Mihail P. Petkov

Open volume defects (measured by positron annihilation spectroscopy) in thin film hydrogen-silsesquioxane spin-on-glass; correlation with dielectric constant

We used Doppler broadening positron annihilation spectroscopy as a nanovoid characterization tool in the study of low dielectric constant (low-k) hydrogen-silsesquioxane (HSSQ) thin films. The high void sensitivity of this method, combined with depth-resolving capability, enables one to observe changes in the local electronic environment in a thin film. We established a correlation between the annihilation parameters and the dielectric properties for a series of samples subjected to various annealing conditions in nitrogen. Qualitative differences are found between the pore structures of isochronally and isothermally annealed films, suggesting a complex relationship between the film dielectric constant and pore size and pore density. Results showing changes in the chemical environment caused by exposure to various processing environments are also presented. First, the changes in the HSSQ films were determined after a year of exposure to ambient air in which the film properties changed with time due to wat...

Porosity characterization by beam-based three-photon positron annihilation spectroscopy

We present a straightforward and fast positron annihilation spectroscopy (PAS) technique for measuring the 2 to 3 photon annihilation ratio of Ps (electron-positron) atoms (3γ PAS), utilized here for the nondestructive characterization of mesoporous (pore size >1 nm) dielectric films. Examples are given for ∼1-μm-thick foamed methyl-silsesquioxane (MSSQ) films, produced by mixing MSSQ (0–90 wtu200a% fraction) with a sacrificial foaming agent (porogen). Probing these films as a function of depth allows one to monitor Ps escape from interconnected pores and to determine the threshold for pore interconnectivity to the film surface. A classical treatment of Ps diffusion is used to calculate the open and closed porosity fractions as a function of the initial porogen load.

Probing capped and uncapped mesoporous low-dielectric constant films using positron annihilation lifetime spectroscopy

We have measured uncapped mesoporous low-dielectric-constant films using positron annihilation lifetime spectroscopy (PALS), a nondestructive technique, which yields both pore-size distributions and the threshold for pore interconnectivity. Pairs of fully cured capped and uncapped identical films, initially containing 5%–50% porogen additions, exhibited similar signatures in PALS, establishing a technique in which film capping is unnecessary. We also found that it was possible to distinguish between closed and percolated pores, without film capping, by comparing lifetime spectra of a film taken using different detector configurations. Interconnected pores were observed in cured samples, which had greater than 20% porogen additions.

Doppler broadening positron annihilation spectroscopy: A technique for measuring open-volume defects in silsesquioxane spin-on glass films

Doppler broadening positron annihilation spectroscopy is used to measure the concentration, spatial distribution, and size of open-volume defects in low dielectric constant (low-k) hydrogen- and methyl-silsesquioxane thin films. A simple correlation between the number of open-volume defects and the dielectric constant is obtained. In addition, the depth-resolving capability enables profiling of the local electronic environment of open-volume defects as a function of depth. The potential for using this technique for measuring k as a function of film depth is also discussed.

A simple positron lifetime spectrometer for a magnetically guided low-energy beam

We present a new, simple, and inexpensive positron lifetime spectrometer intended for the depth-resolved characterization of thin films and buried interfaces. The spectrometer operates on a conventional magnetically guided positron beam with energies ranging from 1 to ∼50 keV. Given is a detailed description of the performance of the apparatus, built on thorough experimental investigations and computer simulations. A timing resolution of 350±13u200aps at full-width-at-half-maximum was obtained. The count rate for thin films (low positron energies) was of the order of 1000 s−1. A maximum peak-to-background ratio>105, aiding the measurements of long-living (10–100 ns) positronium in voids, was achieved by constant beam rate reduction and by beam chopping. Examples are presented for measured lifetimes in well-characterized systems.

A relation between surface oxide and oxygen-defect complexes in solid-phase epitaxial Si regrown from ion-beam-amorphized Si layers

We present a direct evidence that ion implantation through thin (⩽5 nm) surface oxide layers is a source of O impurities, which form O-defect complexes during thermal treatment. The impurity-defect complexes are identified by correlating the results from positron annihilation spectroscopy, secondary-ion mass spectroscopy, and Monte Carlo simulations. The O atoms are introduced in the bulk by multiple recoil implantation by the primary ions. The signatures of large VmOn formations are observed at 800u200a°C, which implies the existence of smaller species at lower temperatures.