Damage to low-k porous organosilicate glass from vacuum-ultraviolet irradiation

Abstract

We investigate the effects of VUV and UV radiation on a number of low-k dielectric films. Two different systems were used to investigate the effects: (1) a synchrotron radiation system as a pure VUV radiation source, and (2) an electron-cyclotron resonance (ECR) plasma system as a plasma source (VUV plus ions). Using the synchrotron-radiation system, we find VUV causes trapped charge accumulation within low-k dielectric films by electron depopulation from the defect states. For organosilicate glass (SiCOH) , the defect states were located 1 eV above the valence band of the dielectric. A model was developed to calculate in-situ charge accumulation. Trapped charges can be depleted with UV-lamp exposure. We examined the use of different energy barriers between layers so that less charge will be accumulated. Using the ECR plasma system, the photon effects can be separated from charged particle effects using a capillary-array window to cover the low-k dielectric films so that only photons from plasma can reach the dielectric. Photon fluence from the plasma can be predicted with a model and measured with a VUV monochromator. Photons from the plasma were shown to be responsible for trapped-charge accumulation within the dielectric, while it was found that ions bombardment results primarily on charge on the surface of the dielectrics.