Study of the material properties and suitability of plasma-deposited fluorine-doped silicon dioxides for low dielectric constant interlevel dielectrics

Abstract

A major challenge for back-end interconnection technology as device geometries shrink is the development of low dielectric constant materials with good gap-filling properties that are suitable for microelectronics manufacturing. Recently, there has been much interest in fluorine-doped silicon dioxides (SiOF) as such a material. The advantages of a silicon dioxide based film from an integration standpoint make these films very attractive for manufacturing. In this study, SiOF films have been prepared in a conventional parallel-plate dual-frequency plasma-enhanced chemical vapor deposition reactor. By varying the deposition parameters, SiOF films with indices of refraction from 1.38 to 1.46 and corresponding changes of as much as 20% in the dielectric constants have been produced. Fourier transform infrared data for these films have been correlated with fluorine concentration by secondary ion mass spectroscopy measurements. The presence of fluorine can also be observed in the capacitance-voltage (CV) characteristics for the films. Fluorine interface states trap electrons which delay the onset of accumulation in the CV measurements for p-type silicon. In a similar way, the fluorine-induced trap states affect the onset of inversion for n-type silicon. Some films with high fluorine concentrations have been observed to be unstable with respect to moisture absorption. The reliability and stability data for these films are presented.