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 surfaceband 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.
Received 23 November 2012Accepted 07 January 2013Published online 25 January 2013
The authors would like to acknowledge the support and encouragement from Dr. B. Tufts, Dr. J. Maiz, and Dr. B. Boyanov of Intel Corporation during the course of this research. The authors would also like to acknowledge invaluable discussions with Dr. P. Lenahan and Dr. B. Bittel from Penn State University concerning spin defects in SiO2 and other inorganic materials.
Article outline: I. INTRODUCTION II. EXPERIMENTAL III. RESULTS AND DISCUSSION IV. CONCLUSIONS