Thick Gate Oxide Growth for Rounded STI Corners
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Solution Overview
Problem
The existing methods for producing high-voltage thick gate oxides at Shallow Trench Isolation (STI) corners result in sharp corners, affecting the reliability and performance of semiconductor devices, and are either costly or provide only partial improvements.
Innovation Solution
A method involving thermal oxidation growth with specific steps and materials, including pad and mask silicon oxides and nitrides, is used to thicken, passivate, and smooth the gate oxide at STI corners, ensuring improved reliability and performance while maintaining a low-cost and simple process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional STI process is used for high-voltage device fabrication, then the process is simple and cost-effective, but sharp corners appear at STI corners resulting in poor reliability
Solution Approach 1:
The patent divides the STI structure into two types: first STI (deep trench) and second STI (shallow trench with rounded corners). By segmenting the isolation structures, the patent achieves different functions - the first STI provides deep isolation while the second STI provides corner rounding to eliminate sharp corners. This segmentation resolves the contradiction by allowing a relatively simple process to produce reliable thick gate oxide without sharp corners.
Solution Approach 2:
The patent performs preliminary actions by forming the first STI deep trenches and filling them with dielectric material before forming the second STI. The pad oxide and pad nitride layers are also deposited in advance to facilitate subsequent processing. These preliminary actions prepare the structure for reliable thick gate oxide formation while maintaining process simplicity.
2Reliability
If a double STI process is adopted to thicken gate oxide at STI corners, then reliability is improved, but a separate photomask is required resulting in high cost
Solution Approach 1:
The patent merges the functions of forming isolation structures and rounding STI corners into a single integrated process flow. The first STI and second STI are formed using the same photomask and processing steps, eliminating the need for a separate photomask that would be required in a double STI process. This merging maintains reliability while reducing manufacturing cost.
Solution Approach 2:
The patent creates a universal process that serves multiple functions: forming deep isolation trenches, creating rounded corner structures, and preparing surfaces for thick gate oxide growth. The pad oxide and pad nitride layers serve multiple purposes including protection, etch stop, and surface preparation. This multi-functionality reduces the need for additional process steps and photomasks.
3Manufacturing precision
If an oxide layer deposition process is used to improve STI corner gate oxide, then some improvement is achieved, but reliability is poorer compared to thermal oxide growth
Solution Approach 1:
The patent changes the physical and chemical parameters of the oxidation process by using thermal oxidation at controlled temperatures (800-900°C for first oxidation, 900-1100°C for second oxidation) with specific oxygen flow rates and processing times. These parameter changes enable precise control of oxide thickness and quality, achieving both manufacturing precision and high reliability through thermal oxidation rather than deposition.
Solution Approach 2:
The patent uses thermal oxidation with oxygen as the oxidant to grow high-quality silicon dioxide layers. The thermal oxidation process provides accelerated and controlled oxidation that produces dense, reliable gate oxide with excellent electrical properties, superior to deposition methods. The controlled oxygen environment and temperature profiles ensure high reliability.
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 method effectively thickens and smooths the gate oxide at STI corners, enhancing the reliability and performance of high-voltage devices while reducing costs and complexity.
Implementation Method 1
performing first thermal oxidation growth to passivate STI corners in the high-voltage gate oxide region
Implementation Method 2
performing second thermal oxidation growth to produce a high-voltage thick gate oxide
Implementation Method 3
STI silicon oxide filling and chemical mechanical polishing (Oxide Filling and CMP) is performed
Data Source
AI summary
A method for making a high-voltage thick gate oxide, which includes depositing a pad silicon oxide on a silicon substrate and depositing a pad silicon nitride on the pad silicon oxide; performing shallow trench isolation photolithography, etching, silicon oxide filling and chemical mechanical polishing; sequentially depositing a mask silicon nitride and a mask silicon oxide on a silicon wafer; removing the mask silicon oxide and the mask silicon nitride in a high-voltage thick gate oxide region, and remaining the pad silicon nitride between two shallow trench isolations in the high-voltage thick gate oxide region; performing first thermal oxidation growth; removing the pad silicon nitride between the two shallow trench isolations in the high-voltage thick gate oxide region; performing second thermal oxidation growth to produce a high-voltage thick gate oxide.