Scanning Acoustic Microscope of 3D-Interconnect

The College of Nanoscale Science and Engineering of the University at Albany in collaboration with International SEMATECH is investigating the use of Scanning Acoustic Microscope (SAM) for analyzing 3D Interconnects. SAM is a non‐destructive metrology technique which utilizes high frequency ultrasound to generate a microscopic image of the internal parts of a specimen. The goal of this project is to develop microscopic techniques for evaluating Through‐Silicon Vias (TSVs) for 3D‐Interconnects. Preliminary data shows voids and other defects in the interface between bonded wafers as shown in Figure 1. Our SAM laboratory system operates at 230 MHz and has a spatial resolution of 5–10 μm and focal length of 5.9 mm on a silicon wafer. The spatial resolution and sampling depth depend on the ultrasonic frequency, sound velocity, focal length and diameter of piezoelectric crystal. Typically, the silicon wafers have a thickness of 775 μm before they are bonded. Our initial work is focused on blanket wafers in order to develop the bonding process. The next step is to bond wafers with test die where the patterning obscures the interface. This paper will discuss the limitations of SAM and compare it to infrared microscopy which is another important imaging capability for 3D Interconnect. We also discuss the current status of research into more advanced acoustic microscopy methods and how this might impact 3D Interconnect imaging.