Optical Device Lift-Off via Composite Substrate Heating
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Solution Overview
Problem
The existing lift-off method for transferring optical device layers from epitaxy substrates to transfer substrates often results in substrate warpage due to thermal expansion differences, leading to incomplete buffer layer breaking and damage to the optical devices.
Innovation Solution
A lift-off method that includes a composite substrate heating step to relieve spring back in the epitaxy and transfer substrates before applying a laser beam to break the buffer layer, ensuring reliable peeling of the epitaxy substrate and preventing damage to the optical device layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the transfer substrate is bonded to the optical device layer through heating to form a composite substrate, then the bonding strength is improved, but substrate warpage occurs due to thermal expansion differences
Solution Approach 1:
The patent applies preliminary anti-action by heating the composite substrate before laser processing to counteract the warpage effect. The pre-heating causes thermal expansion that compensates for the differential thermal expansion between the epitaxy substrate and transfer substrate, thereby relieving spring back and preventing warpage during subsequent cooling and laser processing stages.
2Productivity
If the laser beam is applied to break the buffer layer without pre-heating, then the processing speed is improved, but incomplete buffer layer breaking occurs due to spring back
Solution Approach 1:
The patent applies preliminary action by heating the composite substrate to a predetermined temperature before applying the laser beam. This pre-heating action ensures that the substrate is in the appropriate thermal state to prevent spring back, thereby enabling complete and uniform buffer layer breaking when the laser is applied, without compromising processing speed.
3Device complexity
If the epitaxy substrate is peeled without relieving spring back, then the peeling process is simplified, but damage to the optical device layer occurs due to unbroken buffer layer areas
Solution Approach 1:
The patent applies parameter changes by controlling the temperature parameter of the composite substrate before peeling. By heating the substrate to a specific temperature range, the mechanical properties of the buffer layer and substrate interface are modified, ensuring complete buffer layer breaking and enabling clean peeling that preserves the integrity of the optical device layer without increasing process 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 ensures reliable peeling of the epitaxy substrate without damaging the optical device layer, maintaining the quality of the optical devices by ensuring complete buffer layer breaking and reducing substrate warpage.
Implementation Method 1
applying a laser beam having a wavelength transmissive to the epitaxy substrate and absorptive to the buffer layer from the back side of the epitaxy substrate to the buffer layer, thereby breaking the buffer layer
Implementation Method 2
the optical device wafer and the transfer substrate are heated to about 250° C. Accordingly, the composite substrate is slightly warped at room temperature because of a difference in coefficient of thermal expansion between the epitaxy substrate and the transfer substrate
Data Source
AI summary
A lift-off method transfers an optical device layer in an optical device wafer to a transfer substrate. The optical device layer is formed on the front side of an epitaxy substrate through a buffer layer. A composite substrate is formed by bonding the transfer substrate through a bonding agent to the front side of the optical device layer, thereby forming a composite substrate. The buffer layer is broken up by applying a laser beam having a wavelength transmissive to the epitaxy substrate and absorptive to the buffer layer from the back side of the epitaxy substrate to the buffer layer after performing the composite substrate forming step, thereby breaking the buffer layer. An optical device layer is transferred by peeling off the epitaxy substrate from the optical device layer after performing the buffer layer breaking step, thereby transferring the optical device layer to the transfer substrate.