The copper/plasma-polymerized octofluorocyclobutane interface

To satisfy the demand fur increased signal transmission speed and device de nsity in the next generation of multilevel integrated circuits, a material with a permittivity less than 3 is needed, that has compatibility with copp er and copper processing. The authors found that plasma polymerized octoflu orocyclobutane (PPOFCB) is a smooth, transparent, film that adheres strongl y to the substrate and has a relatively high fluorine to carbon (F/C) ratio , indicative of a low permittivity. This paper considers the copper/PPOFCB interface by investigating the effects of an OFCB plasma both on copper and on the deposited PPOFCB. X-ray photoelectron spectroscopy (XPS) of copper surfaces exposed to an OFCB plasma, for times as short as 1 s and as long a s 30 min, was used to characterize the copper, the PPOFCB and the interface between them. During a 1 s OFCB plasma exposure, copper fluorination occurs, producing Cu F (with a F ion peak appearing in the F-1, spectrum) as well as the deposit ion of fluorocarbon species (with a CF, peak in the F-1, spectrum). During the next few seconds of OFCB plasma exposure, the amount of fluorocarbon de posited begins to dominate the surface, although oxidized copper and oxidiz ed hydrocarbon contaminant are still observed. The copper substrate beneath a 15 nm PPOFCB film is not detectable via XPS. The F/C ratio for PPOFCB ca n be as high as 1.68 after brief deposition times (30 s), reaching a platea u value of 1.5 after several more minutes of plasma exposure: this reductio n in F/C to a plateau is associated with ion bombardment and vacuum UV defl uorination. PPOFCB is a smooth, planarizing him, with plasma polymerization occurring predominantly on the surface and reducing the RMS roughness from 0.97 to 0.46 nm for the copper substrate. (C) 2001 Elsevier Science Ltd. A ll rights reserved.