Elastic modulus and structural evolution of diamond-like carbon films deposited by RF-PACVD

Abstract

Dependence of the elastic modulus of diamond-like carbon (DLC) films on film thickness was investigated by the recently suggested free overhang method. The DLC films of thickness ranging from 50 to 1300 nm were deposited on Si (100) wafer by 13.56-MHz radio frequency plasma assisted chemical vapor deposition (RF-PACVD) process. In the free overhang method, the elastic modulus of thin film could be measured without considering the substrate effect since the substrate was completely excluded from the measurement. It was observed that the elastic modulus of the very thin film was smaller than that of the thick film in both cases where the ion energy was higher and lower than the optimum value for dense and hard DLC film deposition. However, at the optimum ion energy, the elastic modulus was independent of film thickness. Raman spectroscopy analysis showed that the change of elastic modulus in very thin DLC films was intimately related to the structural evolution which occurred in the initial stage of the film deposition. When the ion energy was lower than the optimum value, more polymeric component was deposited in the initial stage. On the other hand, a more graphitic component was involved in very thin films at an ion energy higher than the optimum value.