@article{karoui_karoui_2010, title={A density functional theory study of the atomic structure, formation energy, and vibrational properties of nitrogen-vacancy-oxygen defects in silicon}, volume={108}, ISSN={["1089-7550"]}, DOI={10.1063/1.3387912}, abstractNote={The atomic structure, energy, stability, vibrational spectra, and infrared absorption intensities of major intrinsic nitrogen-related defects in nitrogen doped silicon crystals have been investigated using ab initio density functional theory and semi-empirical quantum mechanics methods. The defects that are of interest are nitrogen-vacancy-oxygen complexes which are believed to affect oxygen precipitation and void formation as well as nitrogen concentration measurement in nitrogen-doped silicon. Several chemical reactions involving nitrogen, Si vacancies and oxygen interstitial have been studied. After relaxation, the local vibrational modes of each complex are calculated within the harmonic oscillator approximation and the infrared absorption intensities are evaluated from the dipole moment derivatives. By cross correlating the stability and the infrared active lines of the defect, and taking into consideration the symmetry group of each complex, we were able to emphasize which nitrogen related complexes are likely to control the oxygen precipitation and voids formation and to assert a new calibration relationship for nitrogen concentration measurement in nitrogen doped Czochralski and float zone silicon wafers.}, number={3}, journal={JOURNAL OF APPLIED PHYSICS}, author={Karoui, F. Sahtout and Karoui, A.}, year={2010}, month={Aug} }
 @article{stoddard_duscher_karoui_stevie_rozgonyi_2005, title={Segregation and enhanced diffusion of nitrogen in silicon induced by low energy ion bombardment}, volume={97}, ISSN={["1089-7550"]}, DOI={10.1063/1.1866480}, abstractNote={A sample of nitrogen-doped, single crystal Czochralski silicon was subjected to several different surface preparations. Secondary ion mass spectrometry depth profiling has shown that prolonged glancing-angle bombardment by 3–5kV Ar+ ions significantly increases the nitrogen concentration in the near surface by up to an order of magnitude over the bulk value. Concentrations are observed to be elevated over the bulk value to a depth up to 25μm. Nitrogen-implanted samples and samples with a 1nm surface nitride did not exhibit nitrogen segregation under the same conditions, but a sample with 100nm of surface nitride did exhibit ion bombardment induced drive-in. In nitride-free samples, the source of the nitrogen is indicated to be a nitrogen-rich layer in the first micron of material. The diffusion behavior of nitrogen in silicon is discussed and the Crowdion mechanism for diffusion is suggested as the enabling mechanism for the enhanced low temperature diffusion.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Stoddard, N and Duscher, G and Karoui, A and Stevie, F and Rozgonyi, G}, year={2005}, month={Apr} }
 @article{kvit_karoui_duscher_rozgonyi_2004, title={"Umbrella"-like precipitates in nitrogen-doped Czochralski silicon wafers}, volume={84}, ISSN={["1077-3118"]}, DOI={10.1063/1.1669069}, abstractNote={Nitrogen effect on nucleation of oxygen precipitates in Czochralski Si has been investigated by transmission electron microscopy, Z-contrast imaging, and electron energy loss spectrometry (EELS). We have examined unusual “umbrella” shape oxygen precipitates in bulk of ingot in depths of more than 40 μm. Two predominant orientations of “umbrella” have been found along [110] and [−1−10] directions. We have investigated the distribution of nitrogen, oxygen, and interstitial Si by EELS profile taken simultaneously with HR Z-contrast image. The mechanism of nitrogen-enriched oxygen precipitates nucleation has been discussed.}, number={11}, journal={APPLIED PHYSICS LETTERS}, author={Kvit, A and Karoui, A and Duscher, G and Rozgonyi, GA}, year={2004}, month={Mar}, pages={1889–1891} }
 @article{karoui_karoui_rozgonyi_hourai_sueoka_2004, title={Characterization of nucleation sites in nitrogen doped czochralski silicon by density functional theory and molecular mechanics}, volume={95-96}, DOI={10.4028/www.scientific.net/ssp.95-96.99}, abstractNote={Extended defect nucleation and growth in nitrogen doped Czochralski silicon crystals are investigated in terms of trapping vacancy and oxygen atoms by ni trogen-pairs using molecular mechanics. The results have been correlated to the formation ener gy and stability of nitrogen-vacancyoxygen complexes obtained by ab-initio density functional theory. We found that N2 in a split interstitial position and V2N2 when formed from VN2 are very stable and have a strong affinity for oxygen, whereas the interaction energy between these defects and vacanc ies is weak. VN2 can only be weakly coupled to oxygen atoms, whereas it reconstructs into stable V 2N2 by trapping a vacancy. These results are in agreement with the degree of stability of nitrogen-vacancy-ox ygen complexes and indicate that N 2 and V2N2 are nucleation centers for oxygen precipitation rather than for void formation.}, number={2004}, journal={Diffusion and Defect Data. [Pt. B], Solid State Phenomena}, author={Karoui, F. S. and Karoui, A. and Rozgonyi, G. A. and Hourai, M. and Sueoka, K.}, year={2004}, pages={99–104} }
