Buried Void Inspection in High Bandwidth Memory with Picosecond Laser Acoustics

Abstract

Hybrid bonding is essential for advanced semiconductor packaging, but voids formed during the process can compromise reliability and performance. Traditional non-destructive inspection methods struggle to detect sub-micron voids beneath silicon or metal layers. This work introduces Picosecond Laser Acoustics (PLA), a technique using femtosecond laser pulses to generate and detect acoustic echoes from buried interfaces. Operating in an ASOPS configuration, PLA enables high-resolution imaging of voids as small as 1 µm. Principal Component Analysis (PCA) is used to visualize defects from acoustic and thermal signals. PLA is non-destructive, coupling-free, and ideal for hybrid bonding process control.