Time resolved Langmuir probe measurements in inductively coupled plasmas

Summary form only given. There has been much interest in inductively coupled plasmas for semiconductor processing and for integrated optic applications. We are concerned with several processes using Inductively Coupled Plasma, such as deep silicon oxide etching using fluorocarbon gases (CF/sub 4/, C/sub 2/F/sub 6/, CHF/sub 3/) and their mixtures with methane (CH/sub 4/) or hydrogen (H/sub 2/), low-k etching using fluorocarbon gases mixed with oxygen (O/sub 2/) or nitrogen (N/sub 2/) and resist etching in oxygen, fluorocarbon or SF/sub 6/ plasmas. Our main aims are to develop, understand and optimize these processes. When considering etching, a fundamental process parameter is the ion flux impinging the substrate, as well as the Electron Energy Distribution Function (EEDF). We use Langmuir probe diagnostic to measure these two parameters. Most of the gases used are polymerizing gases and deposition on the probe tip is a major problem to be addressed to obtain reliable probe measurements. Furthermore, all the gases studied (except nitrogen) have a common point, their strong electronegativity, that leads to another problem to be faced. Actually, we have observed strong plasma oscillations when using electronegative gases. This kind of plasma instabilities were attributed to a periodic capacitive to inductive discharge jump because of a periodic negative ion creation. As a consequence of the plasma oscillations, probe acquisitions are disturbed and do not allow to determine plasma electrical characteristics. Hence, time resolved probe measurements must be employed in order to follow electron and ion densities variation during instability. In this work we present our first studies concerning time resolved probe measurements during instabilities. First, we have identified for the different gases used, the instability window (source power versus pressure). We show for example that C/sub 2/F/sub 6/ plasmas present oscillations over a very large range of power and pressure. Second, for non polymerizing gases, we have measured time resolved electron and ion densities during plasma oscillations.