Shallow Trench Isolation Height Uniformity via Dry Chemical Etching
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Solution Overview
Problem
Current methods for forming shallow trench isolation (STI) structures in semiconductor devices lead to erosion of STI regions during subsequent etching and cleaning processes, resulting in non-uniform heights and increased leakage currents, which can cause device yield reduction and additional polishing defects.
Innovation Solution
A dry chemical removal process is employed, involving the formation of a patterned mask with a polish stop layer, etching to define a trench, overfilling with silicon dioxide, and using a selective dry chemical oxide etching process to reduce the isolation structure height, followed by a selective wet etching process to remove the polish stop layer, thereby maintaining uniformity and reducing material loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wet etching or deglaze process is performed to remove insulating material remnants, then the pad nitride layer surface is cleaned, but the isolation structure thickness is reduced by 10-80 nm resulting in non-uniform heights
Solution Approach 1:
The patent replaces wet chemical etching with a mechanical polishing process (CMP - chemical mechanical polishing) to remove insulating material remnants. The polish stop layer provides a mechanical stopping point that ensures uniform removal depth across the wafer, eliminating the non-uniform thickness reduction (10-80 nm) caused by wet etching while still achieving complete removal of oxide remnants from the pad nitride layer surface.
2Productivity
If multiple etching and cleaning processes are performed on STI regions, then device fabrication is completed, but erosion of STI regions occurs leading to increased leakage currents
Solution Approach 1:
The patent applies preliminary protective action by forming a polish stop layer (nitride layer) before the isolation structure formation that is resistant to the subsequent polishing and etching processes. This stop layer protects the underlying pad nitride layer and prevents erosion of the isolation structure during fabrication, thereby preventing increased leakage currents while still allowing completion of all necessary fabrication steps.
Solution Approach 2:
The patent introduces a polish stop layer as an intermediary protective layer between the pad nitride layer and the isolation structure formation process. This intermediary layer withstands the mechanical and chemical stresses of polishing and etching processes, preventing direct damage to the pad nitride layer and isolation structure, thus maintaining their integrity and preventing leakage current increases.
3Strength
If densification anneals are performed to reduce isolation structure erosion, then etch resistance is improved, but stress differences in silicon dioxide materials increase causing polishing defects
Solution Approach 1:
The patent inverts the traditional approach by placing the protective nitride layer (polish stop layer) beneath the isolation structure rather than relying on annealing the isolation structure itself for protection. This inverted structure provides etch resistance from the bottom up, protecting the pad nitride layer during fabrication without inducing stress differences in the silicon dioxide that would cause polishing defects.
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 eliminates the need for densification anneals, reduces stress differences in silicon dioxide materials, allows for better process control, and prevents particle defects, resulting in more consistent and effective isolation structures with reduced leakage currents and improved device yields.
Implementation Method 1
performing a dry, selective chemical oxide etching process that removes silicon dioxide selectively relative to the material of the polish stop layer
Implementation Method 2
performing a selective wet etching process to remove the polish stop layer selectively relative to the isolation region
Data Source
AI summary
A method includes forming a patterned mask comprised of a polish stop layer positioned above a protection layer above a substrate, performing at least one etching process through the patterned mask layer on the substrate to define a trench in the substrate, and forming a layer of silicon dioxide above the patterned mask layer such that the layer of silicon dioxide overfills the trench. The method also includes removing portions of the layer of silicon dioxide positioned outside of the trench to define an isolation structure, performing a dry, selective chemical oxide etching process that removes silicon dioxide selectively relative to the material of the polish stop layer to reduce an overall height of the isolation structure, and performing a selective wet etching process to remove the polish stop layer selectively relative to the isolation region.