Superjunction Power Device Graded Sidewall Termination
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Solution Overview
Problem
Maintaining charge balance in the corner and edge termination regions of power semiconductor devices with superjunction structures is challenging, leading to decreased breakdown voltage and reduced robustness, which narrows the manufacturing process window and increases yield loss due to fabrication variations.
Innovation Solution
Incorporating superjunction structures with reduced column charge and grading in the termination region, ensuring higher breakdown voltage than the active cell region, thereby widening the manufacturing process window and ensuring breakdown occurs primarily in the core region, enhancing device robustness and UIS performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If superjunction structures are used in termination regions to maintain charge balance, then breakdown voltage is improved, but manufacturing precision deteriorates due to sensitivity to fabrication variations
Solution Approach 1:
The patent applies different superjunction structures to different regions: the core region uses conventional superjunction structures with specific doping profiles, while the termination region uses a modified superjunction structure with reduced column charge and graded sidewalls. This local differentiation allows the termination region to have higher breakdown voltage margin without compromising the overall device performance, thereby widening the manufacturing process window.
Solution Approach 2:
The patent modifies key parameters of the superjunction structure in the termination region, specifically reducing the column charge and implementing graded sidewall doping profiles. These parameter changes increase the breakdown voltage in the termination region, creating a safety margin that compensates for fabrication variations and widens the manufacturing process window.
2Device complexity
If conventional superjunction structures are used in termination regions, then device complexity is reduced, but robustness deteriorates due to decreased breakdown voltage margin
Solution Approach 1:
The patent introduces a specialized superjunction structure specifically for the termination region with reduced column charge and graded sidewalls, while keeping the core region structure conventional. This localized modification enhances breakdown voltage margin and robustness without significantly increasing overall device complexity, as the modified structure follows similar fabrication processes.
3Strength
If graded sidewall superjunction structures are implemented in termination regions, then breakdown voltage is increased, but ease of manufacture deteriorates due to additional processing steps
Solution Approach 1:
The graded sidewall doping profile is established during the epitaxial growth process itself, rather than requiring separate post-processing steps. The doping concentration is gradually varied during growth to create the desired graded profile, which simplifies the overall fabrication process while achieving the target breakdown voltage enhancement.
Data Source
AI summary
A method for forming a superjunction power semiconductor device includes forming multiple epitaxial layers of a first conductivity type on a semiconductor substrate and implanting dopants of a second conductivity type into each epitaxial layer to form a first group of implanted regions in a first region and a second group of implanted regions in a second region in each epitaxial layer. The multiple epitaxial layers are annealed to form multiple columns of the second conductivity type having slanted sidewalls across the first to last epitaxial layers. The columns include a first group of columns formed by the implanted regions of the first group and having a first grading and a second group of columns formed by the implanted regions of the second group and having a second grading, where the second grading is less than the first grading.