Adhesion study of low-k/Si system using 4-point bending and nanoscratch test

Abstract Chemical vapour deposited (CVD) low- k films using tri-methyl-silane (3MS) and tetra-methyl cyclo-tetra-siloxanes (TMCTS) precursors were studied. A 4-point bend test (4PBT) was performed to assess the adhesion property of the low- k films to Si substrates and the results were compared with that of simpler method, nanoscratch test (NST), as a quality control tool despite its drawbacks. Adhesion energy, G c , of the low- k /Si interface as measured by 4PBT and critical scratch load, P c , as obtained by NST display a linear relationship with hardness and modulus of the low- k film. The lowering of G c as the hardness of the film decreases can be explained by the effects of the C introduction into the Si O networks found in these films. Lower carbon content for higher hardness films is thought to cause them to be more “silica-like”, and thus, exhibit better adhesion with the Si substrate. Two failure modes were observed for specimens under 4PBT. On one hand, films with low hardness ( G c ( 2 ) with an adhesive separation of low- k from the Si substrate. On the other hand, films of high hardness (>5 GPa) display interfacial energies in excess of 10 J/m 2 with delamination of epoxy from the Si substrate, thus, indicating excellent adhesion between the low- k films and Si substrate. For the low hardness films, good correlation exists between P c and G c . However, the two data points of the high hardness films that gave the two highest P c and G c values do not lie on the correlation line drawn for the low hardness film data points due to different factors governing the failure in both tests and a change in the 4PBT failure mechanism.