Fluorinated–chlorinated SiO2 films prepared at low temperature by remote plasma-enhanced chemical-vapor deposition using mixtures of SiF4 and SiCl4

Abstract

Fluorine-chlorine-doped silicon-dioxide films have been deposited at 200 °C by the remote plasma-enhanced chemical-vapor-deposition technique using SiF4 and SiCl4 as silicon precursors in combination with O2/He/H2 mixtures. The behavior of the deposition rate and structural properties of the films as a function of SiF4 ratio, R=SiF4/(SiF4+SiCl4), was studied for two O2 flow rates by means of ellipsometry, chemical etch rate measurements, and infrared (IR) spectroscopy. Due the higher reactivity of SiCl4 compared with that of SiF4, films deposited with R<0.8 have high deposition rates (400–1410 Å/min), high refractive indices (1.46–1.59), and contain more chlorine than fluorine. On the contrary, films prepared using high SiF4 ratios (R>0.8) are deposited at lower rates (38–400 Å/min), have low refractive indices (1.43–1.46), and contain more fluorine. Etch rate and IR measurements indicate that all fluorinated–chlorinated SiO2 films deposited with an O2 flow rate of 130 sccm do not contain Si–OH or Si–H bonds and are more resistant to being chemically attacked than films deposited with 40 sccm of this gas. In this study, I–V and C–V measurements were used to compare the dielectric properties of stable fluorinated–chlorinated films prepared with an O2 flow rate of 130 sccm and the two highest SiF4 ratios; R=0.9 and R=1. The fluorine content measured by resonant nuclear reactions with the F19(p,αγ)16O nuclear reaction is 2.6 at. % for the film deposited with R=0.9 and 5.9 at. % for that deposited with R=1. The dielectric constants are 3.8 and 3.7, respectively. Although the deposition rate is higher for the former film (190 Å/min) than for the latter (38 sccm), both films have a leakage current density lower than 1×10−7 Å/cm2 and their dielectric breakdown occurs at electric fields higher than 8.2 MV/cm. These results indicate that the use of SiCl4 in combination with SiF4 is a good approximation to prepare and to increase the deposition rate of hydrogen-free fluorinated–chlorinated SiO2 films with low dielectric constants and good electrical integrity.