TFT Substrate Manufacturing with Segmented Resist Etching
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Solution Overview
Problem
The manufacturing of active matrix type TFT array substrates for liquid crystal display devices faces challenges in productivity and yield due to the incomplete removal of metal films during the formation of back channel regions, leading to short-circuits and operational failures, particularly when the number of TFT formation places per source line is limited.
Innovation Solution
A method involving the formation of a TFT substrate with a semiconductor film stack, including an intrinsic and impurity semiconductor film, and a conductive film for a source line, where a resist with thin and thick film portions is used to etch the conductive film and semiconductor films, and a dummy back channel region is created outside the TFT area to reduce the area ratio and prevent residual metal film issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the number of TFT formation places per source line is limited, then the source line length is reduced, but the metal film cannot be completely removed by etching during back channel region formation, leading to short-circuits and operational failures
Solution Approach 1:
The patent segments the etching process into multiple stages by using a resist with different thickness portions. The thin-film portion etches the metal film while the thick-film portion protects it, enabling selective removal of metal in back channel regions without affecting source line integrity. This segmentation allows complete metal removal even when TFT formation places are limited.
Solution Approach 2:
The patent applies local quality by creating a resist with spatially varying thickness. The thin-film portion is positioned over back channel regions where metal removal is needed, while the thick-film portion is positioned over source line regions where metal must be preserved. This local differentiation enables precise control of etching depth and location.
2Ease of manufacture
If middle-tone exposure is applied to reduce the number of masks, then the manufacturing cost is reduced, but residual metal film formation occurs in back channel regions causing short-circuits
Solution Approach 1:
The patent changes the physical parameter of the resist from uniform thickness to non-uniform thickness with distinct thin-film and thick-film portions. This parameter change enables the single resist to perform multiple functions: the thin-film portion allows complete metal removal in back channel regions, while the thick-film portion prevents over-etching in source line regions, achieving both cost reduction and precision improvement.
3Adaptability or versatility
If the source line is used for both display signal transmission and additional circuit formation, then the functionality is enhanced, but the number of TFT formation places per source line is restricted, leading to incomplete metal film removal
Solution Approach 1:
The patent segments the resist into thin-film and thick-film portions that correspond to different functional regions. The thin-film portion enables complete metal removal for additional circuits in back channel regions, while the thick-film portion maintains source line integrity for signal transmission, allowing both functions to coexist without manufacturing defects.
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 improves the yield and productivity of TFT substrates by reducing residual metal film formation and preventing short-circuits, allowing for more flexible source line lengths and enabling the incorporation of additional circuitry, thus enhancing the functionality and reliability of the display devices.
Implementation Method 1
etching the conductive film for a source line, the impurity semiconductor film, and the intrinsic semiconductor film by using the resist as a mask
Data Source
AI summary
In a method of manufacturing a TFT substrate in accordance with an exemplary aspect of the present invention, an intrinsic semiconductor film, an impurity semiconductor film, and a conductive film for source lines are formed in succession, and a resist having a thin-film portion and a thick-film portions is formed on the conductive film for source lines. Then, etching is performed by using the resist as a mask, and after that, a part of the conductive film for source lines is exposed by removing the thin-film portion of the resist. Next, the exposed conductive film for source lines is etched by using the thick-film portions of the resist a mask, so that the impurity semiconductor film is exposed. Then, by etching the exposed impurity semiconductor film, a back channel region of a TFT 108 is formed. Further, a dummy back channel region 18a, which is irrelevant to the operation of the finished product, is also formed in a portion other than the TFT 108 region.