Trench Semiconductor Device Sidewall Oxide Thickness Control
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Solution Overview
Problem
Existing methods for forming semiconductor devices with oxide-lined trenches face challenges such as increased stress at the sidewall to bottom oxide interface, difficulty in filling trenches with conductive material, and limited oxide thickness at the bottom due to thick oxide growth at the trench opening.
Innovation Solution
A method involving the formation of trenches with a first oxide thickness on sidewalls and a second, thicker oxide on the bottom, using a protective layer to maintain sidewall oxide thickness and facilitate conductive material filling, while allowing for increased bottom oxide thickness without stressing the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick oxide is formed at the top of the trench simultaneously with the bottom oxide, then the sidewalls are protected during processing, but the trench opening is narrowed and conductive material filling becomes difficult
Solution Approach 1:
The oxide formation process is segmented into two distinct steps: first forming a thin sidewall oxide layer to protect the trench walls, then selectively removing this oxide from the top region before forming the thick bottom oxide. This segmentation allows the sidewalls to be protected during processing while maintaining an open trench top for easy conductive material filling.
Solution Approach 2:
A thin sidewall oxide layer is formed preliminarily before the thick bottom oxide formation. This preliminary oxide layer protects the sidewalls during subsequent processing steps, and is then selectively removed from the top region using isotropic etching, allowing the trench opening to remain wide for conductive material filling.
2Reliability
If a thick oxide is formed at the top of the trench, then sidewall protection is improved, but the oxide thickness at the bottom of the trench is limited
Solution Approach 1:
The oxide formation is segmented into a thin sidewall oxide step and a separate thick bottom oxide step. The thin sidewall oxide provides protection during processing, while the subsequent thick bottom oxide formation is not constrained by the presence of top oxide, allowing greater bottom oxide thickness to be achieved.
Solution Approach 2:
The thin sidewall oxide is formed as a preliminary protective layer before the thick bottom oxide formation. This preliminary layer is then selectively removed from the top region, enabling the bottom oxide to grow to greater thickness without the constraint of simultaneous top oxide formation.
3Length of stationary object
If oxide is formed on the bottom portion first and then on the sidewalls, then the bottom oxide thickness is sufficient, but stress increases at the sidewall to bottom oxide interface
Solution Approach 1:
A thin sidewall oxide layer is formed preliminarily before the thick bottom oxide formation. This preliminary sidewall oxide acts as a stress buffer, reducing stress concentration at the sidewall to bottom oxide interface during the subsequent thick bottom oxide growth process.
Solution Approach 2:
The thin sidewall oxide layer serves as a cushioning layer formed beforehand to prevent stress concentration at the interface. This preliminary protective layer absorbs and distributes the stress that would otherwise concentrate at the sharp interface, preventing oxide thinning and device failure.
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 approach reduces stress, ensures adequate trench opening width for conductive material filling, and maintains consistent sidewall oxide thickness, enhancing the reliability and performance of semiconductor devices like power MOSFETs.
Implementation Method 1
Silicon dioxide or oxide was formed on the bottom portion of the trench and subsequently an oxide was formed along the sidewalls of the trench
Data Source
AI summary
In one embodiment, a trench semiconductor device is formed to have an oxide of a first thickness along the sidewalls of the trench, and to have a greater thickness along at least a portion of a bottom of the trench.