Shallow Trench Isolation Etching for Reduced Cone Formation
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Solution Overview
Problem
The fabrication of shallow trench isolation structures in semiconductor devices often results in trench cones, which can affect the high voltage performance of integrated devices, especially when adapted for high voltage applications, as they alter the average thickness of the STI structure.
Innovation Solution
The technique involves separate etch steps for forming shallow trenches with different etching parameters, including silicon to etch retardant selectivity ratios, feature dimensions, and bias power, to minimize cone formations, allowing for precise control of sidewall slopes and reducing trench cone occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single etch step is used for all shallow trenches, then the manufacturing process is simple, but trench cones are formed that affect high voltage performance
Solution Approach 1:
The patent divides the etching process into multiple separate etch steps, each optimized for specific trench types (e.g., first etch step for small feature dimensions, second etch step for large feature dimensions). This segmentation allows each etch step to use tailored parameters such as etching selectivity ratios and bias power levels, thereby preventing trench cone formation while maintaining process manageability.
2Manufacturing precision
If separate etch steps are used for different trench regions, then trench cone formation is reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies different etching parameters to different spatial regions of the substrate. Specifically, first etching parameters (including selectivity ratios and bias power) are used for first regions with small feature dimensions, while second etching parameters are used for second regions with large feature dimensions. This local quality approach optimizes each region's trench formation independently, reducing cone formation while keeping the overall process structured and controllable.
3Measurement precision
If high etching selectivity ratio is used, then small feature dimension trenches are precise, but cone formation increases in large feature dimension trenches
Solution Approach 1:
The patent changes etching parameters between different etch steps and regions. For small feature dimension trenches, high etching selectivity ratios are used to achieve precision. For large feature dimension trenches, different parameters (including adjusted selectivity ratios and bias power levels) are applied to prevent cone formation. This dynamic parameter adjustment resolves the contradiction between precision and uniformity across different feature sizes.
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 effectively reduces trench cone formation, enhancing the precision of small feature dimension trenches and improving high voltage performance by maintaining vertical sidewalls and minimizing defects, thus optimizing the electrical isolation and high voltage capabilities of the STI structures.
Implementation Method 1
a bias power used for controlling a plasma anisotropic etch
Data Source
AI summary
Techniques of fabricating shallow trench isolation structures that reduce or minimize the number of trench cones during the formation of shallow trenches. The disclosed techniques introduce separate etch steps for etching shallow trenches with small feature dimensions and for etching shallow trenches with large feature dimensions. As an example, the disclosed techniques involve etching a first shallow trench in a first region of a substrate with a first etching parameter, and etching a second shallow trench in a second region of a substrate with a second etching parameter different from the first etching parameter. Among other things, the etching parameter may include an etching selectivity ratio of silicon to an etch retardant that contributes to cone formations. Because of the separate etch steps, the disclosed techniques allow the sidewall slopes between the first and second shallow trenches to be within a few degrees of deviation.