Polycrystalline Silicon TFT Films With Low-Defect Solid-Phase Crystallization
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Solution Overview
Problem
Existing methods for fabricating polycrystalline silicon films for TFTs, such as excimer laser annealing, are costly and result in defects like 'scan mura' in AMOLED displays, while solid phase crystallization improves image uniformity but suffers from inadequate TFT performance due to high crystalline defect density.
Innovation Solution
The methods involve forming a crystalline silicon thin film on a foreign substrate with reduced crystalline defect density by initiating nucleation and crystal growth from a surface/interface away from the substrate during solid phase crystallization, using techniques such as forming multiple intrinsic and doped silicon layers and annealing to propagate crystallization through these layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If excimer laser annealing is used to fabricate polycrystalline silicon films, then crystallization speed is improved, but manufacturing cost increases and scan mura defects occur
Solution Approach 1:
The patent replaces the mechanical laser scanning system with a thermal field-based solid phase crystallization method. Instead of using excimer laser annealing that requires complex laser equipment and scanning mechanisms, the invention employs controlled thermal processing that achieves crystallization through uniform heating, thereby eliminating the need for expensive laser systems and reducing manufacturing costs while avoiding scan mura defects
Solution Approach 2:
The patent changes the crystallization parameters by controlling temperature profiles and processing conditions to achieve complete crystallization without laser scanning. By optimizing the thermal parameters (temperature, time, atmosphere), the method achieves adequate TFT performance through solid phase crystallization, eliminating the trade-off between speed and cost associated with laser annealing
2Reliability
If excimer laser annealing is used to fabricate polycrystalline silicon films, then crystallization is achieved, but scan mura defects appear in AMOLED displays
Solution Approach 1:
The patent replaces the laser scanning mechanism with a uniform thermal field approach. By using solid phase crystallization with controlled heating, the method eliminates the scanning process that causes differential crystallization at scan boundaries, thereby preventing scan mura defects while maintaining crystallization quality
Solution Approach 2:
The patent creates a uniform thermal field during crystallization to ensure equivalent crystallization conditions across the entire substrate. This equipotential approach ensures that all regions of the polycrystalline silicon film crystallize under the same conditions, eliminating the potential differences that cause scan mura defects in laser-annealed films
3Object-generated harmful factors
If solid phase crystallization is used to improve image uniformity, then scan mura defects are eliminated, but TFT performance becomes inadequate due to high defect density
Solution Approach 1:
The patent optimizes the thermal processing parameters including temperature profiles, holding times, and atmospheric conditions to achieve complete crystallization with minimized defect formation. By carefully controlling these parameters, the method achieves adequate TFT performance through solid phase crystallization, eliminating the trade-off between image uniformity and device performance
Solution Approach 2:
The patent employs preliminary thermal treatment steps before the main crystallization process to prepare the amorphous silicon film for optimal crystallization. This preliminary action includes controlled heating and holding phases that reduce internal stresses and prepare the material structure, resulting in lower defect density and improved TFT performance after crystallization
4Stability of the object's composition
If solid phase crystallization is used to crystallize amorphous silicon films, then image uniformity is improved, but intra-grain defects reduce effective defect-free area
Solution Approach 1:
The patent optimizes crystallization parameters including temperature, time, and atmospheric conditions to control grain growth and minimize intra-grain defect formation. By adjusting these parameters, the method achieves a balance between maintaining image uniformity and maximizing the defect-free area within grains, thereby improving manufacturing precision
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 thermal budget and defect density in the crystalline silicon films, leading to improved performance of TFT devices with higher resolution displays and increased production yield.
Implementation Method 1
annealing to cause crystallization of the doped silicon film, the second intrinsic silicon film, and the first intrinsic silicon film
Implementation Method 2
nucleation and crystal growth of precursor film starts from a surface/interface located away from the substrate surface during the solid phase crystallization process
Data Source
AI summary
A method of producing a polycrystalline silicon TFT includes forming nickel patterns on a substrate, forming a phosphorus doped silicon layer over the substrate and nickel patterns, and forming an intrinsic silicon layer on the phosphorus doped silicon layer. Alternatively, the intrinsic silicon layer can be formed on the substrate, the phosphorus doped silicon layer on the intrinsic silicon layer, and the nickel patterns on the phosphorus doped silicon layer. The structure is annealed to crystallize the phosphorus doped silicon and intrinsic silicon layers. A method of forming a crystalline silicon layer of a TFT device includes forming a first silicon film, forming a phosphorus doped silicon film on the first silicon film, forming a nickel film on the phosphorus doped silicon film, and annealing the structure to crystallize the phosphorus doped silicon and first silicon films. The first silicon and phosphorous doped silicon films are amorphous at formation.