運用數位微鏡晶片發展全域彩色差動共焦量測系統

Development on Chromatic Differential Confocal Measuring System by using Digital Micro-Mirror Device

林豐禾(Feng-He Lin)

指導教授 ： 陳亮嘉

國立臺灣大學/工學院/機械工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.10873

摘要

本研究旨在發展一套運用數位微鏡晶片之全域式彩色差動共焦顯微系統，利用數位微鏡片能快速翻轉且精準控制的特性，控制微鏡陣列中每一個鏡片之翻轉，使入射光源依序排列形成數位結構光；並控制各個點光源之間距，大幅降低各個點光源之橫向交談，配合軸向色散之技術，將不同波長之光聚焦在不同深度，使系統不需進行縱向掃描即可獲得待測物之深度資訊。同時，可利用數位微鏡片產生一組大小不同之虛擬針孔，由其深度響應曲線全寬半高的不同，利用差動演算法以建立光強比值與深度關係之校正曲線，消除待測物反射率全域不均勻之影響，並以傅氏光學為基礎，推導出有限針孔大小之光強深度響應曲線，模擬兩大小不同針孔之差動演算法以驗證方法理論之可行性，最後透過微鏡片的依序翻轉來完成橫向掃描，取代傳統機械式的掃描，並消除機台震動造成的誤差。本研究針對階高為10.4 μm之標準光柵片進行高度之校正，以驗證系統之重複度與精度，量測結果之平均高度差為10.99 μm，重複度為0.502 μm，平均誤差為5.67%，其平均誤差來源應來自光強之跳動與光源非完全均勻，未來可透過光學系統之設計獲得改善。

關鍵字

自動化光學檢測 ； 彩色共焦 ； 全域式量測 ； 數位微鏡裝置 ； 橫向交談 ； 差動演算法

並列摘要

Full-field chromatic differential confocal measuring system by using digital micro-mirror device is proposed and implemented. With precision controlling each micro-mirror on DMD and operating with structured patterns, a DMD can function as an array of pinholes to realize full-field confocal measurement without any lateral mechanical scanning or suffering lateral signal cross talk problem encountered in conventional line-scan or full-field scan methods. By using the chromatic objective, the incident light is dispersed and the different wavelength light can simultaneously focus along a designated depth range. Thus, the technique can measure the depth information without need of any vertical scanning. Meanwhile, the proposed method uses DMD to produce two sets of different sizes of virtual pinholes formed by two sizes of illuminated pixel zones on DMD. Because the FWHM of the depth response curve of each illuminated zone is different from each other, a differential confocal algorithm can be used to establish the differential confocal ratio which can eliminate varying influence of surface reflectivity and establish a depth transform curve from the differential ratio. To test the feasibility of the proposed method and verify its measurement accuracy, a pre-calibrated step height was measured by the developed measuring system. From the preliminary experimental results, it is verified that the repeatability with one-standard deviation on the height measurement is 0.502 μm in a measuring rage of 20 μm while the maximum measured error is 5.67 % of the measurable range. The major error is still too excessive and is mainly caused by the dark current of the detecting sensor and lighting intensity instability, in which the differential ratio cannot be established accurately. The problem will be continuously tackled by improving the detection accuracy of the differential ratio.

並列關鍵字

automated optical inspection (AOI) ； chromatic confocal microscopy ； surface profilometry ； differential algorithm ； full-field measurement ； digital micro-mirror device (DMD).

參考文獻

[1] Tanaami, T., et al. "High-speed 1-frame/ms scanning confocal microscope with a microlens and Nipkow disks." Applied Optics, 2002. 41: p. 4704-4708.

[2] Lee, C., et al. "Noninterferometric differential confocal microscopy with 2-nm depth resolution." Optics Communications, 1997. 135(4–6): p. 233-237.

[3] Wang, Y., et al. "A lateral differential confocal microscopy for accurate detection and localization of edge contours." Optics and Lasers in Engineering, 2014. 53(0): p. 12-18.

[4] Zhao, W., et al. "Improvement of confocal microscope performance by shaped annular beam and heterodyne confocal techniques." Optik - International Journal for Light and Electron Optics, 2005. 116(3): p. 111-117.

[5] Molesini, G., et al. "Focus-wavelength encoded optical profilometer." Optics Communications, 1984. 49(4): p. 229-233.