Oxide TFT Tapered Etching for Step Coverage
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Solution Overview
Problem
The existing manufacturing techniques for oxide thin-film transistors (TFTs) face challenges in achieving favorable step coverage characteristics and stable interfacial electrical characteristics due to the vertical side walls formed by wet etching, leading to potential breaks in wiring and degraded performance of the oxide semiconductor film with high mobility.
Innovation Solution
A thin-film transistor structure is developed with a semiconductor layer comprising an oxide semiconductor film and an oxide conductive film, where the oxide conductive film is etched at a higher speed than the oxide semiconductor film to form a substantially tapered shape, enhancing electrical characteristics and preventing wiring breaks, and the source and drain electrodes are connected through the oxide conductive film to improve interface electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet etching is used to form the oxide semiconductor film pattern, then the manufacturing process is simple and cost-effective, but vertical side walls are formed resulting in poor step coverage and potential wiring breaks
Solution Approach 1:
The patent segments the etching process into two distinct stages: first etching the oxide conductive film to form a tapered profile, then etching the oxide semiconductor film. This segmentation allows each etching step to be optimized independently, resolving the contradiction between process simplicity and step coverage quality.
Solution Approach 2:
The oxide conductive film is etched preliminarily before the oxide semiconductor film etching. This preliminary action creates the desired tapered shape that improves step coverage characteristics, preventing wiring breaks while maintaining manufacturing efficiency.
2Manufacturing precision
If the oxide semiconductor film is etched to form a pattern, then the active layer is defined, but vertical side walls result in degraded electrical characteristics at connection interfaces
Solution Approach 1:
The patent separates the etching of the oxide conductive film and oxide semiconductor film into distinct process steps. This allows the oxide conductive film to be etched to a tapered shape first, which then serves as a foundation for subsequent oxide semiconductor film etching, ensuring both accurate patterning and reliable electrical interfaces.
Solution Approach 2:
The oxide conductive film serves as an intermediary layer that is etched first to create a tapered structure. This intermediary action prepares the surface geometry that enables subsequent oxide semiconductor film etching to achieve both precision and electrical reliability.
3Manufacturing precision
If conventional amorphous silicon is used in the active layer, then dry etching can be used to form tapered shapes, but the manufacturing cost and process complexity increase
Solution Approach 1:
The patent changes the material parameter from conventional amorphous silicon to oxide semiconductor film, which enables the use of wet etching instead of dry etching. This material parameter change allows tapered shapes to be formed through simpler wet etching processes, reducing device complexity while maintaining manufacturing precision.
Solution Approach 2:
The patent substitutes the mechanical dry etching process with a chemical wet etching process. By using oxide semiconductor material that is soluble in alkaline developers, the complex mechanical dry etching system is replaced with a simpler chemical etching system that still achieves tapered shape formation.
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 enhances the electrical characteristics at the connection interface between the source and drain electrodes and the oxide semiconductor film, preventing wiring failures and improving the yield and performance of the thin-film transistor.
Implementation Method 1
the oxide conductive film is etched with a mixed liquid of phosphoric acid, acetic acid, and nitric acid at a higher speed than the oxide semiconductor film
Implementation Method 2
the oxide conductive film is etched with a mixed liquid of phosphoric acid, acetic acid, and nitric acid at a higher speed than the oxide semiconductor film
Data Source
AI summary
An oxide semiconductor film and an oxide conductive film are stacked to form a semiconductor layer. The oxide conductive film is made of a material by which the oxide conductive film is etched at a higher speed than the oxide semiconductor film for example with a PAN chemical containing phosphoric acid, nitric acid, and acetic acid. A source electrode and a drain electrode are electrically connected to the oxide semiconductor film through the oxide conductive film at least at an end portion of the source electrode and an end portion of the drain electrode facing each other. A channel region made of the oxide semiconductor film is formed between the source electrode and the drain electrode. The oxide semiconductor film has a substantially tapered shape in cross section at an end face thereof.