A comparative study on the measurement of toughness of stacks containing low-k dielectric films

Good adhesion strength of thin film stack is desirable for the integrated circuits (IC) manufacturing stage such as chemical mechanical planarisation (CMP). The scratch test and four-point bending test are two most commonly used methods to find the adhesion properties of thin film because of their simplicity and quantifiability. In this research, scratch test is used to find the practical adhesion energy (Wpa) of thin film stack and four-point bending test is used to find the critical strain energy release rate (Gc). The comparison of Wpa from scratch test and Gc from four-point bend test reveals that, for the same thin film stack, Wpa value is comparatively higher than Gc. The scratch test is semi-quantitative, in that the normal load at which a predefined failure event or delamination occurs is defined as a measure of adhesion. However, the four-point bending test is more quantitative in finding the adhesion properties. Thus, for practical application, such as CMP process, the Gc measurements from four-point bending test are recommended as references.