Effects of pore morphology on the diffusive properties of a porous low- κ dielectric

Abstract

Porous methylsilsesquioxane-based spin-on films with pore sizes of 1.5-2 nm and porosities ranging from 0% to 32% have been exposed to a variety of processing environments such as fluorocarbon or oxygen containing plasmas and TaN atomic layer deposition to determine the integratability of the films. The porosity of the low- κ films was found to decrease during processing due to tantalum and fluorine indiffusion (fluorine potentially depositing as fluorocarbon film in the pores) while oxygen indiffusion depleted carbon (possibly by forming volatile CO and C O2). Carbon removal from the low- κ film alters the film's dielectric constant and refractive index. The depth of the indiffusion appears to be independent of diffusant (fluorocarbon, oxygen, or tantalum), ranging from 40 to 150 nm, and to correlate directly to the pore structure. It was also found that water (moisture) in these films significantly affects the measured porosity as well as can be used to reduce the indiffusion of fluorine containing molecules by a factor of 2. The diffusivity of various molecules in the low- κ films was estimated by using a Deal-Grove model and found to increase linearly with porosity (ranging from 1× 10-8 to 1.6× 10-7 cm2 s) while the "reaction" rate constant was found to increase nonlinearly with porosity (ranging from 4× 10-6 to 2.3× 10-5 cms). © 2007 American Vacuum Society.