Coating thickness estimation in silicon wafer using ultrafast ultrasonic measurement

Peipei Liu; Kiyoon Yi; Hoon Sohn

doi:10.1117/12.2558380

22 April 2020 Coating thickness estimation in silicon wafer using ultrafast ultrasonic measurement

Peipei Liu, Kiyoon Yi, Hoon Sohn

Proceedings Volume 11381, Health Monitoring of Structural and Biological Systems XIV; 113811E (2020) https://doi.org/10.1117/12.2558380
Event: SPIE Smart Structures + Nondestructive Evaluation, 2020, Online Only

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 (10¹² Hz), and measure the corresponding responses with a sampling rate up to PHz (10¹⁵ Hz). In this system, the femtosecond pulse laser beam is split into pump and probe pulses for a pulse-echo ultrasonic measurement. The pump pulse produces ultrafast ultrasound onto the target silicon wafer, and the ultrasound travels through the thickness direction. Then, the waves reflected from the coating layer are measured using an optically delayed probe pulse. Using the proposed system, the coating thicknesses of silicon wafers in the range of 50 nm to 200 nm were successfully estimated.

Citation Download Citation

Peipei Liu, Kiyoon Yi, and Hoon Sohn "Coating thickness estimation in silicon wafer using ultrafast ultrasonic measurement", Proc. SPIE 11381, Health Monitoring of Structural and Biological Systems XIV, 113811E (22 April 2020); https://doi.org/10.1117/12.2558380

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