Wang Dezhao, Zhou Weihu, Zhang Zili, Meng Fanchang
College of Opto-Electronic Engineering, Changchun University of Science and Technology, Changchun 130022, China.
Photoelectric Technology R&D Center, Institute of Microelectronics of the Chinese Academy of Sciences, Beijing 100029, China.
Sensors (Basel). 2024 Aug 9;24(16):5157. doi: 10.3390/s24165157.
Cu pillars serve as interconnecting structures for 3D chip stacking in heterogeneous integration, whose height uniformity directly impacts chip yield. Compared to typical methods such as white-light interferometry and confocal microscopy for measuring Cu pillars, microscopic fringe projection profilometry (MFPP) offers obvious advantages in throughput, which has great application value in on-line bump height measurement in wafer-level packages. However, Cu pillars with large curvature and smooth surfaces pose challenges for signal detection. To enable the MFPP system to measure both the top region of the Cu pillar and the substrate, which are necessary for bump height measurement, we utilized rigorous surface scattering theory to solve the bidirectional reflective distribution function of the Cu pillar surface. Subsequently, leveraging the scattering distribution properties, we propose a hybrid bright-dark-field MFPP system concept capable of detecting weakly scattered signals from the top of the Cu pillar and reflected signals from the substrate. Experimental results demonstrate that the proposed MFPP system can measure the height of Cu pillars with an effective field of view of 15.2 mm × 8.9 mm and a maximum measurement error of less than 0.65 μm.
铜柱用作异构集成中3D芯片堆叠的互连结构，其高度均匀性直接影响芯片良率。与用于测量铜柱的典型方法（如白光干涉测量法和共聚焦显微镜法）相比，微观条纹投影轮廓测量法（MFPP）在吞吐量方面具有明显优势，这在晶圆级封装的在线凸块高度测量中具有很大的应用价值。然而，具有大曲率和光滑表面的铜柱给信号检测带来了挑战。为了使MFPP系统能够测量铜柱顶部区域和基板，这对于凸块高度测量是必要的，我们利用严格的表面散射理论求解铜柱表面的双向反射分布函数。随后，利用散射分布特性，我们提出了一种明暗场混合MFPP系统概念，能够检测来自铜柱顶部的弱散射信号和来自基板的反射信号。实验结果表明，所提出的MFPP系统能够测量有效视场为15.2 mm×8.9 mm、最大测量误差小于0.65μm的铜柱高度。
