An Electrical, Compositional, and Structural Study on Low-k Silsesquioxane Dielectric Thin Films

Abstract

Dependencies of parameters of atomic structure, composition, direct current (dc) conductivity, and spectrum of defect states of low- methyl silsesquioxane (MSQ) films on temperature of their isochronal annealing in nitrogen–oxygen ambient are investigated. The annealing temperature varies from , whereas annealing time was constant for all samples. Thermogravimetric analysis and differential scanning calorimetry techniques are employed for experimental determination of the glass transition temperature, 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 mixture, especially at temperatures above the . Annealing in this ambient at the causes significant diminishment in concentrations of SiC- and complexes, layer thickness, and volume fraction of pores, whereas concentrations of the H–OH, N–O, C–O and complexes, as well as the density of dangling bonds of silicon and nitrogen atoms (negatively charged and spatially isolated states, and donorlike fourfold-coordinated 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.