Laser Crystallization Mask Alignment Pattern Design
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Solution Overview
Problem
Existing laser crystallization methods for polycrystalline silicon in LCD devices face misalignment issues between the mask and laser beam, leading to deteriorated crystallinity, especially when using multi-pattern masks for both driving and pixel TFTs, which complicates the fabrication process and increases production costs.
Innovation Solution
A mask for laser crystallization is designed with alignment patterns including a first pattern group matching the crystallization pattern and a second pattern group of radial bars surrounding the first, allowing for precise alignment of the laser beam by measuring symmetry and position of the polycrystalline silicon pattern, ensuring accurate irradiation and minimizing misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a multi-pattern mask is used for crystallizing both driving and pixel TFTs, then the fabrication process can be simplified and production costs reduced, but misalignment between the mask and laser beam deteriorates crystallinity
Solution Approach 1:
The mask is divided into multiple pattern groups (first pattern group corresponding to pixel TFTs, second pattern group corresponding to driving TFTs, and alignment pattern group). Each pattern group can be selectively used for different crystallization processes, allowing simplified multi-pattern fabrication while maintaining precise alignment through the dedicated alignment patterns.
2Reliability
If the laser beam irradiates the silicon film multiple times during laser annealing, then crystallization can be achieved, but silicon oxide is created on the top surface due to oxidation in ambient air
Solution Approach 1:
The laser annealing process is performed in a vacuum environment (10^-7 to 10^-6 Torr) rather than ambient air. This inert atmosphere prevents oxidation of the silicon film surface during multiple laser irradiations, eliminating silicon oxide formation while maintaining effective crystallization.
3Measurement precision
If alignment patterns with radial bars are added to the mask, then laser beam alignment precision is improved, but the mask complexity increases
Solution Approach 1:
The alignment patterns (including radial bars) serve a dual function: they are both part of the mask structure for pattern formation and simultaneously serve as alignment reference marks. The radial bars automatically provide alignment information when observed, eliminating the need for separate alignment mechanisms and reducing overall system complexity.
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 enhances the crystallinity and uniformity of the polycrystalline silicon layer, improves process efficiency, and reduces production costs by allowing for precise alignment and efficient use of the laser beam, even with frequent mask movement and rotation.
Implementation Method 1
irradiating a laser beam onto the amorphous silicon layer through the crystallization pattern
Implementation Method 2
crystallizing the amorphous silicon layer to form a polycrystalline silicon layer
Implementation Method 3
aligning the laser beam with the mask by measuring a symmetry of the polycrystalline silicon pattern formed by the alignment pattern
Data Source
AI summary
A mask for laser crystallization includes a transmissive portion defining a crystallization pattern and an alignment pattern. The alignment pattern includes a first pattern group having a size corresponding to the crystallization pattern and a second pattern group having a plurality of radial bars surrounding the first pattern group. A shielding portion surrounds the transmissive portion.