Microelectronic Engineering 60 (2002) 133–141 www.elsevier.com / locate / mee Comparison of techniques to characterise the density, porosity and elastic modulus of porous low-k SiO xerogel films 2 a b a a, c * C. Murray , C. Flannery , I. Streiter , S.E. Schulz , M.R. Baklanov , d e e e a K.P. Mogilnikov , C. Himcinschi , M. Friedrich , D.R.T. Zahn , T. Gessner a Chemnitz University of Technology, Center of Microtechnologies, D-09107 Chemnitz, Germany b ¨ ¨ Paul-Drude-Institut f ur Festkorperelektronik, Hausvogteiplatz 5 –7, D-10117 Berlin, Germany c IMEC, Leuven, Belgium d Institute of Semiconductor Physics, Novosibirsk, Russia e Chemnitz University of Technology, Institute of Physics, D-09107 Chemnitz, Germany Abstract A range of mesoporous xerogel low-k dielectric films were prepared and characterised using complementary techniques: Laser-generated surface acoustic waves, ellipsometric porosimetry, Rutherford backscattering and nanoindentation. The density, porosity, pore size distribution, cumulative surface area, elastic modulus and hardness of the films were measured as well as their dielectric constants. Dielectric constant values of k 5 1.7–2.3 were measured for samples with porosities of 36–55%. Mean pore radii values of 2.2–4.2 nm and 3 23 surface areas of 280–240 m cm were also obtained. Using porosity and mean film density values determined 23 using different techniques, the film skeletal density of these samples were calculated to be ¯ 1.4 g cm , almost 40% lower than that of dense SiO . The elastic moduli of the films were found to be E , 4 GPa.  2002 2 Elsevier Science B.V. All rights reserved. Keywords: Xerogel; Thin film; Low-k dielectric; Porous; SiO ; Spin-on; Characterisation; Porosity; Elastic modulus 2 1. Introduction As low-k materials begin to make the move into mainstream microelectronic fabrication processes, mesoporous silica has become one of the principal candidate materials capable of achieving ultra-low dielectric constant values of k , 2. While the introduction of pores into the solid material reduces its dielectric constant, it also reduces its mechanical strength. This has implications for further processing where high mechanical forces are used, e.g., during chemical mechanical polishing (CMP). A *Corresponding author. Tel.: 149-371-531-3651; fax: 149-371-531-3131. E-mail address: ses@zfm.tu-chemnitz.de (S.E. Schulz). 0167-9317 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0167-9317(01)00589-5