CH4或CH4+Ar介质阻挡放电中的离子能量和类金刚石膜制备

实验上，利用纯CH₄及CH₄+Ar在几百帕量级气压下的介质阻挡放电 制备类金刚石膜，研究了气压p与放电间隙d乘积(pd值)以及Ar的体积百分比R_Ar 对膜硬度的影响.理论上，从离子与气体分子的双体碰撞出发，利用较高折合电场强度E/n( 电场强度与粒子数密度之比)下离子及中性粒子速度分布的双温模型、离子在其他气体中运 动时遵守的朗之万方程及离子在混合气体中运动时遵守的布兰克法则，对CH⁺4和Ar⁺离子能量进行了分析.结果表明：1)CH₄介质阻挡 放电中，pd值由1.862×10³Pa mm降低至2.66×10²Pa mm时，CH+₄能量由5.4eV增加到163eV，类金刚石膜硬度由2.1GPa提高到17.6GPa ; 2) 保持总气压p=100Pa,放电间距d=5mm不变，在CH₄中加入Ar气，当R_Ar 由20％增加至83%时，CH⁺₄的能量由69eV增加到92eV,而Ar＋能量由93eV降低至72eV.虽然CH⁺₄能量增加有助于提高 沉积膜硬度，但当R_Ar大于67%，高强度Ar⁺轰击会导致膜表面石墨 化，膜硬度降低.为了验证离子能量理论模型的正确性，实验测量了H₂介质阻挡 放电中离子能量，测量结果与理论计算之间最大相对误差为16%. 关键词： 离子能量 介质阻挡放电 类金刚石膜

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

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 (R_{Ar) 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< sup>+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.