Study On Propagation Characteristics Of Surface Acoustic Waves In ULSI Interconnected Layer Structures And Applications

Laser-generated surface acoustic waves technology is an accurate,fast,and non-destructive detection technique,which is suitable for characterizing the mechanical properties of ULSI interconnect films.In this paper,the propagation characteristics of surface acoustic waves in the layer structure of ULSI interconnects are deeply studied,and some innovations and improvements of characterization method and experiment are developed.In characterization method,the model of surface acoustic waves propagating in semi-infinite solids is introduced.Using the characteristic that surface acoustic waves propagate along different crystal directions with different propagation velocities in anisotropic substrates,a method of that measure Young's modulus and density of film simultaneously is proposed.Measured two experimental curves of the two crystal orientations of the sample,and the two parameters of the film could obtain by matching the two curves.The model of surface acoustic waves propagating in single layer film/substrate is introduced.The relationship between the dispersion curve and film ? substrate parameters is summarized by numerical examples.Especially,the relationship between the dispersion curve in a single layer film/substrate and the film thickness is given from a qualitative and quantitative view.A method for thickness determination based on theoretical dispersion curve v(fh)and experimental dispersion curve v(f)is developed.The method provides a series of thickness values at different frequencies f,and the mean value is considered as the final result of the measurement.The thicknesses of six interconnect films are determined by SAWs,and the results are compared with the manufacturer's data.The relative differences are in the range from 0.4 % to 2.18 %,applying the same principle,a method for thickness determination through an experimental curve is proposed.The film thicknesses of the three films are measured.Compared with the manufacturer's data,the relative differences are in the range of 0.88% to 2%.The model of surface acoustic waves propagating in Multilayer film/substrate is analyzed.The surface acoustic wave dispersion curves of low-k/SiO2/Si(110),low-k/Cu/Si(110),Cu/SiO2/Si(110)are calculating.The relationship between the dispersion curve in Multilayer film/substrate and film,substrate parameters is summarized.In the experiment,an alignment device for the surface acoustic wave experimental system is designed,which solves the problem that the optical adjustment process is cumbersome,slow,and the adjustment effect is low.The efficiency of the optical adjustment is greatly improved.A double-probe piezoelectric sensor for measuring the surface acoustic wave velocity is also designed,which eliminates the measurement error of the distance x2-x1 and effectively improves the accuracy of the surface acoustic wave velocity measurement.