Deposition of diamond-like carbon and analysis of ion energy in CH4 or CH4+Ar dielectric barrier discharge plasma

Abstract

Diamond-like carbon (DLC) films were deposited by dielectric barrier discharge ( DBD) from CH4 or CH4 +Ar at pressure of several hundred Pa . The dependence of the film hardness on the product of p and d (p is the gas pr essure and the d is the discharge space) and Ar volume concentration (RAr) was investigated experimentally. The kinetic energies of CH+4 and Ar+ ions were analyzed theoretically based on the two-t emperature model for high reduced field E/n (the ratio of electric field strengt h to the gas number density), in which ions were assigned a temperature much hig her than the gas temperature, on the Langevin equation in other gas and on the B lanc law in mixed gases. The results showed that, 1) for CH4 DBD, whe n decreasing pd from 1.862×103Pa mm to 2.66×102Pa mm, th e kinetic energy of CH+4 increases from 5.4 to 163eV, whil e the hardness of deposited DLC films increases from 2.1 to 17.6 GPa. 2) For CH+4Ar DBD, when increasing Ar volume concentration from 20% to 83%, the kinetic energy of CH+4 increases from 69 to 92 eV, whereas the kinetic energy of Ar+ decreases from 93 to 72eV. The increase of film hardness with increasing Ar volume concentration up to 67% can be attributed to the increase of CH+4 kinetic energy. Howe ver, the impinging of energetic Ar+ on the film surface reduces the f ilm hardness owing to graphitization. For verification of the theoretical model on ion energy analysis, the kinetic energy of ions in H2 DBD were mea sured and compared with that from theoretical analysis.