Back-Channel-Etched IGZO TFT Substrate with C-Axis Crystallized Active Layer
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Solution Overview
Problem
The manufacturing process of back-channel-etched (BCE) IGZO TFT substrates is complicated and requires multiple photolithography steps, and the use of copper etching solutions can damage the IGZO active layer, affecting its stability and electrical properties.
Innovation Solution
A method involving the formation of a first IGZO thin film using polycrystalline IGZO particles as seed crystals, followed by sputtering to create a C-axis crystallized IGZO thin film, which forms an active layer resistant to copper etching, reducing the need for special etching solutions and simplifying the process while maintaining stable electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If copper etching solution is used to etch source and drain in BCE-structured IGZO TFT, then the number of photolithography processes is reduced by 1, but the characteristics of the superficial layer of IGZO thin film are affected and oxygen balance changes, deteriorating TFT substrate stability
Solution Approach 1:
A protective layer is introduced as an intermediary between the copper etching solution and the IGZO active layer. This protective layer prevents direct contact between the etching solution and the IGZO, thereby protecting the oxygen balance and characteristics of the IGZO thin film while still allowing the copper etching process to proceed with reduced photolithography steps.
Solution Approach 2:
The patent applies preliminary protective measures by forming a protective layer before the copper etching process. This preliminary action prevents the harmful effects of the etching solution on the IGZO active layer, maintaining the oxygen balance and electrical characteristics while enabling the simplified BCE structure manufacturing process.
2Ease of manufacture
If conventional a-Si TFT is used, then the manufacturing process is simpler, but the mobility is limited to about 1 cm2/(Vs) which cannot meet high-resolution display requirements
Solution Approach 1:
The patent changes the material parameter from conventional a-Si to IGZO (indium gallium zinc oxide), which fundamentally alters the mobility characteristic from ~1 cm2/(Vs) to >10 cm2/(Vs). This parameter change enables high-resolution display requirements to be met while maintaining compatibility with existing manufacturing processes through the protective layer approach.
Solution Approach 2:
The patent uses composite material structure combining IGZO active layer with protective layer materials that are compatible with copper etching processes. This composite approach enables the high mobility benefits of IGZO while protecting against the harmful effects of copper etching solutions, achieving both high performance and manufacturability.
3Reliability
If IGZO TFT with ESL structure is used, then the IGZO is protected from being affected in source/drain etching process, but the manufacturing process becomes complicated requiring six photolithography processes
Solution Approach 1:
The patent extracts and removes the ESL (etch stop layer) from the traditional IGZO TFT structure, eliminating the need for six photolithography processes. Instead, a simplified protective layer is introduced that provides the necessary protection during copper etching while requiring fewer manufacturing steps, thus reducing device complexity while maintaining reliability.
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 method ensures the stability and electrical performance of the BCE TFT substrate by preventing damage from copper etching and reducing the complexity of the manufacturing process, achieving stable electrical properties without the need for special copper etching solutions.
Implementation Method 1
depositing a second IGZO thin film on the first IGZO thin film and the gate insulating layer by a sputtering process
Implementation Method 2
a portion of the second IGZO thin film corresponding to the portion above the first IGZO thin film being presented as a C-axis crystallized IGZO thin film
Data Source
AI summary
The invention provides a BCE TFT substrate and manufacturing method thereof. The method comprises forming a first IGZO thin film with polycrystalline IGZO particles in a predetermined area of active layer before sputtering IGZO, the polycrystalline IGZO particles in the first IGZO thin film used as seed crystal during sputtering to grow a C-axis crystallized IGZO in good crystalline state to form a second IGZO thin film. The first and second IGZO thin films form an active layer. Because the surface of the active layer is presented as C-axis crystallized IGZO, the active layer is not damaged by the copper etchant during etching source and drain so as to ensure stable performance of active layer and to avoid the development of special copper etching solution. As such, the BCE TFT substrate has stable electrical performance. The BCE TFT substrate manufactured by the above manufacturing method has stable electrical performance.