AVS 59th Annual International Symposium and Exhibition
    Plasma Science and Technology Wednesday Sessions
       Session PS-WeM

Paper PS-WeM6
Separation of Radical and Photon Effects on Nanoporous Low-k Films

Wednesday, October 31, 2012, 9:40 am, Room 25

Session: Advanced BEOL/Interconnect Etching
Presenter: J. Lee, University of California Berkeley
Authors: J. Lee, University of California Berkeley
D.B. Graves, University of California Berkeley
Correspondent: Click to Email
Porous low-k materials are highly susceptible to damage from plasma species during various stages of plasma processing. Oxygen plasma, possibly the most damaging, causes significant carbon loss throughout the film, making the material hydrophilic. Absorption of water results in an increase in the dielectric constant and degradation of dielectric properties. Various O2 plasma species, such as oxygen radicals (O) and vacuum-ultraviolet (VUV) photons, can be shown to cause this carbon loss. Separation of these species to analyze individual effects can be achieved by covering the sample with a MgF2 window to allow only VUV photons to pass or by placing the sample out of the line-of-sight of the plasma to obtain radical effects, since radicals are able to diffuse to, and into, the porous material. By doing this, we can analyze the carbon loss for each individual specie through bulk measurements using Fourier-transform infrared (FTIR) spectroscopy and compare them to uncovered, direct O2 plasma exposures. Dilute HF dip etches only C-depleted SiO2, allowing a measure of the depth of C removal by radicals or VUV photons. Oxygen radicals create a nearly C-free modified layer that deepens at a rate proportional to exposure time and that increases with pressure, presumably because of the increase in O density. By contrast, VUV photons travel fairly deep into the film due to relatively low absorption cross-sections, so photon effects gradually occur throughout this penetration depth at a slower rate. Yet, VUV photons alone do not directly result in carbon loss; molecular oxygen is also needed to form volatile species for permanent removal. The results clearly show that radicals and VUV photons generate the damaged layer in different ways and at different rates.