Spatially resolved CF, CF2, SiF and SiF2 densities in fluorocarbon containing inductively driven discharges

Laser-induced fluorescence was used to measure the spatially resolved CF, CF2, SiF and SiF2 radical densities in inductively driven discharges containing fluorocarbon gases while etching silicon. Measurements of the spatially resolved radical densities were performed in fluorocarbon containing gases such as C2F6, CHF3 and C4F8 as functions of the induction coil power, pressure and bias power above a silicon surface. Measurements of these four species provide information on parent gas dissociation products as well as etch products evolved from the surface. The spatial distributions of these radical species were quite different and did not follow all the optical emission. The spatial distribution of the CF density was peaked in the center of the plasma. The CF2 density had a local maximum in the center of the plasma. However, the CF2 density outside the glow region was a factor of 2-6 higher than the density inside the glow region, depending on the gas. The etch product SiF had a maximum at a radial distance of 2-3 cm from the center of the plasma, and then monotonically decreased towards the edge of the plasma region. While the peak density was a function of the plasma parameters, the general shape of the SiF spatial distribution was independent of the plasma conditions and gas. The SiF2 density had a maximum at a radial distance of approximately 7 cm from the center of the plasma. At this location, the SiF2 plasma-induced optical emission was approximately 10% of the value in the center of the discharge. The SiF2 spatial distribution was dependent on the induction coil power. The location of the peak in the SiF2 density did not depend on the plasma confinement structures or material. The scaling of the CF, CF2 and SiF densities in the center of the plasma with inductive power showed the importance of gas heating in determining the number density in the center of the plasma. (C) 2002 Elsevier Science B.V. All rights reserved.