protect the superjunction impurities from thermal diffusion during MOS processing.
2Productivity
If the pitch of the superjunction structure is reduced to achieve finer devices, then device integration is improved, but impurity diffusion during thermal history becomes more prominent, degrading the superjunction structure quality
Solution Approach 1:
By forming the MOS structure before the superjunction structure, the patent eliminates thermal diffusion damage that would otherwise occur during MOS formation. This allows fine-pitch superjunction structures to be created without impurity diffusion degrading the precise doping profiles needed for high-density integration.
Solution Approach 2:
The patent changes the fabrication parameter sequence by reversing the order of structure formation. This parameter change (fabrication sequence) fundamentally alters the thermal history experienced by the superjunction impurities, enabling fine-pitch structures to maintain their doping precision despite the complexity of creating densely packed superjunction columns.
Data Source
AI summary
To provide a semiconductor device having a structure capable of forming a superjunction with less thermal history, a semiconductor device is provided, the semiconductor device including a contact trench formed between two gate trenches, penetrating through a source region, and including its lower end arranged in a base region, and a second conductivity-type protruding portion formed protruding toward a lower side from the lower end of the base region in a region opposite to the lower end of the contact trench, wherein the depth from the upper end of the source region to a lower end of the protruding portion is 3 μm or more, and a carrier concentration Nd in a first conductivity-type region adjacent to the protruding portion in a lateral direction perpendicular to a depth direction and a carrier concentration Na of the protruding portion satisfy a predetermined equation.