Measurement On Adhesion Property Of Low-k Thin Film By Surface Acoustic Waves Using The Cohesion Zone Model

With the rapid development of microelectronics industry we also face with more and more problems. The low-k film poor interfacial adhesion character largely limits its applications in ultra large scale integrated circuit manufacturing process. The adhesion strength between the low-k film and substrate is an important performance index, and the evaluating of the quality of the coating adhesion strength is the important precondition for process optimization. At the present stage, the main method of measuring thin film adhesion property essentially plate with an external load, and measure critical load value when the film damages. So these measurement methods have damage to the samples, and the results of measuring is not accurate. An accurate and nondestructive method of measuring the low-k film adhesion is very significant and highly desired. The surface acoustic wave technology uses the dispersion phenomena when surface waves propagate in the film and substrate structure to nondestructively detect the mechanical properties of low-k film. Because of the surface acoustic wave being sensitive to the characteristics of film near to the surface, the surface acoustic wave technology could not only measure Young's modulus of the thin film, but also detect the adhesion property between film and substrate. SAW technology is a kind of advanced and innovative methods of ULSI interconnection film mechanical properties testing.This paper establishes the cohesion zone model which can be applied to the characterization of film and substrate, and derives the relations of parameters of cohesion zone model. The CZM is applied to finite element simulation of interface adhesion between film and substrate. This paper uses the numerical examples of finite element method to identify the key parameters affecting the film adhesion, maximum normal traction (?max) and the normal characteristic length (?n). The method of variable controlling is applied to determine the proportional relationship between the key parameters and the adhesion quality. Appling wave equations of the surface wave propagating in the solid medium, the paper uses the matrix calculation tool to determine the relationship between the surface wave dispersion curves and the key parameters which character the film adhesion, and the results can be applied to dispersion curve matching that determine the film adhesion. In this paper, laser stimulated surface wave technique is applied in adhesion properties measurement of the dense and porous low-k films, and results of the surface acoustic wave detection are compared with the traditionally scratch method. The adhesion properties determined by CZM-SAW technique have the same trends with the results tested from the traditional nanoscratch technique. The testing results of surface acoustic wave method have more resolution ratio, which proves the feasibility of detecting the adhesion property of the film and substrate applying the surface acoustic wave technology, and the surface acoustic wave technology has great application prospect.