Silicon-via (Si-via) hole metrology and inspection by grayfield edge diffractometry

Abstract

This paper introduces a novel silicon-via (Si-via) hole metrology and inspection method based on grayfield edge diffractometry, enabling simultaneous measurement of Si-via hole geometry and roughness. The edge diffraction interferogram occurs when incident light interacts with the via edge. A grayfield imaging system consists of a pair of axicon lenses, two objective lenses and imaging system was developed to capture the fringes. Here, a pair of axicon lenses shape the collimated beam into a donut-shaped beam profile. The shaped beam has an adjustable focus point, allowing scanning along the Si-via hole depth axis. The cross-correlation approach to comprehensive analysis of the fringes was performed to extract via roundness and via-edge roughness (VER). The relationship between cross-correlation output and VER was characterized, assuming the line-edge roughness (LER) represents VER. The proposed method was cross-verified with the conventional microscopy approach. In addition, the through-focus scanning optical microscopy method was also used to intuitively characterize the fringe feature in three-dimension. In conclusion, the proposed method can characterize Si-via hole's roundness and estimate VER, showcasing potential adaptability for automated Si-via hole inspections in wafer-level hybrid bonding applications.