Extent of plasma damage to porous organosilicate films characterized with nanoindentation, x-ray reflectivity, and surfa
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A.M. Jonas Unité de Physique et de Chimie des Hauts Polymères, Université Catholique de Louvain, Belgium
J.M. Molina-Aldareguia, M.R. Elizalde, and I. Ocaña CEIT and TECNUN (University of Navarra), 20018 San Sebastián, Spain (Received 29 May 2006; accepted 24 August 2006)
It is known that porous organosilicate glass (OSG) dielectrics tend to lose functional groups and become denser upon the chemical and physical action of the plasmas, but an accurate analysis and estimation of the depth and degree of film densification is not straightforward. In this study, we show that the combination of techniques like x-ray reflectivity, surface acoustic waves, and nanoindentation in depth-sensing and modulus mapping mode allow a complete and self-consistent physical analysis of the damage induced by the direct exposure of porous OSG films to different plasma ambients in reactive ion etching mode. We demonstrate for the chosen dielectric that the characteristics of the damage regions such as density and elastic modulus are very similar regardless of the reducing or oxidizing nature of the plasma. Nevertheless, the physical depth of the damage region shows large variation. Capabilities and limitations of each of the chosen analysis techniques are also discussed.
I. INTRODUCTION
Plasma-induced modification of dielectric films is a major concern for fabrication of advanced interconnects structures.1,2 Porous low-dielectric constant materials are susceptible to extensive damage,3 and a few nanometers of dielectric chemical or physical modification have a critical impact on the electrical performance and mechanical reliability of advanced interconnects.4,5 A thorough estimation of the type and extent of dielectric modification is a challenging task. The first problem is the difficulty in isolating clearly the modified portion of the dielectric from the undamaged part of the film due to a typical graded transition between the two regions. Second, the thicknesses of interest for the modified regions are in the order of a few tens of nanometers, making the probing of physical, electrical, and mechanical properties of such thin layers a challenge in itself. Nowadays, porous organosilicate glasses (OSGs) are the most favored class of low-dielectric constant materials for advanced interconnect technology nodes. OSG materials are based on a backbone silica structure to
which functional methyl groups are attached.3 The exposure of OSG films to a plasma ambient leads invariably to the loss of CH3 hydrophobic groups and the densification of their silica backbone. Both effects (loss of hydrophobicity and densification) lead to an unwanted and uncontrolled increase of the dielectric constant of the film. The extent of this damage is strongly dependent on the type of plasma conditions such as chemistry and power/amount of physical bombardment and on the porosity of the OSG film.6,7 Often, for the sake of easy quantification, the amount of damage is reported in terms of “equivalent SiO2” thickness,4 even though this work will show that the da
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