Coating thickness estimation in silicon wafer using ultrafast ultrasonic measurement

Abstract

Considering the diminishing dimensions of modern silicon wafers (50-100 µm thick and their coating layers are in an nm scale) and potential defect sizes, spatial resolutions for the corresponding non-destructive evaluation (NDE) solutions should be in the order of sub-µm or nm. However, the spatial resolutions of current NDE techniques are often in the range of µm or mm. In this study, an ultrafast ultrasonic measurement system is developed using a femtosecond pulse laser. The proposed ultrafast ultrasonic measurement system can generate ultrasonic waves up to several THz (10