Run‐to‐Run Evolution of Fluorocarbon Radicals in C 4 F 8 Plasmas Interacting with Cold and Hot Inner Walls

Abstract

In order to clarify the cause of poor reproducibility of the high‐aspect‐ratio contact/via hole etching using high‐density plasmas, interactions between radical species in fluorocarbon plasmas and the inner wall of the reactor have been studied. In this paper time‐dependent evolution of wall temperatures, total pressure, and radical densities in (inductively coupled plasma) generated in both cold and hot wall reactors have been investigated and their correlations are discussed. The temperature rise of the reactor wall during plasma operation causes the decomposition of fluorocarbon polymer films which are formed from higher order fluorocarbon radicals as well as lower order radicals into lower order radicals, and consequently plasma parameters such as the pressure and radical densities fluctuate. Though intensive water cooling of the whole reactor achieved good reproducibility, a thick polymer film deposition on the wall causes another problem of particle contamination. On the other hand, wall heating at high temperatures actually suppresses polymer deposition, but it has been found that the conversion from higher order radicals to lower order radicals still occurs on the wall. The radical is predominantly produced in cold wall reactors, while the radical appeared rapidly with wall temperatures of 220–240°C, and the density equaled the radical density around 250°C. This implies that an excess amount of both radicals possibly influences the gas‐phase chemistry in the plasma and degrades the reproducibility even in a hot wall reactor. © 2000 The Electrochemical Society. All rights reserved.