Coaxial‐line type microwave plasma CVD system to fabricate SiN films

Abstract

AbstractThis paper considers the fabrication of silicon nitride films by means of the vapor phase deposition with a microwave glow discharge. With a cavity‐type coaxial line microwave discharge tube, a plasma has been confined in a desired space and the film has been fabricated successfully outside the plasma. Hence, the substrate is not damaged nor heated by plasma bombardment. Fabrication has been successful with the substrate at room temperature. The deposition rate depends on the location of the substrate table. When the table is sufficiently far away so that an almost uniform film thickness is obtained for a substrate 6 cm in diameter, the deposition rate is 2 to 7 Å/s with the microwave power of 100 W. Depending on the fabrication conditions, the optical energy gap varies from 2 to 5 eV. Then the color of the film (∼l μm) changes from brown to transparent.A new method has been proposed for finding the Si/N ratio and the film density from the measurement of the infrared absorption spectrum and the index of refraction. Based on the computed results, the film quality has been studied. When the flow rate of SiH4 gas is kept sufficiently small, a sufficiently strong transparent film can be fabricated with the Si/N ratio of 0.75 and the density of 2.3 g/cm3. When the substrate temperature is increased, the film density is increased and the deposition rate is reduced. It is found that the reduction of the deposition rate is due to that of the adsorption rate of the radicals.