Evaluation of Thinfilm Adhesion

Abstract

Recently materials are used to artificially bonding the different materials as a conventional single material. Since the interface that is artificially bonding of different materials, relatively weak section than the film and the substrate. So, the most preferentially failure occurs in a variety of external conditions. That is why the adhesion is regarded as the major property in determining the reliability of the product in a thin film system. The study was continued by many researchers to evaluate the quantitative adhesion for a long time, so that a variety of test methods have been developed. However, most of the conventional methods for evaluating adhesion, based on interfacial separation methods and interfacial fracture method, have limitations. There are three important issues in evaluating the quantitative value of adhesion: the first, effect of film/substrate deformation and fracture is important to the adhesion test results. so, it is necessary to re-interpret the results through the analysis of the film and substrate effect. Second, need to accurate measurement of the crack length and area for a few nanometer thickness film. And third, the applicable test method limited by the characteristics of the material. In the case of hard films, fracture or delamination of the film occurs before the interface. For the bending test, film or substrate should be a bending above certain level. In other words, evaluation for very soft materials is possible. In this thesis, in order to overcome the conventional testing method limitations, a new model proposed using the instrumented indentation test(IIT). Instrumented indentation testing (IIT) has recently attracted significant research interest in this connection, since its testing procedure is relatively simple and can be performed locally and above all high load- displacement resolution. Indentation testing at the thin-film system sample may also obtain a load-displacement curve that included the effect the combination of the thin film/substrate and the interface unlike Bulk sample testing. To interpret the load-displacement curve, "Total work of indentation" in the thin-film system was defined the sum of "work of film" and "work of substrate" and "work of adhesion". Using the formulated hardness, modeling for work of film and substrate plastic deformation effect at indentation test condition. Also, assume that relatively soft materials of plastic volume constraint by the hard materials. Constraint plastic zone volume of a relatively soft material by the interface was defined by the interface parameter. The interface parameter derived using the Expanding Cavity Model and interfacial constraint effect. Based on the previous analysis deriving the work of the adhesion excluding the film/substrate deformation effect. The work of adhesion varies with the experimental conditions, it was constraint volume normalization. Finally the adhesion evaluation method using the indentation test was proposed. To verify the validity of the proposed model, compared to indentation test and SAICAS test, a kind of peel test for metal/ceramic based thin film specimens. The results between two methods show good agreement. Those results show that indentation test is effective for estimation of thin-film adhesion.