Array Substrate Gate Structure for Stable LTPS TFT Heat Treatment
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Solution Overview
Problem
Existing TFT manufacturing processes face challenges in achieving stable TFT characteristics and reducing wiring line resistance, particularly when heat treatment temperatures are below 450°C, leading to defects and instability in polysilicon films.
Innovation Solution
The proposed solution involves an array substrate design with a gate electrode and gate wiring line structure that includes an aluminum film covered by a protective metal film with a higher melting point. This structure, combined with a polysilicon semiconductor film and specific impurity concentration regions, allows for heat treatment at temperatures equal to or higher than 450°C without defects, thereby stabilizing TFT characteristics and reducing wiring line resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment temperature is increased to 450°C or higher to stabilize TFT characteristics and recover polysilicon crystallinity, then TFT characteristics become stable, but aluminum layer defects (hillocks) occur due to moisture diffusion and thermal reaction
Solution Approach 1:
A protective film comprising a silicon oxide film and a silicon nitride film is introduced as an intermediary layer between the gate insulating film and the aluminum layer. The silicon oxide film prevents moisture diffusion to the aluminum layer, while the silicon nitride film provides thermal reaction barrier. This mediator structure enables heat treatment at 450°C or higher without causing aluminum layer defects, thus stabilizing TFT characteristics while preventing harmful thermal effects.
Solution Approach 2:
The protective film is formed beforehand before the aluminum layer is deposited, creating a pre-established barrier that cushions the aluminum layer against moisture and thermal reactions during subsequent heat treatment processes. This prior cushioning approach ensures that when high-temperature heat treatment is performed to recover polysilicon crystallinity and stabilize TFT characteristics, the aluminum layer is already protected from developing defects.
2Loss of energy
If aluminum layer is used in gate electrode to reduce wiring line resistance, then wiring line resistance decreases, but defects occur during heat treatment due to moisture diffusion and thermal reaction
Solution Approach 1:
The protective film acts as an intermediary barrier that allows the aluminum layer to maintain its low-resistance function while protecting it from moisture diffusion and thermal reactions during heat treatment. The silicon oxide film specifically prevents moisture from reaching the aluminum layer, and the silicon nitride film provides additional thermal protection, enabling the aluminum layer to function effectively without developing defects.
Solution Approach 2:
The gate electrode structure employs a composite material approach by combining aluminum (for low resistance) with the protective film system (silicon oxide + silicon nitride layers). This composite structure leverages the electrical conductivity of aluminum while the protective film components provide barrier functions, creating a multi-functional gate electrode that achieves both low wiring line resistance and defect-free reliability after heat treatment.
3Reliability
If heat treatment temperature is kept below 450°C to prevent aluminum layer defects, then aluminum layer remains intact, but polysilicon film crystallinity recovery becomes insufficient and TFT characteristics become unstable
Solution Approach 1:
The protective film serves as a mediator that decouples the heat treatment process from the aluminum layer, allowing the temperature to be raised to 450°C or higher without causing aluminum defects. This enables sufficient thermal energy to be applied to the polysilicon film for complete crystallinity recovery and stable TFT characteristics, while the protective film mediates against harmful effects on the aluminum layer.
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 effectively stabilizes TFT characteristics and reduces wiring line resistance, enabling the production of high-stability TFTs suitable for large-screen in-vehicle liquid crystal panels with touch panel functions.
Implementation Method 1
a protective metal film made of a metal material having a melting point higher than a melting point of aluminum, and covering an entire surface of the aluminum film
Implementation Method 2
in a case where a polysilicon film (low temperature polycrystalline silicon (LTPS)) is used as a semiconductor film of the TFT, recovery of crystallinity of the polysilicon film becomes insufficient at a heat treatment temperature of less than 450° C.
Implementation Method 3
performing, after forming the gate electrode and the gate wiring line, heat treatment at a temperature equal to or higher than 450° C.
Data Source
AI summary
An array substrate includes: a semiconductor film disposed on an upper-layer side of an insulating substrate; a gate insulating film disposed in a layer above the semiconductor film; a gate electrode disposed in a layer above the gate insulating film; an interlayer insulating film disposed in a layer above the gate electrode; a thin film transistor including a source electrode and a drain electrode disposed on the upper-layer side of the gate electrode via the interlayer insulating film; and a gate wiring line continuously formed with the gate electrode of the thin film transistor, wherein the gate electrode and the gate wiring line include an aluminum film, and a protective metal film made of a metal material having a melting point higher than a melting point of aluminum, and covering an entire surface of the aluminum film.