Pulsed CO2 Laser Transfer of Device Layers on Bonded Substrates
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Solution Overview
Problem
Existing methods for transcribing a device layer from a silicon substrate using a CO2 laser face challenges due to the substrate's transmittance to NIR laser beams, leading to device layer damage and unstable separation, as the peak power of continuous CO2 laser waves is insufficient for effective separation.
Innovation Solution
A substrate processing method using a CO2 laser beam radiated in a pulse shape to increase peak power, combined with an acousto-optic modulator to control frequency, allowing stable separation and transfer of the device layer from a second substrate to a first substrate while minimizing thermal damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous CO2 laser wave is used for separation, then the laser beam can be continuously applied to the separation interface, but the peak power is insufficient for effective separation and device layer damage occurs
Solution Approach 1:
The patent applies periodic pulsed laser action instead of continuous laser wave. The laser is radiated in pulses with specific duty cycles (1%-50%) to achieve high peak power during the pulse duration while maintaining average power within safe limits. This periodic action enables effective separation at the interface without continuous thermal exposure that damages the device layer.
Solution Approach 2:
The patent changes the temporal parameters of laser radiation by switching from continuous wave to pulsed mode. Key parameters adjusted include pulse width (1μs-100ms), duty cycle (1%-50%), and frequency (10Hz-100kHz). These parameter changes enable the laser to deliver high peak power for effective separation while controlling thermal accumulation to prevent device layer damage.
2Reliability
If the laser power is increased to improve separation effectiveness, then separation can be achieved, but thermal damage to the device layer increases
Solution Approach 1:
By using pulsed laser radiation with duty cycles of 1%-50%, the system achieves high peak power during pulses for effective separation while allowing cooling during inter-pulse periods. This periodic action prevents continuous thermal accumulation that would damage the device layer, resolving the contradiction between separation effectiveness and thermal damage prevention.
Solution Approach 2:
The pulsed laser delivers energy in short bursts that rapidly heat the separation interface to achieve separation before heat can diffuse to the device layer. The short pulse durations (1μs-100ms) allow the process to complete quickly, skipping over the thermal diffusion time scale that would otherwise cause device layer damage.
3Reliability
If a CO2 laser is used for separation, then the laser wavelength matches the absorption characteristics, but the substrate transmittance to NIR laser beams causes unstable separation
Solution Approach 1:
The patent introduces a localized laser absorption layer at the separation interface that specifically absorbs the CO2 laser wavelength. This absorption layer creates localized heating at the interface between the semiconductor substrate and the sacrificial layer, ensuring stable and controlled separation. The local quality change (adding absorption layer) compensates for the substrate's general transmittance to NIR lasers.
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
The method enables stable and efficient separation of substrates with reduced thermal impact, facilitating the transfer of the device layer without damaging the silicon substrate, thereby improving processing efficiency and throughput.
Implementation Method 1
A laser beam is radiated in a pulse shape from a rear surface side of the second substrate to a laser absorption layer formed between the second substrate and the device layer
Implementation Method 2
combined with an acousto-optic modulator to control frequency
Data Source
AI summary
A substrate processing method of transcribing, in a combined substrate in which a first substrate and a second substrate are bonded to each other, a device layer formed on a surface of the second substrate to the first substrate is provided. A laser beam is radiated in a pulse shape from a rear surface side of the second substrate to a laser absorption layer formed between the second substrate and the device layer.