Polycrystalline Silicon Layer Uniformity in Thin Film Transistors
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Solution Overview
Problem
Existing methods for forming polycrystalline silicon layers, such as solid-phase crystallization and excimer laser crystallization, face challenges like high temperature deformation, expensive equipment requirements, and non-uniform crystallization, while metal-induced crystallization methods leave residual metal catalysts affecting thin film transistor characteristics.
Innovation Solution
A method involving the formation of two amorphous silicon layers with different film qualities, crystallized using a metal catalyst to create polycrystalline silicon layers with varying grain sizes and silicide content, where the second layer has a smaller grain size and lower silicide content, thereby improving transistor uniformity without increasing metal catalyst amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solid-phase crystallization is used to form polycrystalline silicon layer, then crystallization is achieved, but substrate deformation occurs due to high temperature heat treatment
Solution Approach 1:
The patent changes the temperature parameter from high temperature (solid-phase crystallization) to low temperature (metal-induced crystallization at 400-600°C), thereby achieving crystallization without substrate deformation. The metal catalyst enables crystallization at lower temperatures, fundamentally altering the thermal parameter of the process.
Solution Approach 2:
The patent introduces a metal catalyst (intermediary substance) to facilitate crystallization. The metal catalyst acts as a mediator that enables silicon atoms to rearrange into crystalline structures at lower temperatures, avoiding the need for high-temperature heat treatment that causes substrate deformation.
2Productivity
If excimer laser crystallization is used to form polycrystalline silicon layer, then rapid crystallization is achieved, but expensive laser equipment is required and uniform crystallization is difficult
Solution Approach 1:
The patent replaces the complex laser system (optical/mechanical system) with a simpler thermal processing system using metal catalyst. Instead of using expensive excimer laser equipment to achieve rapid crystallization, the patent uses metal-induced crystallization which can be performed with conventional heating equipment, thereby substituting complex machinery with a simpler chemical-catalyzed process.
Solution Approach 2:
The patent uses a thin metal catalyst layer (nanometer-scale) that can be deposited cheaply and then removed or left as a minimal residue. This disposable-like approach replaces the need for expensive, reusable laser equipment, using a low-cost material intervention instead of high-cost equipment.
3Temperature
If metal-induced crystallization is used to form polycrystalline silicon layer, then low temperature crystallization is achieved, but large quantities of metal catalyst remain affecting thin film transistor characteristics
Solution Approach 1:
The patent applies local quality by creating different amorphous silicon layers with different properties (first layer with first quality, second layer with second quality). This allows different regions of the silicon layer to have different characteristics, enabling the channel region to have optimal properties for transistor performance while maintaining low-temperature crystallization benefits.
Solution Approach 2:
The patent segments the amorphous silicon layer into multiple layers (first amorphous silicon layer and second amorphous silicon layer) with different qualities. This segmentation allows selective optimization of different regions, ensuring that the channel-forming region has the desired properties while managing metal catalyst distribution.
4Ease of manufacture
If single amorphous silicon layer is crystallized to form polycrystalline silicon layer, then simple process is maintained, but uniformity of thin film transistor characteristics is insufficient
Solution Approach 1:
The patent implements local quality by creating amorphous silicon layers with different qualities in different regions. The first and second amorphous silicon layers have different film qualities, which after crystallization result in polycrystalline silicon layers with different grain sizes and properties, enabling uniform transistor characteristics across the device.
Solution Approach 2:
The patent uses a composite structure of multiple amorphous silicon layers with different qualities before crystallization. This composite approach, where layers have different compositions or structures (one with metal catalyst, one without or with different catalyst), results in a polycrystalline silicon layer with improved uniformity and controlled grain size distribution.
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 uniformity of thin film transistor characteristics and prevents leakage current increases by controlling defect density and grain size without excessive metal catalyst usage, effectively addressing the limitations of previous methods.
Implementation Method 1
crystallizing the first amorphous silicon layer and the second amorphous silicon layer using a metal catalyst to form a first polycrystalline silicon layer and a second polycrystalline silicon layer
Implementation Method 2
The first polycrystalline silicon layer and the second polycrystalline silicon layer may include silicide formed by bonding of the metal catalyst and silicon
Data Source
AI summary
A method of forming a polycrystalline silicon layer includes forming a first amorphous silicon layer and forming a second amorphous silicon layer such that the first amorphous silicon layer and the second amorphous silicon layer have different film qualities from each other, and crystallizing the first amorphous silicon layer and the second amorphous silicon layer using a metal catalyst to form a first polycrystalline silicon layer and a second polycrystalline silicon layer. A thin film transistor includes the polycrystalline silicon layer formed by the method and an organic light emitting device includes the thin film transistor.