Nanoscratch evaluation of adhesion and cohesion in SiC/low-k/Si stacked layers

Abstract

A nanoscratch method combined with atomic force microscope and transmission electron microscope observations was used to estimate the adhesive and cohesive strengths of SiC/low-k/Si stacked layers with the aim of correlating the fracture strength with the results of chemical mechanical polishing (CMP) tests. It was found that the friction coefficient was an effective signal for detecting the occurrence of failure in the microstructure during the scratch test. Fracture strength was characterized using the critical normal load at the first abrupt decrease in the friction coefficient. A specimen (A) having a low-k layer with a lower modulus and lower hardness displayed a lower friction coefficient, a lower critical load, and ductile adhesive failure resulting from delamination at the interface between the low-k layer and Si substrate. In contrast, a specimen (B) having a low-k layer with a higher modulus and higher hardness exhibited a higher friction coefficient, a higher critical load and brittle cohesive failure that occurred in the low-k layer. It was also found that specimen A always had a higher critical load level than specimen B regardless of the scratching speed, loading rate, and stylus radius. Dependence of the critical load on specimen thickness was also examined. These nanoscratch measurements corresponded with the results of the CMP process, which suggests that the process characteristics can be predicted with this nanoscratch method.