Metal-Induced Crystallization of Amorphous Silicon in Oxidizing Atmosphere
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Solution Overview
Problem
Conventional metal-induced crystallization (MIC) of amorphous silicon in non-oxidizing atmospheres results in high defect density due to residual metal contamination, limiting the performance of polycrystalline silicon thin-film transistors (TFTs) used in flat-panel displays.
Innovation Solution
The MIC process is modified to include a two-phase annealing procedure, where the initial phase occurs in a non-oxidizing atmosphere for a short duration to allow metal catalyst diffusion, followed by a longer annealing in an oxidizing atmosphere to reduce defect density through silicon interstitial generation and diffusion to crystal grain boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional MIC process is used in non-oxidizing atmosphere, then crystallization speed is improved, but defect density increases due to residual metal contamination
Solution Approach 1:
The MIC process is divided into two distinct phases: a first phase in non-oxidizing atmosphere for rapid crystallization, and a second phase in oxidizing atmosphere for defect reduction. This segmentation allows each phase to optimize for its specific function, resolving the contradiction between speed and quality.
Solution Approach 2:
The atmospheric conditions (oxidizing vs. non-oxidizing) are changed between phases to achieve different objectives. The first phase uses non-oxidizing atmosphere to prevent metal oxidation during rapid crystallization, while the second phase switches to oxidizing atmosphere to remove residual metal and reduce defects.
2Manufacturing precision
If longer annealing time is used to reduce defect density, then manufacturing cost increases, but device performance improves
Solution Approach 1:
Changing the atmospheric parameter from non-oxidizing to oxidizing in the second phase enables effective defect reduction at moderate annealing times. The oxidizing atmosphere facilitates metal removal through oxidation, achieving low defect density without requiring excessively long processing times.
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 field-effect mobility, current on-off ratio, and lowers the threshold voltage of TFTs, resulting in improved device characteristics and performance.
Implementation Method 1
The MIC process involves usage of a metal catalyst to facilitate crystallization of a-Si during heat-treatment
Implementation Method 2
metal catalyst diffusion
Implementation Method 3
annealing in an oxidizing atmosphere to reduce defect density through silicon interstitial generation and diffusion
Implementation Method 4
silicon interstitial generation and diffusion to crystal grain boundaries
Implementation Method 5
The MIC process involves usage of a metal catalyst to facilitate crystallization of a-Si during heat-treatment
Implementation Method 6
transformation of the amorphous silicon layer into the polycrystalline silicon layer
Data Source
AI summary
Techniques are provided for forming thin film transistors having a polycrystalline silicon active layer formed by metal-induced crystallization (MIC) of amorphous silicon in an oxidizing atmosphere. In an aspect, a transistor device, is provided that includes a source region and a drain region formed on a substrate, and an active channel region formed on the substrate and electrically connecting the source region and the drain region. The active channel region is formed with a polycrystalline silicon layer having resulted from annealing an amorphous silicon layer formed on the substrate and having a metal layer formed thereon, wherein the annealing of the amorphous silicon layer was at least partially performed in an oxidizing ambience, thereby resulting in crystallization of the amorphous silicon layer to form the polycrystalline silicon layer.