Dependencies of parameters of atomic structure, composition, direct current (dc) conductivity, and spectrum of defect states of low-k methyl silsesquioxane (MSQ) films on temperature of their isochronal annealing in nitrogen-oxygen (N-2-O-2) ambient are investigated. The annealing temperature varies from 300 to 900 degrees C, whereas annealing time (60 min) was constant for all samples. Thermogravimetric analysis and differential scanning calorimetry techniques are employed for experimental determination of the glass transition temperature, T-g for the MSQ. X-ray diffraction, specular X-ray reflection, and Fourier-transform infrared spectroscopy are applied for structural characterization, whereas deep-level transient spectroscopy is used in studies of the distribution of defect states in the bandgap. Experimental results reveal that composition, morphology, dc conductivity, and defect spectrum of the material are strongly influenced by annealing of the MSQ films in N-2-O-2 mixture, especially at temperatures above the T-g=526.4 +/- 0.8 degrees C. Annealing in this ambient at the T-a> T-g causes significant diminishment in concentrations of SiC- and SiCH3 complexes, layer thickness, and volume fraction of pores, whereas concentrations of the H-OH, N-O, C-O and Si-O-2 complexes, as well as the density of dangling bonds of silicon and nitrogen atoms (negatively charged and spatially isolated Si-3(-) states, and donorlike fourfold-coordinated N4+ defects, respectively), increase dramatically. Possible mechanisms of the observed changes in the structural and electrical parameters, as well as in defect spectrum of annealed MSQ material, are discussed. (c) 2005 The Electrochemical Society. All rights reserved.