Rectangular Excimer Laser Annealing for Polysilicon Grain Uniformity
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Solution Overview
Problem
The existing excimer laser annealing method for fabricating polysilicon layers results in small and non-uniform grains due to a low lateral temperature gradient, leading to low electron mobility and inefficiencies in the production process, as it requires multiple movements of the laser generator and has difficulty in controlling energy application.
Innovation Solution
A method using a precision stepper motor-controlled excimer laser generator to emit pulse laser beams in a rectangular shape, allowing for the formation of a polysilicon layer with larger grains by creating a larger lateral temperature gradient through strategically spaced rectangular areas and interval areas on the amorphous silicon layer, with precise energy control and substrate heating to promote uniform grain growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the excimer laser generator moves up and down multiple times to melt each area of the amorphous silicon layer, then the polysilicon layer can be fabricated, but the production cycle duration increases
Solution Approach 1:
The laser beam is divided into multiple independent pulse beams arranged in a rectangular shaft shape, allowing simultaneous melting of multiple areas rather than sequential processing. This segmentation of the beam enables parallel processing of the amorphous silicon layer, significantly reducing the production cycle duration while maintaining fabrication quality.
Solution Approach 2:
Multiple pulse excimer laser beams are combined into a single rectangular shaft-shaped beam structure that can process multiple areas simultaneously. By merging the functionality of multiple sequential laser passes into one combined beam configuration, the invention eliminates repeated positioning movements and reduces the overall production cycle time.
2Manufacturing precision
If the lateral temperature gradient is kept low in the ELA process, then the amorphous silicon layer can be melted uniformly, but the polysilicon grain sizes remain small and electron mobility is reduced
Solution Approach 1:
The rectangular shaft-shaped laser beam creates localized high-temperature zones with steep temperature gradients at the boundaries between melted and non-melted areas. This local quality variation promotes heterogeneous nucleation at the interfaces, generating numerous crystallization seeds that grow into large, uniform polysilicon grains with high electron mobility.
Solution Approach 2:
The invention dynamically controls the laser beam parameters including pulse duration, frequency, and spatial distribution to optimize the temperature gradient. By adjusting these dynamic parameters, the process achieves both uniform melting within each area and sufficient temperature differences at boundaries to promote grain growth, thereby improving electron mobility.
3Manufacturing precision
If the energy of the laser beam is increased to promote grain growth, then larger polysilicon grains can be formed, but the energy control becomes difficult and seed density may drop below the SLG point
Solution Approach 1:
The laser beam energy is distributed across multiple pulse beams in a rectangular shaft configuration, with each pulse delivering partial energy to a specific area. This partial action approach ensures that the total energy remains below the SLG point threshold, preventing excessive melting and seed loss, while still providing sufficient energy for grain growth through cumulative heating and controlled temperature gradients.
Solution Approach 2:
The multiple pulse beams are applied in a continuous or near-continuous sequence across the amorphous silicon layer, maintaining continuous useful action for melting and crystallization. This continuous processing ensures uniform energy distribution and prevents localized energy excess that could cause seed density to drop, while still achieving the necessary total energy input for large grain formation.
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 production efficiency by forming polysilicon layers with larger and more uniform grains, resulting in higher electron mobility and improved performance of thin film transistors, while reducing the production cycle time and maintaining substrate integrity.
Implementation Method 1
an excimer laser generator for generating a pulse excimer laser beams collectively having the shape of a generally rectangular shaft is provided to melt a first area of the amorphous silicon layer with the pulse excimer laser beams
Implementation Method 2
the melted silicon starts crystallizing from the seeds of crystallization to finally form a polysilicon layer
Implementation Method 3
with precise energy control and substrate heating to promote uniform grain growth
Data Source
AI summary
An exemplary method for fabricating a polysilicon layer includes the following steps. A substrate (10) is provided and an amorphous silicon layer (12) is formed over the substrate. An excimer laser generator (13) for generating a pulse excimer laser beams collectively having the shape of a generally rectangular shaft is provided to melt a first area (15) of the amorphous silicon layer with the pulse excimer laser beams. The excimer laser generator is moved a distance to melt a second area of the amorphous layer spaced a short distance away from the first area. At least a subsequent third melted area spaced a short distance away from the second melted area is formed, with each subsequent melted area is spaced as short distance away from the immediately preceding melted area.