Nondestructive determination of interfacial adhesion property of low-k/Si by the surface acoustic waves

Nondestructive surface acoustic wave (SAW) technique promoted for interfacial adhesion investigation is employed to study the adhesion properties of both the porous and the dense low dielectric constant (low-k) films deposited on the silicon substrate. Spring boundary model is employed by introducing the parameters of distributed shear and normal spring constant per unit area (KT and KN) between the film and the substrate to take the adhesion property into account to calculate the theoretical SAW dispersion curves. Broadband SAW signals are generated by short pulse ultraviolet laser source and detected by a piezoelectric transducer. Interfacial adhesion properties of the low-k samples can be obtained by fitting the experimental dispersion curve with the theoretical ones. The smooth experimental dispersion curves with maximum frequency up to 150 and 200 MHz are achieved for the porous and dense low-k samples, respectively. The determination result indicates that the adhesion property of dense low-k film is much better than that of the porous low-k sample used in this study. The determined adhesion result by SAW exhibits the same trend with the test of the nanoscratch.