Polysilicon TFT Metal-Induced Crystallization Leakage
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Solution Overview
Problem
Conventional manufacturing methods for polysilicon thin film transistors (TFTs) face issues with metal impurities causing current leakage due to the use of metal-induced crystallization, which degrades the electrical characteristics of TFTs.
Innovation Solution
A method involving the deposition of an amorphous silicon layer on a substrate, patterning to form source, drain, and channel regions, followed by the selective application of an inducing metal layer for crystallization, and subsequent thermal treatments to minimize metal impurity concentration in the channel region through the use of phosphorus doping to absorb residual nickel, thereby reducing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If metal-induced crystallization is used to crystallize amorphous silicon, then crystallization temperature is reduced to 500°C or less, but metal atoms remain in channel regions as impurity atoms causing current leakage
Solution Approach 1:
The patent divides the amorphous silicon layer into different regions (source/drain regions and channel region) and applies metal layer selectively only to source/drain regions. This segmentation allows MIC to occur in source/drain regions while preventing metal contamination in the channel region, resolving the contradiction between achieving low-temperature crystallization and preventing current leakage.
Solution Approach 2:
The patent applies different treatments to different regions: metal layer is deposited on source/drain regions to enable MIC and form polysilicon, while the channel region remains as amorphous silicon without metal layer. This local differentiation allows each region to have optimal properties - source/drain regions achieve low-temperature crystallization while channel region remains free from metal impurities.
2Productivity
If metal layer is deposited on amorphous silicon layer, then crystal growth is promoted and crystallization temperature is decreased, but metal impurity concentration increases in the crystallized region
Solution Approach 1:
The patent extracts the metal layer from the channel region by selectively depositing it only on source/drain regions using photolithography and sputtering. This extraction ensures that metal-induced crystallization and rapid crystal growth occur only where metal is present, while the channel region avoids metal impurity contamination entirely.
Solution Approach 2:
The patent uses photolithography patterns as an intermediary to control where the metal layer is deposited. This intermediary mechanism enables precise spatial control of metal placement, allowing crystal growth promotion in source/drain regions while preventing metal impurity introduction in the channel region.
3Stability of the object's composition
If conventional annealing thermal treatment is used to crystallize amorphous silicon, then complete crystallization is achieved, but long annealing time at high temperature is required which is not suitable for glass substrates
Solution Approach 1:
The patent changes the crystallization mechanism from thermal annealing to metal-induced crystallization. By introducing metal atoms as a catalyst, the crystallization process occurs at lower temperatures (500°C or less) and shorter times. This parameter change in the crystallization mechanism enables complete crystallization without requiring long high-temperature annealing that would damage glass substrates.
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 effectively reduces the leakage current and improves the electrical characteristics of polysilicon TFTs by minimizing metal impurity concentration in the channel region, leading to enhanced performance and reliability.
Implementation Method 1
it has been found that some metals can function as catalysts for promoting crystal growth, and the crystallization temperature of the a-Si can be decreased by depositing a layer of metal on the a-Si. This method is called metal-induced crystallization (MIC) method.
Implementation Method 2
doping the source region and the drain region with a first impurity for collecting the inducing metal; and a second impurity according to the conductive type of the source region and the drain region
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3C
AI summary
Embodiments of the disclosed technology relate to a method for manufacturing a thin film transistor (TFT) with a polysilicon active layer comprising: depositing an amorphous silicon layer on a substrate, and patterning the amorphous silicon layer so as to form an active layer comprising a source region, a drain region and a channel region; depositing an inducing metal layer on the source region and the drain region; performing a first thermal treatment on the active layer provided with the inducing metal layer so that the active layer is crystallized under the effect of the inducing metal; doping the source region and the drain region with a first impurity for collecting the inducing metal; and performing a second thermal treatment on the doped active layer so that the first impurity absorbs the inducing metal remained in the channel region.