Sensitivity Improvements for Picosecond Ultrasonic Thickness Measurements in Gold and Tungsten Nanoscale Films  

作　　者：Jiaqi Dong Chengyuan Yao Yuanhao Zhu Shaojie Li Bowen Liu JinTao Fan Chunguang Hu Youjian Song Minglie Hu 

机构地区：[1]Key Laboratory of Opto-Electronic Information Science and Technology of Ministry of Education,School of Precision Instruments and Opto-Electronics Engineering,Tianjin University,Tianjin 300072,China [2]State Key Laboratory of Precision Measuring Technology and Instruments,Tianjin University,Tianjin 300072,China

出　　处：《Nanomanufacturing and Metrology》2024年第2期1-12,共12页纳米制造与计量（英文）

基　　金：supported by the National Natural Science Foundation of China(Grant No.52075383);the National Key Research and Development Program of China(Grant Nos.2022Y FF0708300,2022YFF0706002).

摘　　要：Picosecond ultrasonics,as a nondestructive and noncontact method,can be employed for nanoscale metallic film thickness measurements.The sensitivity of the system,which determines the measurement precision and practicability of this technique,is often limited by the weak intensity of the ultrasonic signal.To solve this problem,we investigate the distinct mechanisms involved in picosecond ultrasonic thickness measurement for two types of metals,namely tungsten(W)and gold(Au).For thickness measurement in W films,theory and simulation show that optimizing the pump and probe laser wavelengths,which determine the intensity and shape of the ultrasonic signal,is critical to improving measurement sensitivity,while for Au film measurements,where acoustic-induced beam distortion is dominant,the signal intensity can be optimized by selecting an appropriate aperture size and sample position.The above approaches are validated in experiments.A dual-wavelength pump-probe system is constructed based on a passively mode-locked ytterbium-doped fiber laser.The smoothing method and multipeak Gaussian fitting are employed for the extraction of ultrasonic time-of-flight.Subnanometer measurement precision is achieved in a series of W and Au films with thicknesses of 43-750 nm.This work can be applied to various high-precision,noncontact measurements of metal film thickness in the semiconductor industry.

关 键 词：Picosecond ultrasonics Thickness measurement Optical pump-probe Beam distortion technique 

分 类 号：TB383[一般工业技术—材料科学与工程]