Development of Negative Oxygen and Fluorine Ion Sources with Helicon-Wave Discharge

在这项工作中，开发了用于材料加工的高效负氧离子和氟离子源。构建了用于产生负离子的螺旋波放电装置。产生了10^&lt；12&gt；-10^&lt；13&gt；cm；-3&gt；的高密度氧等离子体和CF4等离子体。为了有效地产生负离子，在高密度等离子体中形成了两种等离子体相，即在放电开启阶段形成5-6 eV的高密度高温等离子体，在放电截止阶段形成约1 eV的高密度低温等离子体。飞行时间质谱仪和激光光解离实验证实，在放电欧姆的余辉中有效地产生了负离子。在空间上控制等离子体参数形成的片状等离子体的外部低温区也有效地产生了负离子，高密度氧等离子体和CF4等离子体中的主要负离子物种分别是原子负离子O^-和F^-。原子负离子随着电子密度的增加而增加，负离子的产生过程主要是慢电子与被激发分子或分子自由基的解离结合，主要衰变过程是正负离子之间的相互中和，通过形成高密度的高温等离子体和低温高密度的等离子体可以实现高效的负离子产生。通过在时间和空间上控制高密度氧和氟等离子体的参数，可以形成具有两个相或两个区域的等离子体。通过这项工作，得出了高效负离子源设计的指导原则。

In this work, efficient negative oxygen and fluorine ion sources for materials processing have been developed.A helicon-wave discharge device for the production of negative ions was constructed. High-density oxygen and CF_4 plasmas of 10^<12>-10^<13> cm^<-3> were produced. Two kinds of plasma phases were formed in the high-density plasmas for the efficient negative ion production, namely a high-density and high-temperature plasma of 5-6 eV in the discharge-ON phase, and a high-density and low-temperature plasma of about 1 eV in the discharge-OFF phase. It was confirmed by time-of flight mass spectrometry and laser photodetachment that negative ions were produced efficiently in the afterglow of the discharge-OFF ohase. Negative ions were also efficiently produced in the outer low-temperature region of a sheet plasma, which was formed by controlling plasma parameters spatially.The dominant negative ion species in the high-density oxygen and CF_4 plasmas were atomic negative ions, O^- and F^-, respectively. The atomic negative ions increased with increase in electron density.The main production process of negative ions was dissociative attachment of slow electrons to excited molecules or molecular radicals, and the dominant decay process was mutual neutralization between negative and positive ions.Efficient negative ion production can be realized by forming a high-density and high-temperature plasma, and a low-temperature and high-density plasma. The plasmas with the two phases or regions can be formed by controlling parameters of high-density oxygen and fluorine plasmas temporally and spatially. A guiding principle of the design for efficient negative ion sources has been obtained by this work.