Biaxial Elastic Modulus of Very Thin Diamond-like Carbon (DLC) Films

Jin-Won Chung, Churl-Seung Lee, Dae-Hong Ko, Jun Hee Han, Kwang-Yong Eun and Kwang-Ryeol Lee

Elastic modulus of very thin diamond--like carbon (DLC) film could be measured by recently suggested free hang method.  The DLC films of thickness ranging from 33 to 1100 nm were deposited on Si wafer by radio frequency plasma assisted chemical vapor deposition (r.f.-PACVD) or filtered vacuum arc (FVA) process.  Because the substrate was removed to obtain sinusoidal free hang of the DLC film, this method has an advantage over other methods in that the measured value is not affected by the mechanical property of the substrate. This advantage is more significant when measuring the mechanical property of very thin film deposited on the substrate of large difference in mechanical properties.  The measured biaxial elastic modulii were reasonable values as can be judged from the plain strain modulus of thick films measured by nanoindentation.  While the biaxial elastic modulus of the film deposited by FVA is independent of the film thickness, the film deposited by r.f.-PACVD exhibited the decreased elastic modulus with decreasing film thickness when the film is thinner than 500 nm. Although the reason for the different behavior could not be clarified at the present state, difference in the structural evolution during the initial stage of the film growth seems to be the reason.