Semiconductor Isolation Trench Corner Rounding via Pad Oxide Etching
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Solution Overview
Problem
Conventional trench isolation methods in semiconductor devices, such as STI, suffer from electrical field concentration at sharp corners, requiring additional processing steps and experiencing variability due to liner thickness variations, which are critical at small dimensions.
Innovation Solution
A method involving a three-step etching process to form a trench with rounded corners, where a pad oxide layer is etched laterally to create recesses, followed by high-temperature anneal to form a diffusion oxide, and subsequent removal to achieve precise corner rounding, ensuring electrical separation without extending into the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If trench corners are left sharp in STI process, then manufacturing is simpler, but electrical field concentration occurs that negatively changes electrical parameters
Solution Approach 1:
The patent performs preliminary corner rounding by etching recesses in the pad oxide layer before trench formation. This preliminary action creates a rounded profile that prevents electrical field concentration at the trench corners, resolving the contradiction by preparing the structure in advance to avoid later electrical issues while maintaining manufacturing simplicity.
Solution Approach 2:
The patent intentionally creates rounded corners instead of sharp angles by forming recesses in the pad oxide layer with curved profiles. This curvature eliminates the electrical field concentration that occurs at sharp corners, thereby improving electrical parameter stability while keeping the manufacturing process straightforward.
2Reliability
If trench corners are rounded using known techniques, then electrical field variation is reduced, but additional processing steps such as trench liner formation are required
Solution Approach 1:
The patent combines the corner rounding function with the existing pad oxide layer that is already part of the STI process. By etching recesses in the pad oxide layer, the corner rounding is integrated into the standard process flow without requiring separate liner formation or additional processing steps, thus maintaining reliability while avoiding increased device complexity.
Solution Approach 2:
The pad oxide layer serves multiple functions: it acts as an etch stop layer, a sacrificial layer for corner rounding, and the final isolation material. This multi-functionality eliminates the need for separate trench liners or additional processing steps, resolving the contradiction by making the existing structure perform multiple roles including corner rounding.
3Shape
If trench corners are rounded using liner thickness variations, then corner rounding is achieved, but variability in rounding magnitude occurs that is critical at small dimensions
Solution Approach 1:
The patent controls the corner rounding by adjusting etch parameters (etch time, power, gas flow) rather than relying on liner thickness. This allows precise control of the rounding magnitude with high consistency, eliminating the variability inherent in liner-based methods and achieving the required manufacturing precision for small dimensions.
Solution Approach 2:
The patent replaces the mechanical/physical approach of using liner thickness to control rounding with a controlled chemical etching process. This substitution provides better precision and consistency because etch parameters can be tightly controlled and reproduced, eliminating the thickness variations that plague liner-based methods at small dimensions.
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 electrical field variations, minimizes additional processing steps, and maintains critical dimensions, enhancing the reliability and precision of semiconductor trench isolation structures.
Implementation Method 1
a pad oxide layer is etched laterally to create recesses
Implementation Method 2
followed by high-temperature anneal to form a diffusion oxide
Implementation Method 3
high-temperature anneal to form a diffusion oxide
Implementation Method 4
subsequent removal to achieve precise corner rounding
Data Source
AI summary
A method for forming a semiconductor isolation trench includes forming a pad oxide layer over a substrate and forming a barrier layer over the substrate. A masking layer is formed over the barrier layer and is patterned to form at least one opening in the masking layer. At least a part of the barrier layer and at least a part of the pad oxide layer are etched through the at least one opening resulting in a trench pad oxide layer. Etching of the trench pad oxide layer stops substantially at a top surface of the substrate within the isolation trench. An oxide layer is grown by diffusion on at least the top surface of the substrate corresponding to the at least one isolation trench. The method further includes etching the oxide layer and at least a portion of the substrate to form at least one isolation trench opening.