This study reports the use of ammonia to inhibit the growth of previously nucleated ruthenium islands and force the nucleation of additional islands such that thinner films form as the islands coalesce with continued growth. Ruthenium films are grown at 448 K in a chemical vapor deposition process on SiO2/Si(001) using triruthenium dodecacarbonyl, Ru3(CO)12, with and without a constant partial pressure of ammonia. Film growth was performed at a Ru3(CO)12/Ar pressure of 47.2 mTorr. The ammonia partial pressure varied from 0 to 27.8 mTorr. X-ray photoelectron spectroscopy was used to analyze the samples in situ. Ex situ characterization included scanning electron microscopy, atomic force microscopy, and x-ray diffraction and x-ray reflectivity. Nucleation studies limited to the first 10 min of growth revealed the maximum nanoparticle (island) density of 8.1 × 1011 cm−2 occurred at an intermediate ammonia pressure (5.25 mTorr) compared to a density of 3.1 × 1011 cm−2 for no ammonia addition. Extending film growth to 120 min and varying the ammonia partial pressure during the first 10 min followed by 5.25 mTorr ammonia pressure for the final 110 min reveals the importance of nucleation on film smoothness. A model describing the inhibition effects of ammonia during nucleation and growth is presented.
Ruthenium was deposited on SiO 2 /Si(001) substrates at 473 K by chemical vapor deposition (CVD) using triruthenium dodecacarbonyl with and without an overpressure of CO. Carbon monoxide was employed to inhibit the growth of previously nucleated islands to allow the formation of additional nuclei. Carbon monoxide also competed with the precursor for free hydroxyl sites on SiO 2 sites where precursor adsorption and decomposition is favored. Total pressure was maintained at 84 mTorr, and CO was introduced at partial pressures of 2.5 and 8.4 mTorr at various intervals during 15 min growth runs. The nucleation density decreases with increasing CO overpressure when CO and precursor are injected simultaneously from the beginning; in this case, CO blocks the free hydroxyls where the Ru precursor dissociates. When 8.4 mTorr CO is introduced for 5 min to the CVD chamber after a 10 min period of deposition without CO, the maximum nucleation density was achieved (16.4 × 10 11 /cm 2 ), which is twice as much as the Ru particle density found for 15 min deposition without added CO. After 10 min of growth, hydroxyl groups have mostly reacted and the injected CO adsorbs on Ru nanoparticles, inhibiting growth and forcing additional Ru nucleation on the SiO 2 substrate. Growth was extended to 2 h to explore the influence of CO on ultrathin Ru film characteristics. The film grown without CO for 10 min and then with 8.4 mTorr CO for 1 h 50 min was thinner and smoother than the film grown without CO for 2 h because CO adsorption on the Ru surface slows the Ru islands/film growth rate.
Nucleation and film growth characteristics are reported during chemical vapor deposition of Ru on SiO2 using triruthenium dodecacarbonyl [Ru3(CO)12] and ruthenium bis(di-t-butylacetamidinate) dicarbonyl [Ru(tBu-Me-amd)2(CO)2]. Films grown from Ru3(CO)12 follow the three dimensional (3D) Volmer–Weber growth mode. In contrast, films grown from Ru(tBu-Me-amd)2(CO)2 follow the pseudo-layer-by-layer growth mode with two dimensional wetting layer islands forming before 3D particle growth is observed on the islands. A relationship between free isolated hydroxyl [(Si-OH)i] group density and Ru nucleation density is found for Ru3(CO)12 and is associated with (Si-OH)i acting as the reaction sites for activation of Ru3(CO)12 and in turn generating an adjustable adatom concentration. Carbon monoxide and ammonia addition to the gas phase during film growth from Ru(tBu-Me-amd)2(CO)2 lead to smoother films by inducing surface reconstructions during the 3D phase of pseudo-layer-by-layer growth; these gases also lead to films with lower resistivity and lower crystalline character.
Successful use of kinetic models of thermal damage processes depends critically upon the identification of a quantitative measure of thermal damage. Most clinically relevant processes are qualitative in nature and are not easily studied by the standard Arrhenius formulation. Quantitative markers of thermal damage include: 1) loss of birefringence properties in muscle and collagen, 2) loss of hemoglobin from red blood cells, 3) uptake of enzymatically active dyes and 4) diffusion of dyes across vessel walls. When a quantitative marker is used the kinetic coefficients estimated from experiments over different time scales are significantly different. Application of coefficients determined in long term studies (exposure times on the order of hours) to short term exposures (electrosurgical coagulation or short laser pulses) is questionable and often leads to counter-intuitive predictions of damage boundaries. Short term exposures, on the other hand, are by definition not of constant temperature and often defy estimation of the coefficients from the transient history. We present and compare several sets of estimated thermal damage coefficients for similar and differing processes and a preliminary method for extracting estimates from transient histories.
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