Detection of defect states in low-k dielectrics using reflection electron energy loss spectroscopy

Abstract

Reflection electron energy loss spectroscopy (REELS) has been utilized to measure the band gap (Eg) and energy position of sub-gap defect states for both non-porous and porous low dielectric constant (low-k) materials. We find the surface band gap for non-porous k = 2.8–3.3 a-SiOC:H dielectrics to be ≅ 8.2 eV and consistent with that measured for a-SiO2 (Eg = 8.8 eV). Ar+ sputtering of the non-porous low-k materials was found to create sub-gap defect states at ≈ 5.0 and 7.2 eV within the band gap. Based on comparisons to observations of similar defect states in crystalline and amorphous SiO2, we attribute these sub-gap defect states to surface oxygen vacancy centers. REELS measurements on a porous low-k a-SiOC:H dielectric with k = 2.3 showed a slightly smaller band gap (Eg = 7.8 eV) and a broad distribution of defects states ranging from 2 to 6 eV. These defect states are attributed to a combination of both oxygen vacancy defects created by the UV curing process and carbon residues left in the film by incomplete removal of the sacrificial porogen. Plasma etching and ashing of the porous low-k dielectric were observed to remove the broad defect states attributed to carbon residues, but the oxygen vacancy defects remained.