(607d) Diagnostics of Inductive-Coupled Ch2f2/Cf4 Plasma Using Langmuir Probe and Quadruple Mass Spectrometry

Wei, T. - Presenter, Chung-Yuan University
Liu, C. - Presenter, Chung-Yuan University

CH2F2/CF4 plasma is widely used in the deposition of fluorocarbon film and anisotropic etching of SiO2 film. A detailed understanding on the plasma characteristics is essential to process development and control. In this work, the plasma diagnostics tools (including OES, Langmuir probe and QMS) were used to investigate the influences of operating parameters on the inductive-coupled CH2F2/CF4 plasma. A model for Langmuir probe characteristics was developed to evaluate the electro-negativity of the plasma containing multiple ionic species. The diagnostics results were then correlated to the properties of deposited fluorocarbon films. It was found that CH2F2/CF4 plasma is highly electro-negative at low-power and high-pressure conditions. The primary negative ion is F- in CH2F2/CF4 plasma. The dominant positive ion is CHF2+ for pure CH2F2 plasmas at low RF powers. As the input power is increased, abundant C3 ions (C3Fy+ or C3HxFy+) are produced, C3H3F2+, C3H2F3+ and C3HF4+ ions being the dominant ones. Only trace amounts of C2 ions exist in the plasma. The ion composition in the pure CH2F2 plasma is correlated to the Power/Pressure ratio. When only 5% CF4 is added to CH2F2 plasma, the dominant positive ion shifts to CF3+, and the most abundant C3 ions changes from C3H3F2+ to C3HF4+. The F/C ratio of the deposited film is found to correlate well to the F/C ratio of the positive ions in the plasma. Although the plasma density is only slightly changed with increasing the CF4 flow rate, the dominant positive-charged species become all perfluorocarbon ions when the feed contains 40% CF4, which results in the drastic decrease of deposition rate.