@article{niu_ashcraft_hinkle_parsons_2004, title={Effect of N-2 plasma on yttrium oxide and yttrium-oxynitride dielectrics}, volume={22}, ISSN={["1520-8559"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000222091800002&KeyUID=WOS:000222091800002}, DOI={10.1116/1.1666880}, abstractNote={In this article, we report the effect of nitrogen plasma, during and after deposition, on nitrogen incorporation into yttrium oxide dielectric films. Films are deposited using a yttrium β-diketonate precursor (Y(tmhd)3) introduced downstream from a O2 or N2 plasma. The precursor acted as a significant source of oxygen, and only small amounts of N (<10 at. %) were incorporated in the films. Chemical bonding, concentration, and distribution of N in Y-oxide films after deposition and after high-temperature anneal were characterized using x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Auger electron spectroscopy. C–N is the primary form of nitrogen bonding in the as-deposited films, and IR results indicate the exchange of N with O to form C–O bonds occurs during prolonged exposure to air. High-temperature annealing releases N from the surface of as-deposited films, and results in a film structure that is resistant to further N incorporation. Results suggest that yttrium oxynitride is likely inherently unstable, especially in contact with ambient moisture.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Niu, D and Ashcraft, RW and Hinkle, C and Parsons, GN}, year={2004}, pages={445–451} }
 @article{gougousi_niu_ashcraft_parsons_2003, title={Carbonate formation during post-deposition ambient exposure of high-k dielectrics}, volume={83}, ISSN={["0003-6951"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000186068400033&KeyUID=WOS:000186068400033}, DOI={10.1063/1.1623316}, abstractNote={When thick films of group-III (La, Y)- and group-IV (Hf, Zr)-based high-k dielectrics are exposed to ambient for several months, Fourier transform infrared spectroscopy shows formation of carbonate species in the film bulk, likely due to reaction with atmospheric CO2. Group-III-based films show signs of carbonate feature growth within 10 min of air exposure, especially in films processed at relatively low temperatures (<600 °C). Carbonate formation is verified also for group-IV-based films, but at a significantly reduced concentration. Post-exposure annealing can reduce the carbonate observed in the IR spectra. However, post-exposure annealing likely does not remove carbon contamination, and it results in interface silicon oxide growth. The observed reactions of high-k films with the ambient may impose significant constraints on the post-deposition handling of high-k films.}, number={17}, journal={APPLIED PHYSICS LETTERS}, author={Gougousi, T and Niu, D and Ashcraft, RW and Parsons, GN}, year={2003}, month={Oct}, pages={3543–3545} }
 @article{niu_ashcraft_chen_stemmer_parsons_2003, title={Chemical, physical, and electrical characterizations of oxygen plasma assisted chemical vapor deposited yttrium oxide on silicon}, volume={150}, ISSN={["1945-7111"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000182184200051&KeyUID=WOS:000182184200051}, DOI={10.1149/1.1566415}, abstractNote={Understanding and controlling interface and bulk chemical stability of chemical vapor deposited high-k dielectrics is an important research issue. We report thin Y 2 O 3 films deposited by oxygen plasma assisted chemical vapor deposition using two yttrium diketonate precursors. Unacceptable large hysteresis in capacitance-voltage data, presumably due to the incorporation of fluorine. is observed for the films from the F-containing precursor. For films deposited with the hydrogenated precursor and exposed to air after deposition, transmission electron microscopy shows a triple layer structure after annealing, and electron energy loss spectroscopy and X-ray photoelectron spectroscopy show the film to be stoichiometric Y 2 O 3 on top and yttrium silicate/SiO 2 at dielectric/Si interface. This structure is also confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, and atomic force microscopy. Prenitridation of the silicon surface prior to dielectric deposition impedes the reaction with the substrate. promoting the Y 2 O 3 structure. A substantial consumption of silicon substrate is directly demonstrated by a carefully designed etching experiment. Possible mechanisms consistent with the observed results, including Si diffusion, crystallization of Y 2 O 3 , and reaction with absorbed OH, are discussed.}, number={5}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Niu, D and Ashcraft, RW and Chen, Z and Stemmer, S and Parsons, GN}, year={2003}, month={May}, pages={F102–F109} }
