Moisture Adsorption in Plasma-Damaged Porous Low-k Dielectrics
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1079-N02-09
Moisture Adsorption in Plasma-Damaged Porous Low-k Dielectrics Ekaterina Vinogradova1, Casey E Smith1,2, DW Mueller1, Andrew J McKerrow3,4, and Rick Reidy1 1 Materials Science and Engineering, University of North Texas, PO Box 305310, Denton, TX, 76203-5310 2 Sematech, Austin, TX, 78741 3 Texas Instruments, Dallas, TX, 75243 4 Novellus, Tualatin, OR, 97062 ABSTRACT Plasma etch/ash processes can induce changes in low-k film surface/bulk chemistries and topographies resulting in increased water adsorption, surface roughness, and metal intrusion. After ashing, the altered surface character of the low-k can impact wetting, adhesion, and, consequently, the resistance of subsequently deposited barrier layers. In this work, we describe the use of deuterium oxide as means of measuring moisture penetration into low-k films. Film chemistries have been monitored using grazing angle attenuated total reflectance (GATR) and transmission Fourier transform infrared spectroscopy (FTIR). To study moisture adsorption in porous spin-on and CVD low-k films, unashed and ashed films have been exposed to D2O liquid and vapor treatments under “dry” nitrogen. The extent of D2O uptake, removal and exchange reactions has been studied using transmission and GATR FTIR methods because the D2O and OD adsorption peaks are distinct from water and O-H as well as other low-k adsorptions. This method can be used to study Si-OH species because deuterium can exchange with hydrogen within silanols under ambient conditions while methyl groups are much less likely to exchange. Three different low-k films, a porous spin-on MSQ (k=2.2), a porous CVD (k=2.3), and an organosilicate glass (OSG, k=2.85) have been used in this work. In FTIR spectra, unashed low-k films show minimal D2O adsorption. In MSQ hydrogen-ashed films, the data suggest the presence of deuterium oxide and O-D peaks. Further, D2O adsorption appears to be considerably higher for ashed films as would be expected due to the hydrophobicity of these films. In the CVD films, there does not appear to be as marked a difference. This method can permit the introduction of a chemical “marker” into low-k wet and ambient processes allowing one to distinguish among adsorptions from different aqueous sources. INTRODUCTION Integration of porous low-k films is necessary for the continued scaling of integrated circuits;1 however, plasma etch/ash processes and subsequent wet cleans can deleteriously affect these films through material damage/loss, removal of hydrophobic moieties, and densification. The nature and degree of damage is specific to processing, and can significantly increase dielectric constant, reduce dielectric breakdown voltage, permit metallic specie intrusion, increase surface roughness2, and enhance moisture adsorption leading to degradation of device performance and reliability. Loss of hydrophobicity can lead to additional material loss and the intrusion of aqueous species during wet cleans.3 This works attempts to measure moisture adsorption into these films.
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