A method of improving dielectric constant and adhesion strength of methyl silsesquioxane by using a NH3 plasma treatment

Abstract

Low dielectric and porous thin films, such as hydrogen silsesquioxane (HSQ) and methyl silsesquioxane (MSQ) thin films, has been intensively studied as an interlevel dielectric (ILD) material for multi-level interconnection since RC time delay can be reduced by low-k. In this work, we have synthesized a MSQ material that has relatively a low-k (k=2.7-3.0), an intrinsic hydrophobicity, good mechanical hardness and good thermal stability (up to 500 oC). However, it is well known that generally the MSQ has poor adhesion to Cu metal and diffusion barrier thin films. Therefore, we have tried to modify the surface of MSQ films by NH3 plasma treatment to improve the adhesion. As a result, the effects of NH3 plasma treatment on electrical and physical properties of methyl silsesquioxane (MSQ) have been investigated. After the NH3 plasma treatment, the dielectric constant of the MSQ was decreased by about 20 %, and the adhesion of MSQ to W-N diffusion barrier thin film was also significantly improved. However, leakage current density of the plasma treated MSQ films was increased depending on plasma treatment conditions and as increasing the plasma treatment temperature from 150 to 350 C the leakage current density of the MSQ increases as high as a order of magnitude. In this work, we will discuss the effect of nitrogen atom bombardment to the MSQ films on reducing the dielectric constant and wet-ability on the surface of the MSQ film.