Shallow Trench Isolation Etching to Reduce Trench Cone Formation
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Solution Overview
Problem
The formation of trench cones during the fabrication of shallow trench isolation structures affects the high voltage performance of integrated devices, particularly in high voltage applications, due to variations in trench dimensions and polymer by-products.
Innovation Solution
A two-pass etch process is employed, utilizing distinct etching parameters for shallow trenches with small feature dimensions for precision and trenches with large feature dimensions to minimize cone formation, involving separate etch steps with varying silicon selectivity ratios, bias powers, and etch times to achieve vertical sidewalls and reduce polymer accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single etch process is used for all shallow trenches, then the process is simple and fast, but trench cones form in large feature dimension trenches affecting high voltage performance
Solution Approach 1:
The patent divides the etching process into two separate etch steps: a first etch process for small feature dimension trenches and a second etch process for large feature dimension trenches. This segmentation allows each etch process to be optimized independently, preventing trench cone formation in large trenches while maintaining efficiency for small trenches.
Solution Approach 2:
The patent applies different etching parameters (selectivity ratios, bias powers, etch times) to different regions of the substrate based on trench feature dimensions. Small trenches receive one set of parameters while large trenches receive another, ensuring each region gets the optimal treatment for its specific requirements.
2Manufacturing precision
If high selectivity ratio is used to etch small trenches precisely, then small trench precision is improved, but large trenches develop trench cones due to polymer accumulation
Solution Approach 1:
The patent separates the etching of small and large trenches into different process steps, allowing the first etch to use high selectivity ratios for precision without causing polymer accumulation issues in large trenches, which are handled in the second etch with different parameters.
Solution Approach 2:
The patent changes etching parameters between the two etch steps. The first etch uses higher selectivity ratios for precision, while the second etch uses different selectivity ratios and bias powers to minimize polymer accumulation and prevent trench cone formation in large trenches.
3Manufacturing precision
If separate etch steps are used for different trench sizes, then trench cone formation is reduced, but the process complexity increases
Solution Approach 1:
While the patent does segment the etching process into two steps, this segmentation is implemented in a practical manufacturing context where the complexity is managed through automated process control and integration into the existing fabrication flow, balancing precision improvement with acceptable process complexity.
4Manufacturing precision
If long etch time is used to ensure complete trench etching, then etching completeness is improved, but trench cones form in large trenches
Solution Approach 1:
The patent divides the etching into two time-separated steps, allowing the first etch to complete small trenches quickly and the second etch to complete large trenches with optimized parameters, preventing the polymer accumulation that occurs with prolonged single-step etching.
Solution Approach 2:
The patent changes etching parameters including time, selectivity ratio, and bias power between the two etch steps. The second etch uses parameters optimized for large trenches that prevent cone formation while ensuring complete etching, avoiding the need for excessively long single-step etching times.
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 solution effectively reduces trench cone formation, ensuring precise and high-performance shallow trench isolation structures, enhancing the electrical isolation and high voltage capabilities of integrated circuits.
Implementation Method 1
a bias power used for controlling a plasma anisotropic etch
Implementation Method 2
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.