Vertical MOS Termination Trench Corner Design
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Solution Overview
Problem
Vertical MOS transistors with parallel RESURF trenches experience premature breakdown and breakdown instability due to uncontrolled regions of the substrate inside the termination trench at chamfered corners.
Innovation Solution
A semiconductor device design featuring vertical MOS transistors with parallel drain trenches and a RESURF configuration, where the termination trench is strategically positioned with alternating external and internal corners to reduce stress, separated from drain trenches by specific spacings to alleviate breakdown issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If chamfered corners are used to reduce stress on vertical MOS transistor, then stress reduction is achieved, but premature breakdown and breakdown instability occur due to uncontrolled substrate regions inside the termination trench
Solution Approach 1:
The termination trench is designed with different corner configurations at different locations: external corners at chamfered corners to reduce stress concentration, and internal corners at non-chamfered corners to control substrate regions. This local differentiation resolves the contradiction by applying the appropriate corner type at each location to simultaneously achieve stress reduction and breakdown stability.
Solution Approach 2:
The termination trench is segmented into different sections with external corners and internal corners based on their functional requirements. This segmentation allows the structure to simultaneously perform stress reduction at chamfered corners and substrate control at other locations, resolving the reliability issue caused by uncontrolled substrate regions.
2Area of stationary object
If termination trench is positioned close to drain trenches to maximize device area, then area efficiency is improved, but breakdown instability occurs due to uncontrolled substrate regions
Solution Approach 1:
The termination trench employs different corner configurations (external vs. internal) at different locations to simultaneously achieve compact area and controlled substrate regions. This local differentiation allows the structure to maintain close spacing for area efficiency while preventing breakdown instability through proper substrate control at critical locations.
3Ease of manufacture
If termination trench uses uniform corner configuration, then manufacturing is simplified, but stress control and breakdown stability are compromised at chamfered corners
Solution Approach 1:
The termination trench is designed with local quality differentiation, using external corners at chamfered corners for stress control and internal corners at other locations for substrate control. While this increases manufacturing complexity compared to uniform corners, it is achieved through standard photolithography and etching processes, making the complexity manageable while significantly improving reliability.
Data Source
AI summary
A semiconductor device includes a vertical MOS transistor with a plurality of parallel RESURF drain trenches separated by a constant spacing in a vertical drain drift region. The vertical MOS transistor has chamfered corners; each chamfered corner extends across at least five of the drain trenches. A RESURF termination trench surrounds the drain trenches, separated from sides and ends of the drain trenches by distances which are functions of the drain trench spacing. At the chamfered corners, the termination trench includes external corners which extend around an end of a drain trench which extends past an adjacent drain trench, and includes internal corners which extend past an end of a drain trench which is recessed from an adjacent drain trench. The termination trench is separated from the drain trenches at the chamfered corners by distances which are also functions of the drain trench spacing.