Development of new wall control method and plasma-wall interaction in fluorocarbon plasmas

在使用高密度氟碳等离子体进行二氧化硅刻蚀时，存在各种问题，尤其是工艺的重复性。其中一个原因被认为是由于离子诱导的等离子体成分的变化，从沉积氟碳聚合物薄膜的壁上分离出来。在本项目中，我们开发了抑制聚合物沉积以及自由基密度随时间变化的新技术。基于离子轰击的两种方法，即所谓的交替离子轰击法和等离子体电位振荡法，抑制了腔体壁上的聚合物沉积。在这些方法中，离子轰击能量由射频偏置控制。沉积速率随离子轰击能量的增加而降低，当离子轰击能量超过~100 eV时，聚合物沉积消失。同时对氟碳自由基的测量表明，聚合物沉积的抑制使自由基密度的时间变化，即等离子体成分的减少成为可能。这些结果表明，本技术对提高氧化物刻蚀工艺的重复性是有效的。

In silicon dioxide etching using high-density fluorocarbon plasmas, there are various problems, especially for process repeatability. One of the reasons is believed to be variations of plasma composition due to ion-induced speices desoption from walls on which fluorocarbon polymer films are deposited. In the present project, we have developed novel techniques for the suppression of the polymer deposition as well as the time variation of radical densities.The polymer deposition at chamber walls was suppressed by two methods based on ion bombardment, so-called alternating ion bombardment method and plasma potential oscillation method. In these methods, the ion bombarding energy was controlled by RF bias. The deposition rate decreased with the ion bombarding energy, and the polymer deposition vanished for the ion bombarding energy over 〜100 eV.Simultaneous measurements of fluorocarbon radicals revealed that the suppression of the polymer deposition made it possible to reduce the time variation of radical densities, i.e. plasma composition. These results suggested that the present techniques were effective for improvement of the process repeatability in the oxide etching.