Tapered Gate Oxide Structure for Semiconductor Devices
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Solution Overview
Problem
Semiconductor devices face dielectric breakdown and mechanical stress issues due to high electric fields and thermal expansion, leading to performance degradation and potential failure, particularly at the corners of the gate oxide where electric fields are highest.
Innovation Solution
A semiconductor device design featuring a gate oxide that forms a non-perpendicular angle with the semiconductor body, with a tapered geometry including a widened and narrow portion, which disperses electric fields and distributes mechanical stresses across a greater surface area, reducing the likelihood of dielectric breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate oxide is thickened to decrease capacitance and increase threshold voltage, then the on-state resistance increases and device performance deteriorates
Solution Approach 1:
The gate oxide thickness is varied locally across different regions of the gate structure. The oxide is thicker at the highly stressed corner regions to prevent dielectric breakdown, while maintaining optimal thickness in other regions to preserve device performance. This localized variation allows each region to have the specific thickness needed for its functional requirements.
Solution Approach 2:
The gate oxide structure transitions from a symmetric, uniform thickness design to an asymmetric design where the oxide thickness varies across different angular positions. The oxide is deliberately made thicker at corner regions where electric field stress is highest, creating an asymmetric thickness distribution that targets reinforcement where it is most needed without unnecessarily increasing thickness elsewhere.
2Productivity
If the gate oxide thickness is reduced to improve device performance, then the susceptibility to dielectric breakdown increases
Solution Approach 1:
Different regions of the gate oxide have different thicknesses optimized for their specific functional requirements. Regions requiring high performance maintain thinner oxide for lower resistance, while regions requiring high reliability have thicker oxide to prevent breakdown. This local optimization allows simultaneous achievement of both performance and reliability goals.
Solution Approach 2:
The gate oxide thickness parameter is changed across different spatial locations rather than maintaining a single uniform value. By varying this critical parameter locally, the structure achieves optimal performance in some regions while ensuring adequate reliability in others, resolving the contradiction between performance optimization and reliability assurance.
3Ease of operation
If the gate oxide is subjected to high electric fields and thermal expansion, then mechanical stress increases and device failure occurs
Solution Approach 1:
The gate oxide structure is designed with increased thickness at corner regions before the device operates under high stress conditions. This preemptive reinforcement provides a buffer against the high electric fields and thermal expansion that occur during operation, preventing mechanical failure before it can occur. The extra material acts as a cushion against the anticipated stresses.
Solution Approach 2:
The gate structure employs a composite approach where the gate oxide is integrated with the gate electrode and semiconductor substrate in a multi-layer configuration. This composite structure distributes mechanical stresses across multiple materials with different mechanical properties, enhancing overall structural durability while maintaining the electrical functionality required for high switching voltage operation.
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 enhances the mechanical durability and control of gate oxide thickness, reducing the susceptibility to dielectric breakdown and electrical/thermal failure by distributing electric fields and stresses, thereby improving the reliability and performance of semiconductor devices.
Implementation Method 1
disperses electric fields and distributes mechanical stresses across a greater surface area, reducing the likelihood of dielectric breakdown
Implementation Method 2
the high temperatures associated with device fabrication and operation may result in undesirable thermal expansion of the material adjacent the gate oxide. This thermal expansion may sufficiently deform the gate oxide
Data Source
AI summary
A semiconductor device includes a semiconductor body having a first surface vertically spaced apart from a second surface. A first trench vertically extends into the semiconductor body from the first surface and includes first and second sidewalls extending across the semiconductor body in a lateral direction that is parallel to the first surface. A field electrode is arranged in first trench and electrically insulated from the semiconductor body by a field dielectric. A first gate electrode is arranged in the first trench. The first gate electrode is electrically insulated from the field electrode by the field dielectric and is electrically insulated from the semiconductor body by a first gate oxide. The first gate electrode includes widened and tapered portions that are continuously connected and adjacent to one another in the lateral direction. The first gate oxide forms a non-perpendicular angle with the first sidewall in the lateral direction.