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, Gc, of the low-k/Si interface as measured by 4PBT and critical scratch load, Pc, as obtained by NST display a linear relationship with hardness and modulus of the low-k film. The lowering of Gcas the hardness of the film decreases can be explained by the effects of the C introduction into the SiO 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 (5 GPa) display interfacial energies in excess of 10 J/m2with 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 Pcand Gc. However, the two data points of the high hardness films that gave the two highest Pcand Gcvalues 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. © 2005 Elsevier B.V. All rights reserved.
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