SiN Gate Stack Inclined Angle Control for FET Reliability
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Solution Overview
Problem
Existing processes for forming a gate electrode in field effect transistors (FETs) are complex and result in large dispersion in the inclined angle of the opening sides, which affects the moderation of field strength and drain current collapse.
Innovation Solution
A process involving the deposition of silicon nitride (SiN) films using low pressure chemical vapor deposition (LPCVD) and plasma-assisted chemical vapor deposition (p-CVD) techniques, followed by dry-etching to create openings with inclined sides, allowing for a gate electrode that gradually widens from the semiconductor layer, thereby moderating field strength and reducing drain current collapse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wet-etching is used to form inclined sides in the passivation film, then the gate electrode can moderate field strength, but the inclined angle shows large dispersion and the process becomes complex
Solution Approach 1:
The patent replaces wet-etching (chemical/mechanical process) with a deposition process that forms an overhanging structure. By depositing material that naturally creates an overhang during formation, the inclined angle is determined by deposition physics rather than etching chemistry, eliminating the large angle dispersion associated with wet-etching while maintaining the field strength moderation function.
Solution Approach 2:
The patent performs preliminary deposition of the gate electrode material with controlled overhang formation before final patterning. This preliminary action creates the inclined side structure in advance, allowing subsequent processing steps to work with a pre-formed geometric configuration that ensures consistent angle precision without requiring complex etching control.
2Reliability
If multiple insulating films are deposited to form inclined sides, then field strength can be moderated, but the process complexity increases
Solution Approach 1:
The patent combines the formation of inclined sides and the gate electrode structure into a single deposition process. Instead of separately forming insulating films with inclined sides and then adding the gate electrode, the gate electrode material itself is deposited with controlled overhang to simultaneously create both the inclined geometry and the functional electrode, reducing process steps and complexity.
Solution Approach 2:
The gate electrode structure serves multiple functions: it provides the electrical gating function, moderates field strength through its inclined geometry, and defines the opening structure. This multi-functionality eliminates the need for separate insulating film structures that would otherwise be required to achieve field moderation, simplifying the overall device architecture and process flow.
3Reliability
If the gate electrode cross section is gradually increasing, then drain current collapse is reduced, but the manufacturing precision requirement increases
Solution Approach 1:
The patent replaces complex multi-step deposition and etching processes with a single deposition process that naturally forms the gradually increasing cross-section. The overhanging structure is created by controlling deposition conditions rather than through mechanical or chemical removal of material, reducing the number of precision-critical process steps while achieving the desired geometric progression.
Solution Approach 2:
The patent controls the deposition parameters (such as deposition rate, temperature, or gas flow) to naturally produce the gradually increasing cross-section profile. By adjusting deposition conditions, the geometric progression of the cross-section is achieved through material accumulation rather than precise removal, converting a high-precision manufacturing challenge into a controllable deposition parameter optimization.
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 process achieves precise control over the inclined angle of the opening sides, reducing dispersion and enhancing the moderation of field strength, thus improving the breakdown voltage and preventing drain current collapse.
Implementation Method 1
depositing a first silicon nitride (SiN) film on a semiconductor layer by a low pressure chemical vapor deposition (LPCVD) technique
Implementation Method 2
depositing a second SiN film on the first SiN film by plasma 30o assisted chemical vapor deposition (p-CVD) technique
Implementation Method 3
dry-etching the second SiN film and the first SiN film continuously in a portion of the opening of the photoresist mask
Data Source
AI summary
A process of forming a field effect transistor is disclosed. The process includes steps of depositing a first silicon nitride (SiN) film on a semiconductor layer by a low pressure chemical vapor deposition (LPCVD) technique; depositing a second SiN film on the first SiN film by plasma assisted chemical vapor deposition (p-CVD) technique; preparing a photoresist mask on the second SiN film, the photoresist mask having an opening in a position corresponding to the gate electrode; dry-etching the second SiN film and the first SiN film continuously in a portion of the opening in the photoresist mask to form an opening in the first SiN film and an opening in the second SiN film, the openings in the first and second SiN films exposing the semiconductor layer; and filling at least the opening in the first SiN film by the gate electrode. A feature of the process is that the opening in the first SiN film has an inclined side against the semiconductor layer and gradually widens from the semiconductor layer.