Quantitative acoustic microscopy for characterization of the interface strength of diamond-like carbon thin films

Diamond-like carbon (DLC) films are emerging to be ideal materials in a variety of semiconductor, display, and film media applications. As with any deposited film, adhesion of the film to the substrate is of critical importance. The main objective of this paper is to report on the development of a technique based on acoustic microscopy for the quantitative characterization of the interface strength of thin (submicrometer) films. Preliminary results from 0.5 μm DLC films are presented to establish the feasibility of the new technique. Theoretical models of wave propagation indicate the Rayleigh wave velocity (at 600 MHz) is sensitive to the interface condition and could potentially be used to characterize the same. Acoustic material signatures (AMS) of DLC films which had varying levels of adhesion to silicon coated titanium substrates were obtained at 600 MHz using an acoustic microscope. The Rayleigh velocity (extracted from the AMS) had a strong correlation with the adhesion strength measured destructively using a pull tester. A model-based methodology for prediction of the interface strength of thin films through acoustic microscopy is also addressed.