Trench Isolation Cavities for Semiconductor Device Leakage Reduction
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Solution Overview
Problem
Existing semiconductor manufacturing techniques fail to provide effective isolation of power electronic devices from logic circuits on CMOS chips while minimizing silicon area and process complexity, and are often too expensive or difficult to implement, especially when using silicon-on-insulator structures.
Innovation Solution
A method involving etching laterally spaced longitudinal trenches and forming cavities at their bases with insulators, allowing for flexible filling materials and reduced sensitivity to alpha-particles, which includes depositing nitride and oxide layers to create protective spacers and extend cavities laterally, enabling efficient isolation with minimal additional masks and process steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon-on-insulator structures are used for isolation, then device isolation and shielding effectiveness are improved, but manufacturing cost and process complexity increase significantly
Solution Approach 1:
The isolation structure is segmented into discrete trenches rather than requiring a complete silicon-on-insulator substrate. Trenches are etched through the drift region to create isolated regions, dividing the isolation function into localized segments that are cheaper to manufacture while maintaining electrical isolation effectiveness.
Solution Approach 2:
The patent replaces expensive silicon-on-insulator wafers with a cheaper alternative using standard silicon substrates with trench isolation. The isolation is achieved through deposited oxide and nitride layers filled in trenches, which are less costly materials and processes compared to SOI wafer fabrication.
2Reliability
If deep trenches are used for isolation, then isolation effectiveness is improved, but manufacturing precision requirements and process difficulty increase
Solution Approach 1:
Deposited oxide and nitride layers serve as intermediary materials that automatically conform to the trench walls and base. These layers fill the trenches and provide isolation without requiring precise control of trench depth, as the deposit thickness can be controlled more easily than etch depth. The intermediary layers bridge the gap between the trench structure and the isolation function.
Solution Approach 2:
The patent changes the isolation mechanism from relying on precise trench depth parameters to relying on deposited layer thickness parameters. Physical vapor deposition or chemical vapor deposition allows for better control of film thickness compared to etch depth, thereby reducing manufacturing precision requirements while maintaining isolation effectiveness.
3Area of stationary object
If isolation structures occupy minimal silicon area, then device density is improved, but isolation effectiveness may be compromised
Solution Approach 1:
The isolation structure concentrates the isolation function locally at the trench regions rather than requiring a broad area. The trenches are positioned strategically between devices, and the deposited oxide and nitride layers provide high-quality isolation locally at these critical points, achieving effective isolation with minimal silicon area occupation.
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
This method achieves effective isolation and reduced sensitivity to alpha-particles, allowing for high-voltage operation with increased breakdown voltage and reduced surface field effects, while being cost-effective and simpler to manufacture compared to traditional silicon-on-insulator methods.
Implementation Method 1
depositing nitride on the sidewalls of the first and second trenches and the base of the second trenches
Implementation Method 2
forming oxide on the base of the second trenches
Implementation Method 3
an isotropic dry etch is used to etch the silicon under the trenches
Data Source
AI summary
A semiconductor device is formed by forming a second trench 120 at the base of a first trench 18, depositing insulator 124 at the base of the second trench 120, and then etching cavities 26 laterally from the sidewalls of the second trench, but not the base which is protected by insulator 124. The invention may in particular be used to form semiconductor devices with cavities under the active components, or by filling the cavities to form silicon on insulator or silicon on conductor devices.