| 摘要(英) |
This study aims to overcome the measurement challenges of sapphire substrates after machining and proposes a three-dimensional morphology measurement method that integrates image preprocessing with the Shape From Focus (SFF) technique. Sapphire is composed of high-purity single-crystal aluminum oxide (Al?O?), with a hardness second only to diamond, excellent thermal stability, and high wear resistance. It also exhibits a broad transmission range from deep ultraviolet to mid-infrared wavelengths, making it widely used in optoelectronics, microelectronics, and aerospace fields.
Existing techniques such as Differential Interference Contrast (DIC), White Light Interferometry (WLI), and Laser Scanning Confocal (LSC) each cater to different measurement demands. While DIC can observe fine structures in transparent materials, it lacks accurate depth information. WLI offers non-contact, high-precision 3D measurements but can suffer from errors when measuring steep height transitions. LSC provides high-resolution data and strong 3D reconstruction capabilities, but at a relatively high equipment cost. To achieve reliable 3D measurement without significantly increasing costs, this study employs SFF, which reconstructs depth by determining the focal position for different areas across multiple focal-plane images. However, the high transparency and reflectivity of sapphire can lead to glare and bright spots, necessitating effective image preprocessing prior to SFF.
In this research, grayscale equalization, Gaussian filtering, and morphological operations are initially performed to reduce noise and enhance contrast, thereby correcting uneven illumination and reflection-induced distortions. Subsequently, multiple focal-plane images are fused, and an algorithm precisely determines the optimal focal height for each pixel, reconstructing the 3D morphology of a square hole. Experimental results indicate that both vertical and horizontal resolutions are approximately 0.8 μm, with the vertical measurement range extending up to 20 mm, and a horizontal range of about 1.96 mm × 1.64 mm. This approach effectively highlights hole-wall geometry and detail, enabling accurate depth measurement and comprehensive morphological analysis—offering a feasible pathway for optimizing sapphire processing and evaluating epitaxial layer quality.
Furthermore, this study demonstrates that SFF is applicable to transparent, highly reflective materials and showcases the accuracy and stability achieved by integrating image preprocessing. By enhancing image sharpness and mitigating glare and noise, it significantly improves the detection of hole morphology, aiding subsequent adjustments in manufacturing parameters and improving device quality. Given its relatively low cost and flexible system configuration, this measurement method could be further refined in illumination and hardware setups, making it even more advantageous for practical use in optoelectronics and microelectronics. |
| 參考文獻 |
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