LSAWs测量低介电常数介质薄膜杨氏模量的信号处理

Signal Processing in the LSAWs Experiment for Determining Young′s Modulus of Low-k Film

利用脉冲激光激发超声表面波测量低介电常数介质薄膜杨氏模量时(LSAWs实验),必须对实验信号进行有效处理来拟合出表面波在待测样品表面传播时产生的色散曲线.设计了专用的程序滤波器对LSAWs实验中采集的原始信号进行滤波,有效抑制了信号噪声.滤波器加载的Kaiser窗降低了“吉布斯”效应的影响.对原始信号的增零处理增加了频谱的细腻程度.通过傅里叶变换获得了LSAWs实验有效信号的频谱.根据实验信号的相频特性曲线,通过最小二乘法拟合出了LSAWs实验中声表面波在待测样品表面传播时产生的色散曲线.实验表明,阻带噪声衰减为60 dB,获得了截止频率高达120 MHz的色散曲线.

It is essential to reduce the noises of the detected signals in the equipment of measuring the Young＇s modulus of low-k film by laser-generated surface acoustic waves （LSAWs）. A filter was designed by using Matlab software to suppress the noises of the collected signals originated from the LSAWs experiment. The application of Kaiser window decreased the ＂Gibbs＇ effect＂. A dedicated spectrum was obtained by adding extra zeros to the original signals. The qualified phase spectrum was achieved by the FFT process on the filtered signals. A smooth dispersion curve was obtained by the least square method. Results show that a dispersion curve with the cut-off frequency of up to 120 MHz can be achieved with the noise decrease of 60 dB in the stopband.