Measurement of the vacuum-ultraviolet absorption spectrum of low-k dielectrics using X-ray reflectivity

Abstract

During plasma processing, low-k dielectrics are exposed to high levels of vacuum ultraviolet (VUV) radiation that can cause severe damage to dielectric materials. The degree and nature of VUV-induced damage depend on the VUV photon energies and fluence. In this work, we examine the VUV-absorption spectrum of low-k organosilicate glass using specular X-ray reflectivity (XRR). Low-k SiCOH films were exposed to synchrotron VUV radiation with energies ranging from 7 to 21 eV, and the density vs. depth profile of the VUV-irradiated films was extracted from fitting the XRR experimental data. The results show that the depth of the VUV-induced damage layer is a function of the photon energy. Between 7 and 11 eV, the depth of the damaged layer decreases sharply from 110 nm to 60 nm and then gradually increases to 85 nm at 21 eV. The maximum VUV absorption in low-k films occurs between 11 and 15 eV. The depth of the damaged layer was found to increase with film porosity.

Impact of VUV photons on SiO2 and organosilicate low-k dielectrics: General behavior, practical applications, and atomic models

“…As it was shown in 102 for CVD1 films, the penetration depth zpp (if to define zpp by the depth where 95% of initial emission intensity I0 is absorbed, I(z>z1)<0.05<I0) is only 50-75 nm for the range 50-120 nm whereas 147 and 13.5 nm emissions can penetrate deeper up to zpp~150-200 nm. The similar level of photon-penetration depths (zpp~60-96 nm for photons wavelengths ~59-138 nm and very low photoabsorption and Si-CH3 depletion for >175 nm) for low-k films recently measured in 101 .…”

“…Absorption spectra of OSG low-k films were analyzed in refs. 100,101 Choudhury et al 101 measured depth of VUV damage of OSG films exposed to synchrotron VUV radiation with energies ranging from 7 to 21 eV. The films density vs. depth profile of the VUV-irradiated films was extracted from the fitting of the XRR (specular X-ray reflectivity) experimental data.…”

“…At the same time degree of the impact is also limited by the absorption or the penetration depth of VUV photons. The penetration depth for the different wavelengths estimated by different diagnostics (XRR 101 , SIMS 102 , RBS 102 and XPS with depth profiling 150 ) is shown in Figure III.7. It is clear that VUV damage for radiation in the range 70-120 nm was concentrated on OSG film top even at powerful VUV impact.…”

“…Thus, to minimize damage it is necessary to take into account both intensity and spectrum of VUV radiation. The penetration depth of VUV photons in porous OSG low-k measured by XRR (X-ray reflectivity) 101 , SIMS 102 , RBS 102 and XPS with depth profiling 150 . The XPS data was recalculated for the 40%-porosity film.…”

“…The Br atoms were then chemisorbed onto the III-V surface leading to adsorbed surface species such as GaBrx and AsBrx which eventually desorbed into the gas phase as reaction byproducts for GaAs etching. 101 Figure However, additional photo-assisted etching mechanisms have been identified and attributed to the creation and reaction of photo-generated free carriers (electrons and holes) that promote etch related surface reactions in either wet 450,451 or dry mediums (see Figure V.9). 454 Such photo-chemical processes may be further aided by the addition of an applied electrical bias resulting in so called photoelectrochemical etching 460,461,478,491 or photo-assisted anodic etching, 479,480 both of which have been demonstrated to enable highly anisotropic etching.…”