Mask-to-Donor Alignment Using In-Situ Beam Shadow Imaging
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Solution Overview
Problem
The challenge in laser-induced forward transfer (LIFT) processes is achieving precise alignment between a donor substrate and a masked laser beam for transferring microelectronic devices, particularly for small microLEDs, to avoid irradiating adjacent devices and ensure accurate landing on a receiver substrate, while existing fiducial-based alignment methods are inadequate for high-resolution displays.
Innovation Solution
A method that utilizes in-situ observation with a beam profiler to directly view the laser radiation transmitted by the mask and donor substrate, adjusting the alignment of the masked laser beam and donor substrate based on captured imagery to achieve sub-micrometer accuracy, allowing for precise alignment without relying on sacrificial transfers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fiducial-based alignment methods are used for LIFT process, then the alignment process is simple to implement, but the alignment accuracy is insufficient for high-resolution displays
Solution Approach 1:
The patent replaces the mechanical/fiducial-based alignment system with an optical observation system. A beam profiler directly views the laser radiation transmitted by the mask and donor substrate to capture imagery showing the shadow of the device, enabling optical measurement of alignment accuracy better than 0.2 μm without requiring complex fiducial markers or mechanical positioning systems
Solution Approach 2:
The patent introduces a beam profiler as an intermediary device between the laser beam and the alignment measurement system. The beam profiler captures imagery of the laser radiation transmitted through the mask and donor substrate, providing real-time visual feedback on the alignment status and enabling precise adjustment without direct mechanical contact or complex fiducial systems
2Object-affected harmful factors
If the laser beam is masked to irradiate only specific devices, then adjacent devices are protected from irradiation, but alignment precision between the masked beam and devices becomes critical
Solution Approach 1:
The patent implements a feedback mechanism where the beam profiler continuously monitors the alignment between the masked laser beam and the devices by capturing imagery of the transmitted laser radiation. The observed shadow position provides real-time feedback that enables dynamic adjustment of the mask or substrate position, ensuring the masked beam remains precisely aligned with the target device while protecting adjacent devices from irradiation
Solution Approach 2:
The patent replaces mechanical alignment methods with optical observation and control. By using a beam profiler to directly view the laser radiation transmitted by the mask and donor substrate, the system achieves sub-micrometer alignment precision through optical measurement rather than mechanical positioning, enabling precise control of the masked beam's position relative to the devices
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 achieves alignment accuracies better than 0.2 μm, enabling sub-1 μm positioning of microelectronic devices during LIFT, reducing errors and device breakage, and facilitating efficient transfer processes for high-resolution microLED displays.
Implementation Method 1
viewing the laser radiation transmitted by the mask and donor substrate to obtain imagery showing the shadow of the device in the laser radiation
Implementation Method 2
the laser ablation of the adhesive releases the microelectronic device from the donor substrate and propels the microelectronic device away from the donor substrate toward the receiver substrate
Data Source
AI summary
A mask-to-donor alignment method for laser-induced forward transfer includes (a) directing a laser beam onto a mask to produce a masked beam including one or more separate sub-beams, each sub-beam being transmitted by a respective aperture of the mask, (b) viewing each sub-beam, as transmitted by a donor substrate carrying one or more devices, to obtain imagery indicating in each sub-beam a shadow of a corresponding one of the one or more devices, and (c) based on the imagery, adjusting position of the masked beam and the donor substrate, relative to each other, so as to align each device with respect to the corresponding sub-beam. This in-situ observation of the relative alignment between the donor substrate and the masked beam produces an improved alignment accuracy, as compared to the indirect fiducial-based alignment method. Alignment accuracies better than 0.2 μm, and associated sub-1 μm LIFT positioning accuracies, have been demonstrated.