Composition of ion flux and etch rates for Si and SiO/sub 2/ in high density fluorocarbon plasmas

Abstract

Summary form only given. In plasma etching of semiconductors, chemically reactive species to the substrate are provided by both ions and neutrals in the plasma. Oehrlein et al. (1994) have suggested that the composition of the ion flux at the substrate surface may play a role in SiO/sub 2/ and Si etch rates and therefore selectivity. To determine the relative roles of ions and neutrals, measurement of the ion and neutral fluxes to the surface of a substrate will be necessary. As a first step, this study will examine the ion flux at the substrate position in a high density source for CHF/sub 3//H/sub 2/ and C/sub 2/H/sub 2/F/sub 4//O/sub 2/ etching plasmas. These measurements will determine the percentage of each ion species in the total ion flux as the source gas is varied. In order to determine relative fluxes of different ionic species, ions are sampled at the wafer holder location in an electron cyclotron resonance source by a differentially pumped quadrupole mass spectrometer system. We use Ne, Kr, and Ar plasmas along with Langmuir probe measurements to calibrate the mass sensitivity of the quadrupole mass spectrometer. The ion saturation current is measured with a collecting Langmuir probe located 1 cm above the pinhole into the quadrupole system for the same plasma conditions as the quadrupole measurements. For each noble gas, the probe current will be dominated by the flux of a single ionic species, making it possible to use this information to construct a calibration curve for mass spectrometer peak heights.