 @article{karoui_karoui_rozgonyi_yang_2004, title={Oxygen precipitation in nitrogen doped Czochralski silicon wafers. I. Formation mechanisms of near-surface and bulk defects}, volume={96}, ISSN={["1089-7550"]}, DOI={10.1063/1.1773921}, abstractNote={Defect size distributions in nitrogen-doped Czochralski (N-CZ) silicon wafers were obtained using an oxygen precipitate profiler and Wright-Jenkins etching. These showed unique depth dependence in low-high and high-low-high cycled N-CZ wafers. Unique phenomena observed include a high defect concentration at the subsurface that decreases within the top 2μm of the so-called denuded zone. In contrast to N-free CZ Si for which the first high step annealing dissolves the grown-in defects, these appeared to be stable in N-CZ Si. As a result, the defect size distribution in the bulk was found to be independent of the annealing cycle. It was also found that the depth dependent defect concentration correlates well with oxygen and strongly with nitrogen secondary ion mass spectroscopy profiles, suggesting that nitrogen is the leading impurity in the defect formation processes even though introduced at very low concentration. Nitrogen appeared to effectively modify the nucleation regime by a drastic increase of the nuclei density. At low temperature under external stress, nitrogen and oxygen cosegregate to the surface where the stress is applied; such a phenomenon is largely increased at high temperature.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Karoui, A and Karoui, FS and Rozgonyi, GA and Yang, D}, year={2004}, month={Sep}, pages={3255–3263} }
 @article{karoui_rozgonyi_2004, title={Oxygen precipitation in nitrogen doped Czochralski silicon wafers. II. Effects of nitrogen and oxygen coupling}, volume={96}, ISSN={["1089-7550"]}, DOI={10.1063/1.1773922}, abstractNote={Nitrogen segregation and coprecipitation with oxygen in N-doped Czochralski (N-CZ) silicon wafers are investigated as a function of depth based on extended defect structure and chemical composition. High resolution nitrogen and oxygen secondary ion mass spectroscopy imaging revealed strong coupling of oxygen with nitrogen in annealed as well as in “as-grown” N-CZ Si wafers. In both cases, the near-surface regions appeared highly supersaturated in N and O forming a continuum of defects initiated by N-O complexes. The N and O stoichiometry depth profiles were found to depend on the material thermal history. The spatial variation of the stoichiometry ratio was also determined for precipitates using a combination of scanning transmission electron microscope (STEM) in Z-contrast mode with electron energy loss spectroscopy. The precipitate atomic and microstructures, analyzed by high resolution TEM and STEM, clearly demonstrate that second phase precipitate is precursor to a third phase that is an outer oxynitride shell. Nitrogen and oxygen cosegregation from the matrix to the precipitate interface occurs in a similar fashion as in the subsurface region. We propose a mechanism for oxygen precipitation in N-CZ Si based on N segregation to the interface while oxygen is trapped inside the oxynitride shell.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Karoui, A and Rozgonyi, GA}, year={2004}, month={Sep}, pages={3264–3271} }
 @article{stoddard_karoui_duscher_kvit_rozgonyi_2003, title={In situ point defect generation and agglomeration during electron-beam irradiation of nitrogen-doped Czochralski silicon}, volume={6}, ISSN={["1944-8775"]}, DOI={10.1149/1.1614471}, abstractNote={Samples of Czochralski silicon were observed after irradiation by a convergent electron beam in a transmission electron microscope. In a nitrogen-doped sample, the 200 keV electrons induced a vacancy-rich region containing point-defect clusters, surrounded by a ring rich in self-interstitials. No comparable effect existed in nitrogen-free reference samples. It is proposed that Frenkel pairs, created by electron collisions, are separated and stabilized by nitrogen or related complexes. Some interstitials become free to diffuse while the nitrogen, vacancies and oxygen agglomerate. This study demonstrates that the initial formation of voids and precipitate nuclei from point defects can be observed at low temperatures. © 2003 The Electrochemical Society. All rights reserved.}, number={11}, journal={ELECTROCHEMICAL AND SOLID STATE LETTERS}, author={Stoddard, N and Karoui, A and Duscher, G and Kvit, A and Rozgonyi, G}, year={2003}, month={Nov}, pages={G134–G136} }
 @article{rozgonyi_karoui_kvit_duscher_2003, title={Nano-scale analysis of precipitates in nitrogen-doped Czochralski silicon}, volume={66}, ISSN={["1873-5568"]}, DOI={10.1016/S0167-9317(02)00923-1}, abstractNote={Nitrogen-doped Czochralski (CZ) silicon wafers were heat treated with Lo-Hi annealing in argon. Nanoscale defects were then examined by high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) in the Z-contrast mode, and electron energy loss spectroscopy (EELS) analyses using a field emission JEOL 2010 with a resolution below 2 A. The structures of precipitates, stacking faults and interstitial aggregates were found to depend on their location relative to the wafer surface. Precipitate composition, strain at the interface and interface roughness were obtained and are discussed in connection with the point defects generated during crystal growth and modified during wafer annealing. An excellent correlation was found between Z-contrast line scans across the precipitates and the N to O concentration ratio determined with EELS. In the precipitate central region that ratio is between 1 and 6%, whereas at precipitate boundaries it reaches 17%.}, number={1-4}, journal={MICROELECTRONIC ENGINEERING}, author={Rozgonyi, GA and Karoui, A and Kvit, A and Duscher, G}, year={2003}, month={Apr}, pages={305–313} }