 @article{niu_ashcraft_chen_stemmer_parsons_2002, title={Electron energy-loss spectroscopy analysis of interface structure of yttrium oxide gate dielectrics on silicon}, volume={81}, ISSN={["1077-3118"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000176871600036&KeyUID=WOS:000176871600036}, DOI={10.1063/1.1496138}, abstractNote={Interface stability of high dielectric constant gate insulators on silicon is an important issue for advanced gate stack engineering. In this article, we analyze the silicon/dielectric interface structure for thin Y2O3 and Y silicate films deposited by chemical vapor deposition on clean and prenitrided Si(100) using high-resolution transmission electron microscopy, electron energy-loss spectroscopy, and x-ray photoelectron spectroscopy. The analysis shows the films to be stoichiometric Y2O3 on top and Y-silicate/SiO2 at the dielectric/Si interface. Prenitridation of the silicon surface impedes the reaction between the depositing film and the substrate, promoting a Si-free Y2O3 structure. Possible mechanisms leading to the observed Y2O3 and Y silicate structures are discussed.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Niu, D and Ashcraft, RW and Chen, Z and Stemmer, S and Parsons, GN}, year={2002}, month={Jul}, pages={676–678} }
 @article{niu_ashcraft_kelly_chambers_klein_parsons_2002, title={Elementary reaction schemes for physical and chemical vapor deposition of transition metal oxides on silicon for high-k gate dielectric applications}, volume={91}, ISSN={["0021-8979"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000175069000098&KeyUID=WOS:000175069000098}, DOI={10.1063/1.1468253}, abstractNote={This article describes the kinetics of reactions that result in substrate consumption during formation of ultrathin transition metal oxides on silicon. Yttrium silicate films (∼40 Å) with an equivalent silicon dioxide thickness of ∼11 Å are demonstrated by physical vapor deposition (PVD) routes. Interface reactions that occur during deposition and during postdeposition treatment are observed and compared for PVD and chemical vapor deposition (CVD) yttrium oxides and CVD aluminum-oxide systems. Silicon diffusion, metal-silicon bond formation, and reactions involving hydroxides are proposed as critical processes in interface layer formation. For PVD of yttrium silicate, oxidation is thermally activated with an effective barrier of 0.3 eV, consistent with the oxidation of silicide being the rate-limited step. For CVD aluminum oxide, interface oxidation is consistent with a process limited by silicon diffusion into the deposited oxide layer.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Niu, D and Ashcraft, RW and Kelly, MJ and Chambers, JJ and Klein, TM and Parsons, GN}, year={2002}, month={May}, pages={6173–6180} }
 @article{stemmer_klenov_chen_niu_ashcraft_parsons_2002, title={Reactions of Y2O3 films with (001) Si substrates and with polycrystalline Si capping layers}, volume={81}, ISSN={["1077-3118"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000176871600048&KeyUID=WOS:000176871600048}, DOI={10.1063/1.1496500}, abstractNote={We use electron energy-loss spectroscopy in scanning transmission electron microscopy to investigate interfacial reactions of chemical vapor deposited Y2O3 films with the Si substrate and with in situ polycrystalline Si (“poly-Si”) capping layers after postdeposition annealing. We find that in situ capping layers significantly reduce the formation of SiO2 at the interface with the substrate, but silicates form at the substrate and the capping layer interfaces. Predeposition nitridation of the Si surface can impede the reaction at the substrate interface, resulting in crystallization of Y2O3 in the film interior. Possible mechanisms of the silicate formation are discussed.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Stemmer, S and Klenov, DO and Chen, ZQ and Niu, D and Ashcraft, RW and Parsons, GN}, year={2002}, month={Jul}, pages={712–714} }
 @article{niu_ashcraft_parsons_2002, title={Water absorption and interface reactivity of yttrium oxide gate dielectrics on silicon}, volume={80}, ISSN={["0003-6951"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000175464100037&KeyUID=WOS:000175464100037}, DOI={10.1063/1.1477268}, abstractNote={High dielectric constant insulators deposited at low temperatures rapidly absorb water during exposure to the atmosphere, and the resulting OH leads to detrimental interface reactions. We report the effect of atmospheric exposure on ultrathin yttrium oxide, and details of silicon substrate reactions during postdeposition anneals. Infrared absorption analysis indicates significant absorption of water vapor during atmospheric exposure, even for very short times (<15 min). X-ray photoelectron spectroscopy demonstrates that after OH absorption, a thermally activated interface reaction proceeds with an activation energy of 0.33 eV, consistent with substrate reaction with OH present in the film. The OH absorption rate is reduced for annealed films or when capping layers are deposited in situ. Similar oxidation processes are expected to occur in other high-k materials of interest, where the rate of OH absorption will depend on the deposition process and material thermal history.}, number={19}, journal={APPLIED PHYSICS LETTERS}, author={Niu, D and Ashcraft, RW and Parsons, GN}, year={2002}, month={May}, pages={3575–3577} }