基於影像前處理之聚焦成形技術 應用於藍寶石加工孔形貌量測;Shape From Focus Based on Image Preprocessing for Sapphire Machining Hole Morphology Measurement

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Title:	基於影像前處理之聚焦成形技術應用於藍寶石加工孔形貌量測;Shape From Focus Based on Image Preprocessing for Sapphire Machining Hole Morphology Measurement
Authors:	蔡政宏;TSAI, CHENG-HUNG
Contributors:	光機電工程研究所
Keywords:	聚焦成形;三維形貌重建;藍寶石基板;深孔量測;Shape From Focus;three-dimensional morphology reconstruction;sapphire substrate;deep hole measurement
Date:	2025-01-21
Issue Date:	2025-04-09 16:14:58 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究目的為克服藍寶石基板加工後之孔洞量測困境，並提出結合影像前處理與聚焦成形（Shape From Focus, SFF）技術的三維形貌量測方法。藍寶石由高純度單晶氧化鋁（Al₂O₃）構成，硬度僅次於鑽石，熱穩定性與耐磨損性優異，透過率涵蓋深紫外至中紅外波段，廣泛應用於光電、微電子及航空航天領域。現有差分干涉對比（DIC）、白光干涉（WLI）與雷射掃描共焦（LSC）等量測技術，各自適用於不同的形貌檢測需求。DIC 能觀察透明材料細微結構卻缺乏深度資訊，WLI 具非接觸式高精度三維量測優勢，然而高度劇變時易有誤差；LSC 處理解析度高、三維重建能力強，但設備成本較高。為在不大幅增加設備負擔的前提下取得可靠的三維量測結果，本研究選用 SFF 技術，以多焦點影像判斷各區域焦點，重建孔洞深度。藍寶石本身的高透明度與反射性會導致眩光及亮斑，故在 SFF 前必須先進行有效的影像前處理。本研究首先運用灰階等化、高斯濾波及型態學運算，降低雜訊並強化對比度，修正光照不均及反射造成的影像失真。隨後，透過多張不同焦面影像之融合，藉由演算法精準辨識各像素位置的最佳聚焦高度，重建方孔的三維形貌。實驗結果顯示，縱向的解析度均約為 0.8 µm，橫向解析度0.4 µm，其中縱向量測範圍可達 20 mm，而橫向範圍約為 1.96 mm × 1.64 mm。此方法有效突顯孔壁形狀與細節，並能準確量測孔洞深度與形貌特徵，為藍寶石製程優化及外延層品質檢測提供了可行的技術路徑。本研究不但驗證了 SFF 在透明、高反光性材質上的應用價值，也展現了結合影像前處理所能達成的精度與穩定度。透過提升影像銳利度、抑制眩光與雜訊，能大幅強化對孔洞形貌的辨識力，進而協助後續製程參數調整與器件品質提升。由於此量測方法成本相對低廉、系統組裝彈性高，未來若能在照明與硬體配置上持續優化，勢必能進一步深化在光電與微電子領域的實際應用。 ;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 (Al₂O₃), 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.
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