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

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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.