Development of Supersonic Ion-Beam Apparatus and its Application to Low-Energy Ion-Molecule Reactions

研制了一种新型超声速离子束装置，并将其应用于等离子体处理气体的低能离子-分子反应。用质谱法确定了反应速率常数和产物离子分布，用发射光谱法阐明了反应动力学。系统地研究了Ar +与卤化甲烷和简单脂肪烃的热离子-分子反应。结果表明，选用离子流管方法所报告的产物离子分布往往由于高压而偏离初始分布。大多数电荷反应都是通过近共振过程进行的，与电离的弗兰克-康登因子的大小无关。在发射光谱研究的基础上，发现激发态的形成速率常数占总反应速率常数的5%以下。研究了CO_2 +与氯甲烷的离子-分子反应，考察了原子离子与分子离子之间的反应活性差异。CO_2^+反应不仅有近共振电荷转移，而且由于产物的自由度较大，也存在非共振电荷转移。超声速离子束装置已成功地应用于简单簇离子与碳氢化合物的反应。测定了Ar_2^+、ArN_2^+和N_4^+与烃类的总反应速率常数。产物离子分布使我们得出结论，Ar_2^+的反应性与Ar_2^+相似。由于使用离子束装置可以产生高密度的反应性卤素原子，因此它将对晶圆片的反应性蚀刻非常有用。

A new type of supersonic ion-beam apparatus has been developed and applied to low-energy ion-molecule reactions of plasma processing gases. Rate constants and product ion distributions have been determined by using mass spectroscopy, whereas reaction dynamics has been clarified by using emission spectroscopy. Thermal ion-molecule reactions of Ar^+ with halogenated methanes and simple aliphatic hydrocarbons were investigated systematically. It was demonstrated that product ion distributions reported by using a selected ion flow tube method have often deviated from the initially distributions due to high operating pressures. Most of all charge-reactions were found to proceed through near-resonant processes, being independent of the magnitude of Franck-Condon factors for ionization. On the basis of emission spectroscopic studies, it was found that the formation rate constants of excited states occupy below 5% of the total reaction rate constant.Ion-molecule reaction of CO_2^+ with chloromethanes have been studied in order to examine the different reactivity between atomic ions and molecular ions. Not only near-resonant charge-transfer but also non -resonant one occurs in the CO_2^+ reactions due to a larger degrees of freedom in the products. The supersonic ion-beam apparatus has successfully applied to reactions of simple cluster ions with hydrocarbons. The total reaction rate constants of Ar_2^+,ArN_2^+,and N_4^+ with hydrocarbons have been determined. The product ion distributions led us to conclude that the reactivity of ArN_2^+ is similar to that of Ar_2^+. Since a high density of reactive halogen atoms can be generated by using the present ion-beam apparatus, it will be very useful for the reactive etching of a wafer.