Exposure Mask Boundary Patterns for Display Stitch Defects
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Solution Overview
Problem
The divisional exposure method in manufacturing display devices often results in stitch defects such as brightness differences and mura at the boundaries between sub-areas, due to the limitations of existing exposure masks that cannot accurately align with the larger active area of the substrate.
Innovation Solution
The use of an exposure mask with an align exposure portion aligned with pixels on the substrate and a boundary exposure portion having patterns with varying sizes and shift intervals, which gradually increase or decrease as distance from the align exposure portion, to minimize stitch defects and reduce the number of exposure shots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a divisional exposure method is used to manufacture display devices with large active areas, then the exposure can be completed in multiple shots, but stitch defects such as brightness differences and mura occur at the boundaries between sub-areas
Solution Approach 1:
The exposure mask includes a boundary exposure portion with patterns that are exposed before the main pixel patterns. This preliminary exposure creates a gradient in the photoresist layer at the boundary regions, which compensates for the discontinuities that would otherwise occur at the stitch lines between multiple exposure shots. The boundary patterns are designed with varying sizes and positions to pre-condition the photoresist for seamless merging of adjacent exposure areas.
Solution Approach 2:
The exposure mask applies different exposure strategies to different regions: the align exposure portion uses standard alignment with pixels, while the boundary exposure portion uses varied pattern sizes and positions that change gradually across the boundary region. This local differentiation allows the boundary areas to be exposed with compensating gradients while maintaining standard exposure for the majority of the pixel area, thus resolving the stitch defect problem without affecting overall manufacturing efficiency.
2Productivity
If the number of exposure shots is reduced, then manufacturing efficiency improves, but coverage of the entire active area becomes insufficient
Solution Approach 1:
The exposure mask is segmented into distinct functional portions: an align exposure portion for standard pixel alignment, a boundary exposure portion for creating gradient transitions at stitch lines, and potentially an over-exposure portion for extended coverage. This segmentation allows each portion to be optimized for its specific function while working together to achieve complete coverage of the active area in a reduced number of shots.
Solution Approach 2:
The boundary exposure portion extends the exposure coverage beyond the standard pixel boundaries in the lateral dimension. By including boundary patterns that protrude into adjacent exposure areas and using varying pattern sizes, the mask achieves coverage compensation without requiring additional exposure shots, thus maintaining productivity while ensuring complete area coverage.
3Device complexity
If standard alignment is used for all exposure portions, then the exposure process is simple, but stitch defects occur at the boundaries between sub-areas
Solution Approach 1:
The exposure mask applies different exposure strategies to different regions: the align exposure portion uses standard alignment with pixels, while the boundary exposure portion uses varied pattern sizes and positions that change gradually across the boundary region. This local differentiation allows the boundary areas to be exposed with compensating gradients while maintaining standard exposure for the majority of the pixel area, thus resolving the stitch defect problem without affecting overall manufacturing efficiency.
Solution Approach 2:
The boundary exposure portion utilizes parameter changes in the pattern geometry, specifically varying the size and position of patterns across the boundary region. These parameter variations create the necessary exposure gradients to prevent stitch defects, while the align exposure portion maintains standard parameters for efficient pixel-level alignment. This selective parameter modification resolves the contradiction between simplicity and precision.
Data Source
AI summary
An exposure mask includes an aligning portion and a boundary portion. The aligning portion may be aligned with pixel areas of a substrate and includes a first exposure member and a second exposure member. The boundary portion includes a first exposure element, a second exposure element, a third exposure element, and a fourth exposure element. The first exposure member, the first exposure element, and the second exposure element are positioned in a first row. The first exposure element is positioned between the first exposure member and the second exposure element and is larger than the second exposure element. The second exposure member, the third exposure element, and the fourth exposure element are positioned in a second row. The third exposure element is positioned between the second exposure member and the fourth exposure element and is smaller than the fourth exposure element. Each exposure member/element includes a light transmitter/blocker.