Experimental and theoretical studies on N 1s levels of silicon oxynitride films Masao Takahashi a, * ,1 , Toshiko Mizokuro a , Yasushiro Nishioka b , Hikaru Kobayashi a, * a Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Corporation, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan b Texas Instruments Tsukuba Research and Development Center, Mihogaoka, Tsukuba, Ibaraki 305-0841, Japan Received 6 April 2002; accepted for publication 23 July 2002 Abstract Nitridation of silicon dioxide layers at low temperatures by the use of nitrogen plasma generated by low energy electron impact has been investigated by means of X-ray photoelectron spectroscopy. The nitrogen concentration is increasedbytheapplicationofanegativebiasvoltagetothespecimen,indicatingthatN þ ionsarethereactingspecies. When nitridation is performed above 450 °C, only one peak is observed at 397.9 eV, and it is attributed to N(–Si) 3 (nitrogenatomboundtothreeSiatoms).Forthenitridationbelow400 °C,ontheotherhand,apeakappearsat399.2 eVinadditiontothe397.9eV-peak.Whenthefilmnitridedat400 °Cisheatedat700 °Cinavacuum,theintensityof the399.2eV-peakisslightlydecreased,andnewpeaksappearat399.9,400.7and402.4eV.The399.9,400.7,and402.4 eV-speciesarenotformedwhenthenitridedoxidelayerscontainingno399.2eV-speciesareheatedat700 °C,showing that these species are produced from the 399.2 eV-species. Theoretical calculations using a density functional theory methodshowthatO–N(–Si) 2 (nitrogenatomboundtotwoSiatomsandoneoxygenatom)hasanN1slevelshiftedby þ1.3eVfromthatofN(–Si) 3 ,indicatingthatthe399.2eV-peakisattributabletoO–N(–Si) 2 .Thisspeciesislikelytobe easily formed by the insertion of N þ ions to the SiO 2 surface without an extensive atomic rearrangement. The calcu- lationsalsoshowthatO–N Å –Si(nitrogenradicalboundtobothoneoxygenandSiatoms)andO@N–Si(nitrogenatom with an N@O double bond and an Si–N single bond) have þ1.8 and þ3.1 eV energy shifts, respectively, from the N1speakoftheN(–Si) 3 species,leadingtotheattributionofthe399.9eV-peaktoO–N Å –Siandthe400.7eV-peakto O@N–Si. The calculations also show that the 402.4 eV-peak is attributable to [N(–Si) 4 ] þ (a cation composed by a nitrogenatomboundtofourSiatoms).Theconcentrationsofthe[N(–Si) 4 ] þ andO@N–Sispeciesarealmostconstant throughout the nitrided oxide layers, showing that these species result from the reaction between O–N(–Si) 2 and bulk SiO 2 . The concentration of O–N Å –Si species, on the other hand, is low at the surface and high near the interface, showing that O–N Å –Si is formed by the reaction with Si. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Density functional calculations; Photoelectron spectroscopy; X-ray photoelectron spectroscopy; Compound formation; Silicon; Silicon nitride; Silicon oxides; Insulating films * Corresponding authors. Tel./fax: +81-6-6879-8450. E-mail addresses: takahasi@sanken.osaka-u.ac.jp (M. Takahashi), h.kobayashi@sanken.osaka-u.ac.jp (H. Kobayashi). 1 Tel.: +81-6-6879-8451; fax: +81-6-6879-8454. 0039-6028/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0039-6028(02)02096-4 Surface Science 518 (2002) 72–80 www.elsevier.com/locate/susc