Laser Lift-Off Focus Control for Warped GaN Sapphire Wafers
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Solution Overview
Problem
The large warpage of GaN and sapphire composite substrates during the laser lift-off process leads to laser defocusing, significantly reducing the lift-off yield.
Innovation Solution
A laser lift-off integrated apparatus that includes a laser light source, a lift-off chamber, a heater, a profile measuring device, and a movable device. The profile measuring device acquires surface profile information of the wafer, and the movable device adjusts the wafer's height to maintain the laser focus at the correct position, ensuring precise lift-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser lift-off is performed on GaN/sapphire composite substrate, then free-standing GaN substrate is obtained, but laser defocusing occurs due to warpage, reducing lift-off yield
Solution Approach 1:
The patent introduces a movable device that can dynamically adjust the position of the GaN/sapphire composite substrate in real-time during the laser lift-off process. This dynamic adjustment compensates for the warpage-induced focus shift, maintaining the laser focal point on the lift-off surface throughout the procedure, thereby resolving the contradiction between obtaining free-standing substrates and maintaining laser focus precision.
Solution Approach 2:
The patent implements a feedback mechanism where a detection device continuously monitors the surface profile of the substrate, and this information is fed back to the movable device for real-time position adjustment. This closed-loop feedback system ensures that the laser remains focused on the lift-off surface despite substrate warpage, improving both reliability and manufacturing precision.
2Manufacturing precision
If GaN epitaxial wafer is grown at high temperature, then crystal quality is improved, but large warpage occurs due to thermal mismatch stress, causing laser defocusing
Solution Approach 1:
The movable device dynamically compensates for the warpage shape change by adjusting the substrate position during laser lift-off. This allows the high-temperature growth process to be maintained for crystal quality improvement while the dynamic adjustment counteracts the resulting warpage, preventing laser defocusing.
Solution Approach 2:
The patent converts the harmful effect of warpage into a measurable parameter. By using the detection device to measure the warpage-induced surface profile changes, the system transforms the problematic shape deviation into useful feedback information that drives the position adjustment, ultimately eliminating the negative impact of warpage on laser focus.
3Ease of manufacture
If lattice mismatch stress and thermal mismatch stress are present during growth, then GaN film is formed on sapphire substrate, but large warpage of composite substrate occurs, reducing lift-off yield
Solution Approach 1:
The patent extracts the warpage effect from the manufacturing process by separating it into a measurable parameter. The detection device isolates the warpage-induced surface profile information, and the movable device extracts the necessary position adjustment to compensate for this effect, allowing the GaN film formation process to proceed while eliminating the reliability issue caused by warpage.
Solution Approach 2:
The system uses dynamic position adjustment to compensate for the static warpage caused by mismatch stresses. The movable device continuously adapts the substrate position based on real-time warpage measurements, maintaining laser focus despite the inherent warpage from lattice and thermal mismatch stresses during the lift-off process.
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 solution effectively maintains the laser focus on the lift-off surface, improving the lift-off yield by preventing defocusing issues caused by substrate warpage.
Implementation Method 1
a laser light source configured to perform laser lift-off on a wafer to undergo lift-off
Implementation Method 2
a heater configured to provide temperature required by the wafer to undergo lift-off during a lift-off process
Data Source
AI summary
A laser lift-off integrated apparatus includes a laser light source configured to perform laser lift-off on a wafer to undergo lift-off, a lift-off chamber configured to bear the wafer to undergo lift-off, a heater configured to provide temperature required by the wafer to undergo lift-off during a lift-off process, a profile measuring device configured to acquire surface profile information of the wafer to undergo lift-off, and a movable device configured to, according to the surface profile information acquired by the profile measuring device, adjust a height of the wafer to undergo lift-off such that a focus of the laser light source is at a position where the wafer to undergo lift-off is to undergo lift-off.