BCE-type TFT with Dual-Layer SiOx Passivation for Acid Etch Resistance
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Solution Overview
Problem
The fabrication process of BCE-type thin film transistors (TFTs) without an etch stopper layer faces challenges due to damage from acid-based etching solutions, which deteriorates the oxide semiconductor layer and affects the TFT's characteristics, particularly when using IGZO films, leading to instability and high solubility issues.
Innovation Solution
Incorporating Sn in the oxide semiconductor layer and employing a two-layer passivation structure with a SiOx film as the first protective layer, followed by an oxidation treatment to control hydrogen concentration, and forming a second protective film, which can be an insulating compound film or laminate, to enhance stability and prevent damage during acid-based etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a BCE-type TFT structure without an etch stopper layer is used to improve productivity, then the number of processing steps is reduced, but the oxide semiconductor layer is damaged by acid-based etching solutions
Solution Approach 1:
The passivation film is divided into two distinct layers: a first protective film (SiOx) with low hydrogen concentration to protect against acid etching, and a second protective film providing additional protection. This segmentation allows each layer to perform its specific function optimally while maintaining the BCE-type structure without etch stopper layer.
Solution Approach 2:
The first protective film (SiOx) acts as an intermediary barrier between the acid-based etching solution and the oxide semiconductor layer. It specifically protects the semiconductor layer from acid damage while allowing the etching process to proceed for the source-drain electrode pattern formation.
2Reliability
If IGZO films are used to achieve high carrier mobility, then field-effect mobility is improved, but solubility to inorganic acid-based wet etchants increases causing extreme etching
Solution Approach 1:
The first protective film (SiOx) serves as a mediator that shields the IGZO oxide semiconductor layer from direct contact with inorganic acid-based wet etchants. This prevents the extreme etching and dissolution that would otherwise occur due to the high solubility of IGZO in these etchants.
Solution Approach 2:
The first protective film acts as a sacrificial protective layer that can be removed or degraded after serving its protective function, allowing the underlying oxide semiconductor layer to remain intact and functional with high carrier mobility.
3Device complexity
If a single-layer passivation film is used to simplify the structure, then device complexity is reduced, but protection against acid etching and hydrogen damage is insufficient
Solution Approach 1:
The passivation film is segmented into two functional layers: the first protective film (SiOx) specifically designed to protect against acid etching with controlled hydrogen concentration, and the second protective film providing additional protection and structural support. This segmentation enhances protection capability while maintaining reasonable structural complexity.
Solution Approach 2:
The dual-layer passivation structure combines different materials with complementary properties: SiOx with low hydrogen concentration for acid resistance, and a second protective film material for additional protection. This composite structure provides superior overall protection compared to a single-layer film.
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 results in a BCE-type TFT with improved field-effect mobility, low S value, and stress stability, even when using a Mo-based source-drain electrode, while reducing the number of processing steps and manufacturing costs by eliminating the need for an etch stopper layer.
Implementation Method 1
employing a two-layer passivation structure with a SiOx film as the first protective layer, followed by an oxidation treatment to control hydrogen concentration
Data Source
AI summary
This thin film transistor comprises, on a substrate, at least a gate electrode, a gate insulating film, an oxide semiconductor layer, a source-drain electrode, and two or more protective films. The oxide semiconductor layer comprises Sn, O and one or more elements selected from the group consisting of In, Ga and Zn. In addition, the two or more protective films are composed of at least a first protective film that is in contact with the oxide semiconductor film, and one or more second protective films other than the first protective film. The first protective film is a SiOx film having a hydrogen concentration of 3.5 atomic % or lower.