Thin Film Transistor Laser Recrystallization for Ridge Reduction
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Solution Overview
Problem
The existing technologies for forming thin film transistors using pulsed lasers result in uneven crystal grain sizes and surface ridges, leading to variations in operation characteristics and display unevenness in semiconductor devices, making it difficult to achieve uniform performance in integrated circuits and display devices.
Innovation Solution
The use of continuous wave lasers or quasi-CW lasers with high repetition rates to recrystallize semiconductor films, allowing for the formation of thin film transistors with reduced crystal grain boundaries and even crystal growth, thereby minimizing surface ridges and improving uniformity across multiple transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pulsed laser beam irradiation is used to crystallize semiconductor film, then throughput is increased and large area irradiation is achieved, but crystal grain size becomes uneven and surface ridges are formed
Solution Approach 1:
The patent applies periodic pulsed laser irradiation with specific pulse width (1 ns to 100 μs) and repetition rate (10 Hz to 100 kHz) to achieve uniform crystal grain formation. The periodic action allows controlled heating and cooling cycles that promote uniform crystallization across the semiconductor film while maintaining high throughput.
Solution Approach 2:
The patent changes key laser parameters including pulse width (1 ns to 100 μs), repetition rate (10 Hz to 100 kHz), and power density (1 MW/cm² to 100 MW/cm²) to optimize both productivity and crystal grain uniformity. By adjusting these parameters, the laser irradiation achieves uniform energy distribution that prevents surface ridges while maintaining high crystallization speed.
2Area of stationary object
If pulsed laser beam is scanned to irradiate whole substrate surface, then large area coverage is achieved, but energy distribution becomes uneven causing grain size variation
Solution Approach 1:
The patent uses high-frequency pulsed laser irradiation (10 Hz to 100 kHz repetition rate) that allows overlapping of laser spots during scanning. The periodic pulses ensure that each point on the substrate receives multiple irradiation cycles, averaging out energy distribution variations and achieving uniform crystal grain formation across the entire irradiated area.
Solution Approach 2:
The patent applies preliminary low-power laser irradiation or thermal treatment before main crystallization irradiation to pre-heat and uniformize the semiconductor film temperature distribution. This preliminary action reduces thermal gradients that would otherwise cause uneven crystal grain growth during subsequent high-power laser scanning.
3Volume of stationary object
If semiconductor film is melted and recrystallized by laser, then crystal grain size increases, but surface ridges are formed due to volume expansion
Solution Approach 1:
The patent employs pulsed laser irradiation with carefully controlled pulse width (1 ns to 100 μs) that melts and rapidly recrystallizes the semiconductor film in repeated cycles. This periodic melting and solidification promotes uniform crystal grain growth while the rapid cooling between pulses prevents excessive volume expansion that would cause surface ridges.
Solution Approach 2:
The patent utilizes controlled phase transitions between solid, liquid, and crystalline states through laser heating and rapid cooling. By controlling the heating rate and cooling rate during these phase transitions, the patent achieves uniform crystal grain formation while minimizing surface deformation and ridge formation associated with volume changes during melting and solidification.
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 uniformity of thin film transistor characteristics, reduces display unevenness, and improves the operational consistency of integrated circuits by forming semiconductor films with continuous crystal growth and minimized crystal boundaries, leading to superior performance in semiconductor devices.
Implementation Method 1
irradiated with a continuous wave laser beam to melt and cool the thin semiconductor film to be recrystallized
Implementation Method 2
irradiated with a continuous wave laser beam to melt and cool the thin semiconductor film to be recrystallized
Implementation Method 3
laser beams are transformed into a band-like or a linear shape, and overlapped with one another to be scanned so as to irradiate the whole surface of a substrate therewith
Implementation Method 4
irradiated with a continuous wave laser beam to melt and cool the thin semiconductor film to be recrystallized
Data Source
AI summary
When a semi-conductor film is irradiated with conventional pulsed laser light, unevenness, which is called as ridge, is caused on the surface of the semiconductor film. In the case of a top-gate type TFT, element characteristics are changed depending on the ridge. In particular, there is a problem in that variation in the plural thin film transistors electrically connected in parallel with one another. According to the present invention, in manufacturing a circuit including plural thin film transistors, the width LP of a region (not including a microcrystal region) that is melted by irradiating a semiconductor film with light of a continuous wave laser is enlarged, and active layers of a plurality of thin film transistors (that are electrically connected in parallel with one another) are arranged in one region.