研究目的
To enhance the performance of GaN-based LEDs by developing a low-cost, large-scale method for fabricating various complicated-shaped patterned sapphire substrates (PSS) using selective-area wet etching and partial exposure lithography.
研究成果
The selective-area wet etching method using partial exposure lithography successfully fabricates various PSS morphologies (pyramid, volcano, clover, inverted pyramid) by controlling etching time. This approach enhances light extraction efficiency in LEDs and offers a low-cost, large-scale alternative to existing methods. Future work could optimize parameters for industrial applications and explore nonpolar GaN growth.
研究不足
The method may have limitations in scalability for very large wafers, potential issues with mask durability under prolonged etching, and the need for precise control of exposure and etching parameters to avoid defects.
1：Experimental Design and Method Selection:
The study uses selective-area wet etching with a SiO2 mask fabricated via partial exposure lithography to control etching only on the top of commercial PSS. The process involves precise control of exposure and etching times to achieve different morphologies.
2：Sample Selection and Data Sources:
Commercial 2-inch cone-shaped PSS from Yuan Hong Technical Materials Ltd with specific dimensions (diameter 2.7 μm, height 1.7 μm, space 0.3 μm) is used.
3：7 μm, height 7 μm, space 3 μm) is used. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes plasma-enhanced chemical vapor deposition (PECVD) for SiO2 deposition, spin coater for photoresist, ultraviolet light source for exposure, buffered oxide etchant (BOE), and mixed acid solution (H2SO4:H3PO4=3:1 at 260°C). Materials include SiO2, photoresist, acetone, and sapphire substrates.
4：Experimental Procedures and Operational Workflow:
Steps involve depositing SiO2 on PSS, spin-coating photoresist, partial exposure and developing, etching SiO2 with BOE, removing photoresist, wet etching PSS with mixed acid for varying times, and removing SiO2. Surface morphology is analyzed using SEM and AFM.
5：Surface morphology is analyzed using SEM and AFM. Data Analysis Methods:
5. Data Analysis Methods: SEM and AFM are used to analyze surface morphology, line profiles, and slant angles. Etching rates and morphological changes are quantified based on time and height measurements.
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Patterned Sapphire Substrate
Cone-shaped, diameter 2.7 μm, height 1.7 μm, space 0.3 μm
Yuan Hong Technical Materials Ltd
Used as the base substrate for etching experiments to study morphology evolution.
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SiO2
200 nm thickness
Deposited as a mask layer for selective-area etching.
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Photoresist
Used in lithography for partial exposure to create the etching mask.
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Buffered Oxide Etchant
BOE
Used to etch the SiO2 mask.
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Mixed Acid Solution
H2SO4:H3PO4=3:1
Used for wet etching of the sapphire substrate at high temperature.
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Scanning Electron Microscope
SEM
Used to analyze the surface morphology of etched samples.
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Atomic Force Microscope
AFM
Used to analyze the surface topography and line profiles of etched samples.
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Plasma-Enhanced Chemical Vapor Deposition
PECVD
Used to deposit the SiO2 layer on the PSS.
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