Oxide Semiconductor TFT Circuit Board for Controlled Through-Hole Etching
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Solution Overview
Problem
The challenge in forming through-holes in oxide semiconductor thin film transistors (TFTs) protected by aluminum oxide (AlO) barrier films is the difficulty in controlling the depth of these holes, which can lead to penetration of the drain or source electrodes, causing operational instability and contact resistance issues due to over-etching.
Innovation Solution
A TFT circuit structure is implemented with a cured film acting as an etching stopper under the AlO film, allowing precise control of etching areas during dry etching, and using a two-stage dry etching process with chlorine-based gas for the AlO film and fluorine-based gas for the cured and interlayer films to form through-holes without penetrating the oxide semiconductor or capping metal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If through-holes are formed in multiple steps to penetrate different films (AlO, SiO, SiN), then the through-holes can connect to the drain and source, but the depth of the through-holes becomes difficult to control and may penetrate the drain or source electrodes causing operational instability
Solution Approach 1:
The patent segments the protective film structure into multiple distinct layers (first interlayer insulating film, first film, first AlO film) with different etching characteristics. This segmentation allows the etching process to be controlled in stages, where each layer can be etched with appropriate selectivity, preventing over-etching into the oxide semiconductor while ensuring proper through-hole formation.
Solution Approach 2:
The patent applies preliminary action by forming the gate insulating film on the oxide semiconductor before forming the interlayer insulating film and barrier film. This preliminary structure provides a foundation that protects the oxide semiconductor during subsequent etching processes, ensuring that through-holes are formed with controlled depth without penetrating the sensitive oxide semiconductor layer.
2Ease of manufacture
If different etch conditions are used for AlO, SiO, SiN films, then each film can be etched effectively, but the through-holes need to be formed in multiple steps increasing process complexity
Solution Approach 1:
The patent applies local quality by assigning different materials with distinct etching properties to different locations in the film stack. The first interlayer insulating film, first film, and first AlO film each have tailored etching characteristics that allow them to be etched with different selectivities. This enables a multi-step etching process where each step targets a specific layer with optimized conditions, achieving effective etching of each film type while maintaining overall process manageability.
3Device complexity
If the through-hole formation process is simplified to a single step, then the process complexity is reduced, but the depth control becomes even more difficult and over-etching risk increases
Solution Approach 1:
The patent employs composite materials by creating a multi-layer film structure where each layer has specific etching properties. The combination of the first interlayer insulating film, first film, and first AlO film forms a composite barrier system that can be etched with controlled depth. The different materials provide inherent etching selectivity, allowing precise depth control through a multi-step process while preventing penetration into the oxide semiconductor.
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 stabilizes the operation of TFTs by precisely controlling the depth of through-holes, preventing damage to the oxide semiconductor and ensuring stable electrical connections, thereby maintaining the integrity of the TFTs.
Implementation Method 1
it is effective to use AlO as a blocking film for moisture and hydrogen since the properties of the oxide semiconductor will be affected by such molecules
Implementation Method 2
such through-holes need to be formed in multiple steps
Data Source
AI summary
The invention allows stable fabrication of a TFT circuit board used in a display device and having thereon an oxide semiconductor TFT. A TFT circuit board includes a TFT that includes an oxide semiconductor. The TFT has a gate insulating film formed on part of the oxide semiconductor and a gate electrode formed on the gate insulating film. A portion of the oxide semiconductor that is covered with the gate electrode 104 and a portion of the oxide semiconductor that is not covered with the gate electrode are both covered with a first interlayer insulating film. The first interlayer insulating film is covered with a first film 106, and the first film is covered with a first AlO film.