Super-junction Trench MOSFETs with Closed Cell Layout
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Solution Overview
Problem
Conventional super-junction trench MOSFETs have longer termination areas, which occupy more space and are less cost-effective, limiting their integration and application in advanced semiconductor power devices.
Innovation Solution
A super-junction trench MOSFET design with a termination area of approximately 20 um in length, featuring a novel cell structure with P/N charge balance areas, doped column regions, and a method for manufacturing that includes forming deep trenches, dielectric material deposition, and specific doping and etching processes to reduce termination length and enhance device compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional super-junction trench MOSFETs use multiple guard rings in the termination area, then breakdown voltage and device reliability are improved, but the termination area length increases to about 200 um, occupying more space and reducing integration density
Solution Approach 1:
The patent extracts and removes the multiple guard rings from the termination area, reducing the termination length from 200 um to 20 um. The guard rings are taken out as they are no longer needed with the new cell structure design, directly solving the contradiction by eliminating the space-consuming components while maintaining breakdown voltage through the super-junction mechanism.
Solution Approach 2:
The patent transitions from a planar guard ring structure to a vertical super-junction structure. By changing the dimensionality of the charge balance mechanism from horizontal (guard rings in the termination area) to vertical (alternating P-type and N-type columns extending into the drift region), the termination area length is dramatically reduced while maintaining or improving breakdown voltage characteristics.
2Reliability
If the termination area is extended to ensure adequate voltage blocking, then device reliability is improved, but device size increases, reducing cost-effectiveness and integration density
Solution Approach 1:
The patent changes the doping parameters in the termination area, specifically implementing a P-type doped column region with optimized doping concentration and depth. This parameter optimization allows adequate voltage blocking with a reduced termination area of 20 um, compared to conventional designs requiring 200 um for equivalent performance.
Solution Approach 2:
The patent employs a composite structure in the termination area combining P-type doped column regions with the surrounding N-type drift region. This composite P-N structure creates effective charge balance and electric field management, achieving reliable voltage blocking in a compact 20 um termination area rather than requiring extensive uniform doping regions.
3Reliability
If conventional cell structures are used with adequate termination, then device performance is maintained, but integration density and cost-effectiveness decrease due to larger device footprint
Solution Approach 1:
The patent segments the cell structure into distinct functional regions: active area with super-junction columns, body region, and a compact termination area. This segmentation allows each region to be optimized independently, with the termination area reduced to 20 um while maintaining overall device performance through the segmented architecture and dedicated charge balance regions.
Solution Approach 2:
The super-junction column structure serves multiple functions simultaneously: it provides the primary current conduction path, establishes the breakdown voltage through the drift region, and manages charge balance in the termination area. This multi-functionality eliminates the need for separate guard ring structures, achieving high integration density while maintaining device performance.
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 design achieves a significant reduction in termination length to about one tenth of prior art, making the device more flexible, cost-effective, and suitable for advanced semiconductor power applications with improved performance.
Implementation Method 1
each comprising a void inside the dielectric material; a mesa between the pair of deep trenches; a first doped column region of the first conductivity type with column shape within each the mesa; a pair of second doped column regions of a second conductivity type with column shape adjacent to sidewalls of the pair of deep trenches within the mesa, in parallel with and surrounding the first doped column region forming a first type charge balance area
Implementation Method 2
at least one gate trench filled with doped poly-silicon layer padded by a gate oxide layer, starting from the top surface of the epitaxial layer and down penetrating through the body region and extending into the first doped column in the mesa
Implementation Method 3
a pair of second doped column regions of a second conductivity type with column shape adjacent to sidewalls of the pair of deep trenches within the mesa, in parallel with and surrounding the first doped column region forming a first type charge balance area in conjunction with the first doped column region
Data Source
AI summary
A super-junction trench MOSFET with closed cell layout having shielded gate is disclosed, wherein closed gate trenches surrounding a deep trench in each unit cell and the shielded gate disposed in the deep trench. Trenched source-body contacts are at least formed between the closed gate trenches and the deep trench. The deep trench has square, rectangular, circle or hexagon shape.