A New X-Ray Scattering Method for Determining Pore-Size Distribution in Low-k Thin Films

Abstract

We have successively developed a new x-ray scattering technique for a non-destructive determination of pore-size distributions in porous low-κ thin films formed on thick substrates. The pore size distribution in a film is derived from x-ray diffuse scattering data, which are measured using offset θ/2θ scans to avoid strong specular reflections from the film surface and its substrate. Γ-distribution mode for the pores in the film is used in the calculation. The average diameter and the dispersion parameter of the Γ-distribution function are varied and refined by computer so that the calculated scattering pattern best matches to the experimental pattern. The technique has been used to analyze porous methyl silsesquioxane (MSQ) films. The pore size distributions determined by the x-ray scattering technique agree with that of the commonly used gas adsorption technique. The x-ray technique has been also used successfully determine small pores less than one nanometer in diameter, which is well below the lowest limit of the gas adsorption technique.

Characterization of porosity and dielectric constant of fluorocarbon porous films synthesized by using plasma-enhanced chemical vapor deposition and solvent process

“…However, the reflection method using an x ray with a wavelength shorter than visible light should be more effective for the THFtreated films, since a pore in the film seems to be formed by the soluble components whose geometrical sizes are esti- mated to be on the order of nanometer from their molecular weights. 4 The refractive index of a film to the x ray (n) is represented by 6 nϭ1Ϫ␦Ϫi␤, ͑1͒…”

“…In x-ray reflection on the film surface, the difference of n from unity, ␦, is proportional to the atomic density (␦ϰ), and critical angle of total reflection, c , is given by ͱ2␦. 6 Therefore, one can compare the films in relative difference of the atomic density by measuring the critical angle. Surface morphology of the films was observed with an atomic force microscope ͑AFM͒.…”

Determination of Pore-Size Distributions in Low-k Dielectric Films by Transmission Electron Microscopy

“…Here we focus on disordered distributions of pores; although there has also been much work on dielectric films with ordered arrays of pores, these have different requirements for TEM imaging, which have been documented. 2 Other techniques used for the characterization of pores in low-k films include X-ray diffuse scattering, 3 positron annihilation lifetime spectroscopy (PALS), 4 X-ray reflectivity (XRR), 5 ellipsometric porosimetry (EP), 6 and X-ray porosimetry (described as an XRR version of EP). 7 TEM has a basic advantage over these other techniques as it can provide a real-space picture showing changes in pore distributions at a local scale that might be lost to averaging in measurements conducted over larger regions of sample area.…”