Multi-layer Amorphous Silicon for High Mobility Polysilicon
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Solution Overview
Problem
Current methods for forming polycrystalline silicon layers in TFT devices are limited by grain size and mobility, with existing techniques unable to achieve grain sizes above 300–500 nm and mobilities above 90 cm2/Vs while maintaining low production costs and equipment compatibility with PECVD and excimer laser annealing.
Innovation Solution
A multi-layer amorphous silicon structure is formed by depositing alternating layers using silicon-containing precursors and activation gases, with inert gases and hydrogen-based gases, followed by annealing to enhance crystallinity and mobility, specifically using a process that includes depositing silicon nitride and oxide buffer layers and alternating gas flows to promote strong silicon bonds and large crystalline grain growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional single-layer amorphous silicon structure is used with excimer laser annealing, then the process is simple and compatible with existing equipment, but the grain size is limited to below 300-500 nm and mobility cannot exceed 90 cm2/Vs
Solution Approach 1:
The amorphous silicon layer is divided into multiple sub-layers (first amorphous silicon layer, second amorphous silicon layer, third amorphous silicon layer) with different deposition conditions. Each layer has specific characteristics that contribute to the overall crystallization process, enabling grain sizes exceeding 500 nm while maintaining structural control during annealing
Solution Approach 2:
Different regions of the silicon structure are given different properties through varying deposition gases and conditions. The first layer uses silane-hydrogen for specific nucleation characteristics, the second layer uses silane-inert gas for grain growth control, and the third layer uses silane-hydrogen for surface quality, creating localized quality variations that drive overall grain enlargement
2Manufacturing precision
If conventional single-layer amorphous silicon structure is used with excimer laser annealing, then the process is simple and compatible with existing equipment, but mobility cannot exceed 90 cm2/Vs
Solution Approach 1:
The silicon structure is segmented into multiple layers with distinct deposition characteristics. The first amorphous silicon layer deposited with silane-hydrogen provides a foundation for high mobility, the second layer deposited with silane-inert gas controls intermediate properties, and the third layer deposited with silane-hydrogen optimizes the surface for final annealing, collectively achieving mobility exceeding 90 cm2/Vs
Solution Approach 2:
The deposition parameters are systematically changed across layers - specifically the activation gas composition (hydrogen vs. inert gas) and gas flow ratios are varied to control the atomic structure and bonding characteristics of each layer. These parameter changes create a gradient in material properties that enhances overall mobility after annealing
3Productivity
If multi-layer amorphous silicon structure with alternating gases is used, then grain size can exceed 500 nm and mobility can exceed 90 cm2/Vs, but the deposition process becomes more complex
Solution Approach 1:
The deposition process is segmented into three distinct stages corresponding to three amorphous silicon layers, each with specific gas compositions and flow ratios. This segmentation allows independent optimization of each layer's properties to achieve superior device performance with grain sizes exceeding 500 nm and mobility exceeding 90 cm2/Vs
Solution Approach 2:
The deposition process uses periodic alternation between hydrogen-based activation gas and inert gas activation in a cyclic pattern across the three layers. This periodic action creates alternating regions with different atomic configurations that facilitate grain boundary control and enhance overall crystallization quality during subsequent annealing
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
The method achieves higher crystallinity and mobility in polycrystalline silicon layers, with measured mobilities up to 100 cm2/Vs, improving device performance and maintaining compatibility with existing equipment and processes.
Implementation Method 1
delivering a silicon-containing precursor and a first activation gas to a processing region to deposit the first amorphous silicon layer over a substrate, the silicon-containing precursor and the first activation gas being activated by a plasma
Implementation Method 2
depositing a first amorphous silicon layer, the depositing comprising delivering a silicon-containing precursor and a first activation gas to a processing region to deposit the first amorphous silicon layer over a substrate, the silicon-containing precursor and the first activation gas being activated by a plasma
Implementation Method 3
A common method to crystallize the amorphous silicon structure in industry is through excimer laser annealing (ELA)
Implementation Method 4
annealing the first and second amorphous silicon layers after the dehydrogenation to form a polycrystalline silicon layer
Data Source
AI summary
The embodiments described herein generally relate to methods for forming a multi-layer amorphous silicon structure that may be used in thin film transistor devices. In one embodiment, a method includes positioning a substrate comprising a buffer layer in a process chamber, the process chamber comprising a processing region, forming a plurality of amorphous silicon layers and annealing the amorphous silicon layers to form a polycrystalline silicon layer. Forming the plurality of layers includes delivering a silicon-containing precursor and a first activation gas to the processing region to deposit a first amorphous silicon layer over the buffer layer, the silicon-containing precursor and the first activation gas being activated by a plasma and maintaining a continuous flow of the silicon-containing precursor while delivering a second activation gas, without the first activation gas, to the processing region to deposit a second silicon layer on the first silicon layer.