Solid-State Green Laser Crystallization for Amorphous Silicon TFTs
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Solution Overview
Problem
The instability of excimer laser output and frequent maintenance issues in excimer laser systems used for crystallizing channel portions in amorphous-silicon-type thin film transistors lead to variations in transistor characteristics and increased downtime and running costs, hindering productivity and carrier mobility improvements.
Innovation Solution
A method involving the use of a solid-state green laser, with a wavelength of 532 nm, is employed to microcrystallize the channel portion of amorphous silicon films between source and drain electrodes, improving carrier mobility and stability, while reducing maintenance needs by using the source and drain electrode films as masks for selective annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If excimer laser is used to crystallize channel portion, then carrier mobility is improved, but laser output stability deteriorates
Solution Approach 1:
The patent changes the laser wavelength parameter from 248nm (excimer laser) to 532nm (solid-state green laser), which fundamentally alters the laser-matter interaction mechanism. This parameter change enables stable crystallization of the channel portion while achieving uniform laser output across large substrates, resolving the output stability issue without sacrificing carrier mobility improvement
2Reliability
If excimer laser is used for crystallization, then carrier mobility improves, but maintenance frequency increases
Solution Approach 1:
The patent replaces the excimer laser system (which uses active gas and has maintenance issues) with a solid-state green laser system. This substitution eliminates the need for active gas handling and optical component maintenance, significantly reducing downtime and running costs while maintaining the ability to improve carrier mobility through channel portion crystallization
3Reliability
If excimer laser is used for crystallization, then carrier mobility improves, but uniformity of crystallinity deteriorates
Solution Approach 1:
By changing to a 532nm solid-state green laser, the patent achieves superior beam uniformity and stability across large substrate areas. This parameter change ensures uniform energy distribution during laser irradiation, resulting in consistent crystallinity of the channel portion across the entire substrate, thereby improving manufacturing precision while maintaining carrier mobility enhancement
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 stabilizes laser irradiation across large substrates, reduces variations in transistor characteristics, decreases downtime costs, and enhances productivity by maintaining consistent crystallinity and improving carrier mobility through microcrystallization of the channel portion.
Implementation Method 1
a channel portion of an active layer, which is located between a source electrode and a drain electrode, is crystallized by laser annealing
Implementation Method 2
A solid-state green laser is irradiated onto the amorphous silicon film using the source electrode film and the drain electrode film as masks
Implementation Method 3
The channel portion has a microcrystalline structure, and is formed by irradiating a solid-state green laser onto the amorphous silicon film
Data Source
AI summary
[Object] To provide a method of producing a thin film transistor superior in productivity and capable of preventing variation in transistor characteristics among devices from occurring to improve carrier mobility, and a thin film transistor.[Solving Means] In a method of producing a thin-film transistor according to the present invention, a solid-state green laser is irradiated onto a channel portion of an amorphous silicon film using a source electrode film and a drain electrode film as masks, thereby improving mobility. Since the channel portion of the amorphous silicon film is crystallized by the irradiation of the solid-state green laser, laser oscillation characteristics can be more stable than in a conventional method that uses an excimer laser. Further, laser irradiation onto a large-size substrate at uniform output characteristics in plane becomes possible, with the result that a variation in crystallinity of channel portions among devices can be avoided. Moreover, since a maintenance cycle of a laser oscillator becomes longer, a downtime cost of the apparatus can be reduced and productivity can be improved.