Experimental investigation of ion energy distributions in a dual frequency capacitively coupled Ar/CF4 plasma

摘要

An energy resolved quadrupole mass spectrometer was adopted to determine ion energy distributions (IEDs) impinging on the ground electrode in a dual frequency (DF) capacitively coupled Ar/CF4 (95%/5%) plasma. The influences of discharge parameters, such as power of low frequency (LF power) source, frequency of LF source (LF frequency), and gas pressure, on IEDs of Ar+ and CF3+ were investigated. The enhancement in LF power, which hence means the increase in sheath potential, results in a significant shift in the IEDs of Ar+ and CF3+ toward higher energy area and then a broader energy width. However, the increase in LF frequency leads to narrow and unimodal IEDs, which is probably because the regime of DF CCP has changed during the process. The pressure has a remarkable effect on IEDs structure, i. e., the exhibited saddle-shaped structure of IEDs is obvious in a collisionless sheath at lower pressure but becomes eliminated in a collision sheath at higher pressure. The Ar+ IEDs have low energy regions because of the ion-atomic resonant charge transfer process, while CF3+ ions do not. In addition, some of the experimental results are compared with simulation corresponding to our previous work, and general agreements are obtained.