Nondestructive Determination of Young's Modulus of Interconnecting Thin Films by a Broadband Surface Acoustic Wave‐Interdigital Transducer

Abstract

A facile and rapid method for nondestructive testing (NDT) of the Young's modulus of interconnecting thin films using a broadband surface acoustic wave‐interdigital transducer (SAW‐IDT) is presented herein. A linear periodic SAW‐IDT with 20–125 MHz is designed and fabricated to excite surface acoustic wave (SAW) signals on the samples. By applying burst excitations under different frequencies, the SAW waveforms are picked up by a miniaturized piezoelectric transducer and processed by slant stack transformation. Consequently, the SAW dispersion curves over a wide frequency band are established to match the film parameters. Young's modulus of the 100 and 300 nm thickness of SiO2 films and the 800 and 1500 nm low‐k polyimide (PI) films is characterized. The nanoindentation method, as a control experiment, is also carried out to verify the accuracy of the SAW method, and the test results show that the SAW method can eliminate the effect of the substrate with higher precision. This work shows the advantage of the NDT technique by SAW‐IDT in measuring the Young's modulus of ultrathin films with low cost, controllable frequency range, and high accuracy.

Simultaneous Determination of Young's Modulus and Density of Ultrathin Low‐k Films Using Surface Acoustic Waves

“…The calculation procedure was described in more detail in our previous research. [ 14 ] By performing a peak‐finding operation on each column of the pixel matrix plot, the velocity at each frequency point can be determined, allowing extraction of the SAW dispersion curve. The red solid curve in Figure 6c represents the corresponding experimental dispersion curve obtained through the slant stack method, with the fitted dispersion curve derived through the least square method.…”

“…By analyzing the SAW dispersion curve, the unknown parameters of the film can be determined. [12][13][14] Various methods have been applied to excite Rayleigh-type SAW, among which electronic microdevices reliant on SAW propagation have been notably popular for their low manufacturing expenditure and high frequency. [15][16][17] SAW-based devices, which utilize interdigital transducers (IDT) to generate ultrasonic waves in piezoelectric crystals, find wide application in electronic equipment.…”

“…Previous research successfully measured Young's modulus of polyimide films using a SAW‐IDT with a linear periodic structure. [ 14 ] In this work, a SAW‐IDT‐based experimental system is presented for accurately determining Young's modulus and density of ultrathin porous BD films deposited on a silicon substrate. The high‐frequency SAW‐IDT is designed with LFM, and the SAW dispersion curve is calculated by processing the SAW waveforms using the slant stack method.…”