Polycrystalline Channel Recess Structure for Grain Boundary Control
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Solution Overview
Problem
Laser annealing of amorphous silicon films to form polycrystalline silicon films results in random grain boundary positions, leading to low carrier mobility and significant device-to-device variations in thin film transistors.
Innovation Solution
A method involving the formation of recesses in a dielectric layer and the use of spacers to control lateral recrystallization of amorphous semiconductor material, allowing for the creation of polycrystalline semiconductor regions with larger grain sizes and controlled grain boundary positions, enhancing carrier mobility and device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser annealing is used to form polycrystalline silicon films from amorphous silicon, then the films can be produced efficiently, but the grain boundary positions become random leading to low carrier mobility
Solution Approach 1:
Mandrel structures are formed beforehand on the substrate before depositing the amorphous silicon layer. These mandrels serve as predetermined nucleation sites that guide crystal grain formation during subsequent laser annealing, ensuring grain boundaries form at controlled positions rather than randomly
Solution Approach 2:
The mandrel structures act as intermediary elements between the substrate and the amorphous silicon layer. They mediate the crystallization process by providing template structures that dictate where crystal grains will grow and where grain boundaries will form, translating the random laser annealing process into a controlled grain structure formation
2Ease of manufacture
If conventional recrystallization is used to form polycrystalline silicon, then the process is simple, but the crystal grain size is small and grain boundaries are numerous
Solution Approach 1:
The substrate surface is segmented into multiple regions by forming an array of discrete mandrel structures. Each mandrel serves as a separate nucleation center, creating a segmented crystallization pattern that results in larger individual crystal grains compared to conventional uniform recrystallization
Solution Approach 2:
Different regions of the substrate are given different local structures through the mandrel array pattern. This creates localized nucleation sites with specific geometries that control grain growth in those local regions, resulting in overall larger grain sizes and fewer grain boundaries across the film
3Ease of manufacture
If random grain boundaries are present in polycrystalline silicon channels, then device fabrication is straightforward, but device-to-device variations are significant
Solution Approach 1:
The mandrel structures are formed in advance with precise spatial arrangement and uniform dimensions. This preliminary structuring ensures that when crystallization occurs, all devices on the substrate experience the same grain boundary configuration, eliminating random variations between devices
Solution Approach 2:
The spatial parameters of the mandrel structures (spacing, size, arrangement) are precisely controlled to change the grain boundary configuration from random to deterministic. This parameter control ensures uniform electrical characteristics across all devices fabricated on the substrate
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 improves the performance, stability, and reliability of thin film transistors by enabling the formation of polycrystalline semiconductor regions with controlled grain sizes and boundary positions, leading to increased carrier mobility and uniformity across the substrate.
Implementation Method 1
The amorphous semiconductor layer is recrystallized to form a polycrystalline semiconductor layer
Implementation Method 2
recrystallization of amorphous silicon determines quality of the polycrystalline silicon film
Implementation Method 3
A method involving the formation of recesses in a dielectric layer and the use of spacers to control lateral recrystallization of amorphous semiconductor material
Data Source
AI summary
A method for forming a polycrystalline semiconductor layer includes forming a plurality of spacers over a dielectric layer, etching the dielectric layer using the plurality of spacers as an etch mask to form a recess in the dielectric layer, depositing an amorphous semiconductor layer over the plurality of spacers and the dielectric layer to fill the recess, and recrystallizing the amorphous semiconductor layer to form a polycrystalline semiconductor layer.