Polycrystalline Silicon Film Uniformity via Laser Interference
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Solution Overview
Problem
Existing methods for forming polycrystalline semiconductor thin films using laser beam irradiation result in non-uniform crystal grain sizes and increased complexity, leading to variations in display characteristics and reliability issues in TFTs due to crystal defects and peeling of reflective layers.
Innovation Solution
A method involving the deposition of an insulating film with a specific refractive index on a substrate, followed by the formation of an amorphous thin film, and irradiation with a laser beam of a band shape, where the irradiation position is shifted to create uniform crystal grain boundaries with controlled spacing, reducing variations and improving film uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a laser beam is used to form a polycrystalline semiconductor thin film from an amorphous thin film, then the film can be manufactured with relatively simple equipment, but the crystal grain sizes become non-uniform leading to variations in TFT characteristics
Solution Approach 1:
A reflective layer is introduced as an intermediary between the laser beam and the amorphous thin film. This reflective layer modifies the laser beam's interaction with the film by creating interference patterns that result in uniform crystal grain formation. The reflective layer acts as a mediator that transforms the direct laser-film interaction into a controlled interference-based process, achieving uniform crystal grains while maintaining the simplicity of laser-based manufacturing.
Solution Approach 2:
The invention changes the physical parameters of the laser beam interaction by introducing a reflective layer that alters the optical path. The interference pattern created by the reflective layer changes the energy distribution across the film surface, leading to uniform heating and subsequent uniform crystal grain formation. This parameter change in the laser-film interaction mechanism resolves the non-uniformity issue.
2Manufacturing precision
If a light reflective layer is formed on the amorphous thin film to control crystal grain size, then the crystal grain size can be adjusted, but the process complexity increases due to additional formation and removal steps
Solution Approach 1:
The reflective layer serves multiple functions simultaneously: it controls crystal grain size through interference patterns, acts as a mask for selective crystallization in different regions, and can be integrated with other device structures. This multi-functionality reduces the need for separate process steps, thereby reducing overall process complexity while maintaining precise control over crystal grain size.
Solution Approach 2:
The reflective layer is formed in advance before the laser irradiation process. This preliminary action allows the interference pattern to be established beforehand, ensuring uniform crystal grain formation during the subsequent laser treatment. By performing the reflective layer formation as a preliminary step, the actual crystallization process becomes simpler and more controlled.
3Manufacturing precision
If a light reflective layer is used during laser annealing, then crystal grain size can be controlled, but the reflective layer may peel off due to gas release from the amorphous thin film
Solution Approach 1:
The amorphous thin film undergoes preliminary heating treatment before the main laser annealing process. This preliminary action removes volatile components and gases from the film in advance, preventing gas accumulation that would otherwise cause peeling of the reflective layer during subsequent laser treatment. This preliminary gas removal ensures reliable adhesion while maintaining crystal grain control capabilities.
Solution Approach 2:
The laser irradiation parameters are optimized to rapidly pass through the reflective layer and amorphous film interface, minimizing the time during which gas release could cause peeling. By rushing through the critical interface region quickly with controlled laser parameters, the process achieves crystal grain control without allowing sufficient time for gas accumulation and peeling to occur.
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 a polycrystalline semiconductor thin film with uniform crystal grains, reducing variations in TFT characteristics and enhancing the reliability of semiconductor devices by minimizing crystal defects and surface roughness.
Implementation Method 1
irradiating the amorphous thin film with a laser beam
Implementation Method 2
a polycrystalline semiconductor thin film is formed from the amorphous thin film by irradiating the amorphous thin film with a laser beam
Implementation Method 3
an insulating film having a refractive index n is deposited on a translucent substrate... crystal grain boundaries which extend in the width direction and are disposed at a mean spacing measured along the length direction and ranging from (λ/n)×0.95 to (λ/n)×1.05 inclusive
Implementation Method 4
an insulating film having a refractive index n is deposited on a translucent substrate
Data Source
AI summary
On a translucent substrate, an insulating film having a refractive index n and an amorphous silicon film are deposited successively. By irradiating the amorphous silicon film with a laser beam having a beam shape of a band shape extending along a length direction with a wavelength λ, a plurality of times from a side of amorphous silicon film facing the insulating film, while an irradiation position of the laser beam is shifted each of the plurality of times in a width direction of the band shape by a distance smaller than a width dimension of the band shape, a polycrystalline silicon film is formed from the amorphous silicon film. Forming the polycrystalline silicon film forms crystal grain boundaries which extend in the width direction and are disposed at a mean spacing measured along the length direction and ranging from (λ/n)×0.95 to (λ/n)×1.05 inclusive, and crystal grain boundaries which, in a region between crystal grain boundaries adjacent to each other and extending in the width direction, extend in the length direction and are disposed at a mean spacing measured along the width direction and ranging from (λ/n)×0.95 to (λ/n)×1.05 inclusive.