Dense Oxide STI Structure for Uniform Nanosheet Height Control
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Solution Overview
Problem
The challenge in forming nanosheet transistor devices with multiple device regions separated by shallow trench isolation (STI) areas is maintaining uniform nanosheet height, as existing methods struggle with height control during and after processing due to differences in trench width and quality of STI oxide, leading to variations and potential gate flop-over issues.
Innovation Solution
The method involves forming a semiconductor device with a multistep process that includes depositing a first oxide material in isolation trenches to create a more dense trench isolation layer in one region and a less dense layer in another, using a protective liner to prevent oxidation, and performing selective dry etching to achieve uniform nanosheet heights across different regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer STI oxide is deposited in isolation trenches, then the process is simple, but nanosheet height uniformity deteriorates due to different trench widths in dense array and isolated regions
Solution Approach 1:
The STI oxide is divided into multiple layers with different densities - a first oxide layer deposited in the dense array region trenches and a second oxide layer deposited in the isolated region trenches. This segmentation allows each layer to be optimized for its specific region, resolving the height uniformity issue while maintaining process simplicity
Solution Approach 2:
Different oxide densities are applied to different regions: a less dense first oxide for dense array regions and a more dense second oxide for isolated regions. This local quality approach compensates for the different trench width effects, ensuring uniform nanosheet height across all regions
2Manufacturing precision
If the STI oxide is recessed to control nanosheet height, then height control improves, but gate flop-over risk increases due to undercutting of the oxide
Solution Approach 1:
The oxide density parameter is changed across different regions - using a less dense first oxide in dense array regions and a more dense second oxide in isolated regions. This parameter change allows the oxide to maintain structural integrity during recess operations, preventing undercutting while achieving height control
Solution Approach 2:
The multi-layer oxide structure with varying densities provides beforehand cushioning against the harmful undercutting effect. The denser oxide layers are more resistant to etching, so they protect the gate structure from flop-over while still allowing precise height control through selective recess
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 ensures improved active height control during nanosheet processing and reduces the risk of gate flop-over by maintaining uniform nanosheet heights and minimizing undercutting of the oxide, enhancing the stability of the nanosheet structures.
Implementation Method 1
simultaneously depositing a first oxide material within the plurality of first isolation trenches and the second isolation trench to form a first trench isolation layer. The deposition rate is higher in the second isolation trench than in the plurality of first isolation trenches due to a deposition-loading effect
Implementation Method 2
simultaneously performing a dry etching process in the dense array region and the isolated region that is selective to the second trench isolation layer over the protective liner. The etch rate of the second trench isolation layer is faster in the isolated region than in the dense array region due to a dry etch-loading effect
Data Source
AI summary
A semiconductor device includes a plurality of first nanosheet fin structures located in a dense array region of a substrate. The semiconductor device further includes a plurality of first isolation trenches between adjacent first nanosheet fin structures of the plurality of first nanosheet fin structures. The plurality of first isolation trenches include: a first trench isolation layer, a protective liner formed on top of the first trench isolation layer, and a second trench isolation layer located above the protective liner. The protective liner separates the first trench isolation layer from the second trench isolation layer and the first trench isolation layer is more dense than the second trench isolation layer.