Vertical FET Body Structure for Stable Breakdown Voltage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Vertical field-effect transistors face challenges in stabilizing breakdown voltage due to variations in manufacturing workmanship, particularly at the gate trench tip, and require a design that ensures a breakdown voltage higher than the maximum specified voltage to prevent impact ionization.
Innovation Solution
A semiconductor device with a dual configuration featuring a vertical field-effect transistor structure, including a semiconductor substrate, low-concentration impurity layers, and a body region with alternating shallow and deep regions, where the depth of the second body portion is shallower than the first body portion, allowing for reduced manufacturing variations and controlled terminus structure, thereby stabilizing the breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate trench depth is increased to prevent impact ionization, then breakdown voltage increases, but manufacturing precision deteriorates due to workmanship variations
Solution Approach 1:
The body region is designed with non-uniform depth characteristics, featuring a first body portion with constant depth and a second body portion with varying depth. This local differentiation allows the gate trench to extend to different depths in different regions, preventing impact ionization at the trench tip while maintaining manufacturing feasibility through controlled depth variations.
Solution Approach 2:
The solution transitions from controlling breakdown voltage solely through gate trench depth (one-dimensional approach) to a two-dimensional approach by introducing body region depth variations. The body region's depth profile in the vertical dimension, combined with its lateral extent, creates a structured terminus that controls electric field distribution and prevents impact ionization without requiring excessive gate trench depth.
2Reliability
If the body region depth is increased to stabilize breakdown voltage, then reliability improves, but device complexity increases
Solution Approach 1:
The body region is segmented into two distinct portions: a first body portion with constant depth containing the active region, and a second body portion with varying depth forming the terminus structure. This segmentation allows each portion to be optimized independently for its specific function while maintaining overall structural organization and manufacturability.
Solution Approach 2:
The body region depth parameter is strategically varied across different spatial locations. The first body portion maintains a constant depth parameter, while the second body portion employs a depth gradient that decreases from the gate trench tip outward. This parameter variation stabilizes breakdown voltage by controlling electric field distribution without requiring uniformly deep structures throughout the entire device.
3Reliability
If the gate trench penetrates deeper into the low-concentration impurity layer, then breakdown voltage increases, but manufacturing cost increases due to tighter tolerances
Solution Approach 1:
Rather than requiring the gate trench to uniformly penetrate to great depths across the entire device structure, the solution applies depth control locally. The gate trench extends deeper only where necessary to prevent impact ionization at the terminus, while other regions maintain shallower, easier-to-manufacture depths. This local differentiation reduces overall manufacturing stringency and cost.
Solution Approach 2:
The body region is pre-configured with its depth profile and impurity concentration distribution before gate trench formation. This preliminary structuring of the body region creates a foundation that guides subsequent gate trench fabrication, allowing the trench to be formed to controlled depths without requiring post-processing adjustments or extremely tight tolerances, thereby reducing manufacturing cost.
Data Source
AI summary
A semiconductor device includes a vertical field-effect transistor including: a low-concentration impurity layer; a body region; a gate trench; a gate insulating film; and a gate conductor. The body region includes: a first body portion containing an active region and has a constant depth; and a second body portion adjacent to the first body portion and includes a zone that has a limited length in a second direction orthogonal to the first direction along the top surface of the low-concentration impurity layer, and has a constant depth at a position shallower than the constant depth of the first body portion. The second body portion includes a portion in which a region having relatively high concentration of an impurity and a region having relatively low concentration of an impurity are alternately and periodically present in the first direction in a cross-sectional view of a plane orthogonal to the second direction.