Flask Type Recess Gate Fabrication for Leakage Reduction
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Solution Overview
Problem
As semiconductor devices become highly integrated, the refresh characteristic is difficult to secure during the forming process of a planar gate due to junction leakage caused by increased electric fields and reduced channel length, and the recess gate process introduces horn formation leading to leakage currents.
Innovation Solution
A method for fabricating a semiconductor device with a flask type recess gate involves forming a hard mask pattern, etching the substrate to create first and second recess patterns, oxidizing the sidewalls to form a silicon oxide layer, and removing the passivation and oxide layers to achieve a rounded recess profile, which increases channel length and reduces horn generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a planar gate is formed on a planarized active region, then the manufacturing process is simple, but the channel length is reduced and junction leakage increases
Solution Approach 1:
The gate formation process is segmented into multiple steps: first forming a recess pattern in the active region, then forming the gate structure within the recess. This segmentation allows the gate to be positioned in a recessed area, extending the channel length and reducing the electric field at the junction, thereby improving refresh characteristics while maintaining manufacturing feasibility through systematic process division.
Solution Approach 2:
The invention transitions from a planar gate structure to a recess gate structure by etching the active region to create a vertical dimension. The gate is formed within this recess, effectively utilizing the vertical space to increase the channel length without increasing the lateral footprint, thus improving device performance in highly integrated circuits.
2Reliability
If the channel length is increased to improve refresh characteristic, then the leakage current is reduced, but the device area increases
Solution Approach 1:
The channel length is extended by utilizing the vertical dimension through recess formation. The gate is positioned in a recessed area, allowing the channel to extend deeper into the substrate vertically rather than expanding laterally. This maintains a compact device footprint while achieving the necessary channel length for improved refresh characteristics.
Solution Approach 2:
The gate structure is nested within the recessed active region. The recess acts as a container that holds the gate structure, allowing the channel length to be extended within the confined space of the recess without increasing the overall device area. This nesting approach efficiently packs the extended channel within a compact footprint.
3Reliability
If a recess gate process is used to lengthen channel, then the refresh characteristic improves, but horn formation causes leakage current
Solution Approach 1:
The recess pattern is designed with a rounded bottom profile rather than a sharp corner. This curvature eliminates the horn formation that occurs at sharp recess corners, preventing the concentration of electric charges and the subsequent leakage current. The rounded profile maintains the channel lengthening benefit while eliminating the harmful horn effect.
Solution Approach 2:
The oxidation process, which could potentially create defects, is utilized beneficially to form a rounded profile at the recess bottom. By oxidizing the exposed bottom surface and then removing the oxidized layer, a curved transition is created that eliminates sharp corners and prevents horn formation, converting a potential harmful process into a beneficial shaping mechanism.
4Length of moving object
If the active region is etched into a deep recess pattern, then the channel length increases, but the manufacturing precision becomes more difficult to control
Solution Approach 1:
The etching process is segmented into multiple stages with different depths. A first recess pattern is formed to a predetermined depth, then a second recess pattern is formed to an additional depth. This segmented approach allows better control over the overall recess profile compared to forming a single deep recess, improving manufacturing precision while achieving the desired channel length.
Solution Approach 2:
The recess pattern is designed with a rounded bottom profile instead of sharp corners. This curved profile is more tolerant to manufacturing variations and easier to control during the etching process compared to sharp angular profiles. The rounded shape naturally forms during oxidation and removal processes, providing self-correction and improved precision control.
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 enhances the refresh characteristic and reduces leakage currents by increasing the channel length and rounding the recess profiles, thereby improving the breakdown voltage and reducing stress points.
Implementation Method 1
forming a passivation layer on sidewalls of the first recess pattern and the hard mask pattern
Implementation Method 2
oxidizing sidewalls of the second recess pattern to form a silicon oxide layer
Data Source
AI summary
A method for fabricating a semiconductor device having a flask type recess gate includes forming a hard mask pattern on a substrate, etching the substrate to a predetermined depth using the hard mask pattern to form a first recess pattern, forming a passivation layer on sidewalls of the first recess pattern and the hard mask pattern, etching a bottom surface of the first recess pattern exposed by the passivation layer to form a second recess pattern, oxidizing sidewalls of the second recess pattern to form a silicon oxide layer, removing the passivation layer and the silicon oxide layer in sequential order, and forming a gate pattern over an intended recess pattern including the first recess pattern and the second recess pattern.