Phase-Shift Photomask for LCD Substrate Flatness
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Solution Overview
Problem
The existing manufacturing processes for active matrix amorphous silicon TFT array substrates require multiple photomasks, leading to prolonged lead times, decreased yields, and potential damage to the substrate's flatness, which can result in deteriorated display performance in liquid crystal display devices.
Innovation Solution
A method for manufacturing a liquid crystal display device using a phase-shift photomask to form through holes and trenches on a passivation layer, allowing for the formation of pixel electrodes without additional lithography processes, reducing the number of masks required and maintaining substrate flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple photomasks are used in the manufacturing process, then the pixel electrodes can be formed with good precision, but the number of lithography processes increases, leading to prolonged lead time and decreased productivity
Solution Approach 1:
The patent combines the formation of through holes and trenches into a single lithography process using one photomask. The photomask simultaneously defines both the through hole positions (for pixel electrode formation) and the trench positions (for data line isolation), eliminating the need for separate lithography steps and improving productivity while maintaining precision
Solution Approach 2:
The single photomask serves multiple functions: it patterns the through holes for pixel electrodes, defines the trenches for data line separation, and establishes the relative positioning between these features. This multi-functional approach reduces the total number of masks needed while achieving the required manufacturing precision
2Productivity
If half-tone photoprocess technology is used to reduce the number of photomasks, then the number of lithography processes decreases, but the substrate flatness is damaged, leading to deteriorated display performance
Solution Approach 1:
The patent uses binary (full-tone) photomask patterns instead of half-tone patterns, ensuring that exposed regions receive uniform exposure energy. This approach maintains consistent photoresist development and prevents the substrate flatness deterioration associated with half-tone processing, while still achieving the reduced mask count through clever pattern design
Solution Approach 2:
The patent resolves the flatness issue by changing from half-tone exposure (which varies exposure energy in the same plane) to binary exposure with selective pattern design. The through holes and trenches are formed in different regions that are selectively exposed, avoiding the need for energy modulation and preserving substrate flatness
3Manufacturing precision
If additional lithography processes are used to form through holes and trenches, then the pixel electrodes can be formed with good isolation, but the manufacturing cost increases and lead time is prolonged
Solution Approach 1:
The patent merges the formation of through holes and trenches into a single lithography and etching sequence. The photomask pattern simultaneously defines both features, and a single etching process creates both the through holes (to the substrate) and the trenches (not reaching the substrate), eliminating multiple sequential steps and reducing lead time while maintaining proper isolation
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 reduces the number of photolithography processes, shortens manufacturing lead time, enhances production rate, and maintains display performance by eliminating the need for half-tone processes, thereby decreasing manufacturing costs and improving the flatness of the array substrate.
Implementation Method 1
a phase-shift photomask which is set to make the through hole formation region white, a pixel electrode formation region black, and periphery of the pixel electrode middle tone, wherein irradiation light from a light source shifts its phase when passing through the middle tone region
Data Source
AI summary
The invention provides a novel technology where a TFT array substrate for a display device is formed with three photomasks. The invention is achieved by using the novel technology in combination with a well-known four-masks process. For the novel technology, during the lithography process where a photosensitive acrylic resin film is used to make contacts, taper patterns required for general through holes are formed simultaneously with a fine pattern formed in a light shielding area that is tapered more approximately to vertical, using a photomask with phase-shift effect. Thus the pixel electrode pattern can be separated without using lithography process in subsequent processes.