The negative photoresist SU-8 has attracted much research interest as a structural material for creating complex three-dimensional (3D) microstructures incorporating hidden features such as microchannels and microwells for a variety of lab-on-a-chip and biomedical applications. Achieving desired topological and dimensional accuracy in such SU-8 microstructures is crucial for most applications, but existing methods for their metrology, such as scanning electron microscopy (SEM) and optical profilometry, are not practical for non-destructive measurement of hidden features. This paper introduces an alternative imaging modality for non-destructively characterizing the features and dimensions of SU-8 microstructures by measuring their transmittance of 365 nm ultraviolet (UV) light. Here, depth profiles of SU-8 3D microstructures and thin films are determined by relating UV transmittance and the thicknesses of SU-8 samples imaged in the UV spectrum through the Beer-Lambert law applied to the images on a pixel-by-pixel basis. This technique is validated by imaging the UV transmittance of several prototype SU-8 3D microstructures, including those comprising hidden hollow subsurface features, as well as SU-8 thin-films, and verifying the measured data through SEM. These results suggest that UV transmittance imaging offers a cost-effective, non-destructive technique to quickly measure and identify SU-8 microstructures with surface and hidden subsurface features unlike existing techniques.

中文翻译：

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用于紫外敏感聚合物微结构的无损计量和表征的新型成像技术

负光刻胶 SU-8 作为一种用于创建复杂的三维 (3D) 微结构的结构材料吸引了很多研究兴趣，该结构包含隐藏的特征，例如用于各种芯片实验室和生物医学应用的微通道和微孔。在此类 SU-8 微结构中实现所需的拓扑和尺寸精度对于大多数应用至关重要，但现有的测量方法，如扫描电子显微镜 (SEM) 和光学轮廓测量法，对于隐藏特征的非破坏性测量并不实用。本文介绍了一种替代成像模式，通过测量 365 nm 紫外 (UV) 光的透射率来无损表征 SU-8 微结构的特征和尺寸。这里，SU-8 3D 微结构和薄膜的深度分布是通过将紫外线透射率和在紫外线光谱中成像的 SU-8 样品的厚度相关联来确定的，这些样品的厚度是通过逐像素应用于图像的比尔-朗伯定律来确定的。该技术通过对几种原型 SU-8 3D 微结构的紫外线透射率进行成像来验证，包括那些包含隐藏的中空地下特征的微结构，以及 SU-8 薄膜，并通过 SEM 验证测量数据。这些结果表明，与现有技术不同，紫外线透射成像提供了一种具有成本效益的非破坏性技术，可以快速测量和识别具有表面和隐藏的亚表面特征的 SU-8 微结构。