Ultrashort Pulse Laser Annealing for Homogeneous Semiconductor Crystallinity
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Solution Overview
Problem
Existing laser annealing methods result in inhomogeneous irradiation energy distribution on semiconductor films, leading to variations in crystallinity and semiconductor element characteristics.
Innovation Solution
A laser irradiation method using a pulsed laser oscillator with a pulse width that satisfies specific inequalities (ct<2nd or ct<4nd) and incorporating a non-linear optical element to convert the laser wavelength, ensuring simultaneous irradiation with both primary and secondary beams for a limited time, thereby minimizing interference and achieving homogeneous energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a beam spot from a laser oscillator is used directly for irradiation, then the laser irradiation process is simple, but the energy distribution on the irradiated object becomes inhomogeneous
Solution Approach 1:
The patent divides the single beam spot from the laser oscillator into multiple beam spots using a cylindrical lens array. This segmentation allows the energy to be distributed more homogeneously across the irradiated object by superposing multiple divided beam spots, resolving the contradiction between process simplicity and energy distribution homogeneity.
Solution Approach 2:
The patent introduces a cylindrical lens array as an intermediary optical element between the laser oscillator and the irradiated object. This intermediary component transforms the inhomogeneous beam spot into a homogeneous energy distribution pattern, enabling both simple irradiation process and precise energy control.
2Productivity
If conventional laser annealing is performed with inhomogeneous irradiation energy, then the process can be completed, but the crystallinity in the crystalline semiconductor film becomes inhomogeneous
Solution Approach 1:
By segmenting the laser beam into multiple spots that overlap to create a homogeneous energy distribution, the patent enables uniform crystallization across the semiconductor film. This maintains high productivity while achieving homogeneous crystallinity, as the entire area receives uniform energy treatment simultaneously.
Solution Approach 2:
The patent changes the spatial distribution parameter of the laser energy by using a cylindrical lens array to transform the beam profile. This parameter change from inhomogeneous to homogeneous energy distribution directly improves the homogeneity of crystallinity while maintaining the laser annealing process efficiency.
3Use of energy by moving object
If the pulse width of the laser beam is increased, then the laser energy is sufficient for annealing, but interference between primary and secondary beams increases
Solution Approach 1:
The patent uses ultrashort pulsed laser action with pulse widths of 10 ps or less. This periodic ultrashort pulse delivery provides sufficient peak energy for annealing while the extremely short duration prevents the primary and secondary beams from interfering with each other, as the secondary beam (reflected from substrate rear surface) cannot return during the pulse duration.
Solution Approach 2:
The patent employs ultrashort pulses that rush through the interaction region before the secondary beam can form and cause interference. By completing the useful annealing action in 10 ps or less, the primary beam delivers its energy and exits the interaction zone before the reflected secondary beam can return and create harmful interference patterns.
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 method enables the production of crystalline semiconductor films with improved homogeneity and reduced variations in semiconductor element characteristics, enhancing the throughput and quality of semiconductor devices such as integrated circuits and display devices.
Implementation Method 1
wavelength of the laser beam is converted by a non-linear optical element
Implementation Method 2
irradiating an irradiated object formed over a substrate with a laser beam emitted from a pulsed laser oscillator
Implementation Method 3
laser annealing process
Implementation Method 4
a secondary beam reflected on a rear surface of the substrate
Implementation Method 5
one point in the irradiated object is irradiated simultaneously with both a primary beam incident into the irradiated object and a secondary beam reflected on a rear surface of the substrate
Data Source
AI summary
Even when the laser irradiation is performed under the same condition with the energy distribution of the beam spot shaped as appropriate, the energy given to the irradiated surface is not yet homogeneous. When a semiconductor film is crystallized to form a crystalline semiconductor film using such inhomogeneous irradiation energy, the crystallinity becomes inhomogeneous in this film, and the characteristic of semiconductor elements manufactured using this film varies. In the present invention, an irradiated object formed over a substrate is irradiated with a laser beam having the pulse width that is an order of picosecond (10−12 second) or less.