High Density Trench MOSFET Two-Step Gate Oxide Charge Balancing
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Solution Overview
Problem
Existing high-density trench-based power MOSFETs face challenges in minimizing on-resistance (RdsA) and maximizing switching speed, particularly at deep sub-micron scales, due to lack of charge balancing and high electric fields, which lead to increased resistance and susceptibility to misalignment errors.
Innovation Solution
The development of a high-density trench-based power MOSFET with self-aligned source and body contacts using conductive or semiconductor spacers and a two-step gate oxide, allowing for reduced voltage burden on the epitaxial layer and increased doping concentration, along with a lightly doped P-region to minimize coupling between the gate and drain, enabling precise alignment and scalable design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If trench-based MOSFET design is used to reduce cell pitch, then device density is improved, but on-resistance increases due to lack of charge balancing in drift regions
Solution Approach 1:
The patent applies local quality by implementing a two-step gate oxide structure where the first portion has a different thickness than the second portion. This creates localized regions with different electrical characteristics - the thinner first portion provides stronger electric field for charge balancing in specific areas, while the thicker second portion maintains overall device performance. This local differentiation resolves the contradiction by providing charge balancing exactly where needed in the drift region without compromising overall device density.
2Productivity
If gate oxide thickness is reduced to increase device density, then cell pitch is decreased, but breakdown voltage decreases due to high electric field under trench
Solution Approach 1:
The two-step gate oxide structure creates local quality variations where the first portion (thinner oxide) is positioned to provide enhanced electric field control in regions requiring charge balancing, while the second portion (thicker oxide) is positioned to maintain breakdown voltage in regions requiring voltage support. This spatial differentiation allows the device to achieve both high density and high voltage capability simultaneously.
Solution Approach 2:
The gate oxide is segmented into two distinct portions with different thicknesses. This segmentation allows independent optimization of different functional regions - one portion optimized for electric field control and charge balancing, the other optimized for voltage blocking. The segmented structure resolves the contradiction by distributing different functional requirements to different parts of the gate oxide system.
3Strength
If low doping concentration is used in drift region to support voltage, then breakdown voltage is improved, but on-resistance increases
Solution Approach 1:
The patent changes the parameter of gate oxide thickness locally to compensate for the low doping concentration in the drift region. By creating a thinner first portion of gate oxide in specific areas, the electric field is enhanced locally, providing the necessary charge balancing effect without requiring higher doping concentrations. This parameter change in the gate oxide structure allows the drift region to maintain low doping for voltage support while achieving adequate on-resistance performance through the enhanced electric field from the thinner oxide portion.
4Productivity
If cell pitch is reduced to increase device density, then productivity is improved, but manufacturing precision requirements increase due to alignment sensitivity
Solution Approach 1:
The patent implements preliminary action by forming the first portion of the gate oxide before forming the second portion. This sequential formation allows the first portion to be established as a reference structure, upon which the second portion can be precisely aligned. The preliminary formation of the first portion creates a foundation that simplifies subsequent alignment steps, reducing the overall manufacturing precision requirements despite the reduced cell pitch.
Data Source
AI summary
Aspects of the present disclosure describe a high density trench-based power. The active devices may have a two-step gate oxide. A lower portion may have a thickness that is larger than the thickness of an upper portion of the gate oxide. A lightly doped sub-body layer may be formed below a body region between two or more adjacent active device structures of the plurality. The sub-body layer extends from a depth of the upper portion of the gate oxide to a depth of the lower portion of the gate oxide It is emphasized that this abstract is provided to comply with rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.