Comparative study of deposition characteristics a-C:H films by plasma CVD using methane, acetylene, and cumene

High durability of hydrogenated amorphous carbon (a-C:H) films is one of the significant interests for improving their performance as hard masks in semiconductor processes. In this study, to achieve high-density, low-stress a-C:H films with high deposition rates, we used plasma chemical vapor deposition (CVD) to fabricate a-C:H films using uncommon hydrocarbons precursors like cumene (C₉H₁₂) and compared the film deposition characteristics with conventional hydrocarbons precursors like methane (CH₄) and acetylene (C₂H₂). We evaluated the deposition characteristics of a-C:H films using all the precursors in terms of their concentration, reactor pressure, and self-bias voltage. Additionally, we analyzed the structure of the a-C:H films using Raman spectroscopy. Among all the films deposited, the deposition characteristics (mass density, deposition rate, and stress) of films deposited using cumene demonstrated superior characteristics compared to other molecules, suggesting its potential suitability for advanced applications. The films for cumene showed a wide variation of mass density from 1.0 g/cm³ to 2.0 g/cm³ with changing self-bias voltage. At low self-bias voltages (60 V–230 V), the films were polymer-like with a high hydrogen content, whereas, at high self-bias voltages (580 V–1100 V), the films were hard with a low hydrogen content. On the other hand, each film with methane and acetylene showed a narrower variation of mass density from 1.4 g/cm³ to 2.0 g/cm³ with changing self-bias voltage than that for cumene. These results suggest that the film structure can be diversely controlled through the self-bias voltage depending on the number of carbon atoms in one molecule rather than the type of molecular species.