Low-dielectric-constant-film deposition with various gases in a helicon plasma reactor

Abstract

Low-dielectric-constant SiOF films are deposited using O-2/SiF4 and O-2/FSi(OC2H5)(3) mixtures in a helicon plasma reactor, and good quality films can be obtained without intentional heating or biasing of the substrate. Optical emission spectroscopy (OES) is used to study the relation between the relative densities of the radicals and the film properties. The OES data imply that the source gases are highly dissociated above the RF power of 900 W where the helicon mode is generated. Consequently, the mechanism of helicon plasma chemical vapor deposition (CVD) is different from that of thermal CVD. In the case of thermal CVD, the source gases react chemically on the high-temperature substrate and form films. However, in the case of helicon wave plasma CVD, the source gases are highly dissociated in the high-density plasma and many radicals are produced, that react on the substrate. SiOF films are made in the case of O-2/SiF4 but CF/SiOF composite films are made in the case of O-2/FSi(OC2H5)(3), where FSi(OC2H5)(3) is highly dissociated in plasma and C participates in the film formation. Films with a low dielectric constant of below 3.0 can be made.