 @article{karoui_karoui_rozgonyi_hourai_sueoka_2003, title={Structure, energetics, and thermal stability of nitrogen-vacancy-related defects in nitrogen doped silicon}, volume={150}, ISSN={["1945-7111"]}, DOI={10.1149/1.1621418}, abstractNote={The electronic structure, formation energy, and thermal stability of nitrogen-vacancy related complexes in silicon have been investigated using density functional theory and semi-empirical Hartree-Fock calculations. The calculated energies of formation in the ground state showed that VN 2 was not stable, whereas V 2 N 2 when formed from VN 2 was the most stable, followed by N 2 and V 2 N 2 formed from a divacancy. The calculated free energy changes of the considered chemical reactions confirmed the low stability of VN 2 compared to V 2 N 2 . The latter can form during crystal growth from VN 2 , whereas reactions between N 2 and divacancy can also occur upon wafer heating. At low nitrogen concentration (∼5 X 10 13 cm -3 ), only about 10% of vacancy concentration was converted into VN 2 , while at a high nitrogen concentration (∼10 16 cm -3 ) about 75% of vacancies are trapped by nitrogen. V 2 N 2 appeared to create a potential well of -2.4 eV for oxygen and about -0.3 eV for vacancies, suggesting that the stable V 2 N 2 is a nucleus for oxygen precipitation while it is a weak trapping center for vacancies.}, number={12}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Karoui, A and Karoui, FS and Rozgonyi, GA and Hourai, M and Sueoka, K}, year={2003}, month={Dec}, pages={G771–G777} }
 @article{yoganand_jagannadham_karoui_wang_2002, title={Integrated AlN/diamond heat spreaders for silicon device processing}, volume={20}, ISSN={["0734-2101"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0036863138&partnerID=MN8TOARS}, DOI={10.1116/1.1513643}, abstractNote={Growth and characterization of AlN and diamond films on the backside of a Si (100) wafer and the integration of AlN/diamond heat spreaders into silicon device technology is investigated. AlN film was deposited by pulsed dc reactive magnetron sputtering at 600 °C and diamond film was deposited by microwave plasma chemical vapor deposition at 900 °C. The films were characterized by x-ray diffraction and transmission electron microscopy for crystalline quality, by scanning electron microscopy for morphology, and by infrared thermography for heat spreading characteristics. The heat spreading characteristics of the silicon wafer with the composite AlN/diamond films were found to be superior to that of wafers with no heat spreaders or to the wafers with either single layer diamond or single layer AlN heat spreaders. Deep level transient spectroscopy and secondary ion mass spectroscopy were performed on the samples with and without the heat spreader to determine the concentration of the impurities that may have been introduced during deposition of AlN or diamond. The results showed that the purity of the wafers is not altered due to the deposition of AlN and diamond and subsequent device processing steps such as high temperature oxidation. The device characteristics were studied by fabrication of Schottky diodes on the wafers with the composite AlN/diamond heat spreader and compared with that of devices on wafers with no heat spreader. The device characteristics were found to be similar and unaffected by integration with an AlN/diamond heat spreader. Integration of AlN/diamond heat spreaders with silicon device processing has been shown to be successful.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Yoganand, SN and Jagannadham, K and Karoui, A and Wang, H}, year={2002}, pages={1974–1982} }
 @article{karoui_karoui_kvit_rozgonyi_yang_2002, title={Role of nitrogen related complexes in the formation of defects in silicon}, volume={80}, ISSN={["1077-3118"]}, DOI={10.1063/1.1462874}, abstractNote={Defect size and density distributions were obtained as a function of depth in nitrogen doped CZ silicon (N-CZ) following Hi–Lo–Hi and Lo–Hi annealing, using an oxygen precipitate profiler. The defects were also delineated by Wright etching and Nomarski optical microscopy on both cleaved and bevel polished samples. In addition to the enhanced precipitation and absence of voids previously reported for N-CZ Si, an unexpected mode of precipitation has been found near the annealed wafer surface, just above the traditional denuded zone. This oxynitride precipitate is discussed with regard to N-related complex interactions and point defect supersaturations/injection. High resolution transmission electron microscopy revealed that most precipitates have an octahedral shape with two distinct amorphous phases, which reflect a transition from an initial phase containing both N and O to one with primarily O, as verified with Z-contrast TEM and electron energy loss spectroscopy.}, number={12}, journal={APPLIED PHYSICS LETTERS}, author={Karoui, A and Karoui, FS and Kvit, A and Rozgonyi, GA and Yang, D}, year={2002}, month={Mar}, pages={2114–2116} }