UV Laser Transfer and Cleaning of Microelectronic Devices
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Solution Overview
Problem
The existing laser lift-off process for transferring microelectronic devices leaves behind a gallium residue, which can impede device performance and requires caustic liquid etching for removal, posing challenges for substrates intolerant to liquid etching.
Innovation Solution
A method utilizing UV laser ablation for both the transfer of microelectronic devices by lifting off a gallium-nitride sacrificial layer and the subsequent cleaning of the gallium residue, eliminating the need for caustic liquid etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser lift-off is used to transfer microelectronic devices, then transfer efficiency is improved, but gallium residue is left on the device surface
Solution Approach 1:
The patent converts the harmful gallium residue left by laser lift-off into a beneficial cleaning opportunity by using the same UV laser to ablate and remove the residue. The laser that causes the problem (leaving gallium residue) is the same tool used to solve the problem (remove the residue through controlled ablation).
Solution Approach 2:
The patent implements continuous useful action by performing both the transfer function and the cleaning function in sequence using the same UV laser system. The laser first performs lift-off to transfer devices, then immediately performs ablation to clean residue, eliminating idle time between operations and maintaining continuous productive action.
2Object-generated harmful factors
If caustic liquid etching is used to remove gallium residue, then cleaning effectiveness is improved, but substrate damage risk increases
Solution Approach 1:
The patent replaces the chemical etching system (caustic liquids) with a physical/optical system (UV laser ablation). Instead of using chemical reactions to remove gallium residue, the UV laser directly ablates the residue through photothermal and photomechanical effects, eliminating the need for liquid chemicals that could damage sensitive substrates.
Solution Approach 2:
The patent changes the fundamental parameter of the cleaning process from chemical concentration and reactivity to laser energy density and pulse duration. By controlling laser parameters (wavelength, energy density, pulse width), the process achieves selective removal of gallium residue without affecting the substrate, as the substrate materials have different optical absorption characteristics at UV wavelengths.
3Reliability
If multiple processing steps are used for transfer and cleaning, then process completeness is improved, but processing time increases
Solution Approach 1:
The patent merges two separate processing functions (transfer via laser lift-off and cleaning via residue removal) into a single integrated UV laser processing step. The same UV laser system performs both operations sequentially, eliminating the need for separate equipment, setup changes, and intermediate handling between transfer and cleaning operations.
Solution Approach 2:
The patent implements multi-functionality by using the UV laser system to perform multiple functions: (1) laser lift-off for device transfer, (2) ablation for residue removal, and potentially (3) direct writing for patterning. This universal tool replaces specialized equipment for each function, reducing overall processing time and complexity.
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 effectively transfers microelectronic devices while selectively removing gallium residue using UV laser ablation, offering a more versatile and efficient process that can handle substrates intolerant to liquid etching, reducing processing time and avoiding damage to sensitive substrates.
Implementation Method 1
releasing the microelectronic device from the first substrate by laser ablating the sacrificial layer with a first ultraviolet laser beam
Implementation Method 2
cleaning at least a portion of the gallium residue off the microelectronic device by laser ablating the gallium residue with a second ultraviolet laser beam
Data Source
AI summary
A method for ultraviolet-laser transfer and cleaning of microelectronic devices includes transferring a microelectronic device from a donor substrate to a receiver substrate, and cleaning the microelectronic device after transfer. Prior to transfer, the microelectronic device is coupled to the donor substrate via a sacrificial layer containing gallium. A first ultraviolet laser beam ablates the sacrificial layer to release the microelectronic device from the donor substrate, leaving behind a gallium residue on the newly exposed surface of the microelectronic device. A second ultraviolet laser beam ablates the gallium residue to clean the microelectronic device. The first and second ultraviolet laser beams may be generated by the same ultraviolet laser. As compared to liquid etching, laser ablation of the gallium residue eliminates a wet-chemistry step and may be performed by the same laser apparatus used for transfer. Laser cleaning is particularly advantageous when the receiver substrate is intolerant to liquid etching.