Thin Film Transistor Substrate Etch Stopper for 4-Photomask Process
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Solution Overview
Problem
The high manufacturing cost and complexity of thin film transistor substrates in flat panel displays due to the 5-photomask process, which leads to over-etching and wavy noise issues affecting display quality.
Innovation Solution
A 4-photomask process with an etch stopper on the active layer to prevent over-etching and improve electrical characteristics, while using a single photomask for forming source, drain, and pixel electrodes to reduce manufacturing costs and wavy noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a 4-photomask process is used to reduce manufacturing cost, then manufacturing cost is reduced, but the active layer protrudes from the data line causing wavy noise and display quality degradation
Solution Approach 1:
An etch stopper layer is formed on the active layer before the etching process. This preliminary structure prevents over-etching during the formation of source and drain electrodes, ensuring that the active layer does not protrude from the data line while still using the cost-effective 4-photomask process.
Solution Approach 2:
The etch stopper layer acts as an intermediary between the active layer and the etching process. It serves as a protective barrier that stops the etching action before it can remove the active layer material, thereby preventing the formation of wavy noise while maintaining the simplicity of the 4-photomask process.
2Reliability
If the active layer is made thick to prevent over-etching, then over-etching is prevented, but the electrical characteristics (mobility and sub-threshold) of the thin film transistor are negatively affected
Solution Approach 1:
The etch stopper layer serves as a protective intermediary that prevents over-etching without requiring the active layer to be made thicker. This allows the active layer to maintain its optimal thickness for electrical performance while the etch stopper provides the necessary protection during processing.
Solution Approach 2:
The etch stopper is formed in advance on the active layer before etching begins. This preliminary protective structure ensures that the active layer is protected from over-etching while maintaining its original thickness, thereby preserving the electrical characteristics of the thin film transistor.
3Reliability
If a separate photomask process is added to form an etch stopper, then over-etching is prevented, but the manufacturing cost increases due to a complicated five photomask process
Solution Approach 1:
The formation of the etch stopper layer is merged with the existing 4-photomask process sequence. The etch stopper is formed as part of the second photomask process along with the gate insulating layer, ohmic contact pattern, active layer, source electrode, drain electrode, and data line, avoiding the need for a separate fifth photomask process.
Solution Approach 2:
The etch stopper layer serves multiple functions: it prevents over-etching during source and drain electrode formation, provides a planar surface for subsequent processing, and can be integrated with other layer formations. This multi-functionality allows it to be incorporated into the existing 4-photomask process without requiring an additional photomask step.
Data Source
AI summary
A method of fabricating a liquid crystal display device includes forming a gate electrode; forming a gate insulator on the gate electrode, an active layer on the gate insulator, and an etch stopper on the active layer; depositing an ohmic contact layer, a first metal layer and a second metal layer on the substrate; etching the ohmic contact layer, and the first and second metal layers to form ohmic contact patterns, and first and second metal patterns including source, drain and pixel electrodes using a single photomask.